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+The Project Gutenberg EBook of Manures and the principles of manuring, by
+Charles Morton Aikman
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever. You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Manures and the principles of manuring
+
+Author: Charles Morton Aikman
+
+Release Date: November 16, 2008 [EBook #27274]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK MANURES, PRINCIPLES OF MANURING ***
+
+
+
+
+Produced by Steven Giacomelli, Barbara Kosker and the
+Online Distributed Proofreading Team at https://www.pgdp.net
+(This file was produced from images produced by Core
+Historical Literature in Agriculture (CHLA), Cornell
+University)
+
+
+
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+
+
+
+
+
+
+PRINCIPLES OF MANURING
+
+
+
+
+MANURES
+
+AND THE
+
+PRINCIPLES OF MANURING
+
+
+BY
+
+
+C. M. AIKMAN, M.A., D.Sc., F.R.S.E., F.I.C.
+
+FORMERLY PROFESSOR OF CHEMISTRY, GLASGOW VETERINARY COLLEGE, AND
+EXAMINER IN CHEMISTRY, GLASGOW UNIVERSITY; AUTHOR OF 'FARMYARD MANURE,'
+ETC.
+
+
+
+THIRD IMPRESSION
+
+
+
+WILLIAM BLACKWOOD AND SONS EDINBURGH AND LONDON MCMX
+
+
+D. VAN NOSTRAND COMPANY NEW YORK
+
+
+_All Rights reserved_
+
+
+
+
+TO
+
+
+SIR JOHN BENNET LAWES, BART., D.C.L., LL.D., F.R.S.,
+OF ROTHAMSTED,
+
+AND
+
+SIR J. HENRY GILBERT, M.A., LL.D., F.R.S.,
+
+FORMERLY SIBTHORPIAN PROFESSOR OF RURAL ECONOMY,
+UNIVERSITY OF OXFORD,
+WHOSE FAMOUS INVESTIGATIONS DURING THE LAST FIFTY YEARS
+HAVE SO LARGELY CONTRIBUTED TO BUILD UP
+THE SCIENCE OF MANURING,
+
+THIS WORK,
+
+EMBODYING MANY OF THE ROTHAMSTED RESULTS,
+
+IS DEDICATED.
+
+
+
+
+PREFACE.
+
+
+When the present work was first undertaken there were but few works in
+English dealing with its subject-matter, and hardly any which dealt with
+the question of Manuring at any length. During the last few years,
+however, owing to the greatly increased interest taken in agricultural
+education, the demand for agricultural scientific literature has called
+into existence quite a number of new works. Despite this fact, the
+author ventures to believe that the gap which the present treatise was
+originally designed to fill is still unfilled.
+
+Of the importance of the subject all interested in agriculture are well
+aware. It is no exaggeration to say that the introduction of the
+practice of artificial manuring has revolutionised modern husbandry.
+Indeed, without the aid of artificial manures, arable farming, as at
+present carried out, would be impossible. Fifty years ago the practice
+may be said to have been unknown; yet so widespread has it now become,
+that at the present time the capital invested in the manure trade in
+this country alone amounts to millions sterling. It need scarcely be
+pointed out, therefore, that a practice in which such vast monetary
+interests are involved is worthy of the most careful consideration by
+all students of agricultural science, as well as, it may be added, by
+political economists.
+
+The aim of the present work is to supply in a concise and popular form
+the chief results of recent agricultural research on the question of
+soil fertility, and the nature and action of various manures. It makes
+no pretence to be an exhaustive treatise on the subject, and only
+contains those facts which seem to the author to have an important
+bearing on agricultural practice. In the treatment of its subject it may
+be said to stand midway between Professor Storer's recently published
+elaborate and excellent treatise on 'Agriculture in some of its
+Relations to Chemistry'--a work which is to be warmly recommended to all
+students of agricultural science, and to which the author would take
+this opportunity of acknowledging his indebtedness--and Dr J. M. H.
+Munro's admirable little work on 'Soils and Manures.'
+
+In order to render the work as intelligible to the ordinary agricultural
+reader as possible, all tabular matter and matter of a more or less
+technical nature have been relegated to the Appendices attached to each
+chapter.
+
+The author's somewhat wide experience as a University Extension
+Lecturer, and as a Lecturer in connection with County Council schemes of
+agricultural education, during the last few years, induces him to
+believe that the work may be of especial value to those engaged in
+teaching agricultural science.
+
+He has to express the deep obligation he is under, in common with all
+writers on Agricultural Chemistry, to the classic researches of Sir John
+Bennet Lawes, Bart., and Sir J. Henry Gilbert, now in progress for more
+than fifty years at Sir John Lawes' Experiment Station at Rothamsted.
+His debt of gratitude to these distinguished investigators has been
+still further increased by their kindness in permitting him to dedicate
+the work to them, and for having been good enough to read portions of
+the work in proof. In addition to the free use which has been made
+throughout the book of the results of these experiments, the last
+chapter contains, in a tabular form, a short epitome of some of the more
+important Rothamsted researches on the action of different manures.
+
+To the numerous German and French works on the subject, more especially
+to Professor Heiden's encyclopædic 'Lehrbuch der Düngerlehre' and the
+various writings of Dr Emil von Wolff, the author is further much
+indebted.
+
+Among English works he would especially mention the assistance he has
+derived from the writings of Mr R. Warington, F.R.S., Professor S. W.
+Johnson, Professor Armsby, the late Dr Augustus Voelcker, and others. He
+would also tender his acknowledgments to the new edition of Stephens'
+'Book of the Farm,' and he has to thank its editor, his friend Mr James
+Macdonald, Secretary to the Highland and Agricultural Society of
+Scotland, for having read parts of his proof-sheets.
+
+It is also his pleasing duty to thank his friends Dr Bernard Dyer, Hon
+Secretary of the Society of Public Analysts, Dr A. P. Aitken, Chemist to
+the Highland and Agricultural Society of Scotland; Professor Douglas
+Gilchrist of Bangor; Mr F. J. Cooke, late of Flitcham; Mr Hermann Voss
+of London; and Professor Wright of Glasgow, for having assisted him in
+the revision of proof-sheets.
+
+ANALYTICAL LABORATORY,
+128 WELLINGTON STREET, GLASGOW,
+_January_ 1894.
+
+
+
+
+CONTENTS.
+
+ PART I.--HISTORICAL INTRODUCTION.
+ PAGE
+ Beginning of agricultural chemistry 4
+ Early theories regarding plant-growth 4
+ Van Helmont 4
+ Digby 6
+ Duhamel and Stephen Hales 8
+ Jethro Tull 9
+ Charles Bonnet's discovery of source of plants' carbon 11
+ Researches of Priestley, Ingenhousz, Sénébier, on assimilation
+ of carbon 11-12
+ Publication of first English treatise by Earl Dundonald 13
+ Publication of Theodore de Saussure, 'Chemical Researches on
+ Vegetation,' 1804 14
+ Theories on source of plant-nitrogen 15
+ Early experiments on this subject 16
+ Sir Humphry Davy's lectures (1802-1812) 17
+ State of agricultural chemistry in 1812 17
+ Beginning of Boussingault's researches (1834) 21
+ Publication of Liebig's first report to the British Association 24
+ Refutation of "humus" theory 26
+ Liebig's mineral theory 26
+ Liebig's theory of source of plants' nitrogen 27
+ Publication of Liebig's second report to British Association 30
+ Liebig's services to agricultural chemistry 31
+ Development of agricultural research in Germany 32
+ The Rothamsted Experiment Station 33
+ Sir J. B. Lawes and Sir J. H. Gilbert, the nature and value of
+ their experiments 33
+ Review of the present state of our knowledge of plant-growth 36
+ Proximate composition of the plant 36
+ Fixation of carbon by plants 37
+ Action of light on plant-growth, Dr Siemens' experiments 38
+ Source of oxygen and hydrogen in the plant 39-40
+ Source of nitrogen in the plant 40
+ Relation of the free nitrogen to leguminous plants 42-44
+ Relation of nitrogen in organic forms, as ammonia salts,
+ and nitrates to the plant 46-50
+ Nitrification and its conditions 51
+ Ash constituents of the plant 53
+ Methods of research for ascertaining essentialness of ash
+ constituents of plants 53
+ (_a_) Artificial soils, (_b_) water-culture 53-55
+ Method in which plants absorb their food-constituents 55
+ Endosmosis 55
+ Retention by soils of plant-food 57
+ Causes of retention by soils of plant-food 59
+ Manuring 60
+ "Field" and "pot" experimentation 60
+
+
+ PART II.--PRINCIPLES OF MANURING.
+
+ CHAPTER I.--FERTILITY OF THE SOIL.
+
+ What constitutes fertility in a soil 65
+ I. Physical properties of a soil 66
+ Kinds of soils 67
+ Absorptive power for water of soils 67
+ Absorptive power for water of sand, clay, and humus 68
+ Fineness of particles of a soil 69
+ Limit of fineness of soil-particles 69
+ Importance of retentive power 70
+ Power of plants for absorbing water from a soil
+ experiments by Sachs 73
+ How to increase absorptive power of soils 74
+ Amount of water in a soil most favourable for plant growth 75
+ Hygroscopic power of soils 75
+ Capacity of soils for absorbing and retaining heat 76
+ Explanation of dew 77
+ Heat of soils 78
+ Heat in rotting farmyard manure 78
+ Causes of heat of fermentation 79
+ Influence of colour on heat-retaining power 80
+ Power of soils for absorbing gases 81
+ Gases found in soils 81
+ Variation in gas-absorbing power of soils 82
+ Absorption of nitrogen by soils 82
+ Requirements of plant-roots in a soil 83
+ Influence of tillage on number of plants in a certain area 86
+ Comparison of English and American farming 86
+ II. Chemical composition of a soil 87
+ Fertilising ingredients of a soil 87
+ Importance of _nitrogen, phosphoric acid_, and _potash_ in a
+ soil 88
+ Chemical condition of fertilising ingredients in soils 89
+ Amount of soluble fertilising ingredients in soils 90
+ Value of chemical analysis of soils 90
+ III. Biological properties of a soil 92
+ Bacteria of the soil 92
+ Recapitulation of Chapter I 96
+
+ APPENDIX TO CHAPTER I.
+ NOTE
+ I. Table of absorptive power of soil substances by Schübler 98
+ II. Table of rate of evaporation of water in different soils
+ by Schübler 99
+ III. Table of hygroscopic power of soils dried at 212° F.
+ (Davy) 99
+ IV. Gases present in soil 100
+ V. Amount of plant-food in soils 100
+ VI. Chemical composition of the soil 101
+ VII. Forms in which plant-foods are present in the soil 107
+
+
+ CHAPTER II.--FUNCTIONS PERFORMED BY MANURES.
+
+ Etymological meaning of word manure 109
+ Definition of manures 110
+ Different classes of manures 111
+ Action of different classes of manures 113
+
+
+ CHAPTER III.--POSITION OF NITROGEN IN AGRICULTURE.
+
+ The Rothamsted experiments and the nitrogen question 115
+ Different forms in which nitrogen exists in nature 116
+ Relation of "free" nitrogen to the plant 117
+ Combined nitrogen in the air 118
+ Amount of combined nitrogen falling in the rain 119
+ Nitrogen in the soil 120
+ Nitrogen in the subsoil 121
+ Nitrogen of surface-soil 121
+ Amount of nitrogen in the soil 123
+ Soils richest in nitrogen 123
+ Nature of the nitrogen in the soil 124
+ Organic nitrogen in the soil 125
+ Differences of surface and subsoil nitrogen 126
+ Nitrogen as ammonia in soils 127
+ Amount of ammonia in soils 127
+ Nitrogen present as nitrates in the soil 128
+ Position of nitric nitrogen in soil 128
+ Amount of nitrates in the soil 129
+ Amount of nitrates in fallow soils 129
+ Amount of nitrates in cropped soils 130
+ Amount of nitrates in manured wheat-soils 131
+ The sources of soil-nitrogen 131
+ Accumulation of soil-nitrogen under natural conditions 133
+ Accumulation of nitrogen in pastures 134
+ Gain of nitrogen with leguminous crops 135
+ The fixation of "free" nitrogen 136
+ Influence of manures in increasing soil-nitrogen 136
+ Sources of loss of nitrogen 137
+ Loss of nitrates by drainage 137
+ Prevention of loss of nitrogen by permanent pasture and
+ "catch-cropping" 138
+ Other conditions diminishing loss of nitrates 139
+ Amount of loss of nitrogen by drainage 140
+ Loss of nitrogen in form of "free" nitrogen 141
+ Total amount of loss of nitrogen 142
+ Loss of nitrogen by retrogression 142
+ Artificial sources of loss of nitrogen 144
+ Amount of nitrogen removed in crops 144
+ Losses of nitrogen incurred on the farm 146
+ Loss in treatment of farmyard manure 146
+ Nitrogen removed in milk 147
+ Economics of the nitrogen question 147
+ Loss of nitrogen-compounds in the arts 148
+ Loss due to use of gunpowder 148
+ Loss due to sewage disposal 149
+ Our artificial nitrogen supply 150
+ Nitrate of soda and sulphate of ammonia 150
+ Peruvian guano 151
+ Bones 151
+ Other nitrogenous manures 152
+ Oil-seeds and oilcakes 153
+ Other imported sources of nitrogen 153
+ Conclusion 153
+
+ APPENDIX TO CHAPTER III.
+ NOTE
+ I. Determination of the quantity of nitrogen supplied by
+ rain, as ammonia and nitric acid, to an acre of land
+ during one year 155
+ II. Nitrogen in soils at various depths 156
+ III. Nitrogen as nitrates in cropped soils receiving no
+ nitrogenous manures, in lb. per acre (Rothamsted soils) 157
+ IV. Nitrogen as nitrates in Rothamsted soils 157
+ V. Examples of increase of nitrogen in Rothamsted soils
+ laid down in pasture 158
+ VI. Loss by drainage of nitrates 158
+ VII. Examples of decrease of nitrogen in Rothamsted soils 159
+ VIII. Amount of drainage and nitrogen as nitrates in
+ drainage-water from unmanured bare soil, 20 and 60
+ inches deep 160
+
+
+ CHAPTER IV.--NITRIFICATION.
+
+ Process of nitrification 161
+ Occurrence of nitrates in the soil 162
+ Nitre soils of India 162
+ Saltpetre plantations 163
+ Cause of nitrification 165
+ Ferments effecting nitrification 167
+ Appearance of nitrous organisms 168
+ Nitric organism 169
+ Difficulty in isolating them 169
+ Nitrifying organisms do not require organic matter 169
+ Conditions favourable for nitrification--
+ Presence of food-constituents 170
+ Presence of a salifiable base 171
+ Only takes place in slightly alkaline solutions 172
+ Action of gypsum on nitrification 173
+ Presence of oxygen 173
+ Temperature 175
+ Presence of a sufficient quantity of moisture 176
+ Absence of strong sunlight 176
+ Nitrifying organisms destroyed by poisons 176
+ Denitrification 177
+ Denitrification also effected by bacteria 178
+ Conditions favourable for denitrification 178
+ Takes place in water-logged soils 179
+ Distribution of the nitrifying organisms in the soil 179
+ Depth down at which they occur 180
+ Action of plant-roots in promoting nitrification 181
+ Nature of substances capable of nitrification 181
+ Rate at which nitrification takes place 183
+ Nitrification takes place chiefly during summer 183
+ Process goes on most quickly in fallow fields 184
+ Laboratory experiments on rate of nitrification 185
+ Certain portions of soil-nitrogen more easily
+ nitrifiable than the rest 187
+ Rate of nitrification deduced from field experiments 187
+ Quantity of nitrates formed in the soils of fallow fields 188
+ Position of nitrates depends on season 188
+ Nitrates in drainage-waters 188
+ Amount produced at different times of year 189
+ Nitrification of manures 190
+ Ammonia salts most easily nitrifiable 191
+ Sulphate of ammonia the most easily nitrifiable manure 191
+ Rate of nitrification of other manures 192
+ Soils best suited for nitrification 192
+ Absence of nitrification in forest-soils 193
+ Important bearing of nitrification on agricultural
+ practice 193
+ Desirable to have soil covered with vegetation 194
+ Permanent pasture most economical condition of soil 194
+ Nitrification and rotation of crops 195
+
+ APPENDIX TO CHAPTER IV.
+ NOTE
+ I. Old theories of nitrification 196
+ II. Nitrification takes place in solutions devoid of organic
+ matter 196
+ III. Oxidising power of micro-organisms in soils 197
+ IV. Effect of urine on nitrification in soils 197
+ V. Solution used by Professor Frankland in cultivating
+ nitrificative micro-organisms 198
+ VI. Experiments by Boussingault on rate of nitrification 198
+ VII. Nitrogen as nitrates in Rothamsted soils after bare
+ fallow in lb. per acre 198
+
+
+ CHAPTER V.--POSITION OF PHOSPHORIC ACID IN AGRICULTURE.
+
+ Occurrence of phosphoric acid in nature 199
+ Mineral sources of phosphoric acid 200
+ Apatite and phosphorite 200
+ Coprolites 201
+ Occurrence of phosphoric acid in guanos 202
+ Universal occurrence in common rocks 202
+ Occurrence in the soil 203
+ Condition in which phosphoric acid occurs in the soil 203
+ Occurrence in plants 204
+ Occurrence in animals 205
+ Sources of loss of phosphoric acid in agriculture 205
+ Loss of phosphoric acid by drainage 206
+ Artificial sources of loss of phosphoric acid 206
+ Amount of phosphoric acid removed in milk 207
+ Loss of phosphoric acid in treatment of farmyard manure 208
+ Loss of phosphoric acid in sewage 208
+ Sources of artificial gain of phosphoric acid 208
+
+ APPENDIX TO CHAPTER V.
+ NOTE
+ I. Composition of apatite (Voelcker) 210
+ II. Percentage of phosphoric acid in the commoner rocks 211
+
+
+ CHAPTER VI.--POSITION OF POTASH IN AGRICULTURE.
+
+ Potash of less importance than phosphoric acid 212
+ Occurrence of potash 213
+ Felspar and other potash minerals 213
+ Stassfurt salts 214
+ Occurrence of saltpetre 215
+ Occurrence of potash in the soil 215
+ Potash chiefly in insoluble condition in soils 216
+ Percentage of potash in plants and plant-ash 216
+ Occurrence of potash in animal tissue 217
+ Sources of loss of potash 217
+ Amount of potash removed in crops 218
+ Amount of potash removed in milk 218
+ Potash manures 218
+
+ APPENDIX TO CHAPTER VI.
+ NOTE
+ I. Amount of potash in different minerals 220
+ II. Quantity of potash obtained from 1000 lb. of different
+ kinds of vegetation in the manufacture of potashes 220
+
+
+ PART III.--MANURES.
+
+ CHAPTER VII.--FARMYARD MANURE.
+
+ Variation in its composition 223
+ Made up of three classes of constituents 224
+ _Solid excreta_--
+ Its nature 224
+ Difference in composition of the solid excreta of the
+ different farm animals 224
+ Causes of this difference 225
+ Percentage of manurial ingredients in solid excreta
+ of different animals 226
+ _Urine_--
+ Its nature 228
+ Variation in its composition 229
+ Causes of this variation 229
+ Manurial value of the urine of the different farm
+ animals 230
+ Percentage of the _organic matter_, _nitrogen_, and
+ _mineral substances_ in the food, voided in the
+ solid excreta and urine 232
+ Comparison of manurial value of total excrements of
+ the different farm animals 234
+ Nature of changes undergone by food in process of
+ digestion 235
+ _Litter_--
+ Its uses 236
+ _Straw_ as litter, and its qualifications 237
+ Composition of different kinds of straw 238
+ _Loam_ as litter 239
+ _Peat_ as litter 240
+ Comparison of properties of _peat-moss_ and _straw_ 241
+ The _bracken-fern_ as litter 241
+ _Dried leaves_ as litter 242
+ Manures produced by the different animals--
+ _Horse-manure_--
+ Amount produced 243
+ Its nature and composition 243
+ Amount of straw used for litter 244
+ Sources of loss on keeping 245
+ How to prevent loss 245
+ Use of "fixers," and the nature of their action 245
+ _Cow-manure_--
+ Amount produced 248
+ Its nature and composition 248
+ Amount of straw used as litter 248
+ Sources of loss on keeping 249
+ Advantages of _short dung_ 249
+ _Pig-manure_--
+ Amount produced 250
+ Its nature and composition 250
+ Amount of straw used as litter 251
+ _Sheep-manure_--
+ Amount produced 251
+ Nature and composition 251
+ Amount of straw used as litter 252
+ Methods of calculating amount of manure produced on
+ the farm 252, note
+ Fermentation of farmyard manure--
+ Action of _micro-organic_ life in producing fermentation 255
+ Two classes of _bacteria_ active in this work, _aerobies_
+ and _anaerobies_ 255
+ Conditions influencing fermentation--
+ _Temperature_ 256
+ _Openness to the air_ 256
+ _Dampness_ 257
+ _Composition of manure_ 257
+ Products of fermentation 257
+ Analyses of farmyard manure--
+ Dr Voelcker's experiments 259
+ Variation in composition 259
+ Amounts of _moisture_, _organic matter_
+ (containing _nitrogen_), and _mineral matter_ 260
+ Its manurial value compared with _nitrate of soda_,
+ _sulphate of ammonia_, and _superphosphate_ 260
+ Comparison of fresh and rotten manure--
+ The nature and amount of loss sustained in the process of
+ _rotting_ 261
+ Ought manure to be applied _fresh_ or _rotten_? 262
+ Relative merits of _covered_ and _uncovered_ manure-heaps 263
+ Methods of application of farmyard manure to the field--
+ Merits and demerits of the different methods 265
+ Setting it out in _heaps_ 265
+ Spreading it _broadcast_, and letting it lie 266
+ Ploughing it in immediately 267
+ Value and function of farmyard manure--
+ As a supplier of the necessary elements of plant-food 268
+ As a "universal" manure 269
+ Proportion in which _nitrogen_, _phosphoric acid_, and
+ _potash_ are required by crops 269
+ Proportion in which they are present in farmyard manure 270
+ Farmyard manure _poor in nitrogen_ 270
+ Lawes' and Gilbert's experiments 271
+ How it may be best reinforced by the use of "artificials" 271
+ Indirect value of farmyard manure as a supplier of
+ _humus_ to the soil 273
+ Its influence on soil-texture 273
+ Its influence in setting free inert fertilising matter
+ in the soil 274
+ Rate at which farmyard manure ought to be applied 275
+ Lasting nature of farmyard manure 276
+ Its economic value 276
+
+ APPENDIX TO CHAPTER VII.
+ NOTE
+ I. Difference in amount of excreta voided for food consumed 279
+ II. Solid excreta voided by sheep, oxen, and cows 279
+ III. Urine voided by sheep, oxen, and cows 280
+ IV. Percentage of food voided in the solid and liquid
+ excrements 281
+ V. Pig excrements 281
+ VI. Manurial constituents in 1000 parts of ordinary foods 282
+ VII. Analyses of stable-manure, made respectively with
+ peat-moss litter and wheat-straw 283
+ VIII. Analyses of bracken 283
+ IX. Analyses of horse-manure 283
+ X. The nature of the chemical reactions of ammonia "fixers" 284
+ XI. Analyses of cow-manure 286
+ XII. Composition of fresh and rotten farmyard manure 286
+ XIII. Comparison of fresh and rotten manure 288
+ XIV. Lord Kinnaird's experiments 289
+ XV. Drainings of manure-heaps 290
+ XVI. Amounts of potash and phosphoric acid removed by
+ rotation from a Prussian morgen (.631 acre) 290
+ XVII. Composition of farmyard manure (fresh) 291
+ XVIII. The urine (quantity voided) 291
+
+
+ CHAPTER VIII.--GUANO.
+
+ Importance in agriculture 293
+ Influence on British farming 294
+ Influence of guano not wholly good 295
+ Value of guano as a manure 296
+ Origin and occurrence of guano 297
+ Variation in composition of different guanos 299
+ I. Nitrogenous guano--
+ (_a_) Peruvian guano 300
+ Different deposits of Peruvian guano 301
+ Appearance, colour, and nature of Peruvian guano 303
+ Composition of Peruvian guano 304
+ (_b_) Other nitrogenous manures: Angamos, Ichaboe 306
+ II. Phosphatic guanos--
+ Occurrence of phosphatic guanos 308
+ Inequality in composition of phosphatic guanos 309
+ "Dissolved" phosphatic guano 310
+ "Equalised" or "rectified" guano 311
+ The action of phosphatic guanos as manures 312
+ Proportion of fertilising constituents in guano 314
+ Mode of application of guanos 315
+ Quantity of guano to be used 317
+ Adulteration of guano 318
+ So-called guanos--
+ Fish-guano 320
+ Value of fish-guano 322
+ Meat-meal guano 324
+ Value of meat-meal guano 324
+ Bat guano 325
+ Pigeon and fowl dung 325
+
+ APPENDIX TO CHAPTER VIII.
+ NOTE
+ I. Peruvian guano imported into United Kingdom, 1865-1893 327
+ II. Guano deposits of the world 327
+ III. Composition of concretionary nodules 328
+ IV. Table showing gradual deterioration of Peruvian guano,
+ 1867-1881 329
+ V. Composition of different guanos 329
+ VI. Liebig's theory as to the action of oxalic acid in guano 330
+ VII. Analyses of dung of fowls, pigeons, ducks, and geese 331
+
+
+ CHAPTER IX.--NITRATE OF SODA.
+
+ Amount of exports 332
+ Date of discovery of nitrate deposits 333
+ The origin of nitrate deposits 334
+ Forbes and Darwin on the theory of their origin 335
+ Source of nitric acid in nitrate of soda 337
+ Guano theory of origin of nitrate of soda 337
+ Nitric acid in nitrate of soda probably derived from sea-weed 339
+ Appearance of nitrate-fields 340
+ The method of mining the nitrate of soda 341
+ Composition of _caliche_ 342
+ Extent of the nitrate deposits 342
+ Composition and properties of nitrate of soda 343
+ Nitrate applied as a top-dressing 344
+ Nitrate of soda encourages deep roots 344
+ Is nitrate of soda an exhausting manure? 345
+ Crops for which nitrate of soda is suited 346
+ Method of application of nitrate of soda 347
+ Importance of having a sufficiency of other fertilising
+ constituents 348
+ Conclusions drawn 349
+
+ APPENDIX TO CHAPTER IX.
+
+ Total shipments from South America, 1830-1893 351
+ Total imports into Europe and United Kingdom, 1873-1892 351
+
+
+ CHAPTER X.--SULPHATE OF AMMONIA.
+
+ Value of ammonia as a manure 352
+ Sources of sulphate of ammonia 353
+ Ammonia from gas-works 353
+ Other sources 354
+ Composition, &c., of sulphate of ammonia 355
+ Application of sulphate of ammonia 356
+
+ APPENDIX TO CHAPTER X.
+
+ Production of sulphate of ammonia in United Kingdom, 1870-1892 358
+
+
+ CHAPTER XI.--BONES.
+
+ Early use of bones 359
+ Different forms in which bones are used 360
+ Composition of bones 362
+ The organic matter of bones 363
+ The inorganic matter of bones 363
+ Treatment of bones 364
+ Action of bones 365
+ Dissolved bones 368
+ Crops suited for bones 368
+ Bone-ash 369
+ Bone-char or bone-black 369
+
+ APPENDIX TO CHAPTER XI.
+ NOTE
+ I. Analysis of bone-meal 371
+ II. Analysis of dissolved bones 371
+ III. Composition of bone-ash 372
+ IV. Composition of bone-char 372
+
+
+ CHAPTER XII.--MINERAL PHOSPHATES.
+
+ Coprolites 373
+ Canadian apatite or phosphorite 374
+ Estremadura or Spanish phosphates 375
+ Norwegian apatite 376
+ Charlestown or South Carolina phosphate 376
+ Belgian phosphate 377
+ Somme phosphate 378
+ Florida phosphate 378
+ Lahn phosphate 379
+ Bordeaux or French phosphate 379
+ Algerian phosphate 379
+ Crust guanos 379
+ Value of mineral phosphates as manures 380
+
+ APPENDIX TO CHAPTER XII.
+
+ Imports of phosphates 381
+
+
+ CHAPTER XIII.--SUPERPHOSPHATES.
+
+ Discovery of superphosphate by Liebig 382
+ Manufacture of superphosphate 383
+ Nature of the reaction taking place 385
+ Phosphates of lime 385
+ Reverted phosphate 389
+ Value of reverted phosphate 391
+ Composition of superphosphates 391
+ Action of superphosphates 392
+ Action of superphosphate sometimes unfavourable 395
+ Application of superphosphate 395
+ Value of insoluble phosphates 396
+ Rate at which superphosphate is applied 397
+
+ APPENDIX TO CHAPTER XIII.
+ NOTE
+ I. The formulæ, and molecular and percentage composition,
+ of the different phosphates 398
+ II. Reactions of sulphuric acid and phosphate of lime 398
+ III. Table for conversion of soluble phosphate into insoluble
+ phosphate 399
+ IV. Action of iron and alumina in causing reversion 399
+ V. Relative trade values of phosphoric acid in different
+ manures 400
+
+
+ CHAPTER XIV.--THOMAS-PHOSPHATE OR BASIC SLAG.
+
+ Its manufacture 401
+ Not at first used 403
+ Discovery of its value as a manure 403
+ Composition of basic slag 404
+ Processes for preparing slag 406
+ Solubility of basic slag 408
+ Darmstadt experiments with basic slag 410
+ Results of other experiments 413
+ Soils most suited for slag 414
+ Rate of application 414
+ Method of application 416
+
+ APPENDIX TO CHAPTER XIV.
+
+ Analysis of basic slag 417
+
+
+ CHAPTER XV.--POTASSIC MANURES.
+
+ Relative importance 418
+ Scottish soils supplied with potash 419
+ Sources of potassic manures 419
+ Stassfurt potash salts 420
+ Relative merits of sulphate and muriate of potash 421
+ Application of potash manures 422
+ Soils and crops suited for potash manures 423
+ Rate of application 423
+
+
+ CHAPTER XVI.--MINOR ARTIFICIAL MANURES.
+
+ Scutch 427
+ Shoddy and wool-waste 427
+ Soot 428
+
+
+ CHAPTER XVII.--SEWAGE AS A MANURE.
+
+ Irrigation 431
+ Effects of continued application of sewage 433
+ Intermittent irrigation 434
+ Crops suited for sewage 434
+ Treatment of sewage by precipitation, &c. 436
+ Value of sewage sludge 439
+
+
+ CHAPTER XVIII.--LIQUID MANURE 442
+
+
+ CHAPTER XIX.--COMPOSTS.
+
+ Farmyard manure a typical compost 446
+ Other composts 447
+
+
+ CHAPTER XX.--INDIRECT MANURES.
+
+ Lime 449
+ Antiquity of lime as a manure 449
+ Action of lime 449
+ Lime a necessary plant-food 450
+ Lime of abundant occurrence 452
+ Lime returned to the soil in ordinary agricultural
+ practice 452
+ Different forms of lime 453
+ Caustic lime 453
+ Lime acts both mechanically and chemically 455
+ I. Mechanical functions of lime 455
+ Action on soil's texture 455
+ Lime renders light soils more cohesive 457
+ II. Chemical action of lime 457
+ III. Biological action of lime 459
+ Action of lime on nitrogenous organic matter 460
+ Recapitulation 461
+
+
+ CHAPTER XXI.--INDIRECT MANURES--GYPSUM, SALT, ETC.
+
+ Gypsum 462
+ Mode in which gypsum acts 462
+ Salt 465
+ Antiquity of the use of salt 465
+ Nature of its action 465
+ Salt not a necessary plant-food 466
+ Can soda replace potash? 466
+ Salt of universal occurrence 467
+ Special sources of salt 468
+ The action of salt 468
+ Mechanical action on soils 470
+ Solvent action 470
+ Best used in small quantities along with manures 472
+ Affects quality of crop 472
+ Rate of application 473
+
+
+ CHAPTER XXII.--THE APPLICATION OF MANURES.
+
+ Influence of manures in increasing soil-fertility 474
+ Influence of farmyard manure on the soil 475
+ Farmyard manure _v._ artificials 476
+ Farmyard manure not favourable to certain crops 477
+ Conditions determining the application of artificial manures 477
+ Nature of the manure 478
+ Nitrogenous manures 478
+ Phosphatic manures 480
+ Potash manures 480
+ Nature of soil 481
+ Nature of previous manuring 482
+ Nature of the crop 483
+ Amounts of fertilising ingredients removed from the soil by
+ different crops 484
+ Capacity of crops for assimilating manures 486
+ Difference in root-systems of different crops 488
+ Period of growth 489
+ Variation in composition of crops 490
+ Absorption of plant-food 490
+ Fertilising ingredients lodge in the seed 491
+ Forms in which nitrogen exists in plants 491
+ Bearing of above on agricultural practice 492
+ Influence of excessive manuring of crops 492
+
+
+ CHAPTER XXIII.--MANURING OF THE COMMON FARM CROPS.
+
+ Cereals 493
+ Especially benefited by nitrogenous manures 494
+ Power of absorbing silicates 494
+ Barley 495
+ Period of growth 495
+ Most suitable soil 496
+ Farmyard manure not suitable 497
+ Importance of uniform manuring of barley 497
+ Norfolk experiments on barley 497
+ Proportion of grain to straw 498
+ Wheat 499
+ Rothamsted experiments 500
+ Continuous growth 500
+ Flitcham experiments 500
+ Oats 501
+ A very hardy crop 502
+ Require mixed nitrogenous manuring 502
+ Arendt's experiments 503
+ Avenine 503
+ Quantities of manures 504
+ Grass 504
+ Effect of manures on herbage of pastures 505
+ Influence of farmyard manure 506
+ Influence of soil and season on pastures 507
+ Manuring of meadow land 508
+ Bangor experiments 508
+ Norfolk experiments 509
+ Manuring of permanent pastures 509
+ Roots 510
+ Influence of manure on composition 512
+ Nitrogenous manures increase sugar 512
+ Amount of nitrogen recovered in increase of crop 513
+ Norfolk experiments 513
+ Manure for swedes 514
+ Highland Society's experiments 515
+ Manuring for rich crops of turnips 516
+ Experiments by the author on turnips 516
+ Potatoes 517
+ Highland Society's experiments 518
+ The Rothamsted experiments 519
+ Effect of farmyard manure 520
+ Manuring of potatoes in Jersey 521
+ The influence of manure on the composition 521
+ Leguminous crops 522
+ Leguminous plants benefit by potash 523
+ Nitrogenous manures may be hurtful 523
+ Clover sickness 524
+ Alternate wheat and bean rotation 524
+ Beans 525
+ Manure for beans 525
+ Relative value of manurial ingredients 526
+ Gypsum as a bean manure 526
+ Effect of manure on composition of crop 527
+ Peas 527
+ Hops 528
+ Cabbages 528
+
+ APPENDIX TO CHAPTER XXIII.
+
+ Experiments on bean-manuring 530
+
+
+ CHAPTER XXIV.--ON THE METHOD OF APPLICATION, AND ON THE MIXING OF MANURES.
+
+ Equal distribution of manures 531
+ Mixing manures 532
+ Risks of loss in mixtures 533
+ Loss of ammonia 533
+ Effects of lime on ammonia 535
+ Loss of nitric acid 536
+ Reversion of phosphates 537
+ Manurial ingredients should be applied separately 538
+
+
+ CHAPTER XXV.--ON THE VALUATION AND ANALYSIS OF MANURES.
+
+ Value of chemical analysis 539
+ Interpretation of chemical analysis 539
+ Nitrogen 540
+ Phosphoric acid 541
+ Importance of mechanical condition of phosphate 542
+ Potash 542
+ Other items in the chemical analysis of manures 543
+ Fertilisers and Feeding Stuffs Act 543
+ Different methods of valuing manures 544
+ Unit value of manurial ingredients 544
+ Intrinsic value of manures 545
+ Field experiments 545
+ Educational value of field experiments 547
+ Value of manures deduced from experiments 548
+ Value of unexhausted manures 549
+ Potential fertility of a soil 549
+ Tables of value of unexhausted manures. 551
+
+ APPENDIX TO CHAPTER XXV.
+ NOTE
+ I. Factors for calculating compounds from manurial
+ ingredients 553
+ II. Units for determining commercial value of manures and
+ cash prices of manures 554, 555
+ III. Manurial value of nitrogen and potash in different
+ substances 556
+ IV. Comparative manurial value of different forms of
+ nitrogen and potash 557
+ V. Lawes' and Gilbert's tables for calculating unexhausted
+ value of manures 559
+
+
+ CHAPTER XXVI.--THE ROTHAMSTED EXPERIMENTS.
+
+ Nature of experiments on crops and manures 561
+ Soil of Rothamsted 561
+ Table I. List of Rothamsted field experiments 562
+ Wheat experiments--
+ Unmanured plots 562
+ Wheat grown continuously on same land (unmanured) 562
+ Table II. Results of first eight years 562
+ Table III. Results of subsequent forty years 562
+ Table IV. Wheat grown continuously with farmyard
+ manure (14 tons per annum) 564
+
+ Table V. Wheat grown continuously with artificial
+ manures 565
+ Table VI. Experiments on the growth of barley, forty years,
+ 1852-91 566
+ Table VII. Experiments on the growth of oats, 1869-78 567
+ Table VIII. Experiments on root crops--Swedish turnips 568, 569
+ Table IX. Experiments on mangel-wurzel 568, 569
+ Table X. Experiments with different manures on permanent
+ meadow-land, thirty-six years, 1856-91 570
+ Table XI. Experiments on the growth of potatoes--average for
+ five seasons, 1876-80 571
+ Table XII. Experiments on growth of potatoes (continued)--
+ average for twelve seasons, 1881-92 572
+
+ * * * * *
+
+ INDEX 573
+
+
+
+
+PART I.
+
+HISTORICAL INTRODUCTION
+
+
+
+
+MANURES AND THE PRINCIPLES OF MANURING.
+
+
+HISTORICAL INTRODUCTION.
+
+Agricultural Chemistry, like most branches of natural science, may be
+said to be entirely of modern growth. While it is true we have many old
+speculations on the subject, they can scarcely be said to possess much
+scientific value. The great questions which had first to be solved by
+the agricultural chemist were,--What is the food of plants? and,--What
+is the source of that food? The second of these two questions more
+easily admitted of answer than the first. The source of plant-food could
+only be the atmosphere or the soil. As the composition of the
+atmosphere, however, was not discovered till the close of last century,
+and the chemistry of the soil is a question which is still requiring
+much work ere we shall be in possession of anything like a full
+knowledge of it, it will be at once obvious that the very fundamental
+conditions for a solution of the question were awanting. The beginning,
+then, of a true scientific agricultural chemistry may be said to date
+from the brilliant discoveries associated with the names of Priestley,
+Scheele, Lavoisier, Cavendish, and Black--that is, towards the close of
+last century.
+
+
+_Early Theories on Source of Plant-food._
+
+While this is so, and while we must regard the early attempts made
+towards solving this question as being, for the most part, of little
+scientific value, it is not without interest, from the historical point
+of view, to glance briefly at some of these old interesting
+speculations.
+
+The Aristotelian doctrine, regarding the possibility of dividing matter
+into the so-called four primary elements, _fire_, _air_, _earth_, and
+_water_, which obtained in one form or another till the birth of modern
+chemistry, had naturally an important influence on these early theories.
+
+
+_Van Helmont's Theory._
+
+Among the earliest and most important attempts made to solve the problem
+of plant-growth was that by Jean Baptiste Van Helmont, one of the best
+known of the alchemists, who flourished about the beginning of the
+seventeenth century. Van Helmont believed that he had proved by a
+conclusive experiment that all the products of vegetables were capable
+of being generated from water. The details of this classical experiment
+were as follows:--
+
+"He took a given weight of dry soil--200 lb.--and into this soil he
+planted a willow-tree that weighed 5 lb., and he watered this carefully
+from time to time with pure rain-water, taking care to prevent any dust
+or dirt falling on to the earth in which the plant grew. He allowed this
+to go on growing for five years, and at the end of that period, thinking
+his experiment had been conducted sufficiently long, he pulled up his
+tree by the roots, shook all the earth off, dried the earth again,
+weighed the earth and weighed the plant. He found that the plant now
+weighed 169 lb. 3 ounces, whereas the weight of the soil remained very
+nearly what it was--about 200 lb. It had only lost 2 ounces in
+weight."[1]
+
+The conclusion, therefore, come to by Van Helmont was that the source of
+plant-food was _water_.[2]
+
+
+_Digby's Theory._
+
+Some fifty years later an extremely interesting book was published
+bearing the following title: 'A Discourse concerning the Vegetation of
+Plants, spoken by Sir Kenelm Digby, at Gresham College, on the 23d of
+January 1660. (At a meeting of the Society for promoting Philosophical
+Knowledge by Experiments. London: Printed for John Williams, in Little
+Britain, over against St Botolph's Church, 1669.)' The author attributes
+plant-growth to the influence of a _balsam_ which the air contains. This
+book is especially interesting as containing the earliest recognition of
+the value of saltpetre as a manure. The following is an extract from
+this interesting old work:--
+
+"The sickness, and at last the death of a plant, in its natural course,
+proceeds from the want of that balsamick saline juice; which, I have
+said, makes it swell, germinate, and augment itself. This want may
+proceed either from a destitution of it in the place where the plant
+grows, as when it is in a barren soil or bad air, or from a defect in
+the plant itself, that hath not vigour sufficient to attract it, though
+it be within the sphere of it; as when the root has become so hard,
+obstructed and cold, as that it hath lost its vegetable functions. Now,
+both these may be remedy'd, in a great measure, by one and the same
+physick.... The watering of soils with cold hungray springs doth little
+good; whereas muddy saline waters brought to overflow a piece of ground
+enrich it much. But above all, well-digested dew makes all plants
+luxuriate and prosper most. Now what may it be that endues these liquors
+with such prolifick virtue? The meer water which is common to them all,
+cannot be it; there must be something else enclosed within it, to which
+the water serves but for a vehicle. Examine it by spagyric art, and you
+will find that it is nothing else than a _nitrous salt_, which is
+dilated in the water. It is this salt which gives foecundity to all
+things: and from this salt (rightly understood) not only all vegetables,
+but also all minerals draw their origine. By the help of plain
+_salt-peter_, dilated in water and mingled with some other fit earthy
+substance, that may familiarize it a little with the corn into which I
+endeavoured to introduce it, I have made the barrenest ground far out-go
+the richest, in giving a prodigiously plentiful harvest. I have seen
+hemp-seed soaked in this liquor, that hath in due time made such plants
+arise, as, for the tallness and hardness of them, seemed rather to be
+coppice-wood of fourteen years' growth at least, than plain hemp. The
+fathers of the Christian doctrine at Paris still keep by them for a
+monument (and indeed it is an admirable one) a plant of barley
+consisting of 249 stalks, springing from one root or grain of barley; in
+which they counted above 18,000 grains or seeds of barley. But do you
+think that it is barely the salt-peter, imbibed into the seed or root,
+which causeth this fertility? no: that would be soon exhausted and could
+not furnish matter to so vast a progeny. The salt-peter there is like a
+magnet, which attracts a like salt which foecundates the air, and gave
+cause to the Cosmopolite to say there is in the air a hidden food of
+life."[3]
+
+
+_Duhamel and Hales._
+
+The names of the French writer, Duhamel, and of the English, Stephen
+Hales, may be mentioned in passing as authors of works bearing on the
+question of vegetable physiology. Both of these writers flourished about
+the middle of the eighteenth century. The writings of the former
+contained much valuable information on the effects of grafting, motion
+of sap, and influence of light on vegetable growth, and also the results
+of experiments which the author had carried out on the influence of
+treating plants with certain substances. 'Statical Essays, containing
+Vegetable Staticks; or an Account of some Statical Experiments on the
+Sap of Vegetables, by Stephen Hales, D.D.' (2 vols.), was published in
+London in 1738; and contained, as will be seen from its title, records
+of experiments of very much the same nature as those of Duhamel.
+
+
+_Jethro Tull's Theory._
+
+Some reference may be made to a theory which created a considerable
+amount of interest when it was first published--viz., that of Jethro
+Tull. The chief value of Tull's contribution to the subject of
+agricultural science was, that he emphasised the importance of tillage
+operations by putting forward a theory to account for the fact,
+universally recognised, that the more thoroughly a soil was tilled, the
+more luxuriant the crops would be. As Tull's theory had a very
+considerable influence in stirring up interest in many of the most
+important problems in agricultural chemistry, and as it contained in
+itself much, the value of which we have only of late years come to
+understand, a brief statement of this theory may not be without
+interest.
+
+According to Tull the food of plants consists of the particles of the
+soil. These particles, however, must be rendered very minute before they
+become available for the plant, which absorbs them by means of its
+rootlets. This pulverisation of the soil goes on in nature independently
+of the farmer, but only very slowly, and the farmer has therefore to
+hasten it on by means of tillage operations. The more efficiently these
+operations are carried on, the more abundant will the supply of
+plant-food be rendered in the soil. He consequently introduced and
+advocated the system of horse-hoe husbandry. This theory, he informs us,
+was suggested to him by the custom, which he had noticed on the
+Continent, of growing vines in rows, and hoeing the intervals between
+these rows from time to time. The excellent results which followed this
+mode of cultivation induced him to adopt it in England for his farm
+crops. He accordingly sowed his crops in rows or ridges, wide enough
+apart to admit of thorough tillage of the intervals by ploughing as well
+as by hand-hoeing. This he continued until the plant had reached
+maturity. As to the exact width of the interval most suitable, he made a
+large number of experiments. At first, in the cultivation of wheat, he
+made this interval six feet wide; but latterly he adopted an interval of
+lesser width, that finally arrived at being between four and five feet.
+He likewise experimented on each separate ridge as to which was the best
+number of rows of wheat to be sown, latterly adopting, as most
+convenient, two rows at ten inches apart. The great success which he met
+with in this system of cultivation induced him to publish the results of
+his experiments in his famous work, 'Horse-Hoeing Husbandry.'
+
+While Tull's theory was based on principles at heart thoroughly sound,
+he was carried away by his personal success into drawing unwarrantable
+deductions. Thus he came to the conclusion that rotation of crops was
+unnecessary, provided that a thorough system of tillage was carried out.
+Manures also, according to him, might be entirely dispensed with under
+his system of cultivation, for the true function of all manures is to
+aid in the pulverisation of the soil by fermentation.
+
+The first really valuable scientific facts contributed to the science
+were made by Priestley, Bonnet, Ingenhousz, and Sénébier.
+
+
+_Discovery of the Source of Plants' Carbon._
+
+To Charles Bonnet (1720-1793), a Swiss naturalist, is due the credit of
+having made the first contribution to a discovery of very great
+importance--viz., the true source of the _carbon_, which we now know
+forms so large a portion of the plant-substance. Bonnet, who had devoted
+himself to the question of the function of leaves, noticed that when
+these were immersed in water bubbles were seen, after a time, to collect
+on their surface. De la Hire, it ought to be pointed out, had noticed
+this same fact about sixty years earlier. It was left to Priestley,
+however, to identify these bubbles with the gas he had a short time
+previously discovered--viz., oxygen. Priestley had observed, about this
+time, the interesting fact that plants possessed the power of purifying
+air vitiated by the presence of animal life.[4] The next step in this
+highly interesting and important discovery was taken by John Ingenhousz
+(1730-1799), an eminent physician and natural philosopher. In 1779,
+Ingenhousz published a work in London entitled 'Experiments on
+Vegetables.' In it he gives the results of some important experiments he
+had made on the question already investigated by Bonnet and Priestley.
+These experiments proved that plant-leaves only gave up their oxygen in
+the presence of sunlight. In 1782 he published another work on 'The
+Influence of the Vegetable Kingdom on the Animal Creation.'[5]
+
+The source of the gas, which Bonnet had first noticed to be given off
+from plant-leaves, Priestley had identified as oxygen, and Ingenhousz
+had proved to be only given off under the influence of the sun's rays,
+was finally shown by a Swiss naturalist, Jean Sénébier[6] (1742-1809),
+to be the _carbonic acid gas_ in the air, which the plant absorbed and
+decomposed, giving out the oxygen and assimilating the carbon.
+
+
+_Publication of First English Treatise on Agricultural Chemistry._
+
+In 1795, a book dealing with the relations between chemistry and
+agriculture was published. This work was written by a Scottish nobleman,
+the Earl of Dundonald, and possesses especial interest from the fact
+that it is the first book in the English language on agricultural
+chemistry. The full title is as follows: 'A Treatise showing the
+Intimate Connection that subsists between Agriculture and Chemistry.'
+
+In his introduction the author says: "The slow progress which
+agriculture has hitherto made as a science is to be ascribed to a want
+of education on the part of the cultivators of the soil, and to a want
+of knowledge, in such authors as have written on agriculture, of the
+intimate connection that subsists between the science and that of
+chemistry. Indeed, there is no operation or process not merely
+mechanical that does not depend on chemistry, which is defined to be a
+knowledge of the properties of bodies, and of the effects resulting from
+their different combinations."
+
+In quoting this passage Professor S. W. Johnson remarks:[7] "Earl
+Dundonald could not fail to see that chemistry was ere long to open a
+splendid future for the ancient art that had always been and always will
+be the prime supporter of the nations. But when he wrote, how feeble
+was the light that chemistry could throw upon the fundamental questions
+of agricultural science! The chemical nature of the atmosphere was then
+a discovery of barely twenty years' standing. The composition of water
+had been known but twelve years. The only account of the composition of
+plants that Earl Dundonald could give was the following: 'Vegetables
+consist of mucilaginous matter, resinous matter, matter analogous to
+that of animals, and some proportion of oil.... Besides these,
+vegetables contain earthy matters, formerly held in solution in the
+newly-taken-in juices of the growing vegetables.' To be sure, he
+explains by mentioning in subsequent pages that starch belongs to the
+mucilaginous matter, and that on analysis by fire vegetables yield
+soluble alkaline salts and insoluble phosphate of lime. But these salts,
+he held, were formed in the process of burning, their lime excepted; and
+the fact of their being taken from the soil and constituting the
+indispensable food of plants, his lordship was unacquainted with. The
+gist of agricultural chemistry with him was, that plants 'are composed
+of gases with a small proportion of calcareous matter; for although this
+discovery may appear to be of small moment to the practical farmer, yet
+it is well deserving of his attention and notice.'"
+
+
+_De Saussure._
+
+The year 1804 witnessed the publication of by far the most important
+contribution made to the science up till this time. This was
+'Recherches Chimique sur la Végétation,' by Theodore de Saussure, one of
+the most illustrious agricultural chemists of the century. De Saussure
+was the first to draw attention to the mineral or ash constituents of
+the plant; and thus anticipate, to a certain extent, the subsequent
+famous "mineral" theory of the great Liebig. The French chemist
+maintained that these ash ingredients were essential; and that without
+them plant-life was impossible. He also adduced fresh experiments of his
+own in support of the theory, based on the experiments of Bonnet,
+Priestley, Ingenhousz, and Sénébier, that plants obtain their carbon
+from the carbonic acid gas in the air, under the influence of the
+sunlight. He was of opinion that the _hydrogen_ and _oxygen_ of the
+plant were, probably, chiefly derived from water. He showed that by far
+the largest portion of the plant's substance was derived from the air
+and from water, and that the ash portion was alone derived from the
+soil. To Saussure we owe the first definite statement on the different
+sources of the plant's food. It may be said that the lapse of nearly a
+century has shown his views to be, in the main, correct.
+
+
+_Source of Plant-nitrogen._
+
+There was one question, which, even at that remote period in the history
+of the subject, engaged the attention of agricultural chemists--viz.,
+the question of the source of the plant's _nitrogen_--a question which
+may be fitly described at the present hour as still the burning
+question of agricultural chemistry.[8]
+
+As soon as it was discovered that nitrogen was a constituent of the
+plant's substance; speculations as to its source were indulged in. The
+fact that the air furnished an unlimited storehouse of this valuable
+element, and the analogy of the absorption of carbon (from the same
+source by plant-leaves), naturally suggested to the minds of early
+inquirers that the free nitrogen of the air was the source of the
+plant's nitrogen. As, however, no direct experiments could be adduced to
+prove this theory, and as, moreover, nitrogen was found in the soil, and
+seemed to be a necessary ingredient of all fertile soils, the opinion
+that the soil was the only source gradually supplanted the older theory.
+Little value, however, must be attached to these early theories, as they
+can scarcely be said to have been based on experiments of serious value.
+Indeed it may be safely affirmed, in the light of subsequent
+experiments, that it was impossible for this question to be decided at
+this early period, from the fact that analytical apparatus, of a
+sufficiently delicate nature, was then wholly unknown. Indeed it is only
+within the last few years that it has been possible to carry out
+experiments which may be regarded as at all crucial. A short sketch of
+the development of our knowledge of the relation of nitrogen to the
+plant will be given further on.
+
+
+_Sir Humphry Davy's Lectures._
+
+A series of lectures on agricultural chemistry, delivered by Sir Humphry
+Davy during the years 1802-1812, for the Board of Agriculture, and
+subsequently published in book form in the year 1813,[9] affords us an
+opportunity of gauging, pretty accurately, the state of knowledge on the
+subject at the time.
+
+
+_Position of Agricultural Chemistry at beginning of Century._
+
+In his opening lecture Davy says: "Agricultural chemistry has not yet
+received a regular and systematic form. It has been pursued by competent
+experimenters for a short time only. The doctrines have not as yet been
+collected into any elementary treatise, ... and," he adds, "I am sure
+you will receive with indulgence the first attempt made in this country
+to illustrate it by a series of experimental demonstrations."
+
+He further on remarks: "It is evident that the study of agricultural
+chemistry ought to be commenced by some general inquiries into the
+composition and nature of material bodies, and the law of their changes.
+The surface of the earth, the atmosphere, and the water deposited from
+it, must either together, or separately, afford all the principles
+concerned in vegetation, and it is only by examining the chemical
+nature of these principles that we are capable of discovering what is
+the food of plants, and the manner in which this food is supplied and
+prepared for their nourishment."
+
+Davy goes on further to say: "No general principles can be laid down
+respecting the comparative merits of the different systems of
+cultivation and the various systems of crops adopted in different
+districts, unless the chemical nature of the soil, and the physical
+circumstances to which it is exposed, are fully known."
+
+He recognises the enormous importance of experiments. "Nothing is more
+wanting in agriculture than experiments, in which all the circumstances
+are minutely and scientifically detailed."
+
+In dealing with the composition of plants he says: "It is evident that
+the most essential vegetable substances consist of hydrogen, carbon, and
+oxygen, in different proportions, generally alone; but in some few cases
+combined as carbon and nitrogen. The acids, alkalies, earths, metallic
+oxides, and saline compounds, though necessary in the vegetable economy,
+must be considered as of less importance, particularly in their relation
+to agriculture, than the other principles."
+
+Further on: "It will be asked, Are the pure earths in the soil merely
+active as mechanical or indirect chemical agents, or do they actually
+afford food to the plant?"
+
+This question he answers by saying that "water, and the decomposing
+animal and vegetable matter existing in the soil, constitute the true
+nourishment of plants; and as the earthy parts of the soil are useful in
+retaining water, so as to supply it in the proper proportion to the
+roots of the vegetables, so they are likewise efficacious in producing
+the proper distribution of the animal or vegetable matter. When equally
+mixed with it, they prevent it from decomposing too rapidly; and by
+their means the soluble parts are supplied in proper proportions."
+
+
+_Value of Davy's Lectures._
+
+The chief value of these lectures is due to the fact that they form the
+first attempt to connect in a systematic manner the various scattered
+facts, up to that time ascertained, and to interpret their bearing on
+agricultural practice. We have in them, it is true, a strange mixture of
+facts belonging rather to botany and physiology than to agricultural
+chemistry; still they undoubtedly furnished a great impetus to inquiry,
+and at the same time they did much to popularise the science.
+
+But not merely did Davy summarise and systematise the various results
+arrived at by others, he also made many valuable contributions to the
+science himself. The conclusions he drew from the results he obtained
+were, no doubt, in many cases false, and in other cases exaggerated;
+still the results possess a permanent interest. He may be said to have
+worked out many of the most important _physical_ or _mechanical_
+properties of a soil, although exaggerating the importance of the
+influence of these properties on the question of fertility.[10]
+
+These experiments had to do with the heat- and water-absorbing powers of
+a soil. He experimented on a brown fertile soil, and a cold barren clay,
+and found at what rate they lost heat. "Nothing," he says, "can be more
+evident than that the genial heat of the soil, particularly in spring,
+must be of the highest importance to the rising plant; ... so that the
+temperature of the surface, when bare and exposed to the rays of the
+sun, affords at least one indication of the degree of the fertility."
+
+Again he says: "The power of soils to absorb water from air is much
+connected with fertility.... I have compared the absorbent powers of
+many soils, with respect to atmospheric moisture, and I have always
+found it greatest in the most fertile soils; so that it affords one
+method of judging of the productiveness of land."
+
+Where he erred was in overestimating the functions of the mechanical
+properties of a soil, and in considering fertility to be due to them
+alone.
+
+During the next thirty years or so, little progress seems to have been
+made in the way of fresh experimentation.
+
+
+_Boussingault._
+
+In 1834, Boussingault,[11] the most distinguished French agricultural
+chemist of the century, began that series of brilliant chemico-agricultural
+experiments on his estate at Bechelbronn, in Alsace, the results of which
+have added so much to agricultural science. It was the first instance of
+the combination of "science with practice," of the institution of a
+laboratory on a farm; a combination peculiarly fitted to promote the
+interests of agricultural science, and an example which has been since
+followed with such magnificent results in the case of Sir John Lawes's
+famous Rothamsted Experiment Station, and other less known research
+stations.
+
+Boussingault's first paper appeared in 1836, and was entitled, "The
+amount of nitrogen in different kinds of foods, and on the equal value
+of foods founded on these data."
+
+In the year following other papers were published on such subjects as
+the amount of gluten in different kinds of wheat; on the meteorological
+considerations of how far various agricultural operations--such as
+extensive clearings of wood, the draining of large swamps,
+&c.--influence of climate on a country; and on experiments on the
+culture of the vine.
+
+Boussingault was the first observer to study the scientific principles
+underlying the system of _rotation of crops_. In 1838 he published
+the results of some very elaborate experiments he had carried out on
+this subject. He also was the first chemist to carry out elaborate
+experiments with a view to deciding the question of the assimilation by
+plants of free atmospheric nitrogen. His first contribution to the
+subject was published in 1838, but can scarcely be regarded as
+possessing much scientific value, except in so far as it stimulated
+further research. Some thirteen years later he returned to this
+question; and during the years 1851-1855 carried out most elaborate
+experiments, the results of which, until quite recently, were generally
+regarded as having, along with the experiments of Messrs Lawes, Gilbert,
+and Pugh, definitely settled the question.[12]
+
+In 1839 Boussingault was elected a member of the French Institute, an
+honour paid to him in recognition of his great services to agricultural
+chemistry.[13]
+
+The foregoing is a brief epitome of the history of the development of
+agricultural chemistry up to the year 1840, the year which witnessed the
+publication of one of the most memorable works on the subject, which has
+appeared during the present century--Liebig's first report to the
+British Association, a work which may be described as constituting an
+epoch in the history of the science. Liebig's position as an
+agricultural chemist was so prominent, and his influence as a teacher so
+potent, that a few biographical facts may not be out of place before
+entering upon an estimate of his work.
+
+
+_Liebig._
+
+Liebig was born at Darmstadt in the year 1803. He was the son of a
+drysalter, and early devoted himself to the study of chemistry in the
+only way at first at his disposal--viz., in an apothecary's shop. Soon
+finding, however, his opportunities of study limited, he left the
+apothecary's shop for the University of Bonn. He did not remain long at
+Bonn, but in a short time left that university for Erlangen, where he
+studied for some years, taking his Ph.D. degree in 1822. His subsequent
+studies were carried on at Paris under Gay-Lussac, Thénard, Dulong, and
+other distinguished chemists. Through the influence of A. Humboldt, who
+was at that time in Paris, and whose acquaintance he was fortunate
+enough to make, he was received into Gay-Lussac's private laboratory.
+In 1824--that is, when he was only twenty-one years of age--he was
+appointed Professor _Extraordinarius_ of Chemistry at the University of
+Giessen. Two years later he was appointed to the post of Professor
+_Ordinarius_--an appointment which he held for twenty-five years. In
+1845 he was created Baron, and in 1852 appointed Professor at Munich. He
+died in 1873.
+
+
+_His First Report to British Association._
+
+The report above referred to was made by Liebig at the request of the
+Chemical Section of the British Association. It was read to a meeting of
+the Association held in Glasgow in 1840, and was subsequently published
+in book form, under the title of 'Chemistry in its Application to
+Agriculture and Physiology,' Liebig's position, past training and
+experience were such as to peculiarly fit him for the part of pioneer in
+the new science. As Sir J. H. Gilbert has remarked,[14] "In the
+treatment of his subject he not only called to his aid the previously
+existing knowledge directly bearing upon his subject, but he also turned
+to good account the more recent triumphs of organic chemistry, many of
+which had been won in his own laboratory."
+
+In his dedication to the British Association at the beginning of the
+book, Liebig says: "Perfect agriculture is the true foundation of all
+trade and industry--it is the foundation of the riches of States. But a
+rational system of agriculture cannot be formed without the application
+of scientific principles; for such a system must be based on an exact
+acquaintance with the means of nutrition of vegetables, and with the
+influence of soils and actions of manure upon them. This knowledge we
+must seek from chemistry, which teaches the mode of investigating the
+composition and of studying the characters of the different substances
+from which plants derive their nourishment."
+
+
+_His criticism of the "Humus" Theory._
+
+The first subject which Liebig discusses is the scientific basis of the
+so-called "humus" theory. The humus theory seems to have been first
+promulgated by Einhof and Thaer towards the close of last century. Thaer
+held that humus was the source of plant-food. He stated in his published
+writings that the fertility of a soil depended really upon its humus;
+for this substance, with the exception of water, is the only source of
+plant-food. De Saussure, however, by his experiments--the results of
+which he had published in 1804--had shown the fallacy of this humus
+theory; and his statements had been further developed and substantiated
+by the investigations of the French chemist Braconnot and the German
+chemist Sprengel. Despite, however, the experiments of Saussure,
+Braconnot, and Sprengel, the belief that plants derived the
+carbonaceous portion of their substance from humus still seemed to be
+commonly held in 1840.
+
+While Liebig, therefore, can scarcely be said to have been the first to
+controvert the humus theory, he certainly dealt it its death-blow. He
+reasserted de Saussure's conclusions, and by some simple calculations
+showed very clearly that it was wholly untenable. One of the most
+striking of the arguments he brought forward was the fact that the humus
+of the soil itself consisted of the decayed vegetable matter of
+preceding plants. This being so, how, he asked, could it be the original
+source of the carbon of plants? To reason thus was simply to reason in a
+circle. He pointed out, further, that the comparative insolubility of
+humus in water, or even in alkaline solutions, told against its
+acceptance as correct.
+
+
+_His Mineral Theory._
+
+Having thus controverted the humus theory, he then goes on to deal with
+the question of the source of the various plant constituents. In
+treating of the relation of the soil to the plant, he puts forward his
+"mineral" theory. It cannot be doubted that, while the advance of
+science since Liebig's time has induced us to considerably modify his
+mineral theory, it contained the statement of one of the most important
+facts in the chemistry of plant physiology. He was the first to fully
+estimate the enormous importance of the mineral portion of the plant's
+food, and point the way to one of the chief sources of a soil's
+fertility. Up to this period the ash constituents had been generally
+considered to be of minor importance. By emphasising the contrary
+opinion, and insisting upon their essentialness to plant-life, he gave
+to agricultural research a fresh impetus upon the right lines. His
+statement of his mineral theory was in the main true, but was not the
+whole truth.
+
+De Saussure, as has already been pointed out, to a certain extent,
+anticipated Liebig's mineral theory. He was of the opinion that whatever
+might be the case with some of the mineral constituents of plants,
+others were necessary, inasmuch as they were always found in the ash. Of
+these he instanced the alkaline phosphates. "Their small quantity does
+not indicate their inutility," he sagaciously remarks. Sir Humphry Davy,
+as has already been pointed out, missed recognising the true importance
+of the ash constituents. It was left to Liebig, then, to restate the
+important doctrine of the essentialness of the mineral matter, already
+implied to some extent by de Saussure.
+
+Liebig says: "Carbonic acid, water, and ammonia are necessary for the
+existence of plants, because they contain the elements from which their
+organs are formed; but other substances are likewise necessary for the
+formation of certain organs destined for special functions, peculiar to
+each family of plants. Plants obtain these substances from inorganic
+nature."
+
+While insisting on the importance of the mineral constituents, he did
+so in a more or less general way not sufficiently distinguishing one
+mineral constituent from another.
+
+As all plants contained certain organic acids, and as these organic
+acids were nearly always found in a neutral state--_i.e._, in
+combination with bases, such as potash, soda, lime, and magnesia--the
+plant must be in a position to take up sufficient of these alkaline
+bases to neutralise these acids. Hence the necessity of these mineral
+constituents in the soil. According to him, however, the exact nature of
+the bases was a point of not so much importance. He assumed, in short,
+as has been pointed out by Sir J. H. Gilbert, a greater amount of mutual
+replaceability amongst the bases than can be now admitted.
+
+Passing on to a consideration of the difference of the mineral
+composition of different soils, he attributes this to the difference in
+the rocks forming the soils. "Weathering" is the great agent at work in
+rendering available the otherwise locked-up stores of fertility. He
+attributes the benefits of fallow exclusively to the increased supply of
+these incombustible compounds which were thus rendered available to the
+plant. Treating of this subject, he says: "From the preceding part of
+this chapter" (in which he has been explaining weathering) "it will be
+seen that fallow is that period of culture when the land is exposed to
+progressive disintegration by the action of the weather, for the purpose
+of liberating a certain quantity of alkalies and silica, to be absorbed
+by future plants."
+
+
+_His Theory of Manures._
+
+Treating of manures, he showed how the most important constituents of
+manures were _potash_ and _phosphates_. In the first edition of his work
+he also insisted on the value of _nitrogen_ in manures, condemning the
+want of precautions, in the treatment of animal manures, against loss of
+nitrogen.
+
+In the later editions of his work he seems to have receded from that
+opinion, and considered that there was no necessity for supplying
+nitrogen in manures, since the ammonia washed down in rain was a
+sufficient source of all the nitrogen the plant required. It was here
+that Liebig went astray, first in denying the importance of supplying
+nitrogen as a manure; and secondly, in overestimating the amount of
+ammonia washed down in rain, which has subsequently been shown to be
+entirely inadequate to supply plants with the whole of their
+nitrogen.[15]
+
+
+_His Theory of Rotation of Crops._
+
+In explaining the benefits of the rotation of crops, Liebig propounded a
+very ingenious theory, but one which was largely of a speculative
+nature, and which has since been shown to be unfounded on any scientific
+basis. It was to the effect that one kind of crop excreted matters which
+were especially favourable to another kind of crop. He did not say
+whether he considered such excretion positively injurious to the crop
+which excreted them; but he inferred that what was excreted by the crop
+was what was not required, and what could, therefore, be of little
+benefit to a crop of the same nature following it.
+
+The second portion of Liebig's report dealt with the processes of
+fermentation, decay, and putrefaction.
+
+
+_Publication of Liebig's Second Report to British Association._
+
+In 1842 Liebig contributed his second famous report to the British
+Association, subsequently published under the title of 'Animal
+Chemistry; or, Organic Chemistry in its Applications to Physiology and
+Pathology.' The publication of this report created even greater interest
+than the publication of his first work. In it he may be said to have
+contributed as much to animal physiology, as, in his first, he did to
+agricultural chemistry. His subsequent principal works on agricultural
+chemistry were--'Principles of Agricultural Chemistry,' published in
+1855, and 'On Theory and Practice in Agriculture,' 1856.
+
+
+_Liebig's services to Agricultural Chemistry._
+
+An attempt has been made to sketch in the very briefest manner some of
+the main points in Liebig's teaching, as contained in his famous report
+to the British Association in 1840. Agricultural chemistry up till that
+year can scarcely be described as having a distinct existence as a
+branch of chemistry. Much valuable work, it is true, had already been
+done, especially by his two great predecessors, de Saussure and
+Boussingault; but it was, down to the year 1840, a science made up of
+isolated facts. Liebig's genius formed it into an important branch of
+chemistry, supplied the necessary connection between the facts, and by a
+series of brilliant generalisations formed the principles upon which all
+subsequent advance has been built.
+
+As has already been indicated, Liebig's chief claim to rank as the
+greatest agricultural chemist of the century does not rest upon the
+number or value of his actual researches, but on the formative power he
+exercised in the evolution of the science. His master-mind surveyed the
+whole field of agricultural chemistry, and saw laws and principles where
+others saw simply a confusion of isolated, and, in many cases, seemingly
+contradictory facts.
+
+But great as the direct value of Liebig's work was, it may be questioned
+whether its indirect value was not even greater. The publication of his
+famous work had the effect of giving a general interest to questions
+which up till then had possessed a special interest, and that for
+comparatively few. Both on the Continent and in England a very large
+amount of discussion took place regarding his various theories.
+
+
+_Development of Agricultural Research in Germany._
+
+It was especially in Germany, however, that Liebig's work bore its
+greatest and most immediate fruit. Thanks to the great chemist, the
+German Government recognised the importance of forwarding scientific
+research by State aid. Agricultural Departments were added to some of
+the universities, largely at State expense, while agricultural research
+stations were, one after another, instituted in different parts of the
+country.
+
+The first of the agricultural research stations to be founded was the
+now famous one of Möckern, near Leipzig. It was instituted in the year
+1851. Others followed, until at the present day there are some seventy
+to eighty of these _Versuchs-Stationen_ scattered throughout Germany,
+all well equipped and doing excellent work. Some idea of the activity of
+the German stations may be inferred when it is stated that up to the
+year 1877 the total number of papers embodying the results of their
+experiments published by them amount to over 2000.[16]
+
+To trace the development of agricultural chemistry, subsequent to
+Liebig's time, in the way it has been done prior to the year 1840, is no
+longer possible. This is due to the enormous increase in the number of
+workers in the field, as also to the overlapping nature of their work,
+which renders a strict chronological record wellnigh an impossibility.
+It will be better, therefore, to attempt to give a brief statement of
+our present knowledge on the subject, naming the chief workers in the
+various departments of the subject.
+
+
+_The Rothamsted Experiments._
+
+Before doing so, it is fitting that reference should be made to the work
+and experiments of two living English chemists, who have done much to
+contribute to our knowledge in every branch of the science--viz., Sir
+John Lawes, Bart., and Sir J. H. Gilbert, F.R.S.
+
+The fame of the Rothamsted experiments is now world-wide; and no single
+experiment station has ever produced such an amount of important work as
+the magnificently equipped research station at Rothamsted. The
+Rothamsted station may be said to date from 1843, although Sir John
+Lawes was engaged in carrying out field experiments for ten years
+previous to that date.[17] In 1843 Sir John Lawes associated with
+himself the distinguished chemist Sir J. H. Gilbert, and the numerous
+papers since published have almost invariably borne the two names. The
+expense of working the station has been borne entirely by Sir John Lawes
+himself; who has further set aside a sum of £100,000, the Laboratory,
+and certain areas of land, for the continuance of the investigations
+after his death. The fields under experimentation amount to about fifty
+acres. By a Trust-deed, which was signed on February 14, 1889, Sir John
+Lawes has made over the Rothamsted Experimental Station to the English
+nation, to be managed by trustees.
+
+It is impossible to enter, in any detail, into the nature and scope of
+the Rothamsted experiments.[18] It may be stated that, since the year
+1847, some eighty papers have been published on field experiments, and
+experiments on vegetation; while thirty papers have been published
+recording experiments on the feeding of animals.[19]
+
+What has all along characterised these valuable experiments has been
+their practical nature. While their aim has been entirely scientific,
+the scale of the experiments and the conditions under which they have
+been carried out, have been such as to render them essentially
+_technical_ experiments. For this reason their results possess, and will
+always possess, a peculiar interest for every practical farmer.
+
+The greatest services the Rothamsted experiments have rendered
+agricultural chemistry have been the valuable contributions they have
+made to our knowledge of the function of nitrogen in agriculture; its
+relation in its different chemical forms to plant-life; and the sources
+of the nitrogen found in plants. Researches of a most elaborate nature
+have been carried out on what is still one of the most keenly debated
+questions of the present hour--viz., the relation of the "free" nitrogen
+in the atmosphere to the plant. Of the very highest value also have been
+the elaborate researches of Mr R. Warington, F.R.S., on the important
+question of _Nitrification_, which have been in course in the Rothamsted
+Laboratory for the last fifteen years, and to which full reference will
+be made in the chapter on Nitrification.
+
+To the Rothamsted experiments also we owe the refutation of Liebig's
+mineral theory. In fact it may safely be said that no experimenters in
+the field of agricultural chemistry have made more numerous or valuable
+contributions to the science than these illustrious investigators.
+
+
+_Review of our present Knowledge of Agricultural Chemistry._
+
+Some attempt may now be made to indicate briefly our present knowledge
+of the more important facts regarding plant physiology, agronomy, and
+manuring.
+
+
+_Proximate Composition of the Plant._
+
+The great advance made in the direction of the improvement of the
+accuracy of old analytical processes and the discovery of numerous new
+ones have furnished us with elaborate analyses of the composition of
+plants. We now know that the plant-substance is made up of a large
+number of complex organic substances, formed out of carbon, hydrogen,
+oxygen, and nitrogen,[20] and that these substances form, on an average,
+about 95 per cent of the dry vegetable matter; the other 5 per cent
+being made up of mineral substances. As to the source of these different
+substances, our knowledge is, on the whole, pretty complete. With regard
+to the carbon of green-leaved plants, which amounts to from 40 to 50 per
+cent, subsequent research has confirmed Sénébier and de Saussure's
+conclusions, that its source is the carbonic acid gas of the air. The
+decomposition of the carbonic acid gas is effected by the leaves under
+the influence of sunlight. That a certain quantity of carbon may be
+obtained from the carbonic acid absorbed by plant-roots, is indeed
+probable. Especially during the early stages of plant-growth this source
+of carbon may be of considerable importance. Generally speaking,
+however, it may be said of all green-leaved plants, that the chief
+source of their carbon is the carbonic acid gas in the atmosphere.
+
+
+_Carbon Fixation by Plants._
+
+The exact way in which this decomposition of carbonic acid gas is
+effected by the leaves is not yet clear. It seems to be directly
+dependent, in some way or other, on the chlorophyll, or green colouring
+matter. This decomposition of carbonic acid, and the fixation of the
+carbon by the plant with the formation of starch, takes place only under
+the influence of sunlight. During the night a reflex action takes place,
+which is commonly known as _respiration_, and which is exactly analogous
+to animal respiration.[21] The rate at which the fixation of carbon
+takes place depends on the strength of the sun's rays. It seems to take
+place very rapidly under a strong tropical sun.[22] The action of
+sunlight on the absorption of carbon has been studied by a number of
+observers, among others by Sachs, Draper, Cloez, Gratiolet, Caillet,
+Prillieux, Lommel, &c.
+
+
+_Action of Light on Plant-growth._
+
+Experiments made by several observers, more especially Pfeffer, have
+shown that the yellow rays of the solar spectrum are the most potent in
+inducing this decomposition.
+
+Some interesting experiments have been carried out by different
+observers on the possibility of growing plants under the influence of
+artificial light. While it would seem that the light from oil-lamps or
+gaslight is unable to promote growth, except in very exceptional cases,
+the electric light, or other strong artificial light, seems to be
+capable of taking the place of sunlight. Heinrich was the first to show
+that sunlight could be replaced by the magnesium light.
+
+Experiments with the electric light have been carried out by
+Hervé-Mangon in France and Dr Siemens in England. The plants grown under
+the influence of the electric light were observed to be of a lighter
+green colour than those grown under normal conditions, thus indicating a
+feebler growth; in fact, Siemens was of the opinion that the electric
+light was about half as effective as daylight.[23]
+
+These experiments are interesting from an industrial point of view; for
+it is conceivable that at some distant time electricity might be called
+to the aid of the agriculturist.
+
+
+_Source of Plants' Oxygen._
+
+With regard to the source of the oxygen, which, next to carbon, is the
+element most largely present in the plant's substance--amounting to,
+roughly speaking, about 40 per cent--all evidence seems to indicate that
+it is chiefly derived from water, which is also the source of the
+plant's hydrogen. In addition to water, carbonic acid and nitric acid
+may also furnish small quantities. It has been pretty conclusively
+proved that the atmospheric oxygen, while necessary to plant-growth, and
+promoting the various chemical vital processes, is not a direct source
+of the plant's oxygen. The important function played by atmospheric
+oxygen in certain stages of the plant's growth has been long recognised.
+Malpighi, nearly two hundred years ago, observed that for the process of
+germination atmospheric air was necessary; and shortly after the
+discovery of the composition of the air was made, oxygen was identified
+as the important gas in promoting this process. Oxygen is also
+especially necessary during the period of ripening.
+
+
+_Source of Plants' Hydrogen._
+
+Hydrogen, which amounts to about 6 per cent, is, as has already been
+pointed out, chiefly derived from water. It is possible that ammonia
+also may form a source.
+
+
+_Source of Plants' Nitrogen._
+
+When we come to treat of the source of the nitrogen, which is found in
+the plant's substance to an extent varying from a fraction of a per cent
+to about 4 per cent, we enter on a much more debated question.
+
+What is the source, or, what are the sources, of plant-nitrogen? is a
+question to the solution of which more time and more research have been
+devoted than to the solution of any other question connected with
+agricultural chemistry.
+
+The most obvious source is the free nitrogen, which forms four-fifths of
+the atmospheric air. Reference has already been made to this
+question.[24] Priestley was the first of the long list of experimenters
+on this interesting question.
+
+As far back as 1771 he affirmed that certain plants had the power of
+absorbing free nitrogen; and this opinion he supported by the results of
+certain experiments he had made on the subject. Eight years
+later,--viz., in 1779--Ingenhousz further supported this conclusion, and
+stated that all plants could absorb, within the space of a few hours,
+noticeable quantities of nitrogen gas. The first to oppose this theory
+was de Saussure, who, in 1804, carried out experiments which showed that
+plants were unable to utilise free nitrogen.
+
+Subsequent experiments, carried out by Woodhouse and Sénébier, supported
+de Saussure's conclusions. Mention has already been made of
+Boussingault's elaborate researches on the subject.[25] His first
+experiments were carried out in 1838. He concluded that plants did not
+absorb free nitrogen. Georges Ville was the first to reassert the older
+theory, put forward by Priestley and Ingenhousz. His opinion was founded
+on experiments he had carried out during the years 1849-52. The subject
+created so much interest at the time, that a committee of the French
+Academy--consisting of Dumas, Regnault, Péligot, Chevreul, and
+Decaisne--were appointed to investigate Ville's experiments. The result
+of the investigation of the Commission was to confirm Ville's
+experiments. It is a significant fact, however, that the plant
+experimented with by the Commission was _cress--a non-leguminous
+plant_. It has been commonly assumed that the results of recent
+experiments have confirmed Ville's experiments. It is only proper to
+point out that this is not a necessary inference. The assimilation of
+free nitrogen by the _leguminosæ_, so far as modern research has
+revealed, only takes place under the influence of micro-organic life.
+Ville's experiments, however, were supposed to be conducted under
+_sterilised_ conditions.
+
+In the meantime the results of Boussingault's second series of
+experiments, carried out between the years 1851 and 1855, were
+published, and confirmed his earlier experiments.
+
+The results of a large number of experiments subsequently carried out
+were in support of Boussingault's conclusions. Among them may be
+mentioned Mène, Harting, Gunning, Lawes, Gilbert and Pugh, Roy,
+Petzholdt, and Bretschneider.
+
+Such an amount of overwhelming evidence might naturally have been
+regarded as conclusively proving that the free nitrogen of the air is
+not an available source of nitrogen to the plant. The question, however,
+was not decided. In 1876 Berthelot reopened it. From experiments he had
+carried out, he concluded that free nitrogen was fixed by various
+organic compounds, under the influence of silent electric discharges. In
+1885 he carried out further experiments, from which he concluded that
+argillaceous soils had the power of fixing the free nitrogen of the
+atmosphere. This they effected, he was of opinion, through the agency of
+micro-organisms. Schloesing has recently shown that this fixation of
+free nitrogen by soils is extremely doubtful.[26] The gain of nitrogen
+observed under such conditions can be explained by the absorption by the
+soil of combined nitrogen--viz., ammonia--from the air.
+
+Berthelot's early experiments in 1876 had the effect of stimulating a
+number of other experiments, with the result that we now possess the
+solution of this long-debated and most important problem.
+
+The names of the better known investigators on this subject, in addition
+to Berthelot's, are those of Hellriegel, Wilfarth, Dehérain, Joulie,
+Dietzell, Frank, Emil von Wolff, Atwater, Woods, Nobbe, Ward, Breal,
+Boussingault, Wagner, Schultz-Lupitz, Fleischer, Pagnoul, Schloesing,
+Laurent, Petermann, Pradmowsky, Beyrenick, Lawes, and Gilbert.
+
+It is impossible to enter into the details of these most important
+experiments. An attempt may be made, instead, briefly to epitomise them.
+
+
+_Recent Experiments on Nitrogen question._
+
+In the first place, it may be asked, How is it possible that the
+previous elaborate experiments, published prior to 1876, should now
+prove unreliable? A satisfactory explanation may be found in the fact,
+as Lawes and Gilbert have recently pointed out, that the fixation of the
+free nitrogen by the plant, or within the soil, takes place, if at all,
+through the agency of electricity or of micro-organisms, or of both.
+The earlier experiments, however, were so arranged as to exclude the
+influence of either of those agencies.
+
+The question has further been limited in its scope. It is now supposed
+that only plants of the _leguminous_ order have the power of drawing
+upon the free atmospheric nitrogen. Of the experiments above referred
+to, those of Hellriegel and Wilfarth are the most striking and
+important. They found in their experiments, that while the legumes have
+the power of obtaining their nitrogen from the air, cereals have not.
+Similar experiments by Atwater in America, and others, support this
+conclusion.
+
+Their conclusions may be briefly epitomised as follows:--
+
+(_a_) That the leguminous plants--such as peas, &c.--have the power of
+drawing their nitrogen supplies from the free nitrogen of the air in a
+way not possessed by other plants; and that they thus possess two
+sources of nitrogen--the soil and the air.
+
+(_b_) That this absorption of free nitrogen is not effected directly by
+the plant, but is the result, so to speak, of the joint action of
+certain micro-organisms present in certain soils and in the plant
+itself, (_symbiosis_).
+
+(_c_) That this fixation is connected with the formation of minute
+tubercles on the roots of the plants of the leguminous class; and that
+these tubercles may be the home of the fixing organism.
+
+(_d_) That these fixing micro-organisms are not present in all
+soils.[27]
+
+While the relation of free nitrogen to the plant has long been, and
+still is, a very obscure problem, it was early recognised that the
+combined nitrogen present in soils and manures was an important source
+of plant-food. Reference has already been made to the early theory of
+Sir Kenelm Digby regarding the value of nitrates.[28] De Saussure, as we
+have also already seen, was fully impressed with the importance of
+applying nitrogen to the soil as a manure. Liebig's early attitude on
+this question was to the effect, that to apply nitrogen in manures was
+quite unnecessary, as the plant had a sufficient source in the ammonia
+present in the air, which he erroneously supposed was sufficient in
+quantity to supply all the needs of the crops. Despite this early
+recognition of the value of combined nitrogen to the plant, it is only
+of recent years that we have obtained any definite knowledge as to the
+respective value of its different compounds as manures, or as to the
+form in which it is assimilated by the plant. It exists in three
+forms--(1) as organic nitrogen; (2) as ammonia salts; (3) as nitrates
+and nitrites. Much experimental work has during late years been devoted
+to studying the comparative action and merits of these three forms.
+
+
+_Relation of Organic Nitrogen to the Plant._
+
+First, as to the relation of organic nitrogen to the plant. There is a
+large number of different organic compounds which contain nitrogen. That
+the plant is able to assimilate certain of these organic compounds,
+seems, from several experiments, to be extremely probable. From certain
+researches, carried out as far back as the year 1857, Sir Charles
+Cameron concluded that the plant could assimilate one of them--viz.,
+_urea_. From what, however, we have subsequently learned regarding the
+process of "nitrification," it is quite probable that the nitrogen in
+these experiments was first converted into nitrates before being
+assimilated. At any rate, as the plants were not tested for urea, the
+experiments must be regarded as leaving the problem unsolved.
+
+Other experiments were carried out of a similar nature by Professor S.
+W. Johnson, the different kinds of nitrogen experimented with being
+_uric acid_, _hippuric acid_, and _guanine_. But here, again, no
+definite conclusion can be drawn, as no analyses were made of the
+plants. More recently, however, Dr Hampe has carried out experiments
+with _urea_, _uric acid_, _hippuric acid_, and _glycocoll_. These
+experiments may be held as demonstrating the fact that at least one
+organic compound of nitrogen is capable of being assimilated, as urea
+was actually identified as being present in the plants experimented
+with. From further experiments, carried out by Dr Paul Wagner and
+Wolff, _glycin_, _tyrosin_, and _kreatin_ are able to be assimilated by
+the plant.
+
+
+_Plants able to absorb certain Forms of Organic Nitrogen._
+
+We may conclude, then, from these interesting experiments, that plants
+are able to absorb certain organic forms of nitrogen. That they do so in
+nature to any extent is extremely improbable, such organic forms of
+nitrogen being rarely present in the soil, or if present, being
+converted into ammonia or nitrate salts before assimilation.
+
+
+_Nature of Humus in the Soil._
+
+While on the subject of organic nitrogen, reference may be briefly made
+to that substance known as _humus_,--the name applied to the organic
+portion of soils,--a substance which figures so largely in early
+theories of plant-nutrition. The most elaborate investigation of the
+composition of humus has been carried out by Mulder. According to
+Mulder, it is composed of a number of organic bodies, and he has
+identified the following substances--ulmin, humin, ulmic, humic, geic
+acids, &c. These bodies are composed of carbon, hydrogen, and oxygen,
+which are invariably associated with nitrogen. Detmer and Simon have
+further investigated the subject. The true function of humus, it would
+seem, in addition to its numerous mechanical properties, is to furnish,
+by its decomposition, carbonic acid and nitrogen--in the form of
+ammonia and nitric acid--to the soil; the former acting as a solvent of
+the mineral food, the latter as the source of the plant's nitrogen. The
+old theory, therefore, that the presence of humus in a soil is a
+condition of fertility, is not so far removed from the truth. Where
+there is an abundance of humus in the soil there is likely also to be an
+abundance of nitrogen.
+
+
+_Relation of Ammonia to the Plant._
+
+It seems to be beyond doubt that nitrogen is directly absorbed by plants
+in the form of ammonia. Liebig, as we have seen, concluded that this was
+the great source of nitrogen for the plant, and that the ammonia
+compounds present in the air were an all-sufficient supply. Subsequent
+research, while confirming his belief so far as regards the capability
+of plants to assimilate nitrogen in the form of ammonia, has proved that
+the amount of ammonia present in the air is very minute, and utterly
+inadequate to supply the plant with the whole of its nitrogen.
+Investigations have been made on this subject by Graeger, Fresenius,
+Pierre, Bineau, and Ville. According to Ville's researches, which are
+among the most recent, the amount does not exceed 30 _parts per thousand
+million parts of air_.[29] Some conception of the value of this source
+of nitrogen may be gained by estimating the quantity falling, dissolved
+in rain, on an acre of soil throughout the year. Various estimations of
+the total amount of combined nitrogen, which is in this way brought to
+the soil, have been made. A certain amount of discrepancy, it is true,
+is to be found in these various estimations, no doubt largely due to the
+difference in the circumstances under which the investigations were
+carried out. Mr Warington has made several investigations at Rothamsted,
+and, according to his most recently published figures, the total
+quantity only amounts to 3.37 lb. per acre per annum--of which only 2.53
+lb. is as ammonia itself.[30]
+
+As already mentioned, there can be little doubt that plants can absorb
+nitrogen in the form of ammonia. The question of how far plant-leaves
+are able to absorb ammonia is a much debated one. It is probable that if
+they can do so, it is only to a very small extent.[31] The question as
+to whether the plant's roots can absorb ammonia or not, is also a very
+keenly debated one. The point is a very difficult one to decide, and is
+much complicated by the consideration that ammonia, when applied to the
+the soil, is so speedily converted into nitric acid. Despite, however,
+these difficulties, and the vast amount of controversy on the point, the
+experiments of Ville, Hosäus and Lehmann, seem to indicate beyond doubt
+that ammonia is a direct source of nitrogen. Lehmann's experiments would
+seem, further, to indicate that there are certain periods of a plant's
+growth when its preference for ammonia salts seems to be greater than at
+other times. The point, however, it must be confessed, is still an
+obscure one. The great difficulty in deciding it, as has just been said,
+lies in the fact that ammonia salts, when applied to a soil, are, by the
+process of nitrification, converted into nitrates. In experimenting,
+therefore, with ammonia, and noting the results, it is wellnigh
+impossible to say, except by subsequent analyses, whether the nitrogen
+in the ammonia salts has not been converted into nitrates before
+assimilation.
+
+
+_Relation of Nitric Acid to the Plant._
+
+Thirdly, as to nitrogen in the form of nitrates. While it is true that
+plants can absorb nitrogen in certain organic forms and as ammonia
+salts, it is now a well-known fact that the chief, and by far the most
+important, source of nitrogen is nitric acid. Probably more than 90 per
+cent of the nitrogen absorbed by green-leaved plants from the soil is
+absorbed as nitrates. The tendency of all nitrogen compounds in the soil
+is towards conversion into nitric acid. It is the final form of nitrogen
+in the soil. The precise method in which this conversion takes place is
+a discovery of only a few years' standing. The great economic importance
+of this discovery, made by the French chemists Schloesing and Müntz, and
+associated in this country with the names of Warington, Munro, and P. F.
+Frankland, is only gradually being appreciated. It is without doubt one
+of the most interesting made in the domain of agricultural chemistry of
+late years.
+
+
+_Nitrification._
+
+It was in the year 1877 that the two French chemists above referred to
+published the results of some experiments they had carried out, which
+proved that nitrification--the name given to the process by which
+ammonia or other nitrogen salts are converted in the soil into nitric
+acid--was due to the action of micro-organic life.
+
+The basis of the theory rests upon the fact that dilute solutions of
+ammonia salts or urine, containing all the necessary constituents of
+plant-food, if previously sterilised, may be kept for an indefinitely
+long period of time, provided the air supplied be filtered through
+cotton wool,--so as to prevent the entrance of micro-organisms--without
+any formation of nitrates. Introduce, however, into such a solution a
+little fresh soil, and nitrification will soon follow.
+
+The conditions under which the nitrification ferment acts, as well as
+the nature of the ferment, or rather ferments, have subsequently been
+carefully studied by Schloesing and Müntz, Winogradsy, Dehérain,
+Kellner, and other Continental observers, and especially by Warington,
+Munro, and P. F. Frankland in this country. These conditions cannot be
+gone into here. They will be fully discussed in the chapter on
+Nitrification. Briefly stated, they are a certain range of temperature
+(between slightly above freezing-point and 50° C., the maximum activity
+taking place, according to Schloesing and Müntz, at about 30° C.); a
+plentiful supply of atmosphere oxygen (hence the fact observed by
+Warington, that nitrification is chiefly limited to the surface-soil); a
+certain amount of moisture; and the presence of certain of the necessary
+mineral plant constituents, and the presence of carbonate of lime.
+
+The light which these discoveries throw upon the extremely complicated
+question of the fertility of the soil is considerable, as it follows
+that no soil can be regarded as really a fertile one in which the
+process of nitrification does not freely take place. They furthermore
+explain many facts, hitherto observed but not well understood, with
+regard to the action of different nitrogenous manures.
+
+
+_Ash Constituents of the Plant._
+
+We now come to consider the present state of our knowledge on the
+essentialness of the ash or mineral portion of the plant. While a
+portion of the plant's substance which, up to Liebig's time, had
+obtained little notice, it has, since the publication of his famous
+"mineral" theory, obtained an ever-increasing amount of investigation.
+
+Up till 1800 practically nothing was known of the function of the ash
+constituents. In 1802 de Saussure wrote that it was unknown whether the
+constituents of many plants were due to the soils on which they grew, or
+whether they were the products of vegetable growth. Some two years
+later, however, he was enabled to carry out a number of experiments
+which really placed the subject on a firm scientific basis. The
+essentialness of the ash constituents was only, however, placed beyond
+all doubt by Wiegmann and Polstorff's researches, carried out in 1840.
+
+Reference has already been made to the great stimulus given to research
+by the promulgation of Liebig's mineral theory.
+
+
+_Methods of Research._
+
+In epitomising the vast amount of work carried on since 1840, with the
+view of ascertaining the essentialness of the various substances found
+in the ash of plants, two methods of experimentation have been
+followed.
+
+
+_Artificial Soils._
+
+The first of these two methods was that adopted in the famous
+experiments, carried out by Prince Salm-Horstmar, which have done so
+much to further our knowledge on this question. It consisted in growing
+plants on an artificial soil--formed out of sugar-charcoal, pulverised
+quartz or purified sand--to which were added the different food
+constituents.
+
+
+_Water-culture._
+
+While the results obtained by Prince Salm-Horstmar by this method were
+of a most valuable nature, subsequent experimenters have abandoned his
+method for the other method--viz., "water-culture." The medium used in
+this process is pure water; and it is from experiments carried out in
+water-culture that much of our present knowledge, in regard to the
+relation of the ash constituents to the plant, is due.
+
+The names of those who have worked in this department are very numerous.
+Among them may be mentioned Knop, Sachs, Stohmann, Nobbe, Rautenberg,
+Kühn, Lucanus, W. Wolff, Hampe, Beyer, E. Wolff, P. Wagner,
+Bretschneider and Lehmann. The results obtained by these and other
+experimenters have demonstrated the following facts.
+
+The substances which have been found in the ash of plants are: _potash_,
+_soda_, _lime_, _magnesia_, _oxide of iron_, _oxide of manganese_,
+_phosphoric acid_, _sulphuric acid_, _silica_, _carbonic acid_,
+_chlorine_, _lithia_, _rubidia_, _alumina_, _oxide of copper_,
+_bromine_, _iodine_, and occasionally even other substances. Of these,
+however, only six are probably absolutely necessary for
+plant-growth--viz., _potash_, _lime_, _magnesia_, _oxide of iron_,
+_phosphoric acid_, and _sulphuric acid_. Three other substances seem
+also to be almost invariably present, and may possibly be essential--in
+very minute quantities at any rate--viz., _chlorine_, _soda_, and
+_silica_. With regard to _alumina_ and _oxide of copper_, these
+constituents must be regarded as accidental; while _iodine_ and
+_bromine_ only occur in the ash of marine plants.
+
+
+_Method of Absorption of Plant-food._
+
+A department of vegetable physiology which has had much work devoted to
+it is the method in which plant-roots absorb their food. The plant's
+nourishment is absorbed in solution by means of the roots. Its
+absorption takes place, according to Fischer and Dutrochet, who have
+investigated the subject at great length, by the process known as
+_endosmosis_. It has also been established by numerous experiments, that
+different plants require different constituents in different
+proportions.
+
+
+_Water as a Carrier of Plant-food._
+
+The function performed by water, as the carrier of plant-food, and the
+motion of the sap of the plant, are questions which have also received
+much attention. The motion of the plant's sap seems to have attracted a
+great deal of attention at a very early stage of the study of plant
+physiology. As far back as 1679, Marriotte studied it. Among other old
+experimenters were Hales, Guettard, Sénébier, Saint-Martin, de Candolle,
+and Miguel. In more recent times, it has been investigated by Schübler,
+Lawes and Gilbert, Knop, Sachs, Unger, and Hosäus. Some idea of the
+enormous amount of water transpired by plant-leaves may be gained by the
+statement that from 233 lb. to 912 lb. of water are transpired for every
+pound of plant-tissue formed.[32]
+
+
+_Agronomy._
+
+When we come to deal with questions relating to the chemistry of the
+soil, we find that so much investigation has been devoted to this one
+branch of agricultural chemistry as to constitute it a special branch by
+itself--known in France under the name of _agronomie_--and being taught
+in the large agricultural colleges by special professors of the subject.
+The value of studying the properties of soils was recognised at an early
+period. This study was for long largely confined to their _physical_,
+or, what are popularly known as their _mechanical_ properties. Thus Sir
+Humphry Davy ascertained many important facts with regard to the heat
+and water absorbing and retaining properties of soils.
+
+
+_Retention by Soil of Plant-food._
+
+It was not till a later period that the power soils possess of fixing
+from their watery solutions various plant-foods, both organic and
+inorganic, was discovered. The earliest recognition of this most
+important property of soils was made by Gazzeri, who, in 1819, called
+attention to the fact that the dark fluid portion of farmyard manure was
+purified on passing through clay. He concluded that soils, more
+especially clayey soils, possessed the property of being able to fix
+from their watery solutions the necessary plant-food constituents, and
+fix them beyond risk of loss, only affording a gradual supply to the
+plant as required.
+
+The first experiments carried out on this subject were those by Huxtable
+and Thompson in 1850. The liquid portion of farmyard manure was filtered
+through soil and subsequently examined, when it was found to have not
+only lost its colour, but also to have lost its smell. Ammonia and
+ammonia salts were also experimented with, and it was found that soils
+possessed the power of fixing ammonia.
+
+To Thomas Way, however, we are indebted for the most valuable
+contribution on this important subject made by any one single
+investigator. His experiments were not merely carried out with regard
+to ammonia, but also with regard to other bases--such as potash, lime,
+magnesia, soda, &c. Since Way's experiments much work has been done by
+Liebig, Stohmann, Henneberg, and Heiden, as also by Voelcker, Eichhorn,
+Knop, Rautenberg, Pochwissnew, Warington, Beyer, Bretschneider, Sestini,
+Laskowsky, Strehl, Pillnitz, Peters, W. Wolff, Lehmann, and Biedermann.
+
+
+_Bases and Acids fixed by Soil._
+
+From these experiments it may be taken as proved beyond doubt that soils
+have the power of fixing, to a greater or less extent, the following
+bases: ammonia, potash, lime, magnesia and soda; as well as the two
+acids, phosphoric and silicic. The order in which the different bases
+are fixed is an important point. It would seem that the soil has a
+greater affinity for the more valuable manurial substances, such as
+ammonia, potash, and lime, and that these substances are first fixed.
+That in fixing any one of the above-mentioned bases from its solution,
+it can only do so at the expense of another base. Thus, in fixing
+potash, either lime, magnesia, or soda must be given up. Further, when a
+base in solution, as sulphate or chloride, is absorbed by a soil, the
+base is alone fixed, while the sulphuric acid or chlorine is left in
+solution. Lastly, the amount of base absorbed by a soil depends on the
+concentration of its solution, on the nature of its combination, and the
+temperature. Way found in his experiments that a clay soil has more
+power than a peaty soil, and that a peaty soil has more power than a
+sandy soil.
+
+
+_Causes of this Fixation._
+
+So much for the fact of soil absorption; as to the cause or causes of
+this absorption, a great number of theories have been put forward. Those
+may be divided into two classes--those accounting for it as due to
+physical properties of the soil; and those, on the other hand,
+explaining it as due to chemical action.
+
+To the latter class Way's belonged. He explained it as due to the
+formation in the soil of hydrated double silicates, consisting of a
+silicate of alumina, along with a silicate of the base fixed. Brüstlein
+and Peters, on the other hand, were of the opinion that it was purely
+physical in its nature. A theory has been advanced that it is due to the
+formation of insoluble ulmates and humates, formed by the union of ulmic
+and humic acids, along with the bases fixed. Among others who devoted
+investigation to this interesting question, may be mentioned Rautenberg
+and Heiden.
+
+On reviewing the evidence, it seems to be pretty well established that
+it really is mainly a chemical act, due chiefly to the formation of
+double silicates, and doubtless to a certain extent to the formation of
+insoluble humates and ulmates. Heiden's experiments would seem to
+indicate, however, that it is also partly of a physical nature.
+
+With regard to the absorption of phosphoric acid, this has been shown to
+be a chemical act, and depends on the formation of insoluble phosphates
+of calcium, iron, aluminium, and magnesium, the percentage of iron
+especially determining this.
+
+Much analytical work has been accomplished of late years with a view of
+ascertaining the amount of ash in different kinds of plants, and in the
+different parts of the plant.
+
+
+_Action of Manures._
+
+The department of agricultural chemistry which has been most largely
+developed of late years is that connected with the problems of
+_manuring_. It is, from a practical point of view, of most value. It is
+some considerable time since we have recognised that the only three
+ingredients it is, as a rule, expedient to apply as artificial manures,
+are _nitrogen_, _phosphoric acid_, and _potash_. The nature, mode of
+action of the different compounds, and properties of these three
+substances, and their comparative influence in fostering plant-growth,
+together with the economic question of which form is, under various
+circumstances, the most economical for the farmer to use, have together
+given rise to a large number of "field" and "pot" experiments. As the
+principles underlying this practice form the subject of the following
+treatise, any further discussion of the question must be left to the
+following chapters.
+
+ _Note._--The reader interested in the historical development of
+ agricultural chemistry is referred to Sir J. H. Gilbert's
+ Presidential Address to the Chemical Section of the British
+ Association, 1880.
+
+
+FOOTNOTES:
+
+[1] The History of the Chemical Elements. By Sir Henry E. Roscoe, F.R.S.
+(Wm. Collins, Sons, & Co.)
+
+[2] Van Helmont's science was, however, of an extremely rudimentary
+nature, as may be evidenced by the belief he entertained that the smells
+which arise from the bottom of morasses produce frogs, slugs, leeches,
+and other things; as well as by the following recipe which he gave for
+the production of a pot of mice: "Press a dirty shirt into the orifice
+of a vessel containing a little corn, after about twenty-one days the
+ferment proceeding from the dirty shirt, modified by the odour of the
+corn, effects a transmutation of the wheat into mice." The crowning
+point in this recipe, however, lay in the fact that he asserted that he
+had himself witnessed the fact, and, as an interesting and corroborative
+detail, he added that the mice were born full-grown. See 'Louis Pasteur:
+His Life and Labours.' By his Son-in-law. Translated by Lady Claud
+Hamilton. (Longmans, Green, & Co.) P. 89.
+
+[3] He then goes on to relate a number of experiments by Cornelius
+Drebel and Albertus Magnus, showing the refreshing power of this balsam,
+and then those of Quercitan with roses and other flowers, and his own
+with nettles.
+
+[4] Priestley, however, did not realise that _carbonic acid gas_ was a
+necessary plant-food; on the contrary, he considered it to have a
+deleterious action on plant-growth. Percival was really the first to
+point out that carbonic acid gas was a plant-food.
+
+[5] It is recorded as an instance of the scientific enthusiasm of the
+man, that he was wont to carry about with him bottles containing oxygen,
+which he had obtained from cabbage-leaves, as also coils of iron wire,
+with which he could illustrate the brilliant combustion which ensued on
+burning the latter in oxygen gas.
+
+[6] For a full account of Sénébier's researches, see 'Physiologie
+végétale, contenant une description des organes des plantes, et une
+exposition des phénomenes produits par leur organisation, par Jean
+Sénébier.' (5 tomes. Genève, 1800.)
+
+[7] How Crops Grow. By Professor S. W. Johnson. Macmillan & Co.
+(Introduction, p. 4.)
+
+[8] See p. 40 to 45.
+
+[9] Elements of Agricultural Chemistry, in a course of Lectures for the
+Board of Agriculture. By Sir Humphry Davy. (London, 1831.)
+
+[10] This department of agricultural research was subsequently carried
+on by Sprengel, Schübler, and others.
+
+[11] Born in Paris, 1802; died 11th May 1887.
+
+[12] See p. 40.
+
+[13] While much of Boussingault's work was carried out previous to the
+year 1840, he continued to enrich agricultural chemistry with numerous
+valuable contributions up till the time of his death. It may be well
+here to mention the names of his most important contributions to
+agricultural science, made subsequent to 1840.
+
+In 1843 he published, in a work entitled 'Economie Rurale,' the results
+of his numerous experiments and researches. This work is well known to
+English agriculturists from an English translation which appeared in
+1845 (Boussingault's 'Rural Economy,' translated by G. Law. H. Ballière,
+London).
+
+In 1860 appeared the first volume of his last great work, 'Agronomie
+Chimie Agricole et Physiologie' This work, which consisted of seven
+volumes, was not finished till 1884. He died on the 11th of May 1887. It
+may be added that the Royal Society of London awarded him the Copley
+medal in 1887.
+
+[14] See British Association Proceedings, 1880, p. 511.
+
+[15] It may be pointed out that, while the amount of ammonia washed down
+by the rain is small, Schloesing has found in some recent experiments
+that a damp soil may absorb from the air in the course of a year 38 lb.
+of combined nitrogen, chiefly ammonia, per acre. See p. 132.
+
+[16] The example, set by Germany, has been followed by other countries
+in which well-equipped research stations now exist. Perhaps the most
+striking example of the rapid development of the means of agricultural
+research is furnished by the United States of America. At present over
+fifty agricultural experiment stations, more or less well equipped,
+exist at present in that country, all liberally supplied by State aid.
+The earliest to be founded, it may be added, was that at Middletown,
+Connecticut, the date of its institution being 1875.
+
+[17] It may thus claim to be the second oldest experimental station,
+that instituted by Boussingault at Bechelbronn in Alsace being the
+oldest.
+
+[18] For an account of the Rothamsted experiments, and a short biography
+of Sir John Lawes, the reader is referred to a pamphlet by the present
+writer, entitled 'Sir J. B. Lawes, Bart., LL.D., F.R.S., and the
+Rothamsted Experiments' ('Scottish Farmer' Office, 93 Hope Street,
+Glasgow).
+
+[19] Of these numerous elaborate experiments, perhaps those which have
+attracted the most widespread interest amongst agriculturists have been
+those carried out on the growth of wheat on the same land year after
+year for a period of nearly fifty years. The important light which this
+series of experiments has thrown upon the theory of the rotation of
+crops, and the subject of the manuring of cereals, is very great.
+
+[20] Associated in some cases with phosphorus and sulphur.
+
+[21] It must be pointed out that plant-respiration does not take place
+_only_ during the night-time. It probably goes on at all times, but it
+is only during the night-time that its action is apparent, as the
+reverse process of carbon assimilation, which goes on at an incomparably
+greater rate, masks its action during the daytime.
+
+[22] The length of the day has an important influence on plant-growth,
+as is evidenced by the rapid growth of vegetation in Norway and Sweden.
+In these countries there is a late spring, and a short and by no means
+hot summer, but a very long period of daylight.
+
+[23] A point of great interest which these experiments elucidated is
+that nocturnal repose is not absolutely necessary for the growth and
+development of all plants.
+
+[24] See pp. 15 and 22.
+
+[25] See p. 22.
+
+[26] See Chapter III., pp. 120 and 131.
+
+[27] Further reference is made to this subject in Chapter III., p. 136.
+
+[28] See p. 6.
+
+[29] See Phil. Trans., Part II., 1861, pp. 444-446. Lawes & Gilbert.
+Schloesing has found in the air in the neighbourhood of Paris 1 lb. of
+ammonia in 26,000,000 cubic yards; while Müntz found only about half
+that amount in a similar quantity of air on the top of the Pic du Midi.
+
+[30] See Chapter III., pp. 119, 120; Appendix, p. 155.
+
+[31] Some recent experiments by Dyer and Smetham would seem to show that
+comparatively small quantities of ammonia in the air prove actually
+hurtful to plant-life. Thus they found that one volume of ammonia in
+1000 volumes of air was fatal to hardy plants; while one volume in 3000
+volumes killed tender ones.
+
+[32] According to the experiments of Hellriegel and Wollny. The
+quantity, it may be added, varies with the leaf-surface and the length
+of the period of growth of the plant. It is greatest with clovers and
+grasses, and least in the potatoes and roots.
+
+
+
+
+
+PART II.
+
+PRINCIPLES OF MANURING
+
+
+
+
+CHAPTER I.
+
+FERTILITY OF THE SOIL.
+
+
+It is necessary to clearly understand to what the fertility of a soil is
+due ere we can hope to master the theory of manuring.
+
+
+_What constitutes Fertility in a Soil._
+
+The question, What constitutes fertility in a soil? is by no means an
+easy one to answer. If we say, The presence of a plentiful supply of the
+constituents which form the plant's food, our answer will be incomplete.
+Similarly, if we reply, A certain physical condition of the soil--here,
+again, it will be found equally unsatisfactory; for fertility of a soil
+depends both on its physical condition and on its chemical composition,
+and indeed even on other circumstances. It may be well, then, before
+proceeding to treat of the nature and action of the different manures,
+to offer a brief statement of the conditions of fertility so far, at any
+rate, as we at present know them. For it may be well to warn the reader
+that, despite the great amount of work carried out on this subject by
+experimenters, we still have much to learn before we shall be in a
+position fully and clearly to understand the subject of soil-fertility
+in all its bearings.
+
+Apart altogether from the influence exerted by climate, latitude,
+altitude, and exposure, the fertility of a soil may be said to depend on
+the following properties. These we may divide into three groups or
+classes:--
+
+1. Physical or mechanical.
+2. Chemical.
+3. Biological.
+
+
+=I. Physical Properties of a Soil.=--The physical properties of a soil
+are generally admitted to have a very important bearing on its
+fertility. This has been long practically recognised, and perhaps has in
+the past been unduly exalted in importance, at the expense of the no
+less important functions of the chemical.[33] The reason of this is
+doubtless to be ascribed to the fact that it is much easier to study
+the physical properties of a soil than it is to study the chemical; and
+that, while we are in possession of a very large amount of useful
+information with regard to the former, we are at present only on the
+threshold of our knowledge of the latter.
+
+
+_Variety of Soils._
+
+It is a matter of common observation that soils differ widely in their
+mechanical nature. The early recognition of this fact is evidenced by
+the large number of technical terms which have been long in vogue among
+farmers descriptive of these differences. Thus soils are in the habit of
+being described as "heavy," "light," "stiff," "strong," "warm," "cold,"
+"wet," "damp," "peaty," "clayey," "sandy," "loamy," &c., &c.
+
+
+_Absorptive Power for Water._
+
+One of the most important of the physical properties of a soil is its
+power to absorb water.
+
+Water to the plant economy is just as important and necessary as it is
+to the animal economy. Consequently it is of primary importance to
+examine into the conditions which regulate the absorption of this
+important plant-food by the soil.
+
+By the absorptive power of a soil is meant its capacity for drinking in
+any water with which its particles may come in contact. This power
+depends, first, on the predominance of its proximate constituents--viz.,
+_sand_, _clay_, _carbonate of lime_, and _humus_; and secondly on the
+fineness of the soil-particles.
+
+
+_Absorptive Power of Sand, Clay, Humus._
+
+First, then, with regard to the absorptive power of sand, clay, and
+humus. Of these, sand possesses this power to the least extent, clay to
+a greater extent, while humus possesses it most of all.[34]
+
+The extent, therefore, of the absorptive power of a soil depends very
+much on the proportions in which it possesses these three ingredients.
+The more sandy a soil is, the less will its power be of absorbing water;
+and this, there is little doubt, is one of the reasons why a sandy soil
+is, as a rule, an unfertile soil. Of course there are other and even
+more important reasons; but that this absorptive power has an important
+bearing on the question is conclusively proved by the fact that sandy
+soils are more fertile in a climate where rain is frequent than in one
+where much dry weather prevails. The incapacity of a sandy soil to
+absorb a large quantity of moisture is not fraught with such evil
+effects to the crops in the former case, because it is counteracted by
+the climatic conditions, which obviate the necessity, in a soil, of
+possessing great absorptive powers.
+
+The converse, of course, we may mention in passing, holds good of clayey
+soils.
+
+
+_Fineness of Soil-particles._
+
+The second quality in a soil on which its absorptive power depends is
+the fineness of its particles. The great benefit which a soil derives
+from a good tilth, in this respect, was one of the reasons why Tull's
+system of horse-hoeing husbandry was so successful in its results.[35]
+The finer the soil-particles, it may be said generally, the greater is
+the absorptive power of the soil.
+
+
+_Limit to Fineness._
+
+There is, however, a limit to the fineness to which the particles of a
+soil ought to be reduced; for it has been found by experiment that when
+a certain degree of fineness is reached, the absorptive power decreases
+with any further pulverisation. A German experimenter found, for
+example, that a garden loam, capable of absorbing 114 per cent of water
+in its natural state, when pulverised very fine was able to absorb only
+62 per cent of water. Here, clearly, the limit to which it is advisable
+to pulverise a soil had been exceeded.
+
+
+_Reason of the above._
+
+It is not difficult to see why this should be so. The amount of water
+that a soil can soak up is due to the number of pores, or air-spaces, it
+contains of a certain size. If these pores are large and few in number,
+the amount of water absorbed will be naturally less than when they are
+numerous and smaller in size. Up to a certain extent, the more a soil is
+broken the greater will be the number of pores created, of a size to
+permit the water to soak in. Beyond that point the pores become too
+minute, and the soil becomes too compact, each particle clinging
+together too closely.
+
+
+_Retentive Power of Soils for Water._
+
+Now closely connected with this absorptive power of soils, which we have
+just been considering, is the power soils possess of holding or
+retaining the water they absorb. This power, it will be seen at a
+glance, must have an important bearing on the fertility of a soil.
+
+
+_Importance of Retentive Power._
+
+As a considerable interval often elapses between the periods of
+rainfall, soils, if they are to support vegetable growth, must be able
+to store up their water-supply against periods of drought. This is all
+the more necessary when we remember that, in the case of heavy crops,
+the rainfall would often be inadequate to supply the water necessary for
+their growth. In fact, it has been estimated that the average
+evaporation from soils bare of any cultivation is equal to the rainfall.
+That the evaporation from soils covered with vegetation is very much
+greater, has been strikingly shown by a calculation made by the late
+eminent American botanist, Professor Asa Gray, who calculated that a
+certain elm-tree offered a leaf-surface, from which active transpiration
+constantly went on, of some five acres in extent; while it has further
+been calculated that a certain oak-tree, within a period of six months,
+transpired during the daytime eight and a half times more water than
+fell as rain on an area equal in circumference to the tree-top.[36] Just
+as the state of the fineness of the soil-particles has an important
+influence on the absorptive power of soils, so, too, it is found, it has
+an important bearing on the rate at which evaporation takes place.
+Evaporation goes on to the greatest extent in soils whose particles are
+compacted together, capillary action in this case taking place more
+freely, and effecting evaporation from a greater depth of soil. The
+stirring of the surface portion of the soil, as for example by hoeing or
+harrowing, has for this reason an important influence in lessening the
+amount of evaporation, and minimising the risks of drought, by breaking
+the capillary attraction. The amount of evaporation which takes place
+from a soil covered with a crop, depends largely on the nature of the
+crop; a deep-rooted crop, since it draws its moisture from a wider area
+of soil, being more effective in drying a soil than a shallow-rooted
+crop. The difference in the amounts evaporated from a cropped and a bare
+fallow soil has been shown at Rothamsted to equal a rainfall of nine
+inches, the crop being barley. The increase, of course, is due to the
+water which the crop transpires.[37]
+
+It may be generally said that the greater the absorptive power of a
+soil, the greater is its retentive power; for soils that most largely
+absorb water are the most reluctant to part with it.
+
+While these properties are undoubtedly necessary for fertile soils, it
+is needless to add that they may be possessed by a soil to too great an
+extent. The soil that is unable to throw off any excess of water becomes
+cold and damp, and does not admit of proper tillage. Its pores become
+entirely choked up, and the circulation of air, which, as we shall see,
+is of so much importance, is rendered impossible. Plants in such a soil
+are apt to sicken and die, the water becomes stagnant, and certain
+chemical actions are caused which give rise to poisonous gases, such as
+sulphuretted hydrogen, &c. A stiff clayey soil offers a good example of
+the disadvantage of over-retentiveness. Owing to the difficulty such
+soils experience in throwing off their excessive water, they are
+extremely difficult to till; and sowing operations are on that account
+apt to be delayed.
+
+
+_Power Plants have of absorbing Water from a Soil._
+
+It is a strange fact, and one worth noticing in this connection, that
+the power plant-roots have of drawing their moisture from a soil, seems
+to depend on the retentive power of the soil. By this is meant that
+plants have not the means of exhausting the water in a retentive soil to
+such an extent as in a non-retentive soil.
+
+In some extremely interesting experiments, carried out by the well-known
+German botanist Sachs, it was found that plants wilted in a loamy soil,
+whose water-holding capacity was 52 per cent, when its moisture reached
+8 per cent; while in a sandy soil--water-holding capacity 21 per
+cent--the same species of plant did not wilt until its moisture reached
+1-1/2 per cent. Here, then, we see that on one kind of soil the plant
+was able to live, and obtain sufficient water for its needs, while it
+died of thirst in another soil, although that soil contained quite as
+much moisture.
+
+Speaking generally, we may say that Hellriegel's experiments have shown
+that any soil can supply plants with all the water they need so long as
+its moisture is not reduced below one-third of the whole amount it can
+hold.[38]
+
+
+_How to increase Absorptive Power of Soils._
+
+The absence or presence, in excess, of the above properties, suggests a
+word or two on how these natural defects may, to a certain extent, be
+remedied artificially. It stands to reason, that if organic matter in a
+soil renders its absorptive power greater, a simple method of improving
+a soil defective in this property is by the addition of organic matter.
+One of the benefits of ploughing-in green crops on sandy soils is
+undoubtedly due to this fact; the addition of farmyard manure having
+also a similar effect. The absence of a sufficient amount of
+retentiveness, such as is found in sandy soils, in the same way
+suggests, as a remedy, the addition of clay; and, _vice versâ_, where
+the soil is too clayey, the natural method of improvement will be the
+addition of sand.[39]
+
+
+_Shrinkage of Soils._
+
+In drying, soils shrink. Those which shrink least are sandy and chalky
+soils. Humus soils, on the other hand, shrink most.
+
+
+_Most favourable Amount of Water in a Soil._
+
+The amount of water in a soil most favourable for plant-growth is a
+question of considerable difficulty. Too great an amount of moisture
+renders the land cold; air cannot obtain access to the soil-particles,
+and the plants sicken and die. Hellriegel has found that as much as 80
+per cent of what the soil can hold is hurtful to plants, and that from
+50 to 60 per cent is the best amount.[40]
+
+
+_Hygroscopic Power._
+
+A property possessed by soils in relation to water, which is quite
+distinct from absorptive power, is their hygroscopic power. By this is
+meant their power of absorbing water from the air where it is present in
+the gaseous form. This property is identical with the property which
+will be adverted to immediately--viz., capacity for absorbing gases. The
+extent to which soils possess this hygroscopic property seems to be
+regulated very much by the same conditions as regulate their ordinary
+absorptive power.[41] This property is considered to be of great
+importance in the case of soils in hot climates, where their
+agricultural value may be said to depend to a large extent upon it. The
+amount of water, however, absorbed in this way is, comparatively
+speaking, insignificant. Lastly, it may be observed that there are
+certain methods of drying soils afflicted with too much moisture. These
+consist in making open ditches, and thus relieving them of their
+superabundance of water, or in planting certain kinds of trees, such as
+willows and poplars. The amount of green surface presented by the large
+number of leaves of trees, from which the constant evaporation of water
+goes on, is very great. The consequence is that trees may be regarded as
+pumping-engines. It is from this cause that foresters have noticed that
+clay lands are apt to become wetter after the trees growing upon them
+have been cut down.[42]
+
+
+_Capacity for Heat in Soils._
+
+A property which depends largely on those we have just been considering
+is the capacity soils possess of absorbing and retaining heat.[43] The
+temperature of a soil, of course, largely depends on the temperature of
+the air; but this, we must not forget, depends also on the soil itself.
+The heat given forth by the sun's rays strikes the soil, with the result
+that, while so much of its heat is absorbed, a certain portion--and this
+will vary according to the nature of the soil--of its heat is radiated
+into the air.
+
+The changes in the temperature of the soil naturally take place more
+slowly than the changes in the temperature of the air; the depth of soil
+thus affected by those changes varies also in different climes. It has
+been calculated that in temperate climes the changes of temperature
+occurring from day to night are not felt much below three feet down.
+
+
+_The Explanation of Dew._
+
+We have, it may be stated, generally two processes going on. During the
+day the soil is engaged in absorbing its heat from the sun's rays; when
+night comes, and the sun goes below the horizon, the air is chilled
+below the temperature of the soil, which radiates out its stored-up heat
+into the air. The result is that the temperature of the soil is soon
+reduced below the temperature of the air, and the moisture, present in
+the air in the form of vapour, coming in contact with the cold surface
+of the earth, is condensed into dew, which is deposited, and is seen
+best early in the morning before the sun has had time to evaporate it
+again. Dew is most abundant in summer-time, for the reason that the
+difference in temperature of the day and night is then greatest. In
+winter-time it is seen as hoar-frost.
+
+
+_Heat of Soils._
+
+The temperature of a soil, however, is due to other sources than the
+sun's rays. Whenever vegetable matter decays, there is always a certain
+amount of heat generated. Soils, therefore, in which there is a large
+amount of decaying vegetable matter, are certain to receive more heat
+from this source than soils of more purely mineral nature.
+
+
+_Heat in Farmyard Manure._
+
+A good example of the amount of heat that accompanies fermentation, or
+decay of vegetable matter, is seen in the case of rotting farmyard
+manure. The danger of loss of the volatile ammonia from this cause is
+often great, and care must be taken to prevent fermentation going on too
+quickly, and the temperature from becoming too high.[44] The actual
+increase in the temperature of a soil effected by the addition of
+certain bulky organic manures, such as farmyard manure, may thus be
+considerable. In some experiments carried out at Tokio, Japan, it was
+found that the application of 20 tons of farmyard manure per acre
+increased the temperature of the soil to a depth of five inches, for a
+period of nearly a month, on an average, one and a half degrees
+Fahrenheit. The amount of water present in a soil, it may be noticed in
+passing, will have a considerable effect in regulating its temperature,
+a damp soil being, as a rule, a cold soil.
+
+
+_The Cause of the Heat of Fermentation._
+
+It may be asked, How is the decay, or fermentation, of vegetable matter,
+such as farmyard manure, caused? or rather, To what is it due? Decay of
+any substance is just its slow combustion or burning. When a substance
+unites with the active chemical element in air--the oxygen gas--it is
+said to be oxidised. Now, this union of a substance with oxygen is the
+explanation of burning, and the phenomena of burning and decay are
+explained by the same chemical operation. When bodies decay, or when
+they burn, they unite with oxygen: when this union of a body and oxygen
+takes place very quickly, and the result is a flame and very great heat,
+then we call it burning; when, however, it takes place slowly, it is not
+called burning, but simply oxidation or decay. The ultimate products are
+the same, however, whether the body burns or decays; and the process of
+decay is always accompanied by heat, as well as the process of
+burning.[45] It is not, of course, only the vegetable or organic matter
+in a soil that decays, but also the mineral matter. The oxidation,
+however, of the mineral matter in the soil takes place so slowly, and
+the amount of heat generated by this oxidation is so slight, that the
+temperature of the soil can scarcely be said to be much affected by it.
+
+
+_Influence of Colour of a Soil._
+
+There is still another quality of a soil on which its temperature
+depends, and that is its colour. This may seem at first sight to be
+scarcely worth taking into account, and yet it has been shown to have a
+very striking influence on the temperature of a soil. This naturally is
+best seen in climates where there is a good deal of sun. Dark-coloured
+soils have a greater heat-absorbing capacity than light-coloured soils;
+and experiments carried out for the purpose of determining the extent of
+this influence have shown that under certain conditions the difference
+between a soil covered with a black substance, and one covered with a
+white substance, amounted to from 13° to 14° Fahr. Other things being
+equal, a crop on a dark-coloured soil will be sooner ripened than one on
+a light-coloured soil. A soil covered by a crop is cooler than one
+without any crop.
+
+
+_The Power Soils have for absorbing Gases._
+
+We have just seen that one cause of the heat of soils is the oxidation
+which is constantly going on in all soils, but more rapidly in soils
+containing a large quantity of vegetable matter. This suggests a word or
+two on the power soils have of absorbing gases.
+
+The chief gases in the atmosphere are oxygen and nitrogen. Both these
+gases are absorbed by soils, although not in similar proportions.[46]
+With regard to the former, it is well known that a plentiful supply of
+oxygen in the pores of the soil is a necessary condition of fertility.
+This was long ago experimentally proved by de Saussure, who showed that
+plants absorbed oxygen through their roots. At certain periods of their
+growth this demand for oxygen on the part of the plant is greater than
+at other times. For example, seeds in the process of germination require
+to have free access to a plentiful supply of oxygen. This fact
+emphasises the enormous importance of providing a good seed-bed, and of
+seeing that the seed is not buried too deeply.
+
+
+_Carbonic Acid and Ammonia._
+
+In addition to oxygen and nitrogen, the air contains other gases which
+are absorbed by the soil. Of these, carbonic acid is the most abundant.
+By far the largest portion of the carbonic acid which the soil obtains
+from the air, is washed down in solution in the rain.[47] Of the other
+constituents of the atmosphere, the combined forms of nitrogen--viz.,
+_ammonia_, _nitric_, and _nitrous acids_--are the most important. These
+are all absorbed by the soil, but, like carbonic acid, they are chiefly
+washed down by the rain. The amount of ammonia which may be absorbed by
+a soil from the air, is very much greater than was formerly supposed.
+Some recent experiments by Schloesing, referred to in a following
+chapter,[48] show this. A damp soil may in the course of a year absorb
+far more ammonia than that washed down in rain.
+
+
+_Gas-absorbing Power of Soils varies._
+
+The power of different soils to absorb these gases varies. This
+variation depends not only on their physical properties, but also on
+their chemical as well. Soils containing much organic matter have a
+greater capacity for absorbing gases than the more purely mineral ones.
+
+
+_Absorption of Nitrogen._
+
+The absorption of nitrogen by the soil is a question of considerable
+importance. It will be referred to later on under the heading of the
+biological properties of soils, as it is fixed by the agency of
+micro-organisms.[49]
+
+To recapitulate, the chief physical or mechanical properties of a soil
+are its absorptive and retentive powers for water; its capacity for
+heat; and its power of absorbing gases. It will be easily seen how
+tillage operations are calculated to influence these physical properties
+of a soil. Thus, in the case of a stiff soil, tillage increases its
+power for absorbing the atmospheric gases, chiefly oxygen, which are so
+necessary for rendering its fertilising matters available. On the other
+hand, in a light and too open soil it may exert quite a contrary effect.
+
+It may be also well to refer here to the important influence these
+physical properties exercise on the growth of the plant.
+
+
+_Plant-roots require a certain Openness in the Soil._
+
+One of the functions of the soil is to support the plant in an upright
+position, and this is a function which requires in the soil a certain
+amount of compactness or firmness. On the other hand, however, a soil
+must not possess too great compactness, otherwise the plant-roots will
+experience a difficulty in pushing their way downwards. This is
+especially the case during the earlier periods of growth, when the
+plant-roots are as yet extremely tender, and experience great difficulty
+in overcoming much resistance. The importance of preparing a mellow
+seed-bed will be thus at once seen to be based on sound scientific
+principles; and this for a double reason. Not only does the young plant
+require every facility for developing its roots, but also, as has just
+been pointed out, an abundant supply of oxygen is of paramount
+importance during the process of germination.
+
+
+_Soil and Plant-roots._
+
+The whole question of the influence of the mechanical condition of the
+soil on the development of plant-roots is one of the highest importance
+and interest, and is not so generally recognised as it ought to be.
+
+
+_Natural tendency of Plant-roots to grow downwards._
+
+It may be taken as certain that the tangled condition of plant-roots is
+due to the resistance offered by the soil-particles, and that the
+natural tendency of the plant-root is to grow downwards. The roots, in
+short, would probably grow in as symmetrical a form as do the stalks or
+branches, were it not that they are hindered from so doing by the
+soil-particles. Where, then, the soil is such as to offer much
+hindrance, the growth of the plant cannot but be retarded. Some
+extremely interesting experiments have been performed by the eminent
+German chemist Hellriegel on the influence which the closeness of the
+soil-particles has on root-development. In these experiments peas and
+beans were grown in moistened sawdust, more or less compactly
+compressed. It was found that when the sawdust Was compressed to any
+extent, plant-growth took place very slowly, or entirely ceased.
+
+The importance of having plant-roots as widely developed in the soil as
+possible, will be at once seen when we reflect that this means that the
+area of soil from which the plant derives its soil-food is thereby
+greatly increased. Another important consideration is, that the deeper
+plant-roots can penetrate in a soil, the more able--other conditions
+being equal--is the plant to withstand the action of drought, as it can
+draw water for its needs from the deeper layers of the soil, long after
+a plant, whose roots do not penetrate so deeply, has wilted.
+
+
+_Plants require Room._
+
+Another important bearing tillage has on plant-growth may here be
+discussed. A problem of considerable difficulty is presented in the
+question, How many individual plants will a certain piece of soil
+support in a healthy way? For as plants require room, it is imperative
+that they be not too closely crowded together.
+
+The question resolves itself pretty much into one of quality against
+quantity.
+
+Experiments on this subject have shown that a certain area of soil is
+only able to support the healthy growth of a certain number of plants.
+If the limit be exceeded, the result is imperfect development.
+
+
+_Number of Plants on certain Area increased by Tillage._
+
+It is obvious, however, that the more thoroughly tilled a soil is, the
+greater will be the number of plants it will be possible to grow on it.
+The roots, instead of being forced to spread themselves along the
+surface-soil, and thus take up a large amount of room, will find no
+difficulty in striking downwards. Two or three plants may thus be
+enabled to grow in a thoroughly tilled soil in the same space as only
+one could before tillage.
+
+
+_American and English Farming._
+
+The above considerations throw considerable light on what seems to many
+farmers a strange anomaly--viz., the fact that the return of farm
+produce per acre on American farms is, as a rule, very much less than
+that from our own impoverished soils in this country. To many, at first
+sight, this seems to be in direct contradiction to our common belief,
+and to point to the conclusion that the virgin soils of America are,
+after all, actually inferior in fertility to the soils of Britain.
+
+It is not, however, necessary to draw this conclusion, as the facts of
+the case admit of another explanation. The inferior returns obtained
+from American farms are due, not to the fact that the American soil is
+less fertile than the British--for this is not true--but to the fact
+that it is less _intensively_ cultivated.
+
+In America land is cheap and labour is dear; it is consequently found to
+be more economical to cultivate a large tract of land less thoroughly
+than a small area more thoroughly. In Britain the reverse is the case,
+labour being cheap and land being dear. It is thus necessary to make the
+land go as far as possible, and produce as heavy a crop as it is
+possible to produce. There can be little doubt, that were American
+farming to be carried on as intensively as is British farming, the
+present yield would be at least probably doubled.
+
+We have now to consider the second class of properties which influence
+the fertility of a soil. These are _chemical_.
+
+
+=II. Chemical Composition of a Soil.=--Chemically considered, the soil
+is a body of great complexity. It is made up of a great variety of
+substances. The relations existing between these substances and the
+plant are not all of equal importance; some--and these form by far the
+largest proportion of the soil-substance--are concerned in acting simply
+as a mechanical support for the plant, and in helping to maintain those
+physical properties in the soil which, as we have just seen, exercise
+such important functions in the plant's development.
+
+
+_Fertilising Ingredients._
+
+A small portion of the soil-substance, however, takes a very much more
+active part in promoting plant-growth, by acting as direct food of the
+plant. As we have already seen in the Introductory Chapter,[50] the
+substances which have been found in the ash of plants are the following:
+_potash_, _lime_, _magnesia_, _oxide of iron_, _phosphoric acid_,
+_sulphuric acid_, soda, silica, chlorine, oxide of manganese, lithia,
+rubidia, alumina, oxide of copper, bromine, and iodine. The general
+presence of some of these substances is doubtful; the presence of
+others, again, probably purely accidental; while some are only found in
+plants of a special nature, as, for instance, iodine and bromine, which
+are only found in the ash of marine plants.
+
+Of these ash constituents, only the first six substances--those marked
+in italics--are absolutely necessary to plant-growth. In addition to
+these six ash constituents, the plant also derives its _nitrogen_, which
+is a necessary plant-food, chiefly from the soil.[51]
+
+
+_Importance of Nitrogen, Phosphoric Acid, and Potash._
+
+But of these seven constituents of the soil which are necessary to
+plant-growth, some have come to be regarded by the agriculturist with
+very much greater interest than others. This is due to the fact that
+they are normally present in the soil in very much smaller quantities
+than is the case with the other equally necessary food ingredients;
+that, in short, they are nearly invariably present in the soil, in a
+readily available form, in lesser quantities than the plant is able to
+avail itself of, and often, as in impoverished or barren soils, in
+quantities too small for even normal growth. These ingredients are
+_nitrogen_, _phosphoric acid_, and _potash_.[52]
+
+The importance of seeing that all the necessary plant ingredients are
+present in a soil in proper quantities will be at once properly
+estimated when it is stated that the absence or insufficiency in amount
+of one single ingredient is capable of preventing the growth of the
+plant, although the other necessary ingredients may be even abundantly
+present.
+
+With lime, magnesia, iron, and sulphuric acid, most soils are abundantly
+supplied. The substances with which the farmer has to concern himself,
+then, are nitrogen, phosphates, and potash. It is these substances
+therefore, that, as a rule, are alone added as manures.
+
+
+_Chemical Condition of Fertilising Ingredients in Soil._
+
+But in considering the chemical properties of a soil, a simple
+consideration of the quantity of the different ingredients present is
+not enough. A very important consideration is their chemical condition.
+Ere any plant-food can be assimilated by the plant's roots, it must
+first be rendered soluble. The quantity of soluble, or, as it is known,
+_available_, plant-food in a soil is very small. It is, of course, being
+steadily added to each day by the process of disintegration constantly
+going on in soils.
+
+
+_Amount of Soluble Fertilising Ingredients._
+
+The exact nature and dissolving capacity of the soil-water, charged as
+it is, to a greater or less extent, with different acids and salts, as
+well as the dissolving power of the sap of the rootlets of the plant
+itself, render the exact estimation of the available fertilising
+constituents wellnigh impossible. An approximate estimate, however, may
+be obtained by treating the soil with pure water and dilute acid
+solutions. The treatment of the soil with dilute acid solutions is for
+the purpose of simulating, as nearly as may be done, the conditions it
+is submitted to in the soil. By treating a soil with water, we obtain a
+certain amount of plant-food dissolved in the water. This can only be
+regarded as indicating approximately the amount available at that moment
+to the plant. But every day, thanks to the numberless complicated
+reactions going on in the soil, this soluble plant-food is constantly
+being added to. Considerations such as the above, together with our
+ignorance as to the exact combinations in which the necessary minerals
+enter the plant, will serve to indicate the great difficulty of this
+part of the subject.[53]
+
+
+_Value of Chemical Analysis of Soils._
+
+It is largely for these reasons that a chemical analysis of a soil is
+from one point of view of little value in giving evidence of its actual
+fertility. What it demonstrates more satisfactorily is its potential
+fertility. It is useful in revealing what there is present in it, not
+necessarily, however, in an available condition. Under certain
+circumstances it may be made of great value, as, for example, when we
+are anxious to know what will be the result of certain kinds of
+treatment, such as the application of lime, &c.
+
+It is hardly advisable, therefore, to place before the reader a number
+of soil analyses. That he may obtain an approximate idea of the
+composition of a soil, one or two representative analyses will be found
+in the Appendix,[54] along with a short account of the chief minerals
+out of which soils are formed.
+
+A point of considerable interest is the quantity per acre different
+soils contain of nitrogen, phosphoric acid, and potash. Although the
+amount of these ingredients when stated in percentage seems very
+trifling, yet when calculated in lb. per acre, it is seen to be in large
+excess of the amount removed by the different crops. This question will
+be dealt with in succeeding chapters.
+
+A point of further interest is the chemical form in which the necessary
+plant constituents are present in the soil. For information on this
+point the reader is referred to the Appendix.[55]
+
+The third class of properties which affect the fertility of a soil are
+those which have been termed the _biological_.
+
+
+=III. Biological Properties of a Soil.=--The important functions which
+modern discoveries have shown to be discharged by minute organic life in
+the terrestrial economy are nowhere more strikingly exemplified than in
+the important _rôle_ they perform in the soil.
+
+
+_Bacteria of the Soil._
+
+The soil of every cultivated field is teeming with bacteria whose
+function is to aid in supplying plants with their necessary food. The
+nature of, and the functions performed by, these organisms differ very
+widely. Regarding many of them we know very little; every day, however,
+our knowledge is being extended by the laborious researches of
+investigators in all parts of the world, and it is to be anticipated
+that ere long we shall be in possession of many facts regarding the
+nature and the method of the development of these most interesting
+agents in terrestrial economy. That they are present, however, in
+enormous numbers in all soils we have every reason to believe, one class
+of organism connected with the oxidation of carbonic acid gas being
+estimated to be present to the extent of over half a million in one
+gramme of soil[56] (Wollny and Adametz). One class--and their
+importance is very great in agriculture--prepare the food of plants by
+decomposing the organic matter in the soil into such simple substances
+as are easily assimilated by the plant. The so-called "ripening" of
+various organic fertilisers is effected, we now know, entirely through
+the agency of bacteria of this class. Plant-life is unable to live upon
+the complex nitrogenous compounds of the organic matter of the soil, and
+were it not for bacteria these substances would remain unavailable.
+Attention will be drawn in the Chapter on Farmyard Manure to this
+question more in detail. Of these bacteria, among the most important are
+those which are the active agents in the process known as
+"nitrification"--_i.e._, the process whereby organic nitrogen and
+ammonia salts are converted into nitrites and nitrates. The presence of
+these organisms, it would appear, is indispensable to the fertility of
+any soil. There are organisms, on the other hand, which have the power
+of reversing the work of the nitrification bacteria by converting
+nitrates into other forms of nitrogen. The reduction of nitrates in the
+soil is often the source of much loss of valuable nitrogen, which
+escapes in the free state, so that the action of bacteria is not
+altogether of a beneficial nature.
+
+
+_Three Classes of Organisms in the Soil._
+
+So far as the subject has been at present studied, the micro-organisms
+in the soil may be divided into three classes.[57]
+
+
+_First Class of Organisms._
+
+We have, first of all, those whose function it is to oxidise the soil
+ingredients. Organisms of this class may act in different ways. They may
+assimilate the organic matter of the soil and convert it into carbonic
+acid gas and water; or, on the other hand, they may oxidise it by giving
+off oxygen. Some of these organisms, whose action is of the first kind,
+choose most remarkable materials for assimilation. One has been found to
+require ferrous carbonate for its development, which it oxidises into
+the oxide (Winogradsky); while another,[58] the so-called sulphur
+organism, converts sulphur into sulphuretted hydrogen according to some,
+and according to others into sulphates. To this class of organism the
+nitrifying organisms belong. As will be seen more fully in a subsequent
+chapter, two distinct organisms connected with this process have already
+been isolated and studied--one of these effecting the formation of
+nitrites from organic nitrogen or ammonia salts, and the other the
+conversion of nitrites into nitrates. The second method in which these
+oxidising organisms act is by giving off oxygen. There is much interest
+attaching to this fact, as it was supposed till quite recently that all
+evolution of oxygen in vegetable physiology was dependent on the
+presence of light, and also intimately connected with chlorophyll, or
+the green colouring matter of plants. It would seem, however, that among
+the soil organisms these conditions are not necessary, and the evolution
+of oxygen may be carried on in the case of colourless organisms as well
+as in the case of light. With organisms of this kind every soil is
+probably teeming. A typical example is the organism which is the active
+agent in the oxidation of carbonic acid gas, and which has already been
+referred to as existing in the soil in such numbers.[59]
+
+
+_The Second Class of Organisms in the Soil._
+
+The second class of organisms are those which reduce or destroy the soil
+constituents. The most important of these, from the agricultural point
+of view, are those which effect the liberation of nitrogen from its
+compounds. In the putrefaction of organic matter the organisms chiefly
+act, it is probable, in the entire absence of atmospheric oxygen; but
+it would seem, however, that they may also act in the presence of
+oxygen. It is through their agency that the soil may lose some of its
+nitrogen in the "free" form. To this class belong the denitrifying
+organisms already referred to which reduce the nitrates and nitrites in
+the soil.[60]
+
+
+_Third Class of Organisms._
+
+The third class of organisms are those by whose agency the soil is
+enriched. Of this class those fixing the free nitrogen from the air are
+the most important. The nature of these organisms is still somewhat
+obscure, but that leguminous plants have the power of drawing upon this
+source of nitrogen is now a firmly established fact. Further reference
+to these interesting organisms may be delayed to another chapter.
+
+The important point to be emphasised is, that for the healthy
+development of these organisms, which are so necessary in every fertile
+soil, certain conditions must exist. These necessary conditions will be
+treated more in detail later on. It is sufficient to notice that they
+have to do with the physical properties as well as the chemical
+composition of the soil. This furnishes a further reason for the
+necessity of having the mechanical condition of a soil satisfactory.
+
+
+_Recapitulation._
+
+From what we have said, it will be seen that the question of
+soil-fertility is a very complicated one, and depends on numerous and
+varied conditions; that the properties which constitute fertility, while
+seemingly very widely different in their nature, in reality influence
+one another to a very great extent; that not merely is the presence in a
+soil of the necessary plant constituents necessary to fertility, but
+that the possession by the soil of certain physical or mechanical
+properties is equally necessary; while, lastly, we have seen that the
+presence of certain micro-organic life is bound up with the problem of
+fertility in a very direct and practical manner.
+
+The importance of the conditions, other than those of a purely chemical
+nature, have been thus far somewhat prominently emphasised, for the
+reason that in what follows attention will be almost exclusively devoted
+to the purely chemical conditions of fertility. It is well, then, to
+realise that, while the latter conditions are by far the most important,
+so far as the farmer is practically concerned, inasmuch as they are most
+under his control, they are not the only conditions, and are not by
+themselves able to control fertility.
+
+
+FOOTNOTES:
+
+[33] This statement perhaps needs qualification. While the important
+_rôle_ played by the physical qualities of the soil were in the early
+years of the science recognised, of more recent years the chemical
+composition of the soil has been engaging almost exclusive
+investigation. Physical properties of the soil have recently acquired a
+further importance in the eyes of the agricultural chemist, from the
+important influence they exert on what we have here called the
+biological properties of a soil--viz., the development of those
+fermentative processes whereby plant-food is prepared to a large extent.
+
+[34] A good example of the absorptive capacity of a soil containing a
+large quantity of vegetable matter is furnished by peat-bogs, which,
+sponge-like, can absorb enormous quantities of water. (See Appendix,
+Note I., p. 98.)
+
+[35] Jethro Tull, an early well-known agricultural writer, who lived
+about the middle of last century, propounded the theory, that as the
+food of plants consisted of the minute earthy particles of the soil, all
+that was required by the skilful farmer was to see that his soil was
+properly tilled. He accordingly published a work entitled 'Horse-hoeing
+Husbandry,' in which he advocated a system of thorough tillage. (See
+Historical Introduction, p. 10.)
+
+[36] See Introduction, p. 55.
+
+[37] See Introductory Chapter, p. 55.
+
+[38] It is not exactly known why excess of water should prevent normal
+growth in the plant. Probably it is on account of the fact that free
+access of oxygen is hindered in such a case. The roots are thus not
+freely enough exposed to this necessary gas, and fermentative processes
+of the nature of nitrification are not promoted. It may be also due to
+the fact that the solution of plant-food is too dilute when such excess
+of water prevails.
+
+[39] See Appendix, Note II., p. 98.
+
+[40] Some experiments by E. Wollny show this. He found, when
+experimenting with _summer rape_, that the best results were obtained
+when the soil contained only 40 per cent of its total water-holding
+power; when the amount was either lessened or increased the results
+obtained fell off. The effect of either too little or too much water is
+seen in the development of the different organs of the plant as well as
+on its period of growth, much water seeming to retard the growth. The
+quality of the plant seems also to be influenced by this condition.
+Experiments on cereal grains by Wollny show that not merely is the
+texture of the grain influenced, but that much moisture lessens the
+percentage of nitrogen. Wollny is of the opinion that for crops
+generally, the best amount is from 40 to 75 per cent of the total
+water-holding capacity of the soil.
+
+[41] See Appendix, Note III., p. 99.
+
+[42] See p. 55.
+
+[43] The effect of the temperature of the soil on the development of the
+plant is most important. This is especially marked at the period of
+germination, but is felt at subsequent periods of growth. Up to a
+certain temperature the warmer the soil the more rapid the plant's
+development. In this country the temperature most favourable to growth
+is rarely exceeded, or indeed reached.
+
+[44] See Chapter on Farmyard Manure.
+
+[45] As will be seen further on, the fermentation of organic substances
+is caused by the action of micro-organic life.
+
+[46] See Appendix, Note IV., p. 100.
+
+[47] Of course it must be remembered that a large amount of carbonic
+acid in soils comes from the decay of vegetable matter. Soils are twenty
+to one hundred times richer in carbonic acid than the air.
+
+[48] See Chapter III., p. 119.
+
+[49] See Introduction, p. 40.
+
+[50] See Introductory Chapter, p. 54.
+
+[51] See pp. 44 and 135.
+
+[52] Occasionally also _lime_.
+
+[53] See Appendix, Notes V. and VI., pp. 100, 101.
+
+[54] Note VI., p. 101.
+
+[55] Note VII., p. 107.
+
+[56] Even larger estimates of the number of germs in a gramme of soil
+have been made--from three-quarters to one million (Koch, Fülles, and
+others).
+
+[57] These organisms consist of molds, yeast, and bacteria, the
+last-named being most abundant. In the surface-soil, among the bacteria,
+bacilli are most abundant. Micrococei are not abundant.
+
+[58] Investigated by Winogradsky, Olivier, De Rey Pailhade, and others.
+
+[59] Organisms of this kind have been investigated among others by
+Heraüs, Hueppe, and E. Wollny. According to the two first-mentioned
+investigators, certain colourless bacteria effect the formation in the
+absence of light from humus and carbonates a body resembling in its
+nature cellulose.
+
+[60] Investigated by Springer, Gayon and Dupetit, Dehérain, and
+Marguenne.
+
+
+
+
+APPENDIX TO CHAPTER I.
+
+
+NOTE I. (p. 68).
+
+The following determinations by Schübler show the absorptive power of
+different kinds of soil-substances. These were obtained by soaking
+weighed quantities of the soil in water, and allowing the excess of
+liquid to drain away, and weighing the wet earth.
+
+ Per cent of water
+ absorbed by 100
+ parts of earth.
+
+Siliceous sand 25
+Gypsum 27
+Calcareous sand 29
+Sandy clay 40
+Strong clay 50
+Arable soil 52
+Fine calcareous 85
+Garden-earth 89
+Humus 190
+
+It has been calculated that the absorptive power of a mixture of
+different substances is not simply equal to the sum of their separate
+ingredients.
+
+
+NOTE II. (p. 74).
+
+EVAPORATION.
+
+The retentive property of a soil for water tends to retard evaporation.
+The following table by Schübler shows the rate at which evaporation
+proceeds in different soils. The experiment was conducted in the
+following way. The soil experimented upon was saturated with water and
+spread over a disc, and allowed to evaporate for four hours, when it was
+weighed. The amount of time required for the evaporation of 90 per cent
+of the water was also estimated. Of 100 parts of water in the wet soil
+there evaporated, at 60° Fahr.--
+
+ Time required to
+ In four hours-- evaporate 90 per cent.
+From-- per cent. Hours. Minutes.
+
+Quartz 88 4 4
+Limestone 76 4 44
+Sandy clay 52 5 1
+Stiffish clay 46 6 55
+Loamy clay 46 7 52
+Pure grey clay 32 11 17
+Loam 32 11 15
+Fine calcium carbonate 28 12 51
+Humus 21 17 33
+Magnesium carbonate 11 33 20
+
+
+NOTE III. (p. 76).
+
+HYGROSCOPIC POWER OF SOILS.
+
+Davy found the hygroscopic power of soils to be as follows. He found
+that 100 parts by weight of three samples of different sands absorbed 3,
+8, and 11 parts of water, respectively, in one hour; while three loams
+absorbed similarly 1.3, 1.6, and 1.8 parts.
+
+The following samples of soil were dried at 212° Fahr., and exposed to
+an atmosphere saturated with water and a temperature of 62° Fahr., when
+it was found they absorbed the following amounts in twelve hours'
+time:--
+
+Quartz sand 0.0
+Limestone sand 0.3
+Lean clay 2.1
+Fat clay 2.5
+Clay soil. 3.0
+Pure clay. 3.7
+Garden-loam 3.5
+Humus 8.0
+
+
+NOTE IV. (p. 81).
+
+GASES PRESENT IN SOILS.
+
+The air which we find enclosed in the pores of the soil is distinctly
+_poorer_ in oxygen than ordinary air. Boussingault found the percentage
+of oxygen in a sandy soil, freshly manured and wet with rain, to be as
+low as 10.35 per cent; while the air in forest-soil contained 19.5 per
+cent of oxygen, and .93 per cent of carbonic acid. The percentage of
+oxygen in soils depends on the rate of decay of the organic portions.
+The depth of the soil-layer also determines the quantity. This is owing
+to the fact that diffusion takes place more slowly deep down than near
+the surface.
+
+
+NOTE V. (p. 90).
+
+AMOUNT OF SOLUBLE PLANT-FOOD IN THE SOIL.
+
+Two of the most reliable methods of ascertaining an approximation of the
+quantity of soluble soil constituents are (1) by treating the soil with
+distilled water, and (2) by analysing the drainage-water. With regard to
+the former of these two methods, it has been found that even the amount
+of fertilising matter dissolved out by pure distilled water varies. This
+variation depends on the amount of distilled water used, as well as the
+length of time the soil is left in contact with the solvent. By washing
+the soil with different quantities of water, different amounts of
+soluble soil ingredients will be found to have been washed out; for
+although the first washings contain by far the greater portion of the
+soluble matter, each subsequent washing will be found to contain further
+quantities.
+
+A number of experiments have shown that 1000 parts of distilled water
+dissolved out from different soils from one half to one and a half parts
+of soluble constituents; or from .05 to .15 per cent. Of this soluble
+matter from 30 to 67 per cent is mineral in its nature, and from 33 to
+70 per cent organic. Poor sandy soils yield the minimum quantity, while
+peaty soils yield the maximum. The quantity of soluble matter in a
+regular peaty soil may vary from .4 to 1.4 per cent; this consists
+chiefly, however, of organic matter. (See Johnson's 'How Crops Feed,' p.
+312.)
+
+Perhaps a more satisfactory method is by analysing the drainage-water of
+a soil. This has been found to vary very considerably in composition.
+The average of a large number of analyses are .04 to .05 per cent of
+dissolved matter. Of this dissolved matter the largest proportion is
+made up of organic matter, nitric acid, lime, and soda salts. It must be
+borne in mind, however, that even the drainage-water does not furnish an
+exact indication of the amount of dissolved matter in a soil. Much,
+perhaps the largest proportion of dissolved matter, never finds its way
+into the drainage-water. That contained by the drainage-water really
+represents the surplus quantity of dissolved matter which the soil is
+unable to retain, and which is thus washed by the rain into the drains.
+The composition of drainage-water is interesting, as it shows that,
+practically speaking, all the necessary plant ingredients are in a state
+of solution in the soil.
+
+
+NOTE VI. (p. 90).
+
+CHEMICAL COMPOSITION OF THE SOIL.
+
+The most important substances present in soils are as follows: silica,
+alumina, lime, magnesia, potash, soda, ferric oxide, manganese oxide,
+sulphuric acid, phosphoric acid, and chlorine. Of these substances the
+presence of alumina, silica, lime, and, in certain cases, magnesia,
+along with the organic portion of the soil--the humus--has the chief
+influence in determining the nature and the physical properties of a
+soil.
+
+In order to clearly understand to what it is soils owe the nature of
+their chemical composition, it is necessary to consider the composition
+of some of the chief minerals out of the disintegration of which soils
+are formed.
+
+While we know of some seventy elements present in the earth's crust, it
+is practically made up of only some sixteen. These sixteen are--oxygen,
+silicon, carbon, sulphur, hydrogen, chlorine, phosphorus, iron,
+aluminium, calcium, magnesium, sodium, potassium, fluorine, manganese,
+and barium.[61] Of these, oxygen is by far the largest constituent,
+forming, roughly speaking, about 50 per cent.
+
+The main mass of the rocks consists of silica, and this is generally
+combined with alumina, as in clay, forming aluminium silicate, and with
+the commoner alkalies and alkaline earths. Another extremely abundant
+compound is carbonate of lime, which, as limestone, chalk, and marl,
+forms one-sixth of the earth's total rocks.
+
+The word "mineral" means a definite chemical compound of natural
+occurrence. The number of minerals is very great, and it is impossible
+to go into the subject here. Reference can only be made to a few of the
+more prominent ones, which are chiefly concerned in the formation of
+soils.
+
+Those formed out of silicates are, from the agricultural point of view,
+the most important, as they form a very large group; and it is by their
+disintegration that soils are chiefly formed. They consist of silica and
+alumina, along with various other substances, chiefly alkalies and
+alkaline earths. It is important to note one peculiarity about the
+solubility of silicates. We have two classes of silicates: the one,
+which is called "acid," and contains an excess of silica; the other,
+"basic," and which contains an excess of base. Now, while the former of
+these is more or less insoluble, the second is soluble. This fact has an
+important signification in the process of the disintegration of the
+silicate minerals we are about to consider.
+
+The first and most important class are the _Felspars_. Felspar is not
+really a definite mineral, with a definite chemical composition, but
+rather the name of a class of minerals of which there are several
+different kinds. The felspars are composed of silica and alumina, along
+with potash, soda, and lime, with traces of iron and magnesia. Their
+principal constituents, however, are silica and alumina, along with
+either potash, soda, or lime. According as the base potash, soda, or
+lime predominates, the felspar is known as Orthoclase, Albite, and
+Oligoclase, respectively.
+
+The following are the analyses of the three minerals (by the late Dr
+Anderson):--
+
+--------------------+-----------------+-----------------+-----------------
+ | Orthoclase. | Albite. | Oligoclase.
+ +--------+--------+--------+--------+--------+--------
+ | 1. | 2. | 1. | 2. | 1. | 2.
+--------------------+--------+--------+--------+--------+--------+--------
+ Silica | 65.72 | 65.00 | 67.99 | 68.23 | 62.70 | 63.51
+ Alumina | 18.57 | 18.64 | 19.61 | 18.30 | 23.80 | 23.09
+ Peroxide of iron | traces | 0.83 | 0.70 | 1.01 | 0.62 | none
+ Oxide of manganese | traces | 0.13 | none | none | none | none
+ Lime | 0.34 | 1.23 | 0.66 | 1.26 | 4.60 | 2.44
+ Magnesia | 0.10 | 1.03 | none | 0.51 | 0.02 | 0.77
+ Potash | 14.02 | 9.12 | none | 2.53 | 1.05 | 2.19
+ Soda. | 1.25 | 3.49 | 11.12 | 7.99 | 8.00 | 9.37
+--------------------+--------+--------+--------+--------+--------+--------
+ | 100.00 | 99.47 | 100.08 | 99.83 | 100.79 | 101.37
+--------------------+--------+--------+--------+--------+--------+--------
+
+According as these various felspars are present in a soil, so will the
+quality of the soil be. It stands to reason that as the presence of
+potash in a soil is one of the distinguishing features of its fertility,
+much will depend on the extent to which the orthoclase felspar is
+present; and also, not only on the extent, but on the state and degree
+of its disintegration. It is important to note the method of this
+disintegration. It is effected by the absorption of water. This water is
+not merely absorbed mechanically, but actually enters into the
+composition of the mineral. It is not present as moisture merely,
+capable of being expelled at ordinary boiling temperature, but it forms
+what is known as water of composition. In this process of hydration, the
+mineral loses its lustre and crystalline appearance, crumbles away into
+a more or less--according to its state of disintegration--powdery mass.
+A very great change is also effected in its chemical composition; it
+loses nearly all its base. This is effected in the following way. As
+water enters into the mineral's composition, it sets free a certain
+portion of the base; there is thus formed a basic silicate, which, being
+soluble in water, is washed away in solution. This change may be
+illustrated by quoting the analysis of a kaolin clay formed by the
+disintegration of orthoclase felspar.
+
+_Kaolin Clay formed by disintegration of Orthoclase._
+
+ Silica 46.80
+ Alumina 36.83
+ Peroxide of iron 3.11
+ Carbonate of lime 0.55
+ Potash 0.27
+ Water 12.44
+ ------
+ 100.00
+ ------
+
+The chief difference here is the almost total loss of potash and a
+portion of the silica, and the gain of water. The other constituents
+practically remain insoluble.
+
+Another important mineral is _Mica_. Its composition is not unlike
+felspar. It contains silica, alumina, and iron, in considerable
+quantities, also magnesia and potash. There are two kinds of mica--that
+containing potash, and that containing magnesia, in excess. The analyses
+of these two kinds are as follows (by the late Dr Anderson):--
+
+ MICAS.
+ (_a_) Potash. (_b_) Magnesia.
+Silica 46.36 42.65
+Alumina 36.80 12.96
+Peroxide of iron 4.53 none
+Protoxide of iron none 7.11
+Oxide of manganese 0.02 1.06
+Magnesia none 25.75
+Potash 9.22 6.03
+Hydrofluoric acid 0.70 0.62
+Water 1.84 3.17
+ ----- -----
+ 99.47 99.35
+ ----- -----
+
+The decomposition of mica is very slow, however, as it is a peculiarly
+hard mineral.
+
+Other important minerals are _Hornblende_ and _Augite_. These are
+composed of silica, alumina, iron oxide, manganese oxide, lime and
+magnesia. These are the chief minerals out of which soils are formed. It
+is scarcely necessary to say that few soils are made up out of any of
+these three minerals alone. Nearly all rocks are formed out of a mixture
+of these minerals. Where, however, any one mineral predominates over the
+rest, the nature of the soil will be thereby affected. In order to
+illustrate this, it may be well to mention the composition of one or two
+of the commoner rocks.
+
+1. _Granite_, which is so abundant in certain parts of the north of
+Scotland, and which gives rise to the soils in the neighbourhood of
+Aberdeen, is made up of a mixture of quartz, felspar, and mica. It
+depends on the felspar present--_i.e._, whether it is orthoclase,
+oligoclase, or albite--whether the soil will be rich in potash or not.
+Granite containing orthoclase felspar produces a fairly fertile soil. An
+important consideration, which is apt to complicate this question, is
+the situation of such soils. They are generally so high above sea-level,
+that their fertility is seriously impaired on these grounds.
+
+2. _Gneiss_, another common rock, is similar in composition, only that
+it contains very little felspar, and a correspondingly greater amount of
+mica.
+
+3. _Syenite_ contains quartz, felspar, and hornblende.
+
+The rocks of which greenstone and trap are types, are found very largely
+scattered over the country. They are of two kinds, diorite and dolorite.
+
+4. _Limestone_ is of two great classes. We have (1) Common, (2)
+Magnesian. The following are the analyses of these two classes by Dr
+Anderson:--
+
+----------------------+---------------------------+------------------------
+ | Common. | Magnesian.
+ +-------------+-------------+-------------+----------
+ | Mid-Lothian | Sutherland. | Sutherland. | Dumfries.
+----------------------+-------------+-------------+-------------+----------
+Silica | 2.00 | 7.43 | 6.00 | 2.31
+Iron oxide and alumina| 0.45 | 0.76 | 1.57 | 2.00
+Carbonate of lime | 93.61 | 84.11 | 50.21 | 58.81
+Carbonate of magnesia | 1.62 | 7.45 | 41.22 | 36.41
+Phosphate of lime | 0.56 | - | - | -
+Sulphate of lime | 0.92 | - | - | -
+Organic matter | 0.20 | - | - | -
+Water | 0.50 | - | - | -
+ | ----- | ----- | ----- | -----
+ | 99.86 | 99.75 | 99.00 | 99.53
+----------------------+-------------+-------------+-------------+----------
+
+Clays are formed by the disintegration of any of the crystalline rocks;
+the purest clays being formed from felspar. A pure clay consists simply
+of silica and alumina, all the other constituents having been washed
+out. Disintegration, however, seldom reaches such an extent; otherwise
+clay soils would be completely barren, which they are notably not. The
+impurities present in clay, which consist of alkalies, especially potash
+and other mineral ingredients of the plant, are what confer on clay
+soils their fertility. Clays differ, however, very considerably in
+their composition. The following is an analysis of a clay soil by Dr
+Anderson:--
+
+Silica 60.03
+Alumina 14.91
+Peroxide of iron 8.94
+Lime 2.08
+Magnesia 4.22
+Potash 3.87
+Soda 0.06
+Water and carbonic acid 5.67
+ -----
+ 99.72
+ -----
+
+
+NOTE VII. (p. 91).
+
+FORMS IN WHICH PLANT-FOODS ARE PRESENT IN SOIL.
+
+The forms in which the bases necessary for plant-food are present in the
+soil, are chiefly as _hydrated silicates_, and in combination with
+organic acids, forming humates, &c., as well as in the form of sulphates
+and chlorides.
+
+Phosphoric acid is present in combination with iron, alumina, or lime,
+or possibly also as magnesium-ammonium-phosphate. Sulphuric acid is
+generally present in a more or less insoluble condition, in combination
+with iron and lime; whereas chlorine is combined with the alkali bases
+in an easily soluble form. An important point is as to the form in which
+the plant absorbs these food constituents. In this connection reference
+may be made to a theory put forward by a very distinguished French
+agricultural chemist, Professor Grandeau. His theory is that the
+necessary ingredients of plant-food are absorbed into the plant as
+humates, or, at any rate, that the medium of this transference is humic
+acid, and organic acids of a similar nature. This theory, however, while
+ingenious, has not yet been supported by sufficient evidence to make its
+acceptance advisable. It is probable that it is only in the form of
+soluble salts that the plant can absorb its food. It is quite probable,
+however, at the same time, that the exact form in which the different
+food substances enter the plant may be largely determined by
+circumstances. According to Nobbe, chloride of potassium is the most
+suitable form of potassium salts, although the plant may absorb its
+potassium as sulphate, phosphate, or even silicate.
+
+
+FOOTNOTES:
+
+[61] Composition of the earth's solid crust in 100 parts by weight:--
+
+Oxygen 44.0 to 48.7 | Calcium 6.6 to 0.9
+Silicon 22.8 to 36.2 | Magnesium 2.7 to 0.1
+Aluminium 9.9 to 6.1 | Sodium 2.4 to 2.5
+Iron 9.9 to 2.4 | Potassium 1.7 to 3.1
+
+(Roscoe's 'Lessons in Elementary Chemistry,' p. 8.)
+
+
+
+
+CHAPTER II.
+
+FUNCTIONS PERFORMED BY MANURES.
+
+
+Having now considered the general conditions on which fertility of soil
+depends, we are in a position to deal with the nature and function of
+manures.
+
+Manures may be classified in several different ways, and a considerable
+amount of confusion is sometimes caused by the variety of classification
+adopted by different writers on this subject.
+
+
+_Etymological meaning of the word Manure._
+
+Let us, in the first place, clearly understand what we mean by a manure.
+The word manure comes from the French word _manoeuvrer_, which simply
+means "to work with the hand," hence "to till," and this etymological
+meaning of the word illustrates the old belief in the function of
+manures. We have already seen in the historical introduction that,
+according to Tull, the true and only function of manures was to aid in
+the pulverisation of the soil by fermentation. In advancing his system
+of _thorough tillage_, he claimed that since tillage effected the
+pulverisation of the soil, where it was practised, manures could be
+dispensed with.
+
+
+_Definition of Manures._
+
+We no longer, of course, attach this old meaning to the word. The word
+manure is now applied to any substance which by its application
+contributes to the fertility of a soil. As has been shown in the
+previous chapter, the substances necessary for plant-growth which are
+apt to be lacking in a soil, are only generally three in number--viz.,
+_nitrogen_, _phosphoric acid_, and _potash_. A manure, therefore, is
+understood to be any substance containing these ingredients, either
+singly or together, and its commercial value is determined by the amount
+it contains of these substances. But while this is so, it must not be
+forgotten that if we define a manure to be a substance which contributes
+in any way to the fertility of the soil, substances other than these
+above mentioned may be fairly regarded as manures. The fertility of a
+soil, we have seen, depends not merely on the presence of certain
+constituents, but also on their chemical condition--_i.e._, whether they
+are easily soluble or not. It further depends, as we have also seen, on
+the possession by the soil of certain mechanical and biological
+properties. Thus there are substances which act upon the soil's inert
+fertilising matter, and by their action convert it into a more speedily
+available form. There are other substances which by their application
+exert a considerable effect on the texture of the soil, and thereby
+influence its physical and biological properties. All such substances,
+according to the above definition of a manure, must be included under
+the term. It will thus be seen that since fertility in a soil can be
+promoted in a variety of ways, and the functions performed by manures
+are of different kinds, we can divide them into different classes,
+according to their respective action.
+
+
+_Different Classes of Manures._
+
+In the first place, we can divide manures into two great classes,--(1)
+those supplying to the soil necessary plant-food constituents, and thus
+contributing directly to fertility; and (2) those influencing
+soil-fertility in an indirect manner. The first class we may call
+_direct_ manures, and the second _indirect_. Those two classes admit
+further of being subdivided into other smaller classes. Among the direct
+manures we have a number of subdivisions in use. They may be divided
+into _general_ manures and _special_ manures, according as they contain
+all the elements necessary for plant-growth, or only some of them; or
+they may be divided according to their source into _natural_ and
+_artificial_, _mineral_ and _vegetable_. Similarly we have a number of
+subdivisions among the second class, depending on the special nature of
+the action they exert. Some manures act in both capacities--both
+directly and indirectly--and in order that their value be fully
+appreciated must be studied under both heads. The most striking example
+of such a manure is farmyard manure. There are other manures which may
+in certain circumstances act in two different ways. Such a substance is
+lime. There are soils which are actually lacking in a sufficiency of
+lime for the needs of crops. On such soils an application of lime would
+act both as a direct and also as an indirect manure. There may also be
+cases of an exceptional nature, in which magnesia salts or even iron
+salts may act as direct manures. Many manures commonly regarded as
+purely direct manures would exert an indirect influence were the
+quantities in which they were applied sufficiently large. This is the
+case, indeed, with many artificial manures, such as guano, bones,
+nitrate of soda, and basic slag. It has been claimed for nitrate of soda
+that it not merely promotes fertility by supplying nitrogen in its most
+available form to the soil, but that the soda it contains exerts a
+valuable indirect influence in consolidating the soil and increasing its
+absorptive powers. When we reflect, however, on the small quantity of
+this manure which is applied per acre, its mechanical influence must be
+insignificant. The same applies to basic slag, which contains a
+considerable quantity of free lime in its composition. As this manure,
+however, is sometimes applied in considerable quantities, it is
+reasonable to suppose that its indirect value may not be altogether
+insignificant. Indeed we have proof of this in the fact that its most
+favourable action has been found to be on soils rich in organic
+matter.[62] The action of bones and guano, and indeed of all other
+manures containing a large percentage of decomposable organic matter, is
+likewise of a double nature, inasmuch as their decomposition or
+putrefaction in the soil gives rise to the formation of carbonic and
+organic acids, which are capable of exerting a chemical action on the
+soil ingredients. There is one point in connection with the action of
+these manures which is worthy of notice, and it is that, however slight
+their indirect value may be, their action as a direct manure is very
+much accelerated by the way in which their organic matter putrefies. In
+short, they may be described as providing, to a certain extent, the
+solvents which render them available for the requirements of the plant.
+It may be here convenient to classify the manures which we intend
+subsequently to deal with.
+
+I. Manures, action of which is both direct and indirect--_e.g._, _green
+manures_, _farmyard manure_, _composts_, and _sewage_.
+
+II. Manures which may be regarded as having only a direct
+action--_e.g._, _guano_ of all kinds, _bones_ in all forms, _nitrate of
+soda_, _sulphate of ammonia_, _dried blood_, _superphosphates_, _mineral
+phosphates_ of all kinds, _horns_ and _hoofs_, _shoddy_, _wool-waste_,
+_fish-guano_, _muriate of potash_, _sulphate of potash_, and _kainit_.
+
+III. Manures which may be regarded as having only an indirect
+value--_e.g._, _lime_, _mild_ and _caustic_, _marl_, _gypsum_, _salt_,
+&c.
+
+We shall now proceed to discuss the nature and action of these different
+manures, starting with those exercising both a _direct_ and _indirect_
+influence. Before doing so it may be well to consider the occurrence and
+natural sources of the three important soil constituents, nitrogen,
+phosphoric acid, and potash, with a view of seeing to what extent these
+are being removed from our soils by the various natural processes
+constantly going on, as well as by the crops, and how far their natural
+sources are capable of making good this loss--in short, to clearly
+understand the economic reasons for the application of artificial
+manures.
+
+
+FOOTNOTES:
+
+[62] See Chapter on Basic Slag.
+
+
+
+
+CHAPTER III.
+
+THE POSITION OF NITROGEN IN AGRICULTURE.
+
+
+Of manurial ingredients, nitrogen is by far the most important, and on
+the presence and character of the nitrogen it contains, the fertility of
+a soil may be said to be most largely dependent. Most soils, as a rule,
+are better supplied with available ash ingredients than with available
+nitrogen compounds. The expensive nature of most artificial nitrogenous
+manures also gives to nitrogen the first position from an economic point
+of view. A thorough study, therefore, of the different forms in which it
+exists in nature, of the numerous and complicated changes it undergoes
+in the soil, by which it is prepared for the plant's needs, of the
+relation of its different forms to plant-life, and of the natural
+sources of its loss and gain, is of the highest importance if we are to
+hope to understand the difficult question of soil-fertility.
+
+
+_The Rothamsted Experiments and the Nitrogen question._
+
+The position of nitrogen in agriculture is a question of great
+difficulty and complexity. It has engaged much attention, and has had
+devoted to its elucidation much elaborate and painstaking research. To
+the Rothamsted experiments we owe most of the information we possess on
+the subject, and the facts contained in this chapter are almost entirely
+derived from the results of these famous experiments, as embodied in the
+memoirs and writings of Messrs Lawes, Gilbert, and Warington.
+
+
+_Different forms in which Nitrogen exists in Nature._
+
+We have already referred to the nitrogen question in the historical
+introduction. In order, however, to have a comprehensive view of the
+subject, it may be well to recapitulate some of the facts there
+mentioned.
+
+Nitrogen, as we have already seen, exists in the "free" or elementary
+condition, as nitrates and nitrites, as ammonia, and in a large number
+of different organic forms.
+
+
+_Nitrogen in the Air._
+
+It occurs in greatest abundance (amounting to about 80 per cent) in the
+first of these forms in the air. That this free nitrogen, which is
+practically unlimited in quantity,[63] has originally been the source of
+all its other forms, is of course obvious. But this conversion of free
+nitrogen into the various compound forms in which it occurs throughout
+the mineral, vegetable, and animal kingdoms, has been a process effected
+by a variety of indirect methods, and only at the expense of a vast
+amount of time. For practical purposes, the free nitrogen of the air may
+be regarded chiefly as a non-available source for most bodies containing
+it. It may be described as of all forms of nitrogen the least active, as
+far as plant-life is concerned.
+
+
+_Relation of "free" Nitrogen to the Plant._
+
+The relation of the "free" nitrogen to the plant has formed the subject
+of much research, more especially during the last few years, and a brief
+epitome of the main results arrived at has already been given in the
+Introductory Chapter.[64]
+
+That this source of nitrogen is not so inaccessible to the plant as was
+formerly believed, has now been abundantly proved. As the considerations
+which have led to this conclusion, and have suggested the very recent
+elaborate experiments on the fixation of free nitrogen by the plant--the
+results of which bid fair, it would seem, to largely revolutionise our
+agricultural practice--have been due to the study of the relation of the
+soil-nitrogen to the plant, it will be best to defer further discussion
+of this question till we have dealt with the other sources of nitrogen.
+
+
+_Combined Nitrogen in the Air._
+
+In addition to nitrogen in the free state, air contains very small
+quantities of this element in combined forms. We have it in minute
+traces as nitrates and nitrites, as ammonia,[65] and also in still
+smaller traces as organic nitrogen in the minute dust-particles which
+modern researches have revealed as being present in such enormous
+numbers in our atmosphere. What the sources of these nitrates and
+nitrites (which exist in quantities so minute that accurate
+determination of their amount is rendered extremely difficult) are is a
+disputed point. That nitrogen and oxygen unite together to form nitric
+and nitrous oxides under the influence of intense heat, such as the
+electric spark, has been proved beyond doubt. One source, therefore, is
+probably the electrical discharges which are taking place more or less
+frequently on different parts of the earth's surface. Nitrates may also
+be formed in the combustion of nitrogenous bodies.[66] In the burning of
+coal-gas, for example, it is probable that small quantities of nitrates
+may be produced. Similarly the slow combustion or decay of nitrogenous
+organic matter, which constantly takes place all over the earth's
+surface, may be regarded as another source of this form of combined
+nitrogen. Ammonia may be similarly formed by the combustion, either
+quick or slow, of nitrogenous organic matter. It exists in the air as
+nitrate or nitrite of ammonia, and also as carbonate of ammonia.[67]
+
+
+_Amount of combined Nitrogen falling in the Rain._
+
+The importance of the combined nitrogen in the air as a source of
+soil-nitrogen is best gauged by the amount falling annually on the soil
+dissolved in rain. This has been found to vary considerably. In the rain
+falling in the vicinity of large towns the amount is greater than in
+rain falling in the country. Thus at Rothamsted, in England, the average
+amount for several years was only 3.37 lb. nitrogen per annum per acre,
+of which 2.53 lb. were as ammonia,.84 being as nitric acid. At Lincoln,
+in New Zealand, 1.74 lb. fell annually per acre--as ammonia,.74, as
+nitric acid, 1.00; while at Barbadoes the amount was 3.77 lb., of which
+.93 was as ammonia, and 2.84 as nitric acid.[68] That the combined
+nitrogen derived from the air by the soil may be considerably in excess
+of this is highly probable. Soils, especially when damp, may absorb much
+larger quantities from the air of the combined nitrogen it contains. We
+must remember that the air in contact with the soil-surface is
+constantly being changed, and that there is thus a constant renewal of
+the air passed over the ground. The result is that the amount of air
+from which combined nitrogen may be removed is very great.[69]
+
+
+_Nitrogen in the Soil._
+
+It has been remarked as a fact worthy of notice that nitrogen is
+essentially a superficial element. By this is meant that it is only
+found, as a rule, on the earth's immediate surface. This statement can
+only be admitted to be true within certain limits. The chief source of
+nitrogen, in addition to the atmosphere, is, of course, vegetable and
+animal tissue.[70] As vegetable and animal tissue are only found to any
+extent on the earth's surface, nitrogen is therefore chiefly found
+there. The natural deposits of nitrogen salts, such as the
+nitrate-fields of Chili and the saltpetre soils of India, &c., also
+only occur superficially. Notwithstanding these facts, however, the
+amount of nitrogen which exists at probably considerable depths from the
+surface must be very great. There are few sedimentary rocks which do not
+contain it. At Rothamsted a sample of calcareous clay, taken from a
+depth of 500 feet, contained .04 per cent--that is, as much as is found,
+on an average, in the Rothamsted clay subsoils.
+
+
+_Nitrogen in the Subsoil._
+
+On the whole, however, as we have said, nitrogen is chiefly found in the
+surface-soil. The amount found in the subsoil at Rothamsted seems to
+vary very slightly at different depths, the percentage amounting to from
+.06 to .03.[71] Unlike the nitrogen of the surface-soil, that in the
+subsoil seems to be of very ancient origin, being probably derived from
+the remains of animal and vegetable life in the mud deposited at the
+bottom of the ocean. It is more abundant in the case of a clay subsoil
+than in a sandy subsoil.
+
+
+_Nitrogen of Surface-Soil._
+
+Nitrogen has a tendency to collect on the top layers of the
+surface-soil, the first 9 inches or foot containing by far the largest
+proportion of it. In the table given in the Appendix,[72] the rate at
+which it decreases in amount the further down we go is clearly shown.
+Determinations of the respective amounts of nitrogen in every 3 inches
+of the soil, taken to a depth of one foot of the experimental
+wheat-field at Rothamsted, showed that the percentage between the first
+3 inches and the second 3 inches varied very slightly. A more marked
+difference, however, was shown to exist between the nitrogen in the
+second and third 3 inches; while the fourth 3 inches were distinctly
+poorer--differing very little in their percentage of nitrogen from the
+subsoil. This was the case in unmanured soil. In the case of heavily
+manured soil, the increase in the soil's percentage, due to manure, was
+shown to be felt to the depth of a foot, but not much below it.[73]
+
+A careful perusal of the tables in the Appendix will show that the
+quantity of nitrogen in the case of both arable and pasture soils
+steadily decreases for the first 3 feet, but that below this depth
+little decrease is seen, the percentage evidently becoming fairly
+constant.
+
+
+_The amount of Nitrogen in the Soil._
+
+Very considerable difference exists in the amount of nitrogen present in
+different soils. The majority of analyses refer only to the amount found
+in the surface-soil--generally in the first 9 or 12 inches. As the soil,
+further, is not a body exactly homogeneous in its character, very
+considerable difficulty exists in obtaining reliable results. A great
+deal depends, therefore, on the method of sampling and the basis of
+calculation adopted; and it may be that this may occasionally explain,
+to some extent at least, the great discrepancies in the estimation of
+the quantities of nitrogen present in different soils as found by
+different investigators.
+
+
+_Peat-soils richest in Nitrogen._
+
+Of all soils, peat-soils are richest in nitrogen. Professor S. W.
+Johnson found the nitrogen in fifty separate samples of peat to range
+from .4 per cent to 2.9 per cent, the average being 1.5 per cent. On the
+other hand, marls and sandy soils are poorest, the analyses of a number
+of these soils showing only from .004 to .083 per cent for the former,
+and .025 to .074 for the latter. As a general rule most arable soils
+contain over one-tenth per cent of nitrogen, or, say, over 3500 lb. per
+acre. A good pasture-soil, taken to a depth of 9 inches at Rothamsted,
+was found to contain about a quarter per cent. In ten samples of soil,
+taken to a depth of 9 inches, from different parts of Great Britain and
+Ireland, Munro found from .128 to .695 per cent of nitrogen, the average
+being .3278 per cent. The Rothamsted soils, it may be pointed out, are
+probably poor in nitrogen compared with most soils. A. Müller's
+investigations showed that in some of the soils he has analysed, the
+nitrogen amounted to little short of one per cent, while for the others
+the average was over half a per cent; even the poorer soils he examined
+contained about one quarter per cent on an average. Anderson's analyses
+of Scottish wheat-soils showed a variation of from .074 to .22 in the
+surface-soil, while he found in their subsoil from .15 to .92 per cent.
+Boussingault's results are also very much higher. The amount of nitrogen
+in a number of loams coming from widely different localities he examined
+contained from 6000 to 30,000 lb. per acre--the soil taken to a depth of
+17 inches.[74]
+
+
+_Nature of the Nitrogen in the Soil._
+
+When we compare the amount of nitrogen removed by different crops
+(which, even in the case of those most exhaustive of nitrogen, does not
+often amount to more than 150 lb. per acre), with the amount contained
+in the soil, the former amount seems very insignificant when compared to
+the latter. Such being the case, it would seem at first sight that the
+addition of nitrogen in the form of manures is quite superfluous. We
+must remember, however, that while the _total_ amount of nitrogen is
+relatively large when compared to that removed by crops, only a very
+small proportion is in a condition _available_ to the plant. This leads
+us to consider the different forms in which nitrogen is present in the
+soil, and their respective quantities.
+
+
+_Organic Nitrogen in the Soil._
+
+Nitrogen occurs in the soil as organic nitrogen, nitric acid, nitrous
+acid, and ammonia. By far the largest proportion is present in the first
+of these forms. This is a wise provision, for otherwise the soil would
+be apt to become very speedily impoverished in nitrogen; for that
+present as nitrates it has scarcely any power to retain, while that
+present as ammonia is soon converted into nitrates by the process of
+_nitrification_.
+
+The organic nitrogen of the soil, although we are apt to think of it as
+such, is by no means of a homogeneous character, or of equal value as a
+source of plant-food. Some of it, it would seem from recent
+investigations, is in a condition more susceptible of being converted
+into an available form than the rest. Thus in the process of
+nitrification, a process which we shall consider at length immediately,
+there seems to be generally a certain small proportion more ready to
+undergo this change than the rest; so that when this small amount is
+used up nitrification proceeds more slowly. In short, although we as yet
+know very little of the nature of the organic nitrogen of soils, we
+cannot doubt but that there is a constant series of changes in its
+composition taking place, resulting in the gradual elaboration of more
+available forms, until ultimately these are converted into ammonia and
+nitrates.
+
+The great bulk of the organic nitrogen, however, in the soil must be
+regarded as in an _inert_ condition, and by no means available for the
+crop. What the exact chemical form of this nitrogen is it is extremely
+difficult to say. Mulder was of the opinion that a considerable
+proportion was in the form of humate of ammonia. This opinion, as we
+shall have occasion to see immediately, was based on false grounds. It
+is highly probable that it may be in some form approximating to amide
+nitrogen. Its inert character is against the belief that it long remains
+as albuminoid nitrogen.
+
+
+_Different Character of Surface and Subsoil Nitrogen._
+
+A point of very considerable importance to notice is, that the
+nitrogenous organic matter of the surface-soil is very different from
+that found in the subsoil. This difference is shown by the variation in
+the ratio of nitrogen to carbon, which points to the fact that, just as
+we should naturally suppose, the origin of the latter is very much more
+ancient than the origin of the former. Thus in the first 9 inches of old
+pasture-soil at Rothamsted, the ratio was 1:13; while in the subsoil, 3
+feet from the surface, it was only 1:6. In the surface-soil it thus
+approaches more nearly in composition ordinary vegetable matter.
+
+
+_Nitrogen as Ammonia in Soils._
+
+The second form in which nitrogen is present in soil is as ammonia. A
+very considerable misapprehension has existed in the past as to the
+amount of nitrogen in this form in soils. This mistake was due to the
+method adopted in estimating it, which consisted in treating the soil
+with boiling caustic alkalies and counting as ammonia what was given off
+as such. It is now known that certain forms of organic nitrogen--as, for
+example, amides--if treated in this way are slowly converted into
+ammonia. Statements, therefore, which are found in the older text-books,
+representing the amount of ammonia in soils as at over a tenth per cent,
+must be regarded as utterly unreliable. Indeed it is highly probable
+that ammonia only occurs in most soils in very minute traces. From what
+we know of the process of nitrification, we see how it is wellnigh
+impossible that ammonia should exist to any extent in the soil except
+under very exceptional circumstances.
+
+
+_Amount of Ammonia present in the Soil._
+
+In ordinary soils it probably does not amount to more than from .0002
+per cent to .0008 per cent, or an average of .0006 per cent.[75] In
+rich soils, or in garden-soils, the amount may be considerably more.
+Thus Boussingault found in a garden-soil .002 per cent. In peat and in
+peat-mould even a higher percentage has been found--viz.,.018 for the
+former and .05 for the latter.
+
+
+_Nitrogen present as Nitrates in the Soil._
+
+The third form of nitrogen in the soil is nitric acid. It is more
+abundant in this form than as ammonia; but still, compared with the
+organic nitrogen, its amount is trifling. Probably not more than 5 per
+cent of the total nitrogen of a soil is ever present as nitrates. The
+reason of this is twofold. First, as we have already remarked, the soil
+has very little power to retain nitrogen in this form; and secondly,
+where the soil is covered with growing vegetation the nitrates are
+quickly assimilated by the plant as they are formed. It is for this
+reason that we find the quantity of nitrogen as nitrates very much
+greater in fallow soils than in those covered with a crop.
+
+
+_Position of Nitric Nitrogen in Soil._
+
+As we shall have occasion to see more fully in the following chapter on
+Nitrification, the formation of nitrates is chiefly limited to the
+surface-soil, the largest proportion being formed within the first 9 or
+12 inches. For this reason we find the largest quantity of nitrates in
+the surface-soil. But inasmuch as they are easily washed into the lower
+layers of the soil after formation, we often find a considerable
+proportion beyond the first 9 inches. The position of nitrates in the
+soil thus depends very considerably on the season of the year and the
+weather. In dry weather, where the evaporation of the soil-water takes
+place at a considerable rate, the tendency will be to concentrate the
+nitrates in the superficial portion of the soil. In wet weather, on the
+other hand, the tendency will be to wash the nitrates into the lower
+layers.
+
+
+_Amount of Nitrates in the Soil._
+
+The determination of the amount of nitrates in a soil is not of very
+great economic importance; as this varies so much, and depends on such a
+number of different conditions, such as the season, the condition of the
+land, and prevailing weather. A point of very much greater economic
+importance is the total amount formed in the year, and the rate at which
+nitrification takes place. These questions will be discussed elsewhere,
+and therefore need not here be referred to. Some interesting analyses
+made at Rothamsted, however, of the amount of nitrates in soils at
+different depths, merit careful consideration.
+
+
+_Nitrates in Fallow Soils._
+
+In the Appendix to the chapter on Nitrification,[76] will be found a
+table containing the amounts of nitrates found in the first 27 inches of
+fallow soils. The amounts vary from 33.7 lb. to 59.9 lb. per acre. The
+analyses were made in September or October. In four out of the six
+analyses, it will be found that by far the largest proportion is found
+in the first 9 inches. In these cases the preceding summer had been dry,
+and thus the nitrates had not been washed down to any depth. In the
+other two cases the largest amount is found in the second 9 inches of
+soil, and a considerable amount is also found in the third 9 inches.
+
+
+_Nitrates in Cropped Soils._
+
+In the case of cropped soils we find the amount of nitrates very much
+less. A table containing an elaborate series of determinations of
+nitrates in cropped soils, receiving, however, no manure, and taken to a
+depth of 9 feet, will be found in the Appendix.[77] The first 27 inches
+only contain some 5 to 14 lb. per acre, and the most of that is found in
+the first 9 inches. This shows how speedily nitrates are assimilated by
+the growing crop. An interesting point shown by these analyses is that
+nitrates almost entirely cease in cropped soils a certain depth down,
+but that at a still lower depth they again occur in small quantities.
+
+
+_Nitrates in manured Wheat-soils._
+
+Lastly, we give in the Appendix[78] the amount of nitrates found in
+wheat and barley soils, differently manured, at Rothamsted. From a
+perusal of these tables, it will be seen that the amount (under various
+conditions of manuring) of nitrates in the first 27 inches varies from
+21.2 lb. per acre to 52.2 lb. for the wheat-soils, and 20.1 to 44.1 lb.
+per acre for the barley-soils.
+
+
+THE SOURCES OF SOIL-NITROGEN.
+
+We shall now consider the sources of soil-nitrogen, the conditions which
+determine its increase, and the amount of that increase, as well as the
+sources of loss, and the conditions which determine this loss.
+
+
+_That dissolved in Rain._
+
+The natural sources of the soil-nitrogen are several. We have first of
+all the atmospheric nitrogen. Of this let us first consider that present
+as combined nitrogen. This, as we have already seen, consists chiefly of
+nitrates, nitrites, and ammonia, and reaches the soil dissolved in rain
+or in other meteoric forms of water, such as snow, hail, fog,
+hoar-frost, &c.
+
+
+_That absorbed by the Soil from the Air._
+
+It is also absorbed by the soil from the air, especially when the soil
+is in a damp condition, as has been proved by Schloesing's experiments,
+already referred to. The total amount which falls dissolved in the rain,
+per acre per annum, varies very considerably in different parts of the
+world, but in any case only amounts yearly to a few pounds per acre.[79]
+That absorbed by the soil from the air may be probably very much more
+considerable. Schloesing in his experiments found that this latter might
+amount to 38 lb. per acre per annum. These results, however, were
+obtained under circumstances most favourable for absorption--viz., with
+a damp soil and in the vicinity of Paris, where the air is presumably
+richer in combined nitrogen than it is in the country. The nitrogen
+absorbed, it may be mentioned, was almost entirely in the form of
+ammonia. It is to be noted that the nitrogen the soil obtains in this
+way from the combined nitrogen of the air is not all pure gain. With
+regard to the nitrates and nitrites, no doubt most of these are formed
+by electrical discharge, although a small portion of them may be formed
+by the oxidation of ammonia by means of ozone and peroxide of hydrogen.
+With regard to the ammonia and the combined nitrogen present in the
+organic particles in the air, a not inconsiderable proportion is
+probably derived from the soil. Schloesing considers the chief source of
+the ammonia present in the air to be the tropical ocean; but we must
+remember that the source of much of the nitrogen in the tropical ocean
+is, after all, the soil.
+
+Leaving aside for a moment the question of the availability of the free
+nitrogen of the air, let us consider the other sources of soil-nitrogen.
+
+
+_Accumulation of Soil-nitrogen under Natural Conditions._
+
+The chief source is of course the remains of vegetable and animal
+tissue.[80] Plants are the great conservers of soil-nitrogen. By
+assimilating such available forms of it as nitrates, and converting them
+into organic nitrogen, they prevent the loss of this most valuable of
+all soil constituents that would otherwise take place.
+
+They also serve to collect the nitrogen from the lower soil-layers and
+concentrate it in the surface portion. In a state of nature, where the
+soil is constantly covered with vegetation, the process going on,
+therefore, will be one of steady accumulation of nitrogen in the
+surface-soil. To what extent this accumulation goes on, and how far it
+is limited by the conditions of loss, will be considered immediately.
+That it may go on to a very great extent is amply proved by the
+existence of the so-called _virgin_ soils of countries like America and
+Australia. There are cases, also, where the accumulation of nitrogen is
+practically unlimited, although the result in such cases is not
+necessarily a fertile soil. Such cases are peat-bogs. But let us pass on
+to the accumulation of soil-nitrogen under the ordinary conditions of
+husbandry.
+
+
+_Accumulation of Nitrogen in Pastures._
+
+The case which, under the conditions of ordinary farming, most resembles
+a state of nature, is that of permanent pasture. It will be best,
+therefore, to study first the conditions under which gain of nitrogen
+takes place in this case.
+
+
+_Increase of Nitrogen in the soil of Pasture-land._
+
+That there is a steady increase of nitrogen in the soil of land under
+pasture is a fact of universal experience. The older a pasture is the
+richer is its soil in nitrogen. The comparison of the analyses of the
+soil of arable land with the soil of pastures of different ages shows
+this in a striking way.[81] Thus at Rothamsted it was found that while
+the amount of nitrogen in an ordinary arable soil was .140 per cent,
+that in pastures eight, eighteen, twenty-one, and thirty years old was
+respectively .151, .174, .204, and .241 per cent. In the last two
+analyses we have a record of the actual gain in nitrogen made by the
+same pasture, this being .04 per cent in nine years' time. From these
+statistics it may be inferred that the surface-soil of a pasture may
+increase at the rate of 50 lb. per acre per annum. A point of great
+interest in connection with this subject is the fact that there seems to
+be a limit to the accumulation of nitrogen in pastures; for it would
+seem that pastures centuries old are not any richer in nitrogen than
+those thirty to forty years old.
+
+
+_Gain of Nitrogen with Leguminous Crops._
+
+Another case where the gain of nitrogen to the surface-soil is very
+striking is in that of leguminous crops, such as clover, beans, peas,
+&c. This fact has been long recognised--especially with regard to
+clover--by farmers, and has been largely instrumental in leading to the
+investigation of the "free" nitrogen question. That a soil bearing a
+leguminous crop increases in nitrogen at a very striking rate is a
+problem that requires to be solved. A partial explanation of the
+phenomenon is found in the extraordinary capacity such a crop as clover
+has, by means of its multitudinous and ramifying roots, for collecting
+nitrogen from the subsoil. This, however, would only account for the
+increase in nitrogen to a certain extent. There must be some other
+source, and the only other source is the air. That the free nitrogen of
+the air is, after all, available for the plant's needs, is a supposition
+which has long seemed extremely probable, and which, within the last
+few years, has been proved beyond doubt to be a fact in the case of
+leguminous plants.
+
+
+_The Fixation of "Free" Nitrogen._
+
+The method in which these plants are able to make use of the free
+nitrogen is still a point requiring much research. So far as the
+question is at present investigated, it would seem that the fixation is
+effected by means of micro-organisms present in tubercles or root
+excrescences found on the roots of leguminous plants.[82] Not merely has
+this been placed beyond doubt, but attempts have been made to isolate
+and study the bacteria effecting this fixation. From Nobbe's exceedingly
+interesting experiments, recently carried out, it would seem that the
+different kinds of leguminous plants have different bacteria. Thus the
+bacteria in the tubercle on the pea seems to be of a different order
+from the bacteria in the tubercles of the lupin, and so on. This
+discovery is of great importance, it need scarcely be pointed out, as it
+throws much light on the principles of the rotation of crops.
+
+
+_Influence of Manures in increasing Soil-nitrogen._
+
+It may be doubted, however, if under any other conditions there is a
+positive gain of soil-nitrogen. In other cases the amount in the soil is
+only _maintained_ under liberal manuring. In connection with this point
+a very striking fact has been observed with regard to the effect of
+continuous large applications of farmyard manure. It has been found at
+Rothamsted that in such a case, after a while, the manure does not seem
+to increase the soil-nitrogen, although where the nitrogen goes to
+remains a mystery. In the case of the application of artificial manures,
+there does not seem to be almost any appreciable gain to the
+soil-nitrogen. The soil-nitrogen is only increased by means of the
+residue of crops. In this way, of course, by increasing the amount of
+this crop-residue, artificial manures may be said indirectly to increase
+the soil-nitrogen.[83]
+
+
+SOURCES OF LOSS OF NITROGEN.
+
+We now come to consider the sources of loss. The chief source, of
+course, is that by drainage. Land under cultivation will suffer very
+much more from this source of loss than in a state of nature. Our modern
+system of husbandry, involving as it does thorough drainage, can
+scarcely fail to very considerably increase this source of loss.
+
+
+_Loss of Nitrates by Drainage._
+
+The form in which nitrogen is lost in this way is as nitrates. It is a
+somewhat striking fact, and one worthy of note, that of the three
+important manurial ingredients--nitrogen, phosphoric acid, and potash,
+the first of these, in its final and most valuable form, is alone
+incapable of being fixed by the soil, and thus retained from loss by
+drainage.
+
+As nitrates are constantly being formed in the soil, the loss to its
+total nitrogen must be considerable. It is due to the fact of the great
+solubility of nitrates, as well as to the fact, as already mentioned, of
+the incapacity of the soil-particles to fix them. To this one exception
+must be made. According to Knop, small quantities of nitric acid are
+held in the _insoluble_ condition in soils in the form of highly _basic
+nitrates of iron and alumina_. The quantity, however, of these insoluble
+compounds probably amounts to a very minute trace indeed.
+
+
+_Permanent Pasture and "Catch-cropping" prevents Loss._
+
+The amount of loss varies, and will depend on a number of different
+circumstances--thus the nature of the soil, climate, and season of the
+year will all influence its quantity. The way in which the soil is
+cultivated is also another important factor. Where it is constantly
+covered with vegetation, as in the case of permanent pasture, the loss
+will be at a minimum. Under such conditions, plant-roots are always
+there ready to fix, in the insoluble organic form, the soluble nitrates
+as they are formed. A consideration of this fact forms one of the
+strongest arguments in favour of the practice of what is known as
+"catch-cropping." The practice consists in sowing some quickly-growing
+green crop--_e.g._, _mustard_, _vetches_, &c.--so as to occupy the soil
+immediately after harvest, and subsequently to plough it in. The
+nitrates, which it is known are most abundantly formed towards the end
+of summer,[84] and which are allowed to accumulate in the soil from the
+period at which the active growth of, and consequently assimilation of
+nitrates by, the cereal crop have ceased, are thus fixed in the organic
+matter of the plant, and removed from danger of loss by drainage
+incidental to autumn rains.
+
+
+_Other Conditions diminishing Loss of Nitrates._
+
+The nature of the soil is another important condition regulating this
+loss. Some soils are very much opener and more porous than others; in
+such soils, of course, the loss by drainage will be greatest. We are apt
+at first sight, however, knowing the great solubility of nitrates, to
+overrate this source of loss. We have to remember that while nitrates
+are constantly being washed down to the lower layers of the soil, there
+is likewise an upward compensating movement of the soil-water constantly
+taking place. This is due to the evaporation of water from the surface
+of the soil, which induces an upward capillary movement of water from
+its lower to its higher layers.[85] This upward movement of water is
+very much increased, in the case of soil covered with vegetation, by the
+transpiration of the plants. The climate and the season of the year will
+affect the extent of this upward movement. Where there is a heavy
+rainfall it will be very much less than in dry climates. After a long
+period of drought the nitrates will be found to be concentrated in the
+top few inches of the soil; and in hot climates this sometimes takes
+place to such an extent that the surface of the soil has been actually
+covered with a saline crust, caused by the rapid evaporation of
+soil-water under the influence of a burning tropical sun. From this
+point of view it will be seen how very much less powerful a single
+shower of rain is--even although at the time it is heavy--in causing
+loss of nitrates by drainage, than a continuance of wet weather. In the
+former case, where the showers are separated by an interval of dry
+weather, the nitrates washed down into the lower layers of the soil are
+slowly brought up again by the capillary action caused by evaporation.
+
+
+_Amount of Loss by Drainage._
+
+What the actual amount of loss is which takes place in this way it is
+wellnigh impossible to say. What it amounts to under certain definite
+circumstances has been discovered by actual experiment at Rothamsted.
+Taking the circumstances most favourable to extreme loss--viz.,
+unmanured fallow land--the highest amount registered at Rothamsted for a
+year is 54.2 lb. per acre from soil 20 inches deep, while the smallest
+amount is 20.9 lb. In the former case, the drainage-water was equivalent
+to 21.66 inches, while in the latter, to 8.96 inches. The average for
+thirteen years on unmanured fallow soil has been 37.3 lb. (for 20
+inches), 32.6 lb. (for 40 inches), 35.6 lb. (for 60 inches). The point
+of especial interest in this connection is that an annual loss of
+nitrogen, equal to over 2 cwt. of nitrate of soda, may take place from a
+comparatively poor arable soil lying fallow.
+
+The loss on cropped soils is of course very much less--in short, should
+amount to very little--especially in permanent pasture, where it is
+reduced to a minimum. Taking an average, Mr Warington is of opinion that
+the loss in England may be put at 8 lb. per annum per acre.[86]
+
+
+_Loss in Form of Free Nitrogen._
+
+The other chief natural source of loss of nitrogen is due to its escape
+from the soil in its "free" state. This source of loss is very much less
+important than that by drainage, and probably amounts to very little.
+That, however, it takes place is beyond a doubt; and that it may--as we
+shall see by-and-by--under certain circumstances amount to something
+very considerable is also proved. Where large quantities of nitrogenous
+organic matter decay, and where, consequently, the supply of atmospheric
+oxygen is insufficient to effect complete oxidation, "free" nitrogen may
+be evolved in considerable quantities. Similarly, it may be evolved in
+the case of vegetable matter decaying under water. In soils rich in
+organic matter the reduction of even nitrates may take place,
+accompanied with the evolution of free nitrogen, which is thus lost.
+
+
+_Total Amount of Loss of Nitrogen._
+
+What the rate of total loss of nitrogen is from these different sources
+does not admit of easy calculation. Sir John Lawes, in dealing with the
+question of soil-fertility, estimated some years ago, by comparing the
+soil of old pasture at Rothamsted with that which had been under arable
+culture for 250 years, that during that period some 3000 lb. of nitrogen
+per acre had disappeared from the arable land. Examples of decrease of
+nitrogen in Rothamsted soils, under various conditions of culture, will
+be found in the Appendix.[87]
+
+
+_Loss of Nitrogen by Retrogression._
+
+A source of loss of nitrogen may be here mentioned which has to do with
+diminution of amount of available nitrogen, rather than absolute loss of
+nitrogen to the soil, and which we may term _loss by retrogression_.
+Nitrogen in an available form, such as nitrates, has been found to be
+converted into a less available form. This retrogression may be
+effected, as in the case of nitrates, by reduction--_i.e._, by removal
+of the oxygen in combination with the nitrogen, which in many cases may
+be set free, and thus partially although not necessarily entirely lost.
+Such reduction is due to the action of bacteria of the denitrifying
+order.[88] Or, on the other hand, nitrogen may be converted into some
+kind of insoluble form which seems to resist decomposition and lies in
+an inert condition in the soil utterly unavailable for the plants'
+needs. A striking example of this retrogression of nitrogen seems to be
+afforded in the case of farmyard manure. It has been found in the
+Rothamsted experiments, as has been pointed out in the preceding pages,
+that when farmyard manure is applied, year after year, to the same land
+in large quantities, a very considerable percentage of its nitrogen does
+not (_i.e._, within a reasonable number of years) become available for
+the crop's uses. What, indeed, becomes of the nitrogen is a mystery; but
+it is highly probable that some such kind of retrogression as that above
+referred to, whereby the nitrogen is converted into some inert organic
+form, takes place.
+
+
+_Artificial Sources of Loss of Nitrogen._
+
+So far, the sources of loss of nitrogen considered have been what we may
+term _natural_ sources. By this is meant that the loss of nitrogen from
+the above sources takes place in a state of nature, and not merely under
+conditions of cultivation. No doubt the loss due to drainage is very
+much greater under arable farming than would be the case where
+artificial drainage does not obtain; still, under any conditions, this
+loss must be reckoned with. On the other hand, by _artificial_ sources
+of loss are meant those entirely dependent on our modern system of
+agriculture and our modern system of sewage disposal, whereby the
+nitrogen contained in that portion of the produce of the farm which goes
+to supply our food is not returned to the soil, but is totally lost.
+
+
+_Amount of Nitrogen removed in Crops._
+
+The modern tendency towards centralisation in large towns has rendered
+this loss--despite all that has been said to the contrary--a necessity.
+It is extremely difficult, however, to form any estimate of its amount.
+We know, of course, the amount of nitrogen removed from the soil by
+different crops. We cannot, however, estimate how much of this may find
+its way back again to the soil. The amount of nitrogen contained in the
+different crops will be fully dealt with in the chapter on the manuring
+of different crops. It may be, however, not without interest to give
+here some approximate indication of the amount of this loss, in order to
+render the view of the subject as comprehensive as possible.
+
+Recent agricultural returns for Great Britain give the total produce of
+_wheat_ at over 76 million bushels, that of _barley_ at over 69 million,
+and that of _oats_ at over 150 million. Calculating the amount of
+nitrogen, these quantities of wheat, barley, and oats respectively and
+collectively contain, and calculating also how much _sulphate of
+ammonia_ and _nitrate of soda_ these amounts of nitrogen represent, the
+following are the results:--
+
+ Nitrogen. Sulphate of Nitrate of
+ Ammonia. Soda.
+ Bushels. Tons. Tons. Tons.
+Wheat 76,224,940 37,432 176,465 227,266
+Barley 69,948,266 27,324 128,813 165,896
+Oats 150,789,416 56,835 267,936 345,068
+ ----------- ------- ------- -------
+Total 296,962,622 121,591 573,214 738,230
+ =========== ======= ======= =======
+
+Of course these figures, so far as the amounts of nitrogen are
+concerned, can only be regarded as approximate, as it is only possible
+in such calculations to obtain approximate results. Accepting these
+calculations as merely approximate, they are, nevertheless, of the
+highest interest and importance. It is of great importance to understand
+that in the annual produce of our three common cereal crops--supposing
+them to be all consumed off the farm--there is removed from the soil a
+quantity of nitrogen equal to that contained in over _half a million
+tons of sulphate of ammonia, and three quarters of a million tons of
+nitrate of soda._
+
+As has already been remarked, it is impossible to estimate exactly what
+proportion of this total nitrogen finds its way back to the soil. In the
+case of wheat, it may be pointed out that the portion which is used as a
+feeding-stuff--viz., _bran_--is very much richer in nitrogen than the
+flour. While, then, we are unable to estimate with any exactitude this
+source of loss of nitrogen, it cannot for a moment be doubted that it is
+enormous, from what has been already stated. We must remember that the
+portion of the crop richest in nitrogen is that which is generally
+removed--the straw which is grown in producing a bushel of wheat,
+barley, or oats, containing less than half the amount of nitrogen
+contained by a bushel of the grain itself.
+
+
+_Losses of Nitrogen incurred on the Farm._
+
+In addition to the loss due to removal of crops from the farm, there are
+one or two other sources of loss which it may be well to briefly refer
+to.
+
+
+_Loss in Treatment of Farmyard Manure._
+
+There can be little doubt that in the past a very considerable source of
+loss was the improper treatment of farmyard manure. The way in which
+this loss may take place will be fully considered in the chapter on
+farmyard manure. Suffice it to say here, that this may take place by
+volatilisation of the nitrogen as carbonate of ammonia, caused by
+carelessness in allowing the temperature of the manure-heap to rise too
+high; or by drainage of the soluble nitrogen compounds, caused by
+allowing the rich black liquor of the manure-heap to be washed away, and
+not properly conserved.
+
+
+_Nitrogen removed in Milk._
+
+Another source of loss which is apt to be overlooked is the amount of
+nitrogen removed in milk. Professor Storer has calculated that in the
+case of a cow giving 2000 quarts, or 4300 lb., of milk in a year, and
+the milk being all sold as such, there would be carried away from the
+farm 22 lb. of nitrogen.[89]
+
+
+_Economics of the Nitrogen question._
+
+And here, before concluding our survey of the different sources of loss
+of nitrogen, it may be well to regard for a moment the subject from a
+somewhat wider standpoint than that from which we have been considering
+it. The total supply of nitrogen in a combined form is limited. As we
+have pointed out, it may be regarded as the element on which, more than
+any other, life, animal as well as vegetable, depends. To animal life it
+is alone available in combined form; to vegetable life it is chiefly
+also only available in combined form. In the air we have an unlimited
+quantity of nitrogen, but it is almost entirely in an _uncombined_ form,
+and therefore largely unavailable. The conversion of nitrogen from the
+free state to a combined form is a process which takes place only very
+slowly. Any source which diminishes the sum-total of our already all too
+limited supply of combined nitrogen must be regarded as worthy of most
+serious consideration. The question, therefore, of the artificial waste
+of nitrogen daily taking place around us, is one which ought to possess
+for economists a very great interest indeed. This waste has, of late
+years, enormously increased, and would seem to threaten us at no very
+distant date with a nitrogen famine. It is incidental to the use of
+certain nitrogenous substances in the manufacture of various articles,
+and to our present system of sewage disposal.
+
+
+_Loss of Nitrogen-compounds in the Arts._
+
+The articles referred to are such as explosives, starch, textile
+substances, malt liquors, &c. The question is strikingly dealt with in
+an able paper on "The Economy of Nitrogen" in the 'Quarterly Journal of
+Science.'[90]
+
+
+_Loss due to Use of Gunpowder._
+
+The explosives--more particularly gunpowder--are the most important of
+these articles. Gunpowder contains 75 per cent of saltpetre, which in
+its turn contains about 10 per cent of nitrogen. When gunpowder
+explodes, practically the whole of this nitrogen is converted into
+"free" nitrogen. The loss is thus in a sense irreparable. In the paper
+above, referred to, our total annual exports of this substance are
+estimated at 19,000,000 lb.; while the total annual production of the
+world is estimated at not less than 100,000,000 lb. The annual loss of
+nitrogen due to this source alone would amount to about 10,000,000
+lb.[91] Similarly, loss of nitrogen, although to a less extent, is
+caused by the use of other explosives, as well as in the manufacture of
+the other articles above mentioned.
+
+
+_Loss due to Sewage Disposal._
+
+The loss due to our present system of sewage disposal has been already
+taken into account in dealing with the loss due to removal of crops. It
+may be well, however, to treat it from the sewage aspect. Taking the
+amount of nitrogen in the excreta of every individual as, on an average,
+half an ounce, the annual amount voided in the excreta of the total
+population of the British Isles would amount to 365,000,000 lb.[92]--of
+this, the amount in the London sewage alone being 91,000,000 lb.[93] By
+the water system, which is almost universally adopted in this country,
+the above quantity of nitrogen is entirely lost to the soil. A small
+portion of it, it may be argued, is eventually recovered in sea weed and
+fish, which may be used for manure. This, however, is to argue too much
+_sub specie æternitatis_. Not all the nitrogen originally present in the
+excreta finds its way into the sea; for it is highly probable that a
+considerable quantity escapes in the process of the decomposition of the
+sewage as "free" nitrogen.
+
+From the above statement of the sources of loss and gain of nitrogen
+taking place in the soil, it may be pretty safe to conclude that while
+in a state of nature the gain balances the loss, if indeed it does not
+do more, under conditions of arable farming such is very far from being
+the case; and that if fertility of the land is to be maintained,
+recourse to nitrogenous manures must be had,--in short, that the
+application of artificial nitrogenous manures is a necessary condition
+of modern husbandry.
+
+
+_Our Artificial Nitrogen Supply._
+
+Before concluding this chapter, it may be interesting to enumerate very
+briefly the chief sources of our artificial nitrogen supply.
+
+
+_Nitrate of Soda and Sulphate of Ammonia._
+
+The most important artificial nitrogenous manures in use at present are
+nitrate of soda and sulphate of ammonia. Of the former, the annual
+exportation from Chili is close on one million tons, of which quantity
+about 120,000 tons is imported into the United Kingdom. Of sulphate of
+ammonia, on the other hand, the total production in this country is
+about 130,000 tons per annum,[94] the greater proportion of which is
+exported, leaving only from 30,000 to 40,000 tons for consumption.
+Nitrate of soda, it must be remembered, is not entirely used for
+manurial purposes, a small proportion of the above imports being used
+for chemical manufacturing purposes.
+
+
+_Peruvian Guano._
+
+Peruvian guano is another important nitrogenous manure very much less
+abundant now than formerly, as the different guano-beds have become
+nearly exhausted. While the imports of this important manure into the
+United Kingdom amounted in 1870 to nearly 250,000 tons, at present not
+more than 11,000 tons are being imported.
+
+
+_Bones._
+
+A further source of nitrogen is bones, which, of course, are chiefly
+valuable as a phosphatic manure, but which contain also some 3 to 4 per
+cent of nitrogen. Of this valuable manure we import at present about
+30,000 tons, while about 60,000 tons are collected in this country,
+bringing up our total consumption to 100,000 tons.
+
+
+_Other Nitrogenous Manures._
+
+The above mentioned are the most important of nitrogenous manures; there
+are, however, a number of other nitrogenous manures used in this country
+in very much smaller quantities. As most of these substances are made in
+this country, it is very difficult to estimate the amount of their
+annual production with exactness. These substances are as follows:
+fish-guano, meat-meal guano, dried blood, shoddy, scutch, horns and
+hoofs, hair, bristles, feathers, leather-scrap, &c. Of fish-guano, the
+total consumption per annum may be put down at about 8000 tons, of which
+a fourth is imported into this country, the remaining 6000 tons being
+manufactured at home. Of meat-meal guano, dried blood, hoof-guano, &c.,
+about 2500 tons are annually imported, the home production bringing up
+the total amount to some 10,000 tons. Of shoddy, some 12,000 tons are
+manufactured in this country; while scutch--the name given to a manure
+manufactured from the waste products incidental to the manufacture of
+glue and the dressing of skins--is produced only to the extent of a few
+thousand tons annually.
+
+It is a fact worthy of notice, that while the use of phosphatic manures
+has increased very considerably of late years, the same cannot be said
+of nitrogen. According to Mr Hermann Voss, some 34,000[95] tons of
+nitrogen were used in the form of artificial manures in 1873, while now
+only about 28,000 tons are used--_i.e._, some 6000 tons less.
+
+
+_Oil-seeds and Oilcakes._
+
+There still remains a very important source of nitrogen which has not
+yet been mentioned, in the shape of oil-seeds and oilcakes, used for
+feeding purposes. Oilcakes are both manufactured in this country and
+imported in large quantities. Recent Agricultural Returns show the total
+imports of oilcakes at 256,296 tons; that of linseed at 370,000 tons;
+that of rape-seed at 80,000 tons; and that of cotton-seed at 289,413
+tons.
+
+
+_Other imported Sources of Nitrogen._
+
+We have further, in considering this question, to take into account the
+large amount of maize, peas, beans, wheat, and oats which are imported
+into this country, a certain quantity of which is used as cattle-food,
+and will therefore go to enrich their manure. Also the imported straw
+used for purposes of litter must not be forgotten. In 1887 this amounted
+to 52,393 tons.
+
+
+_Conclusion._
+
+In conclusion, it may be asked how far are the artificial sources of
+nitrogen able to make good the loss? In the opinion of such a reliable
+authority as Sir John Lawes, they do not. There are some soils which
+depend almost entirely upon imported fertility, and could not be
+cultivated without it. Upon some of them it is possible that the imports
+of nitrogen are in excess of the exports. Taking the agricultural
+acreage as a whole, however, he is of opinion that there is a decided
+loss of nitrogen, which he estimates at _from 15 lb. to 20 lb. per acre
+per annum_.[96]
+
+
+FOOTNOTES:
+
+[63] The total amount of nitrogen in the air has been estimated
+approximately at four million billion tons.
+
+[64] See Introductory Chapter, pp. 40 to 45.
+
+[65] Although ammonia is more abundant than nitrates and nitrites, it
+only amounts to a few parts per million of air. According to Müntz, the
+air at great heights contains more ammonia than in its lower strata. The
+opposite, however, is the case with regard to nitrates, which are only
+found in air near the surface of the earth. See p. 49.
+
+[66] Nitric acid may also be formed by the oxidation of ammonia by
+ozone, or peroxide of hydrogen.
+
+[67] According to Schloesing, the chief source of the ammonia present in
+the air is the tropical ocean, which yields gradually to the atmosphere,
+under the action of the powerful evaporation constantly going on, a
+large amount of nitrogen in this form. The sources of the nitrogen of
+the ocean are the nitrates which it receives from the drainage of land,
+animal and vegetable matter, sewage, &c.
+
+[68] See Appendix, Note I., p. 155.
+
+[69] To illustrate this point, it may be mentioned that on the least
+windy of days, when the wind is only moving at the rate of two miles an
+hour--and this, it may he added, is so slow as to be scarcely
+noticeable--the air in a space of 20 feet is changed over five hundred
+times in an hour. The combined nitrogen thus absorbed is probably
+entirely in the form of ammonia. It would seem so at any rate, from some
+experiments by Schloesing. See p. 132.
+
+[70] No vegetable or animal cell exists which does not contain nitrogen.
+
+[71] This is less on the whole than what has been found in subsoils by
+Continental investigators. Thus, for example, A. Müller found the
+average of a number of analyses of subsoils to be .15 per cent., and the
+late Dr Anderson found the nitrogen in the subsoil of different Scottish
+wheat-soils to run from .15 per cent to .97 per cent.
+
+[72] See Appendix, Note II., p. 156.
+
+[73] "Under prolonged kitchen-garden culture the subsoil becomes
+enriched with nitrogenous matter to a far more considerable depth; this
+has been shown by the analyses of the soil of the old kitchen-garden at
+Rothamsted. This is doubtless due to the practice of deep trenching
+employed by gardeners."--R. Warington, 'Lectures on Rothamsted
+Experiments.' U.S.A. Bulletin, p. 24.
+
+[74] The comparatively insignificant effect the addition of various
+nitrogenous manures have in increasing the total soil-nitrogen is
+strikingly illustrated in the tables given in the Appendix, Note IV., p.
+157.
+
+[75] See Storer's Agric. Chem., vol. i. p. 357.
+
+[76] See Chapter IV., Appendix, Note VII., p. 198.
+
+[77] See Appendix, Note III., p. 157.
+
+[78] See Appendix, Note IV., p. 157.
+
+[79] See Appendix, Note I., p. 155.
+
+[80] The original source of the nitrogen in the soil must have been the
+nitrogen in the air. When plants first begin to grow on a purely mineral
+soil, they must obtain nitrogen from some source. The small traces
+washed down in the rain will supply sufficient nitrogen to enable a
+scanty growth of the lower forms of vegetable life; whereas these by
+their decay furnish their successors with a more abundant source, which
+rapidly increases, until we have a fair percentage of humus accumulated.
+
+[81] See Appendix, Note V., p. 158.
+
+[82] See Historical Introduction, pp. 40-45.
+
+[83] The evidence demonstrating this is to be found in the fact that the
+amount of carbon found in different soils rises or falls in proportion
+to the nitrogen. See p. 126.
+
+[84] See Chapter IV. on Nitrification.
+
+[85] Diffusion as well as capillary attraction is a means of bringing
+nitrates again to the surface-soil after rain.
+
+[86] See Appendix, Note VI., p. 158, and Note VIII., p. 160; also p.
+154.
+
+[87] See Appendix, Note VII., p. 159.
+
+[88] See following Chapter on Nitrification, p. 178.
+
+[89] According to the Agricultural Returns for 1888, the number of cows
+in milk in Great Britain amounted to 2,450,444. If we multiply this
+number by 22 the result is 54,000,000 lb., or in tons 24,107. This
+quantity represents 154,067 tons of ordinary commercial nitrate of soda.
+
+[90] For 1878 (p. 146 _et seq._) The reader interested in the subject is
+referred to the paper itself.
+
+[91] In tons 4464, and represents 28,530 tons of nitrate of soda.
+
+[92] This in tons 162,946, which represents 1,041,384 tons of nitrate of
+soda.
+
+[93] This in tons 40,625, which represents 259,633 tons of nitrate of
+soda. See paper in 'Journal of Science' already referred to.
+
+[94] Europe's total production may be stated at 200,000 tons.
+
+[95] 10,500 tons of which were as guano.
+
+[96] Mr Warington estimates this at about 8 lb. See p. 141.
+
+
+
+
+APPENDIX TO CHAPTER III.
+
+
+NOTE I. (p. 119).
+
+DETERMINATIONS OF THE QUANTITY OF NITROGEN SUPPLIED BY RAIN, AS
+AMMONIA AND NITRIC ACID, TO AN ACRE OF LAND, DURING ONE YEAR.
+
+(_From Dr Fream's 'Soils and their Properties_,' p. 62.)
+
+----------------------+----------------+---------+----------------+--------
+ | | | Nitrogen per |
+ | | | million, as | Total
+ | | +--------+-------+Nitrogen
+ | Year. |Rainfall.| | | per
+ | | |Ammonia.| Nitric| acre.
+ | | | | Acid. |
+----------------------+----------------+---------+--------+-------+--------
+ | | | | | lb.
+Kuschen | 1864-65 | 11.85 | 0.54 | 0.16 | 1.86
+ " | 1865-66 | 17.70 | 0.44 | 0.16 | 2.50
+Insterburg | 1864-65 | 27.55 | 0.55 | 0.30 | 5.49
+ " | 1865-66 | 23.79 | 0.76 | 0.49 | 6.81
+Dahme | 1865 | 17.09 | 1.42 | 0.30 | 6.66
+Regenwalde | 1864-65 | 23.48 | 2.03 | 0.80 | 15.09
+ " | 1865-66 | 19.31 | 1.88 | 0.48 | 10.38
+ " | 1866-67 | 25.37 | 2.28 | 0.56 | 16.44
+Ida-Marienhütte, mean | | | | |
+ of six years | 1865-70 | 22.65 | | | 9.92
+Proskau | 1864-65 | 17.81 | 3.21 | 1.73 | 20.91
+Florence | 1870 | 36.55 | 1.17 | 0.44 | 13.36
+ " | 1871 | 42.48 | 0.81 | 0.22 | 9.89
+ " | 1872 | 50.82 | 0.82 | 0.26 | 12.51
+Vallombrosa | 1872 | 79.83 | 0.42 | 0.15 | 10.38
+Montsouris, Paris | 1877-78 | 23.62 | 1.91 | 0.24 | 11.54
+ " | 1878-79 | 25.79 | 1.20 | 0.70 | 11.16
+ " | 1879-80 | 15.70 | 1.36 | 1.60 | 10.52
+ | | | | |
+ | +---------+--------+-------+--------
+ | | | | |
+ |Mean of 22 years| 27.63 | | | 10.23
+ | | | | |
+----------------------+----------------+---------+--------+-------+--------
+
+
+NOTE II. (p. 122).
+
+NITROGEN IN SOILS AT VARIOUS DEPTHS.
+
+(1) _Rothamsted Soils._
+
+------------------+---------------------------+---------------------------
+ Depth. | Arable soil. | Old pasture soil.
+------------------+-----------+---------------+------------+--------------
+ | per cent. | lb. per acre. | per cent. | lb. per acre.
+ 1st 9 inches | 0.120 | 3,015 | 0.245 | 5,351
+ 2d 9 " | 0.068 | 1,629 | 0.082 | 2,313
+ 3d 9 " | 0.059 | 1,461 | 0.053 | 1,580
+ 4th 9 " | 0.051 | 1,228 | 0.046 | 1,412
+ 5th 9 " | 0.045 | 1,090 | 0.042 | 1,301
+ 6th 9 " | 0.044 | 1,131 | 0.039 | 1,186
+ | ----- | ----- | ----- | -----
+ Total, 54 inches | - | 9,554 | - | 13,143
+ |-----------+---------------+------------+--------------
+ 7th 9 inches | 0.042 | 1,049 | - | -
+ 8th 9 " | 0.041 | 1,095 | - | -
+ 9th 9 " | 0.044 | 1,173 | - | -
+10th 9 " | 0.043 | 1,076 | - | -
+11th 9 " | 0.043 | 1,112 | - | -
+12th 9 " | 0.045 | 1,198 | - | -
+ | ----- | ------ | ----- | -----
+ Total, 9 feet | | 16,257 | |
+------------------+-----------+---------------+------------+--------------
+
+(2) _Manitoba Soils._
+
+----------+----------|-------------+-----------+----------
+ Depth. | Brandon. | Niverville. | Winnipeg. | Selkirk.
+----------+----------+-------------+-----------+----------
+ | per cent.| per cent. | per cent. | per cent.
+1st foot | 0.187 | 0.261 | 0.428 | 0.618
+2d " | 0.109 | 0.169 | 0.327 | 0.264
+3d " | 0.072 | 0.069 | 0.158 | 0.076
+4th " | 0.019 | 0.038 | 0.107 | 0.042
+----------+----------+-------------+-----------+----------
+
+
+NOTE III. (p. 130).
+
+NITROGEN AS NITRATES IN CROPPED SOILS RECEIVING NO NITROGENOUS
+MANURE, IN LB. PER ACRE (_Rothamsted Soils_).
+
+-------------+----------------+---------+---------+---------+--------
+ | Wheat. | | | |
+ +-------+--------+ Bokhara | | | White
+ | After | After | clover, | Vetches,| Lucern, | clover,
+ Depth. |fallow,|clover, | 1882. | 1883. | 1885. | 1885.
+ | 1883. | 1883. | | | |
+-------------+-------+--------+---------+---------+---------+--------
+ | lb. | lb. | lb. | lb. | lb. | lb.
+ 1st 9 inches| 3.4 | 6.1 | 3.4 | 10.2 | 8.9 | 11.5
+ 2d 9 " | 3.1 | 4.4 | 1.0 | 2.7 | 1.1 | 1.4
+ 3d 9 " | 0.8 | 1.6 | 0.6 | 1.1 | 0.8 | 0.9
+ 4th 9 " | 1.0 | 1.3 | 1.0 | 1.5 | 0.8 | 1.9
+ 5th 9 " | 0.8 | 1.5 | 0.8 | 2.5 | 1.0 | 7.1
+ 6th 9 " | 0.6 | 0.8 | 1.7 | 4.4 | 0.9 | 11.3
+ 7th 9 " | 0.8 | 2.2 | | 4.5 | 0.6 | 13.1
+ 8th 9 " | 0.9 | 1.7 | | 4.9 | 0.8 | 12.6
+ 9th 9 " | 0.7 | 2.4 | | 4.8 | 0.7 | 11.2
+10th 9 " | 2.0 | 2.1 | | 5.1 | 0.6 | 10.7
+11th 9 " | 1.5 | 2.1 | | 6.4 | 0.4 | 11.1
+12th 9 " | 3.8 | 2.8 | | 6.5 | 0.4 | 10.0
+-------------+-------+--------+---------+---------+---------+--------
+
+
+NOTE IV. (p. 124 and p. 131).
+
+NITROGEN AS NITRATES IN WHEAT-SOILS VARIOUSLY MANURED, OCTOBER 1881,
+IN LB. PER ACRE (_Rothamsted Soils_).
+
+----+----------------------------------+------+------+------+--------+-------
+ | | | | | |Excess
+ | | | | | |over
+Plot| Manuring. |1st 9 |2nd 9 |3rd 9 |Total 27|plots
+ | |inches|inches|inches|inches |3 and 4
+----+----------------------------------+------+------+------+--------+-------
+ | | lb. | lb. | lb. | lb. | lb.
+ 3 |No manure, 38 years | 9.7 | 5.3 | 2.8 | 17.8 |
+ 4 | " 30 " | 9.2 | 4.0 | 1.8 | 15.0 |
+16a | " 17 " | 10.6 | 5.0 | 2.3 | 17.9 | 1.5
+ 5a |Ash constituents, 30 years | 12.6 | 7.1 | 4.6 | 24.3 | 7.9
+17a | " " 1 year | 10.3 | 7.5 | 3.4 | 21.2 | 4.8
+ 6a | " and ammonium salts, 200 lb. | 16.5 | 7.5 | 4.7 | 28.7 | 12.3
+ 7a | " " 400 " | 22.8 | 11.3 | 5.7 | 39.8 | 23.4
+ 8a | " " 600 " | 21.1 | 13.9 | 7.8 | 42.8 | 26.4
+ 9a |Ash and sodium nitrate, 550 " | 19.7 | 10.0 | 8.2 | 37.9 | 21.5
+ 9b |Sodium nitrate, " " | 16.3 | 20.1 | 17.7 | 54.1 | 37.7
+10a |Ammonium salts, 400 " | 14.2 | 11.9 | 7.3 | 33.4 | 17.0
+11a |Superphosphate and ammonium salts,| | | | |
+ | 400 lb. | 17.9 | 9.3 | 3.6 | 30.8 | 14.4
+19 |Rape-cake, 1700 lb. | 14.1 | 13.0 | 7.1 | 34.2 | 17.8
+ 2 |Farmyard manure, 14 tons--38 years| 30.0 | 15.4 | 6.8 | 52.2 | 35.8
+----+----------------------------------+------+------+------+--------+-------
+
+NITROGEN AS NITRATES IN BARLEY-SOILS VARIOUSLY MANURED, MARCH 1892,
+IN LB. PER ACRE (_Rothamsted Soils_).
+
+-------+------------------------+-------+-------+-------+-------+--------
+ | | | | | Total | Excess
+ | | 1st 9 | 2d 9 | 3d 9 | 27 | over
+ Plot. | Manuring. |inches.|inches.|inches.|inches.|plot 10.
+-------+------------------------+-------+-------+-------+-------+--------
+ | | lb. | lb. | lb. | lb. | lb.
+10 |No manure | 5.9 | 4.7 | 5.1 | 15.7 | -
+20-40 |Ash constituents (mean) | 6.7 | 7.0 | 6.4 | 20.1 | 4.4
+1 A |Ammonium salts, 200 lb. | 6.1 | 8.3 | 7.0 | 21.4 | 5.7
+2A-4A |Ammonium and ash | | | | |
+ | constituents (mean) | 7.7 | 7.8 | 7.6 | 23.1 | 7.4
+1 AA |Sodium nitrate, 275 lb. | 9.7 | 6.8 | 9.0 | 25.5 | 9.8
+2AA-4AA|Sodium nitrate and ash | | | | |
+ | constituents (mean) | 8.3 | 7.4 | 7.5 | 23.2 | 7.5
+1C |Rape-cake, 1000 lb. | 10.6 | 13.7 | 7.9 | 32.2 | 16.5
+2C-4C |Rape-cake and ash | | | | |
+ | constituents (mean) | 8.8 | 11.9 | 8.7 | 29.4 | 13.7
+7-1 |No manure, 10 years-- | | | | |
+ | formerly dung | 14.8 | 11.8 | 10.9 | 37.5 | 21.8
+7-2 |Farmyard manure, 14 tons| 18.6 | 14.6 | 10.9 | 44.1 | 28.4
+-------+------------------------+-------+-------+-------+-------+-------
+
+
+NOTE V. (p. 134).
+
+EXAMPLES OF INCREASE OF NITROGEN IN ROTHAMSTED SOILS LAID DOWN IN
+PASTURE.
+
+--------------------+----------+---------------
+ | Age of | Nitrogen in
+ | pasture. | 1st 9 inches.
+--------------------+----------+---------------
+ | Years. | Per cent.
+Arable land | - | 0.140
+Barn-field pasture | 8 | 0.151
+Apple-tree pasture | 18 | 0.174
+Dr Gilbert's meadow | 21 | 0.204
+Dr Gilbert's meadow | 30 | 0.241
+--------------------+----------+---------------
+
+
+NOTE VI. (p. 141).
+
+In connection with the loss by drainage of nitrogen in the form of
+nitrates, it may be mentioned that the water of many of the famous
+rivers contains large quantities of nitrates. Thus the water of the
+Seine has been found to contain fifteen parts of nitrates per million of
+water, and the Rhine eight parts per million. Some idea of what this
+amounts to per annum may be obtained by the statement that "the Rhine
+discharges daily 220 tons of saltpetre into the ocean, the river Seine
+270, and the Nile 1100 tons."--(Storer's Agric. Chem., vol. i. p. 318.)
+
+
+NOTE VII. (p. 142).
+
+EXAMPLES OF DECREASE OF NITROGEN IN ROTHAMSTED SOILS.
+
+--------------------------------------+----------------
+ | Nitrogen in
+ | 1st 9 inches.
+--------------------------------------+----------------
+ | Per cent.
+Old pasture | 0.250
+Arable land in ordinary culture | 0.140
+Wheat unmanured, 38 years | 0.105
+Wheat and fallow unmanured, 31 years | 0.096
+Barley unmanured, 30 years | 0.093
+Turnips unmanured, 25 years | 0.085
+--------------------------------------+----------------
+
+MANURING, PRODUCE OF WHEAT, AND ALTERATION IN THE COMPOSITION OF THE
+SOIL IN BROADBALK FIELD, ROTHAMSTED, FROM 1865 TO 1881.
+
+-----+----------------------------------+----------------+----------------------
+ | | Average | Nitrogen per acre
+ | | produce | in 1st 9 inches
+Plot.| Manures per acre, | per acre. | of soil.
+ | annually applied, +-------+--------+------+-----+---------
+ | 16 years, 1865-81. | | | | | Gain or
+ | |Dressed| Total |1865. |1881.| loss in
+ | |grain. |produce.| | |16 years.
+-----+----------------------------------+-------+--------+------+-----+---------
+ | | bush. | lb. | lb. | lb. | lb.
+ 3 |Unmanured |11-7/8 | 1715 | 2507 |2404 | -103
+ 5_a_|Mixed mineral manure |12-3/4 | 1963 | 2574 |2328 | -246
+10_a_|Ammonium salts, 400 lb. |17-7/8 | 2881 | 2548 |2471 | -77
+11_1_|Ammonium salts, with | | | | |
+ | superphosphate |23-1/4 | 3856 | 2693 |2676 | -17
+ 7_a_|Ammonium salts, with mixed mineral| | | | |
+ | manure | 28 | 4993 | 2829 |2908 | +79
+ 9_a_|Nitrate of soda, 550 lb., and | | | | |
+ | mixed mineral manure | 36 | 6949 | 2834 |2883 | +49
+16_a_|Unmanured* |13-1/2 | 2194 | 2907 |2557 | -350
+ 2 |Farmyard manure, 14 tons |31-1/2 | 5356 | 4329 |4502 | +173
+-----+----------------------------------+-------+--------+------+-----+---------
+* During 1852-64 received annually ammonium salts, 800 lb., with mixed mineral
+manure, and yielded an average product of 39-1/2 bushels of grain and 46-5/8
+cwt. of straw.
+
+
+NOTE VIII. (p. 141).
+
+$1$2
+
+--------------+--------+-----------------+----------------------------------
+ | | | Nitrogen as nitrates.
+ | | +-----------------+----------------
+ | | Amount of | Per million of | Per acre.
+ |Rainfall| drainage. | water. |
+ | +--------+--------+--------+--------+--------+-------
+ | |20-inch |60-inch |20-inch |60-inch |20-inch |60-inch
+ | |gauge. |gauge. |gauge. |gauge. |gauge. |gauge.
+--------------+--------+--------+--------+--------+--------+--------+-------
+ |Inches. |Inches. |Inches. | | | lb. | lb.
+March | 1.70 | 0.85 | 0.94 | 7.3 | 8.9 | 1.41 | 1.89
+April | 2.25 | 0.72 | 0.79 | 8.3 | 9.0 | 1.35 | 1.61
+May | 2.48 | 0.80 | 0.79 | 8.4 | 9.1 | 1.53 | 1.63
+June | 2.59 | 0.78 | 0.78 | 9.2 | 9.1 | 1.62 | 1.60
+July | 2.85 | 0.68 | 0.62 | 13.5 | 11.8 | 2.08 | 1.66
+August | 2.69 | 0.84 | 0.76 | 15.1 | 13.3 | 2.87 | 2.28
+September | 2.70 | 0.97 | 0.82 | 17.7 | 13.4 | 3.86 | 2.50
+October | 3.12 | 1.86 | 1.68 | 13.8 | 11.9 | 5.83 | 4.53
+November | 3.20 | 2.44 | 2.32 | 11.8 | 11.4 | 6.50 | 5.98
+December | 2.34 | 1.88 | 1.88 | 9.5 | 10.6 | 4.06 | 4.51
+January | 2.13 | 1.79 | 1.93 | 7.4 | 8.9 | 2.99 | 3.88
+February | 2.16 | 1.84 | 1.74 | 7.7 | 9.1 | 3.19 | 3.57
+ +--------+--------+--------+--------+--------+--------+-------
+March-June | 9.02 | 3.15 | 3.30 | 8.3 | 9.0 | 5.91 | 6.73
+July-September| 8.24 | 2.49 | 2.20 | 15.6 | 13.0 | 8.81 | 6.44
+October-Feb. | 12.95 | 9.81 | 9.55 | 10.2 | 10.4 | 22.57 | 22.47
+ +--------+--------+--------+--------+--------+--------+-------
+Whole year | 30.21 | 15.45 | 15.05 | 10.7 | 10.5 | 37.29 | 35.64
+--------------+--------+--------+--------+--------+--------+--------+-------
+
+
+
+
+CHAPTER IV.
+
+NITRIFICATION.
+
+
+The most important compound of nitrogen for the plant is _nitric acid_.
+It is as nitrates that most plants absorb the nitrogen they require to
+build up their tissue. In nature the nitrogen, present in the soil as
+ammonia and different organic forms, is constantly being converted into
+nitric acid. This conversion of nitrogen into nitrates, known as
+_nitrification_, is a process of very great importance, and, as has been
+already pointed out in the Introductory Chapter, is effected through the
+agency of micro-organisms (ferments).[97] The process of nitrification,
+as well as the nature of the other changes taking place in the soil
+between the various compounds of nitrogen, are as yet but most
+imperfectly understood, but much light has been thrown on this most
+interesting department of agricultural research during the last few
+years; and it cannot be doubted that the increased attention which it is
+receiving from different investigators, both on the Continent and in
+this country, will be fraught with most important results for practical
+agriculture.
+
+
+_Occurrence of Nitrates in the Soil._
+
+The occurrence of nitre,[98] or potassium nitrate, in soils has been
+long known, although it is only within the last few years that we have
+obtained any precise knowledge with regard to the mode of its
+production. While its amount in most soils, especially in this
+country,[99] is very minute, there are certain parts of the world where
+nitrates are found in large quantities. The nitrate fields of Chili and
+Peru are the chief natural sources of nitrates, and they are referred to
+in the chapter on Nitrate of Soda. We have other parts of the world,
+however (in China and India), where soils rich in nitre occur, and which
+in the past have formed a source of the commercial article.[100]
+
+
+_Nitre Soils of India._
+
+The most important of these nitre soils are those found in the
+North-west of India, in the province of Bengal. In these districts the
+soil is of a light porous texture, rich in lime, and situated at a
+considerable height above water-level. They are the sites of old
+villages, and the nitre is found in the form of an efflorescence on the
+surface of different parts of the soil. The occurrence of nitre under
+such conditions is due, partly to the natural richness of the soil in
+nitrogen, and partly to its artificial enrichment through receiving the
+nitrogenous excrements of the inhabitants of the villages and their
+cattle. The constant process of evaporation going on in such a warm
+climate has the effect of inducing an upward tendency of the soil-water,
+the result being a concentration of all the nitre the soil contains in
+its surface layer. This goes on until a regular incrustation is formed,
+and the soil is covered by a white deposit of nitre. Whenever this
+becomes apparent, the surface portion of the soil is scraped off by the
+_sorawallah_, or native manufacturer, and collected and treated for the
+purpose of recovering, in a pure state, the saltpetre.
+
+
+_Saltpetre Plantations._
+
+The large demand for saltpetre, larger than could be supplied by these
+nitre soils, soon gave rise to the semi-artificial method of production,
+formerly so largely practised in Switzerland, France, Germany, Sweden,
+and in many other parts of the Continent, by means of the so-called
+"nitre beds," "nitraries," or "saltpetre plantations." Previous to the
+introduction of this method of manufacture, the demand for saltpetre for
+gunpowder had become so great, that every source of nitre was eagerly
+sought for. Thus, when it was discovered that the earth from the floors
+of byres, stables, and farmyards were particularly rich in nitre, and
+when mixed with wood-ashes formed an important source of it, the right
+to remove these in France was vested in the Government under the
+Saltpetre Laws, which obtained till the French Revolution. This great
+scarcity soon led, however, to a careful investigation being made into
+the conditions under which potassium nitrate was formed in nitre
+soils.[101] These conditions, which included the presence of rich
+nitrogenous matter, warmth, free aeration of the soil, and a certain
+proportion of moisture, became, in the course of years, more and more
+thoroughly understood, and the result was the institution of numerous
+"saltpetre plantations." These generally consisted of heaps of mould,
+rich in nitrogen, mixed with decomposing animal matter, rubbish of
+various kinds, manurial substances, ashes, road-scrapings, and lime
+salts.[102] The heap was interlaid with brushwood, and was watered from
+time to time with liquid manure from stables, consisting chiefly of
+dilute urine. In forming the heap care was taken to keep the mass
+porous, so as to admit of the free access of air. The heap was further
+protected from the rain by covering it with a roof. In course of time
+considerable quantities of nitrates were developed, and the nitre was
+occasionally collected by scraping it from the surface, where it became
+concentrated just as in the nitre soils. In all cases, however, the
+heaps, when considered rich enough in nitre, were treated from time to
+time with water which, by subsequent evaporation, yielded the nitre in a
+more or less pure condition.[103]
+
+This mode of obtaining nitre is no longer practised to any extent, since
+it is now more conveniently obtained from the treatment of nitrate of
+soda with potassium chloride.
+
+
+_Cause of Nitrification._
+
+We have adverted to these nitre plantations as showing how the
+conditions most favourable for the development of nitrification were
+recognised long before anything was known as to the true nature of the
+process. It was only in 1877 that the formation of nitrates in the soil
+was proved to be due to the action of micro-organic life,[104] by the
+two French chemists, Schloesing and Müntz, who discovered the fact when
+carrying out experiments to see if the presence of humic matter was
+essential to the purification of sewage by soil. In these experiments
+sewage was made to filter slowly through a certain depth of soil (the
+time occupied in this filtration being eight days). It was found that
+nitrification of the sewage took place. By treating the soil with
+chloroform[105] it was found that it no longer possessed the power of
+inducing the nitrification of the sewage. When, however, a small portion
+of a nitrifying soil was added, the power was regained. From this it was
+naturally inferred that nitrification was effected by some kind of
+ferment. This conclusion was soon confirmed by subsequent experiments by
+Warington at Rothamsted, who showed that the power of nitrification
+could be communicated to media, which did not nitrify, by simply
+seeding them with a nitrifying substance, and that light was
+unfavourable to the process. Since then the question has formed the
+subject of a number of researches by Mr Warington at Rothamsted, as well
+as by Schloesing and Müntz, Munro, Dehérain, P. F. Frankland,
+Winogradsky, Gayon and Dupetit, Kellner, Plath, Pichard, Landolt, Leone,
+and others. From these researches we have obtained the following
+information with regard to the nature of the organisms concerned in this
+process, and the conditions most favourable for their development.
+
+
+_Ferments effecting Nitrification._
+
+The importance of isolating and studying them microscopically was
+recognised at an early period in these researches. Messrs Schloesing and
+Müntz were the first to attempt this. They reported that they had
+successfully accomplished this, and described the organism as consisting
+of very small, round, or slightly elongated corpuscles, occurring either
+singly or two together. According, however, to the most recent
+researches of Warington, Winogradsky, and P. F. Frankland, nitrification
+is not effected by a _single_ micro-organism, but by _two_, both of
+which have been successfully isolated and studied.[106] The first of
+these to be discovered and isolated was the _nitrous_ organism, which
+effects the conversion of ammonia into nitrous acid; the second, which
+has only been lately isolated by Warington and Winogradsky, effects the
+conversion of nitrous acid into nitric acid. Each of these ferments thus
+has its distinctive function to perform in this most important process,
+the nitric ferment being unable to act on ammonia, as the nitrous
+ferment is unable to convert nitrites into nitrates. Both ferments occur
+in enormous quantities in the soil, and seem to be influenced, so far as
+is at present known, by the same conditions. Their action will thus
+proceed together. Nearly all we know as yet on the subject of their
+nature is with regard to the nitrous ferment.
+
+
+_Appearance of Nitrous Organism._
+
+Mr Warington[107] thus describes the appearance of the nitrous organism:
+"As found in suspension in a freshly nitrified solution, it consists
+largely of nearly spherical corpuscles, varying extremely in size. The
+largest of these corpuscles barely reaches a diameter of 1/1000th of a
+millimeter; and some are so minute as to be hardly discernible in
+photographs, although shown there with a surface one million times
+greater than their own. The larger ones are frequently not strictly
+circular. These forms are universally present in nitrifying cultures.
+The larger organisms are sometimes seen in the act of dividing."
+
+
+_Nitric Organism._
+
+So far as at present known, the nitric organism is very similar in
+appearance to the nitrous organism, so much so that it is difficult to
+distinguish the one from the other. As the same conditions influence
+their development, the process may be regarded as a whole.
+
+
+_Difficulty in isolating them._
+
+A great difficulty has been experienced in the attempt to isolate these
+micro-organisms for the purpose of studying their nature. This arises
+from the fact that they refuse to grow on the ordinary solid cultivating
+media used by bacteriologists. Winogradsky, however, has recently
+succeeded in cultivating them in _a purely mineral_ medium--viz.,
+_silica-jelly_.[108]
+
+
+_Nitrifying Organisms do not require Organic Matter._
+
+The fact that they can develop in media destitute of organic matter, is
+one of very great interest and importance to Vegetable Physiology. It
+implies that they can derive their carbon from carbonic acid--a power
+which it was believed was possessed by green plants alone among living
+structures. For organisms destitute of chlorophyll, the source of their
+protoplasmic carbon, it has been hitherto commonly believed, must be
+_organic matter_ of some sort. While it would appear that the nitrifying
+organisms can, when opportunity affords, feed upon organic matter, yet
+it has been proved beyond doubt that they can also freely develop in
+media entirely devoid of it, and are capable, under such circumstances,
+of deriving their carbon from a purely mineral source.[109] This fact,
+which is subversive of what was believed to be a fundamental law of
+Vegetable Physiology, is one of the most important of the many important
+and interesting facts which these nitrification researches have
+elicited.[110]
+
+
+CONDITIONS FAVOURABLE FOR NITRIFICATION.
+
+We may now proceed to discuss the conditions favourable for
+nitrification.
+
+
+_Presence of Food-constituents._
+
+Among these conditions the first is the presence of certain
+food-constituents. To both animal and vegetable life alike a certain
+amount of mineral food is absolutely necessary. Among these phosphoric
+acid is one of the most important, and in the experiments on
+nitrification it has been found that the nitrifying organisms will not
+develop in any medium destitute of it. That other mineral
+food-constituents are necessary is highly probable, although the
+influence of their absence on the development of the process has not
+been similarly studied. Probably potash, magnesia, and lime salts are
+necessary. In the cultivating solutions used in the experiments on the
+subject, the mineral food-constituents added consisted of lime,
+magnesia, and potash salts and phosphoric acid.[111]
+
+As we have seen above, the presence of organic matter is not necessary
+for the process. In this respect these organisms are differentiated from
+all other ferments hitherto discovered.
+
+
+_Presence of a Salifiable Base._
+
+The presence of a sufficient quantity of a base in the soil with which
+the nitric acid may combine, when it is formed, is another necessary
+condition.[112] The process only goes on in a slightly alkaline
+solution. The substance which acts as this salifiable base is _lime_.
+The presence of a sufficient quantity of carbonate of lime in the soil
+will thus be seen to be of first-rate importance. This furnishes an
+explanation of one of the many benefits conferred by lime on soils. The
+activity of nitrification in many soils may be hindered by the absence
+of a sufficiency of lime salts, and in such cases most striking results
+may follow the application of moderate dressings of chalk. The absence
+of the nitrifying organisms in certain soils, such as peaty and forest
+soils, may be thus accounted for. In such soils humic acids are present
+and the requisite alkalinity is thus awanting.
+
+
+_Only takes place in slightly Alkaline Solutions._
+
+But while a certain slight amount of alkalinity is necessary, this must
+not exceed a certain strength, otherwise the process is retarded. This
+is the reason why strong urine solutions do not nitrify. The amount of
+carbonate of ammonia generated in them by putrefaction renders the
+development of nitrification impossible by rendering the alkalinity of
+the solution too great.[113] The practical importance of this fact is
+considerable, as it shows the importance of diluting urine very
+considerably before applying it as a manure. Similarly, when large
+quantities of lime, especially burnt lime, are applied to soils, the
+result will be to arrest the action of nitrification for the time. The
+presence of alkaline carbonates in the soil, unless in minute
+quantities, is apt, therefore, to seriously interfere with the
+process.[114]
+
+
+_Action of Gypsum on Nitrification._
+
+It has been found by Pichard that the action of certain mineral
+sulphates is extremely favourable to the process, and among these
+_gypsum_. Warington has carried out some experiments on the action of
+gypsum in promoting nitrification. The reason of its favourable action
+is probably because it neutralises the alkalinity of nitrifying
+solutions. It thus permits the process to go on in unfavourable
+conditions. Where, therefore, too great alkalinity exists for the
+maximum development of nitrification, the best specific will be found to
+be gypsum.[115] The practical value of gypsum as an adjunct to certain
+manurial substances, where nitrification is desired to be promoted as
+rapidly as possible, such as sewage and farmyard manure, will thus at
+once become apparent. So far as there is a proper degree of alkalinity
+maintained, the presence of large quantities of saline matter does not
+seem to interfere with the process.
+
+
+_Presence of Oxygen._
+
+The nitrification bacteria belong, it would seem, to the aerobic[116]
+class of ferment--_i.e._, they cannot develop without a free supply of
+oxygen. Exclusion of the air is sufficient to kill them, and in those
+portions of the soil where access of air is not freely permitted,
+nitrification will be found to be correspondingly feeble. Thus it has
+been found in experiments with different portions of soils, that but
+little signs of nitrification occur in the lower soil layers. According
+to experiments by Schloesing on a moist soil, in atmospheres
+respectively containing no oxygen and varying quantities of it, the
+action of oxygen in promoting nitrification was strikingly demonstrated.
+In an atmosphere of pure nitrogen, entirely devoid of oxygen, the
+process no longer took place, but the nitrates already present in the
+soil were reduced and free nitrogen was evolved. In an atmosphere, on
+the other hand, containing 1.5 per cent of oxygen, a considerable amount
+of nitrification took place; while in the presence of 6 per cent,
+nitrification took place to double the extent. An addition of 10 to 15
+per cent again doubled the quantity. When the amount of moisture added
+was increased, the effect of larger percentages of oxygen was found to
+be less marked. The reason of this is that the oxygen probably acts as
+dissolved oxygen; the addition of water meaning at the same time an
+addition of available oxygen. This condition exemplifies the value of
+tillage operations. The more thoroughly a soil is tilled the more
+thoroughly will the aeration of its particles take place, and
+consequently the more favourable will this necessary condition of
+nitrification be rendered. The benefits conferred on clayey soils by
+tillage will in this respect be especially great.
+
+
+_Temperature._
+
+Another of the conditions determining the rate at which nitrification
+takes place, and one which is most important, is _Temperature_.
+According to Schloesing and Müntz the temperature at which maximum
+development takes place is 37° C.[117] (99° F.), at which temperature it
+is ten times as active as at 14° C. (57° F.) Below 5° C. (40° F.) the
+action is extremely feeble. It is clearly appreciable at 12° C. (54°
+F.), and from there up to 37° C. (99° F.) it rapidly increases. From 37°
+C. (99° F.) to 55° C. (131° F.), at which temperature no nitrification
+takes place, its activity decreases; at 45° C. (113° F.) it is less
+active than at 15° C. (59° F.), and at 50° C. (122° F.) it is very
+slight. These results by Schloesing and Müntz have not been exactly
+confirmed by Warington. He has found that a considerable amount of
+nitrification goes on at a temperature between 3° and 4° C. (37° and 39°
+F.), while the highest temperature at which he has found it to take
+place is considerably lower than 55° C. (131° F.) Thus he was unable to
+start nitrification in a solution maintained at 40° C. (104° F.) It
+would thus seem that the nitrifying ferments are able to develop at
+lower temperatures than most organisms; and although nitrification
+entirely ceases during frost, yet in a climate such as our own there
+must be a considerable proportion of the winter during which
+nitrification is moderately active.
+
+
+_Presence of a sufficient quantity of Moisture._
+
+The presence of moisture in a soil is another of the necessary
+conditions of nitrification. It has been shown that it is at once
+arrested, and indeed destroyed, by desiccation. Other conditions being
+equal, and up to a certain extent, the more moisture a soil contains the
+more rapid is the process. Too much water, however, is unfavourable, as
+it is apt to exclude the free access of air, which, as we have just
+shown, is so necessary, as well as to lower the temperature. During a
+period of drought the rate at which nitrification takes place will,
+therefore, be apt to be seriously diminished.
+
+
+_Absence of strong Sunlight._
+
+It has been found that the process goes on much more actively in
+darkness; indeed Warington has found in his experiments that
+nitrification could be arrested by simply exposing the vessel in which
+it was going on to the action of sunshine.
+
+
+_Nitrifying Organisms destroyed by Poisons._
+
+It has already been pointed out that nitrification is arrested by the
+action of antiseptics, such as chloroform, bisulphide of carbon, and
+carbolic acid. Another substance which has been found to have an
+injurious action is ferrous sulphate or "copperas," a substance which is
+apt to be present in badly drained soils, or soils in which there is
+much actively putrefying organic matter. Maercker has found that in moor
+soils containing ferrous sulphate, no nitrates, or mere traces of
+nitrates, could be found. A substance such as gas-lime, unless submitted
+to the action of the atmosphere for some time, would also have a bad
+effect in checking nitrification, owing to the poisonous sulphur
+compounds it contains. Common salt, it would seem, also arrests the
+process; and this antiseptic property which salt exercises on
+nitrification throws a certain amount of light on the nature of its
+action when applied, as it is often done, along with artificial
+nitrogenous manures.
+
+
+_Denitrification._
+
+In connection with the process of nitrification, it is of interest to
+notice that a process of an opposite nature may also take place in
+soils--viz., _denitrification_--a process which consists in reducing the
+nitrates to nitrites, nitrous oxide, or free nitrogen. That a reduction
+of nitrates takes place in the decomposition of sewage with the
+evolution of free nitrogen, was a fact first observed by the late Dr
+Angus Smith in 1867; and the reduction of nitrates to nitrites, and
+nitric and nitrous oxides in putrefactive changes has been subsequently
+noticed by different experimenters, who have further observed that such
+reduction takes place in the case of putrefaction going on in the
+presence of large quantities of water or where there is much organic
+matter.
+
+
+_Denitrification also effected by Bacteria._
+
+This change was supposed to be of a purely chemical nature, and it has
+only been recently discovered that it is effected, like nitrification,
+by means of bacteria. It has been surmised by some that the action of
+denitrification may be effected by the same organisms that effect
+nitrification, and that it depends on merely external conditions which
+process goes on. There is no reason, however, to suppose that this is
+so, and several of the denitrifying organisms have been identified.
+
+
+_Conditions favourable for Denitrification._
+
+That it is a process that goes on to any extent in properly cultivated
+soils is not to be supposed. The conditions which favour denitrification
+are exactly the opposite of those which favour nitrification. It is only
+when oxygen is excluded, or, which practically means the same thing,
+when large quantities of organic matter are in active putrefaction, and
+the supply of oxygen is therefore deficient, that denitrification takes
+place. Schloesing, as we have already seen, found that in the case of a
+moist soil, kept in an atmosphere devoid of oxygen, a reduction of its
+nitrates to free nitrogen took place.
+
+
+_Takes place in water-logged Soils._
+
+The exclusion of oxygen from a soil may be effected by saturating the
+soil with water; and Warington has found in experiments carried out in
+an arable soil, by no means rich in organic matter, that complete
+reduction of nitrates may be effected in this way. It would thus seem
+that the process of denitrification will take place in water-logged
+soils, or in the putrefaction of sewage matter in the presence of large
+quantities of water. Whether this reduction will result in the
+production of nitrites, nitrous oxide, or free nitrogen, depends on
+different conditions. This process is one of great importance from an
+economic point of view, as it reveals to us a source of loss which may
+take place in the fermentation of manures. In the rotting of our
+farmyard manure it is possible that the denitrifying organisms may be
+more active than we have hitherto suspected, and that a considerable
+loss of nitrogen may in this way be effected.
+
+
+_Distribution of the Nitrifying Organisms in the Soil._
+
+The nitrifying organisms are probably chiefly confined to the soil, and
+do not usually occur in rain or in the atmosphere. That, however, they
+are found in spots which we might be inclined to think extremely
+unlikely, is shown by some recent interesting researches carried out by
+Müntz, who discovered that the bare surfaces of felspathic, calcareous,
+schistose, and other rocks at the summit of mountains in the Pyrenees,
+Alps, and Vosges, yielded large numbers of them, and that they occurred
+to a considerable depth in the cracks and fissures of the rocks. The
+nitrifying organisms are also found in river-water, in sewage, and
+well-waters.
+
+
+_Depth down at which they occur._
+
+In Warington's earlier experiments, the conclusion he arrived at was
+that the occurrence of the nitrifying organisms was almost entirely
+limited to the superficial layers of the soil, and that they were seldom
+to be met with much below a depth of 18 inches. His subsequent
+experiments, however, considerably modified this conclusion, and showed
+that nitrification may take place to a depth of at least 6 feet.[118]
+But although it may take place at this depth, it probably, as a general
+rule, is limited to the surface-soil, as it is only there the conditions
+for obtaining circulation of air are sufficiently favourable. A great
+deal, of course, will depend on the nature of the soil--_i.e._, as to
+its texture. In a clayey subsoil the principal hindrance to
+nitrification will be the difficulty of obtaining sufficient aeration.
+In clay soils it is probable, therefore, that nearly all the
+nitrification goes on in the surface layer; in sandy soils it may take
+place to a greater depth.[119]
+
+
+_Action of Plant-roots in promoting Nitrification._
+
+In this connection the action of plant-roots in permitting a more
+abundant access of air to the lower layers of the soil, and thus
+promoting nitrification, is worth noticing. This has been observed in
+the case of different crops. Thus the action of nitrification has been
+found to be more marked in the lower layers of a soil on which a
+leguminous crop was growing than on that on which a gramineous. "The
+conditions which would favour nitrification in the subsoil are such as
+would enable air to penetrate it, as artificial drainage, a dry season,
+the growth of a luxuriant crop causing much evaporation of the water in
+the soil. Such conditions, by removing the water that fills the pores of
+the subsoil, will cause the air to penetrate more or less deeply and
+render nitrification possible. Subsoil nitrification will thus be most
+active in the drier periods of the year" (Warington).
+
+
+_Nature of Substances capable of Nitrification._
+
+What kinds of nitrogenous substances are capable of undergoing this
+process of nitrification are not yet well known. The question is, of
+course, one of great importance, as the rapidity with which a
+nitrogenous body nitrifies will be an important factor in determining
+its value as a manure. Unfortunately, on this subject we know, as yet,
+very little. We are well aware that the nitrogen present in the humic
+matter of the soil is readily nitrifiable. In the experiments on
+nitrification the nitrogenous bodies used have been chiefly ammonia
+salts, so that it is difficult to say whether, in the case of other
+nitrogenous substances, micro-organic life of a different sort has not
+also been active and has converted the nitrogen into ammonia, and
+thereby prepared the way for the process of nitrification.
+
+That various manures, such as bones, horn, wool, and rape-cake are
+readily nitrifiable, has been shown by experiment. Laboratory
+experiments have also been carried out on such different nitrogenous
+substances as ethylamine, thiocyanates, gelatin, urea, asparagin, and
+albuminoids of milk. But in all these experiments, how far these bodies
+have been directly acted upon by the nitrifying organisms, or how far
+they have first undergone a preparatory change in which their nitrogen
+has been first converted into ammonia, is impossible to say. It is at
+least quite probable that all the organic forms of nitrogen have first
+to be converted into ammonia ere they are nitrified.
+
+
+_Rate at which Nitrification takes place_.
+
+A question which is practically of no little importance is the rate at
+which nitrification takes place. From what has been already said as to
+the nature of the conditions favourable for the process, it will be at
+once seen that this will depend on how far these conditions are present
+in the soil. In point of fact the rate at which nitrification takes
+place will vary very much in different soils. A greater difference,
+however, in the rate at which it takes place, will be found even in the
+same soils at different periods of the year. In this country, where the
+most favourable temperature for its development is seldom reached, it
+never goes on at the same rate as in tropical climates. One of the
+causes of the greater fertility of tropical soils is due, doubtless, to
+the very much longer duration of the period of nitrification, as well as
+to its greater intensity. As, however, temperature is not the only
+condition, and the presence of moisture is quite as necessary, it may be
+that its development is seriously retarded in many tropical climates by
+the extreme dryness of the soil during long periods.
+
+
+_Takes place chiefly during the Summer Months_.
+
+Although in this climate, as has already been pointed out, nitrification
+probably goes on during most of the winter months, owing to the fact
+that the temperature of our soils is only occasionally below the
+minimum temperature at which the process takes place, yet there can be
+little doubt that the great bulk of the soil-nitrates are produced
+during a few months in summer. A fair conception of this amount is
+afforded by the interesting experiments on the composition of
+drainage-waters made at Rothamsted, which we shall have occasion to
+refer to immediately. It may be pointed out, however, that it is not
+always safe to take the amount of nitrates found in drainage-waters as
+an infallible indication of this rate, for this amount will depend to a
+certain extent on the amount of rainfall, and would be misleading in the
+case of a long period of drought. On the whole, however, it furnishes us
+with extremely useful data for the elucidation of this important
+problem.
+
+
+_Process goes on most quickly in Fallow Fields._
+
+It has been shown in the Rothamsted experiments that the process goes on
+best in fields lying in bare fallow; and in this fact lies the
+explanation of one of the many reasons why the practice of leaving
+fields in bare fallow, so common in past times, and still practised in
+the case of clay soils in some parts of the country, was so beneficial
+to the land thus treated. But despite this fact, the practice of leaving
+soils in bare fallow can scarcely be justified from this point of view,
+as the loss of nitrates through the action of rain is very great in our
+moist climate.
+
+
+_Laboratory Experiments on Rate of Nitrification._
+
+Several interesting experiments have been carried out with the object of
+affording data for estimating the rate at which the process may go on in
+our soils under certain conditions. An old experiment, carried out by
+Boussingault, illustrates, in a general way, how rapid the process is
+under favourable circumstances. A small portion of rich soil was placed
+on a slab protected by a glass roof, and was moistened from time to time
+with water. The amount of nitrate of potash formed under these
+circumstances was estimated from time to time during a period of two
+months. During the first month (August) the percentage was increased
+from .01 to .18 (equal to about 5 cwt. of nitrate of potash per acre).
+The increase during the second month (September) was very much
+less,--indeed only about a seventh of the amount.[120] The soil
+experimented with was an extremely rich garden soil, and all the
+conditions for nitrification were most favourable.
+
+Of recent experiments on the rate of nitrification, the most striking,
+perhaps, are those by Schloesing. He mixed sulphate of ammonia with a
+quantity of soil fairly rich in organic matter, and containing 19 per
+cent of water. During the twelve days of active nitrification no less
+than 56 parts of nitrogen per million of soil were nitrified per day.
+Taking the soil to a depth of 9 inches, this would be equal to more
+than 1 cwt. per acre--an amount of nitrogen equal to that contained in
+6 cwt. of commercial nitrate of soda. These experiments are interesting
+as showing what is probably the maximum rate of nitrification under the
+most favourable circumstances, and where there is an abundant supply of
+easily nitrifiable nitrogen. That nitrification ever takes place in our
+soils to this extent is not to be for a moment supposed.
+
+Warington, in his Rothamsted experiments, has found that the greatest
+rate, working with ordinary arable soil (first 9 inches) from the
+Rothamsted farm, was .588 parts per million of air-dried soil per
+day--_i.e._, 1.3 lb. per acre (equal to about 8 lb. of nitrate of soda).
+Similar soil, when supplied with ammonia salts, showed nearly double
+this quantity. Higher results were obtained by Lawes and Gilbert with
+rich Manitoba soils, the average rate being .7 parts per million per
+day.
+
+The last of these interesting laboratory experiments on the rate of
+nitrification we shall refer to, are those by Dehérain. He experimented
+with soils containing different amounts of nitrogen and moisture. With a
+soil containing .16 per cent of nitrogen he obtained, during a period of
+90 days, rates of nitrification varying from .71 to 1.09 per million
+parts of soil. The maximum quantity was formed when the soil contained
+25 per cent of moisture. On a soil considerably richer--viz.,.261 per
+cent of nitrogen--a higher rate of nitrification took place--1.48 parts
+per million. The highest rate obtained in these experiments showed,
+when calculated to pounds per acre, about 5-1/2, taking the soil to a
+depth of 9 inches. When the soil was alternately dried and moistened the
+process was most rapid.
+
+
+_Portion of Soil-nitrogen more easily Nitrifiable than the rest._
+
+Lastly, it may be noticed that in the above-cited experiments, and
+others of a similar kind, the process goes on most rapidly at first, and
+steadily diminishes thereafter. This is due to the fact, that there is
+generally a certain quantity of nitrogen in most soils in a more easily
+nitrifiable condition than the rest, so that when this becomes oxidised
+nitrification proceeds more slowly. It would further seem that the
+nitrogen of the subsoil is less easily nitrified than that of the
+surface-soil.
+
+
+_Rate of Nitrification deduced from Field Experiments._
+
+While the above experiments throw much light on the question of the rate
+at which nitrification may go on under different circumstances, the
+results furnished by actual analyses of soils and their drainage-waters
+are of still more practical value; and the Rothamsted experiments
+fortunately furnish us with a number of these valuable results.
+
+
+_Quantity of Nitrates formed in the soils of Fallow Fields._
+
+These researches had to be carried out on soil taken from fields lying
+in bare fallow; for no true estimate of the amount of nitrates formed
+could have been obtained from _cropped_ fields. In the first 27 inches
+of soil of six separate fields, nitrate-nitrogen was found to vary from
+36.3 lb. to 59.9 lb. per acre. In four of these fields the largest
+proportion was found in the first 9 inches of soil; in the remaining
+two, in the second 9 inches; while the third 9 inches in two fields
+showed almost as large a proportion as the first 9 inches.[121]
+
+
+_Position of Nitrates depends on Season._
+
+The position of nitrates in the soil depends largely on the season; for,
+as has been already pointed out, their production is almost entirely
+limited to the surface-soil, and it is only by being washed down in rain
+that they find their way to the lower layers. A wet season, therefore,
+has the effect of increasing their percentage in the lower soil-layers.
+
+
+_Nitrates in Drainage-waters._
+
+As there is a certain proportion of nitrates that finds its way even
+below the first 27 inches of soil, the above results do not show their
+total production. To accurately estimate this amount we must ascertain
+the quantity escaping in drainage-water. Here, again, the Rothamsted
+experiments furnish us with valuable data. The amount found in
+drainage-waters of course naturally varies very much, and depends
+largely on the rainfall; but taking an average of twelve years, this has
+been found to amount to between 30 and 40 lb. per acre--an amount not so
+very far short of that found in the first 27 inches of the soil itself.
+This was from comparatively poor soil, it must be remembered, and a much
+larger quantity would undoubtedly be produced in the case of richer
+soils. Adding then the results together, we find that in soils like
+those at Rothamsted, when in bare fallow, between 80 and 90 lb. of
+nitrogen are converted into nitrates in some fourteen months' time--an
+amount equal to about 5 cwt. of nitrate of soda. It is a fact of no
+little practical significance that nearly one-half of this large
+quantity is found in the drainage-water.
+
+
+_Amount produced at Different Times of the Year._
+
+Some indication of the rate at which nitrification takes place during
+the different months of the year is obtained from a study of the results
+of the analyses of drainage-waters which we have just referred to. This,
+however, it must be remembered, only furnishes us with a very
+approximate indication. The month showing the greatest amount of
+nitrates in the drainage-water must not necessarily be regarded as that
+during which nitrification has been most active, for the amount chiefly
+depends on the rainfall. In illustration of this it will be found that
+the drainage-water during the autumn and early winter months contains
+most nitrates, not because nitrification is most active then, but
+because the rainfall is greatest, and a large proportion of the nitrates
+formed during the drier summer months is being only then washed from the
+soil. The amount of nitrates in drainage-waters steadily diminishes from
+autumn through the winter months, and is least in spring. The total
+amount of nitrates found in the drainage-water is, therefore, not a safe
+guide. What, however, does furnish us with a more reliable indication is
+the _percentage_ of nitrates in the drainage-water. Regarding the
+results of the analyses of drainage-water (see Appendix) from this point
+of view, it will be seen that this is greatest during the month of
+September, and least during April.[122]
+
+
+_Nitrification of Manures._
+
+A subject which has not yet been specially referred to, but which is of
+great practical importance, is the nitrification of manurial substances.
+It is unfortunate that the amount of research hitherto devoted to this
+important question has been slight, and that the knowledge we possess is
+therefore very limited.
+
+
+_Ammonia Salts most easily Nitrifiable._
+
+One fact, however, about which there can be little doubt, is that
+nitrogen in the form of ammonia salts is, of all compounds of nitrogen,
+the most easily nitrifiable. Indeed, as we have already indicated, it is
+highly probable that the conversion of the different forms of organic
+nitrogen into ammonia is an intermediate stage in the nitrification of
+these bodies. At any rate it seems to be invariably the case that when a
+mixture of nitrogen compounds, including ammonia salts, are allowed to
+nitrify, the nitrogen in the form of ammonia is the first to become
+nitrified.
+
+
+_Sulphate of Ammonia most easily Nitrifiable Manure._
+
+It follows from this that sulphate of ammonia, the most common of
+ammoniacal manures, is one of the most speedily nitrified when applied
+to the soil. The rate at which the nitrification of this manure takes
+place naturally varies according to the quantity applied, and other
+circumstances, such as the nature of the soil and the weather, &c. That,
+under favourable circumstances, the conversion of ammonia into nitrates
+is very rapid, has been shown by a number of experiments. Dehérain has
+found that when sulphate of ammonia was mixed with soil at the rate of 2
+cwt. per acre, nitrification took place at the rate of 1/100th of its
+nitrogen per day.
+
+_Rate of Nitrification of other Manures._
+
+Of other nitrogenous manures, guano, it would seem, comes next to
+sulphate of ammonia in the rate at which it becomes nitrified in the
+soil; while next to guano stand green manures, dried blood, meat-meal,
+&c. As we should expect, such a manure as shoddy is very slowly
+nitrified. The rate at which the nitrogen compounds in farmyard manure
+become nitrified, when incorporated with the soil, vary very much
+according to circumstances. It goes on probably at a greater rate than
+the ordinary nitrification of soil-nitrogen. It is a somewhat striking
+fact that the effect of adding nitrate of soda to the soil may be at
+first to check nitrification. That the addition of common salt, even in
+small quantities, has this result, is at any rate certain. The presence
+of salt to the extent of one-thousandth of the weight of the soil, has a
+prejudicial effect.
+
+_Soils best suited for Nitrification._
+
+To recapitulate, then, nitrification is effected through the agency of
+micro-organisms, which are present to a greater or less extent in all
+soils. It requires for its favourable development air, warmth, moisture,
+absence of strong light, presence of a salifiable base--viz., carbonate
+of lime--the presence of certain mineral food-constituents, such as
+phosphates, and a certain amount of alkalinity. It consequently takes
+place to the least extent in barren sandy soils. Soils rich, light, well
+ventilated, uniformly moist, warm, and chalky, are best suited for its
+development. Other things being equal, it develops better in a
+fine-grained soil than in a coarse-grained soil, because, in the case of
+the former, aeration and uniform moistening of the soil are best
+secured.
+
+
+_Absence of Nitrification in Forest-soils._
+
+A point of considerable interest is the practical absence of the process
+in forest-soils. The absence, or occurrence in the most minute traces,
+of nitrates in forest-soils has been accounted for by the lowness of the
+normal temperature of such soils and their extreme dryness. This latter
+condition is accounted for by the enormous transpiration of water which
+takes place through the trees, especially in summer-time, which is such
+as to render the soil almost air-dry. Lastly, it may be accounted for by
+the want of mineral food ingredients.
+
+
+_Important Bearing of Nitrification on Agricultural Practice._
+
+Before concluding this chapter, it may be well to draw attention to the
+important bearing which nitrification has on agricultural practice. The
+light which our present knowledge--imperfect as it is--of this most
+interesting process throws on the theory of the rotation of crops is
+very striking, for it shows how the adoption of a skilful rotation may
+be made to prevent the loss of enormous quantities of the most valuable
+of all our soil-constituents,--the one on the presence of which
+fertility may be said most to depend--viz., nitrogen.
+
+
+_Desirable to have Soil covered with Vegetation._
+
+The constant production of nitrates going on in the soil, the inability
+of the soil to retain them, and the consequent risk of their being
+removed in drainage, furnish a strong argument in favour of keeping our
+soils as constantly covered with vegetation as possible.
+
+
+_Permanent Pasture most Economical Condition of Soil._
+
+From the point of view of conservation of soil-nitrates, permanent
+pasture may be said to be the most economical condition for the soil to
+be in. In such a case the nitrates are assimilated as they are formed,
+and, by being converted in the plant into organic nitrogen, they are at
+once removed from all risk of loss. A consideration, therefore, of the
+process of nitrification furnishes many arguments in favour of laying
+down land in permanent pasture--a practice which of late years has been
+increasingly followed in many parts of the country. As, however, it is
+not possible or desirable to carry out this practice beyond certain
+limits, the rotation which most nearly conforms to the condition of
+keeping the soil covered with vegetation, and most approximates in this
+respect to permanent pasture, is most to be recommended.
+
+
+_Nitrification and Rotation of Crops._
+
+The chief risk of loss of nitrates is in connection with a cereal crop
+such as wheat. Where turnips follow wheat, there is a period during
+which the soil is left uncovered, and during which most serious loss of
+nitrates is apt to ensue. The risk of loss is enhanced by the fact that
+the assimilation of nitrates by cereals ceases before the season of
+their maximum production in the soil. The soil is then left bare of
+vegetation during the autumn, which is the most critical period of all,
+and the result must be serious loss. In order to minimise this loss, the
+practice of growing catch-crops has been had recourse to. As, however,
+this practice will be dealt with elsewhere, nothing further need here be
+said.
+
+
+FOOTNOTES:
+
+[97] As the formation of nitrites is a stage in the process, the term
+_nitrification_ includes the formation of nitrites as well as nitrates.
+
+[98] Nitre seems to have been known as early as the thirteenth century.
+
+[99] Lawes and Gilbert, for example, have shown that in the Rothamsted
+soils it only amounts to a few parts per million of soil.
+
+[100] See Appendix, Note I., p. 196.
+
+[101] The artificial production of nitre seems to have been first
+effected by Glauber in the seventeenth century.
+
+[102] The lime-rubbish from old buildings, especially those parts which
+have come in contact with the earth, or plastering from the walls of
+damp cellars, barns, stables, &c., have been found to be rich in nitrate
+of lime, and, as has been long well known, constitute by themselves a
+valuable manure. The formation of the nitrate of lime can be accounted
+for by the contact of the lime with nitrogenous matter of different
+kinds.
+
+[103] As much of the nitric acid in this solution was present as nitrate
+of lime, it was usually treated with a solution of potassium carbonate,
+the result being the precipitation of the lime as carbonate, pure
+saltpetre being left in solution, according to the following equation--
+
+K_{2}CO_{3} + Ca(NO_{3})_{2} = 2 KNO_{3} + CaCO_{3}.
+
+Under the French mode of manufacture, the process was considered to have
+developed satisfactorily when 1000 lb. of earth, at the expiration of
+two years, yielded 5 lb. of nitre.
+
+[104] Pasteur had already in 1862 expressed the opinion that
+nitrification might probably be in some way connected with ferments. A.
+Müller (see 'Journal of Chemical Society,' 1879, p. 249) was the first
+to advance the opinion that nitrification was due to the action of a
+ferment. This conclusion he was led to by the observation that while the
+ammonia in sewage was converted into nitric acid, no change took place
+in solutions of ammonia or urine prepared in the laboratory.
+
+[105] Bisulphide of carbon and phenol (carbolic acid) have also been
+experimented with in connection with their antiseptic action on
+nitrification. In these experiments the former had a similar effect to
+chloroform; the phenol, however, while hindering it did not entirely
+suspend it, due probably to the difficulty of bringing the phenol vapour
+into thorough contact with the soil-particles.
+
+[106] Winogradsky has named the nitrous organism _nitrosomonas_, and the
+nitric organism _nitrobaeter_.
+
+[107] From a series of Lectures delivered by him in connection with
+Lawes Agricultural Trust, in the United States.
+
+[108] This silica-jelly consists of dialysed silicic acid, ammonium
+sulphate, potassium phosphate, magnesium sulphate, calcium chloride, and
+magnesium carbonate.
+
+[109] This fact is all the more striking when we remember that this
+decomposition of carbonic acid is best effected in the dark, since light
+is prejudicial to nitrification.
+
+[110] See Appendix, Note II., p. 196, and Note III., p. 197.
+
+[111] See Appendix, Note V., p. 198.
+
+[112] This is shown by the fact that nitrification will only continue in
+a solution of carbonate of ammonia till one-half the ammonia is
+nitrified. It then stops. The base, with which the nitrous acid combines
+as it is formed, being at that stage entirely used up, nitrification is
+no longer possible. With regard to urine solutions the same is the case.
+Nitrification thus will only take place where there is a sufficiency of
+base.
+
+[113] See Appendix, Note IV., p. 197.
+
+[114] It would seem that an alkalinity much exceeding four parts of
+nitrogen per million is prejudicial to the process.
+
+[115] According to Warington, solutions containing 50 per cent of urine
+become nitrifiable when sufficient gypsum is added. The gypsum
+neutralises the alkalinity of nitrifying solutions by converting the
+alkaline ammonium carbonate into neutral ammonium sulphate, the calcium
+carbonate being precipitated.
+
+[116] See Chapter on Farmyard Manure.
+
+[117] As practically illustrating this fact, a solution kept at 10° C.
+required ten days, while a solution kept at 30° C. required only eight
+days for nitrification.
+
+[118] In sixty-nine trials no failure to produce nitrification by
+seeding with soil from a depth, of 2 feet was experienced. Similarly in
+eleven trials only one failure took place with soil from a depth of 3
+feet. With clay soil from a depth of 6 feet success took place to the
+extent of 50 per cent. No nitrification was obtained with clay from a
+depth of 8 feet. Entire failure was experienced with chalk subsoil. The
+process thus diminishes in activity the lower down we go.
+
+[119] Koch has found that in soils he has examined few organisms were
+found at a depth below 3 feet.
+
+[120] See Appendix, Note VI., p. 198.
+
+[121] For full analytical results see Appendix, Note VII., p. 198.
+
+[122] We find the least amount in the month of April. In the water, from
+a 20-and 60-inch gauge respectively, the amounts were 1.35 lb. and 1.61
+lb. per acre (rainfall 2.25 inches). From then on to November the amount
+steadily increases. In the latter month it reaches its maximum--viz.,
+6.50 lb. (20-inch gauge) and 5.98 lb. (60-inch gauge) per acre (rainfall
+2.30 inches). See Appendix to Chapter III., Note VIII, p. 160.
+
+
+
+
+APPENDIX TO CHAPTER IV.
+
+
+NOTE I. (p. 162).
+
+OLD THEORIES OF NITRIFICATION.
+
+According to the old theories, nitrification was regarded as a simple
+case of the oxidation of nitrogen by the oxygen of the air, or by ozone.
+The union of nitrogen and oxygen, however, probably takes place only at
+very high temperatures, such as are formed during electric discharges.
+It is needless to point out that the union of nitrogen and oxygen in
+this way is not likely to occur in soils. According to other theories,
+nitrification was effected by means of the oxidation of ammonia.
+Ammonia, however, can only be oxidised to nitric acid by means of
+certain powerful oxidising agents, such as ozone or hydrogen peroxide.
+As, however, these substances are not found in the soil, it is much to
+be doubted whether nitric acid is ever formed in the soil in this way.
+It is possible, however, as held by some, that ferric oxide is capable
+of inducing this conversion. On the whole, however, most evidence points
+to the conclusion that all nitric acid produced in the soil is formed
+through the agency of micro-organic life.
+
+
+NOTE II. (p. 170).
+
+The important fact that nitrification can take place in solutions
+practically devoid of organic matter, was first shown by Dr J. H. M.
+Munro ('Chemical Society Journal,' August 1886, p. 561). It was further
+corroborated by Warington and P. F. Frankland. Winogradsky, however,
+has carried out the most conclusive experiments on the subject. "He
+prepared vessels and solutions, carefully purified from organic matter,
+and these solutions he sowed with the nitrifying organism. Finding that
+under these conditions the nitrifying organism increased enormously and
+displayed its full vigour, he proceeded further to determine the amount
+of carbonaceous organic matter formed in solutions after the
+introduction of the organism. By making the nitrification intensive, he
+was able to obtain considerable quantities of carbon from the nitrified
+solutions by the process of wet combustion. In his third memoir he
+publishes figures which apparently show a close relation between the
+amount of nitrogen oxidised, and the amount of carbon assimilated; the
+ratio is about 35:1."--See Bulletin of U.S. Department of Agriculture,
+No. 8, containing Lectures on Rothamsted Experiments by R. Warington,
+F.R.S., p. 50.
+
+
+NOTE III. (p. 170).
+
+The oxidising power of the micro-organisms of soil is not confined to
+the oxidation of ammonia or of organic matter. Müntz has shown that soil
+is capable of oxidising iodides to hypo-iodides and iodates, and
+bromides to hypo-bromides and bromates. This is a very important result,
+and seems to indicate that nitrification is part of a general oxidising
+action, and that we must not assume that nitrites or nitrates are
+produced because they are in themselves of advantage to the organism.
+
+
+NOTE IV. (p. 172).
+
+"When urine in different degrees of dilution was treated with soil, 1
+gram of soil being added to 100 c.c. of diluted urine, nitrification
+commenced in the 1-per-cent solution in 11 days, in the 5-per-cent
+solution in 20 days, in the 10-per-cent solution in 62 days, in the
+12-per-cent solution in 90 days. The alkalinity of the last-named
+solution when nitrification commenced was equal to 447 mgs. of ammonia
+per litre. A solution with an alkalinity of 500 mgs. of ammonia per
+litre is apparently unnitrifiable."--American Department of Agriculture
+Bulletin, Warington's Lectures on Rothamsted Experiments, p. 51.
+
+
+NOTE V. (p. 171).
+
+Professor P. F. Frankland in his experiments used the following
+solutions:--
+
+ grms.
+NH_{4}Cl .5 }
+H_{3}PO_{4} .1 }
+MgSO_{4} .02 > In 1000 c.c. of distilled water.
+CaCl_{2} .01 }
+CaCO_{3} 5.00 }
+
+
+NOTE VI. (p. 185).
+
+Experiment by Boussingault on Rate of Nitrification.
+
+ Percentage of Nitrate
+ 1857. of Potash. = lb. per acre.
+August 5 .01 34
+August 17 .06 222
+September 2 .18 634
+September 17 .22 760
+October 2 .21 728
+
+
+NOTE VII. (p. 188).
+
+NITROGEN AS NITRATES IN ROTHAMSTED SOILS AFTER BARE FALLOW IN LB.
+PER ACRE.
+
+------------+-----------+---------------------------+-----------+----------
+ | Alternate | Four-course rotation. | |
+ | Wheat +-----------+---------------+ |
+ Depth of | and | Super- | | Claycroft | Foster's
+ Soil. | Fallow. | phosphate | Mixed Manure. | Field. | Field.
+ | | only. | | |
+ +-----------+-----------+-------+-------+-----------+----------
+ | 1878. | 1878. | 1878. | 1882. | 1881. | 1881.
+------------+-----------+-----------+-------+-------+-----------+----------
+ | lb. | lb. | lb. | lb. | lb. | lb.
+ 1st 9 ins. | 28.5 | 22.3 | 30.0 | 40.1 | 16.4 | 14.6
+ 2d 9 ins. | 5.2 | 14.0 | 18.8 | 14.3 | 26.5 | 24.6
+ 3d 9 ins. | - | - | - | 5.5 | 15.9 | 17.3
+------------+-----------+-----------+-------+-------+-----------+----------
+ Total | 33.7 | 36.3 | 48.8 | 59.9 | 58.8 | 56.5
+------------+-----------+-----------+-------+-------+-----------+----------
+
+
+
+
+CHAPTER V.
+
+THE POSITION OF PHOSPHORIC ACID.
+
+
+We now come to consider the position of phosphoric acid in agriculture.
+The question is, however, very much simpler in its nature than that of
+nitrogen, and may be consequently discussed in a much shorter space.
+
+Most soils, as we have already had occasion to point out, are better
+supplied with available ash-plant ingredients than available nitrogen
+compounds. The quantity of phosphoric acid absorbed by the plant is also
+less than that of nitrogen; and lastly, the different chemical compounds
+of phosphoric acid occurring in the soil are not nearly so numerous as
+those of nitrogen. Phosphoric acid, however, must be regarded as ranking
+next to nitrogen in its importance as a soil-constituent.
+
+
+_Occurrence of Phosphoric Acid in Nature._
+
+That phosphoric acid is of universal occurrence may be assumed from the
+fact of the almost universal occurrence of vegetable life on the
+earth's surface; for plants are unable to grow without it. While thus of
+practically universal occurrence, its amount in most soils is very
+trifling. As the only source of it in the soil is from the
+disintegration of the different rocks, a short description of its
+occurrence in the mineral kingdom may first be given.
+
+
+_Mineral Sources of Phosphoric Acid._
+
+It was first discovered in the mineral kingdom towards the close of last
+century; but we have only of late years ascertained any exact knowledge
+of its percentage in the different rocks out of which soils are formed.
+This has been shown in many cases to be very trifling. It most
+abundantly occurs as _apatite_, a mineral consisting of calcium
+phosphate, with small quantities of calcium fluoride or calcium
+chloride. This apatite, or phosphorite, is found in certain parts of the
+world in large masses; but as a rule, it only occurs in small quantities
+in most rocks. It may be stated that the older rocks are, as a general
+rule, richer in it than those of more recent formation; and Daubeny has
+drawn attention to this fact as furnishing a useful guide in estimating
+the probable richness of a soil in phosphoric acid. The older,
+therefore, a rock is, the richer it is likely to be in phosphoric acid.
+
+
+_Apatite and Phosphorite._
+
+Of apatite there are a variety of kinds, which differ in their
+appearance as well as in their composition. It occurs chiefly in a
+crystalline form, and is found sometimes in regular crystals, but it
+also occurs in the amorphous form. In colour it may be white, yellow,
+brown, red, green, grey, or blue. Two classes of apatite are found. The
+first consists of calcium phosphate along with calcium fluoride; and in
+other kinds of apatite the calcium fluoride is replaced by calcium
+chloride. Phosphorite is another name for apatite, but is chiefly
+applied to impure amorphous apatite. The percentage of phosphate of lime
+in different kinds of apatite may be stated at from 70 to 90 per cent.
+It occurs in very large quantities in Canada, the Canadian apatite being
+very rich in phosphate of lime--80 to 90 per cent. In many parts of the
+world it forms portions of mountain-masses, and is quarried, crushed,
+and used for artificial manurial purposes. Further details of its
+occurrence and chemical composition will be found in the Appendix.[123]
+
+
+_Coprolites._
+
+In many parts of the world round nodules, largely consisting of
+phosphate of lime, have been found, to which the name "coprolites" has
+been given, on the assumption that they consisted of fossilised animal
+excrements. These coprolites, or osteolites as they have also been
+called, vary in the percentage of phosphate of lime they contain.
+Sometimes this amounts to 80 per cent, but as a rule it is very much
+less. They also in the past have formed an important source of manure,
+and will be referred to subsequently.
+
+
+_Guano._
+
+We have, lastly, phosphoric acid occurring in large quantities in
+guano-deposits, chiefly found on the west coast of South America. These
+deposits, which have been of enormous importance as a source of
+artificial manure, are of animal origin, and will be discussed at
+considerable length in a chapter specially devoted to the subject; so
+that we need do no more than mention them here.
+
+Phosphoric acid is also found in the form of phosphate of lime in
+certain rocks as "layers" and "pockets."
+
+
+_Universal Occurrence in Common Rocks._
+
+But while it is thus found in considerable quantities in various parts
+of the world, and while no anxiety need thus be felt as to its abundance
+for artificial manurial purposes, its occurrence in the common rocks,
+which, as we have already pointed out, is practically universal, is in
+many cases very minute.
+
+Fownes first identified it in the felspathic rocks in 1844; and since
+then its percentage in granite, lava, trachyte, basalt, porphyry,
+dolomite, gneiss, syenite, dolerite, diorite, and a number of other
+rocks, has been determined by numerous investigators. For analyses of
+these rocks the reader is referred to the Appendix.[124]
+
+
+_Occurrence in the Soil._
+
+That no soil is actually without phosphoric acid is highly probable, but
+in many soils it is present in the merest traces, and even in fertile
+soils it is rarely present in quantities over two-tenths of a per cent;
+while half that amount may be taken as an average for most fairly
+fertile soils. This would be about 3500 lb. per acre, calculating the
+soil to a depth of 9 inches. In exceptional cases it has been found to
+the extent of .3 per cent; and in the famous Russian _black earth_ it
+has been found to amount to .6 per cent.[125] Like nitrogen, it is found
+in greatest amount in the surface portion of the soil, but its amount at
+different depths does not vary to the same extent as we have found to be
+the case with nitrogen.
+
+
+_Condition in which Phosphoric Acid is present in the Soil._
+
+Unlike nitrogen, phosphoric acid occurs in the soil almost entirely in
+an _insoluble_ form; and when applied to the soil in a soluble form, is
+speedily converted into an insoluble condition. Its most commonly
+occurring forms are as phosphates of lime, iron, and alumina. These
+facts are of importance to remember, as they explain why phosphoric acid
+is not found in drainage-water in any quantity. It also shows how little
+the risk of loss from drainage is in the application of artificial
+phosphatic manure to the soil.
+
+
+_Occurrence in Plants._
+
+The percentage of phosphoric acid in plants, like other
+ash-constituents, is subject to considerable variation, and depends on a
+variety of conditions, such as the state of the plant's development,
+nature of soil, climate, season, treatment with manures, &c. All these
+conditions have a certain influence. The different parts of the plant
+have been found to contain it in different quantities. The tendency of
+phosphoric acid is to travel up to the higher portions of the plant with
+the progress of growth, and to finally accumulate in the seed. As
+illustrating this, it may be mentioned that the inner portion of the
+stalk of a ripe oat-plant has been found to contain only a seventeenth
+of the amount of phosphoric acid found in the same portion of the stalk
+of a young oat-plant. Similarly it may be mentioned that, while the ash
+of the grain of rye and wheat contains nearly half their weight of
+phosphoric acid, the percentage present in the ash of other parts of the
+plant amounts only to from 5 to 16 per cent. The percentage of
+phosphorus is greater in young plants than in mature plants; it is
+greater also in quickly developed plants than in slowly developed
+plants.
+
+In the plant, phosphorus is present chiefly in the albuminoids; and its
+absorption from the soil takes place in greatest quantity during the
+period of maximum growth. In beans and peas an oil containing phosphorus
+has been found.
+
+
+_Occurrence in Animals._
+
+That phosphorus in different forms exists in animal tissue is well
+known. It is found both in the brain and in the nerves, as well as in
+nearly all the fluids of the animal body. It is, however, in the bones
+that it is most abundant, the mineral portion of which is almost
+entirely made of phosphate of lime,--a fact which renders bones such a
+valuable artificial manure. Altogether, phosphoric acid occurs in the
+animal body to the extent of 2.3 per cent. There is a point which we
+shall have occasion to draw the student's attention to further on in
+discussing the nature of farmyard manure--and that is, that the urine of
+the common farm animals is practically devoid of phosphoric acid.
+
+
+_Sources of Loss of Phosphoric Acid in Agriculture._
+
+As we have already done in the case of nitrogen, we may now attempt to
+form some conception of the sources of loss and gain of phosphoric acid
+in the soil. The sources of loss may be divided into natural and
+artificial. Of natural sources of loss we have only one, and that is
+loss by drainage.
+
+
+_Loss of Phosphoric Acid by Drainage._
+
+We have already seen that the condition in which phosphoric acid is
+present in the soil is as insoluble phosphate. In drainage-water it
+occurs in mere traces. Minute though the amount seems when stated as
+percentage, and small as it appears beside the loss (from the same
+source) of nitrogen, it is yet, if considered for large areas,
+sufficiently striking. Thus it has been estimated that in the river Elbe
+there is carried off by drainage from the fields of Bohemia 2-3/4
+million pounds (1200 tons) of phosphoric acid annually. This, it is
+true, is a very trifling amount compared with the annual loss of
+nitrogen from an equal area; but then it must be remembered, on the
+other hand, the sources of gain to the soil of this ingredient are not
+so numerous as are those of nitrogen, the only sources of phosphoric
+acid being in the manure applied to the soil, and that coming from the
+gradual disintegration of phosphatic minerals.
+
+
+_Artificial Sources of Loss._
+
+The other sources of loss may be classed under the term artificial, and
+are connected with agricultural practice. Just as we have seen that in
+the case of nitrogen enormous quantities of that substance are
+constantly being removed from the soil in those crops which are
+consumed off the farm, so, too, enormous quantities of phosphoric acid
+are being removed in the same way. As illustrating this fact, it may be
+mentioned that Professor Grandeau has recently estimated that in the
+entire crops grown in France in one year there are about 298,200 tons of
+phosphoric acid; while the amount returned in the dung of farm animals
+is only 157,200, or only about one-half of what is removed in the crops,
+leaving a deficit of 147,000 tons to be made good by the addition of
+artificial phosphatic manures, if the fertility of the soil is to be
+maintained. The same authority has calculated that in the bones of the
+entire farm animals in France there is no less a quantity than 76,820
+tons of phosphoric acid.
+
+As an example of how, in many cases, the amount of phosphoric acid
+removed from the farm is very often much greater than that restored, a
+case quoted by Crusius may be cited. This was a farm of 670 acres
+(Saxon) which had received only farmyard manure, and from which, during
+sixteen years, 985.67 cwt. of phosphoric acid had been sold off in the
+crops; while only 408.33 cwt. had been restored in the manure, leaving a
+loss of 577.34 cwt.
+
+
+_Phosphoric Acid removed in Milk._
+
+A further source of loss is the phosphoric acid removed in milk. In the
+total annual yield of milk from one cow there may be from 11 to 12 lb.
+of phosphoric acid.
+
+
+_Loss in Treatment of Farmyard Manure._
+
+The risks of loss of phosphoric acid in the treatment of farmyard manure
+are not so great as in the case of nitrogen. There is, however, a
+considerable risk, through want of proper precautions, of the soluble
+phosphates being washed away by rain.
+
+
+_Loss in Sewage._
+
+The loss of phosphoric acid incurred by the present method of sewage
+disposal is not so large as the loss of nitrogen, inasmuch as the
+quantity of phosphoric acid contained in human excreta is very much
+less. Roughly speaking, it may be said to amount to a little less than
+one-third of the nitrogen lost in this way.
+
+
+_Sources of Artificial Gain of Phosphoric Acid._
+
+To balance these losses, we have a practically unlimited supply of
+mineral phosphates for application as artificial manure, as well as
+large quantities of other manures, many of them already mentioned in
+connection with nitrogen, such as bones and guanos of all kinds. Quite
+recently, also, a large source of phosphoric acid has been opened up in
+the basic slag, a rich phosphatic bye-product obtained in considerable
+quantity in steel-works from the basic process of steel manufacture. We
+have also large quantities of phosphoric acid in the imported
+feeding-stuffs, for statistics regarding which we would refer our
+readers to a previous chapter. The question of the actual amount
+contained in these sources is not of the same interest as in the case of
+nitrogen, and need not therefore detain us. We have sufficiently
+indicated the importance of phosphoric acid in agriculture by the
+statements above given. All further consideration of phosphoric acid
+must therefore be deferred to future chapters.
+
+
+FOOTNOTES:
+
+[123] See Appendix, Note I., p. 210.
+
+[124] See Appendix, Note II., p. 211.
+
+[125] These results, as indeed all soil percentages, are calculated on
+the soil in a dry condition.
+
+
+
+
+APPENDIX TO CHAPTER V
+
+
+NOTE I. (p. 201).
+
+COMPOSITION OF APATITE (Voelcker).
+
+ (_Krageröe, Norway._)
+
+Lime 52.16
+Phosphoric acid 41.25
+Chlorine 4.10
+Fluorine 1.23
+Oxide of iron 0.29
+Alumina 0.38
+Potash and soda 0.17
+Water 0.42
+ ------
+ 100.00
+ ======
+
+Apatite is found in considerable quantities in America, Germany, France,
+Spain, Hungary, Norway, and Great Britain. According to Rose, apatite is
+made up of three molecules of tribasic calcium phosphate (Ca(PO_4)_2),
+combined with one molecule of calcium fluoride (Ca F_2) or one molecule
+of calcium chloride (CaCl_2) respectively.
+
+The composition of the pure mineral should be--
+
+ _Chlorapatite._
+ Per cent.
+Calcium phosphate 89.38
+Calcium chloride 10.62
+
+ _Fluorapatite._
+
+Calcium phosphate 92.31
+Calcium fluoride 7.69
+
+
+NOTE II. (p. 203).
+
+The following is a list of the commoner rocks in which the percentage of
+phosphoric acid has been determined. The results are taken from analyses
+by Nesbit, Schramm, Bergemann, Rose, Dehérain, Handtke, Petersen,
+Nessler, Muth, Fleischmann, Storer, and others:--
+
+ Per cent.
+Felspar 1.7
+Granite 0.09 0.25 0.58 0.68
+Lava 1.21 1.8
+Trachyte 0.30 0.66
+Basalt 0.50 1.11
+Porphyry 0.26
+Marl 1.45 2.31 3.8
+Calcareous stones 0.064 0.176
+Dolomite 1.24
+Lias chalk 1.39
+Gneiss 0.18 0.78 1.51
+Syenite 0.10
+Dolerite 0.3 1.1 1.2
+Diorite 0.5 0.69
+
+
+
+
+CHAPTER VI.
+
+THE POSITION OF POTASH IN AGRICULTURE.
+
+
+We may, lastly, consider the position of _potash_ in agriculture, the
+only ash ingredient of the plant, in addition to phosphoric acid, which
+it is as a rule necessary to add as a manure.
+
+
+_Potash of less Importance than Phosphoric Acid._
+
+It is of far less importance than phosphoric acid, from the fact of its
+much more abundant occurrence in the soil, as well as from the fact that
+under the ordinary conditions of agriculture, although removed from the
+soil in considerable quantities by crops, it finds its way back again in
+the farmyard manure; for it has not the same tendency to accumulate in
+large quantities in the grain or seed as we have seen to be the case
+with phosphoric acid. On this account straw contains a much greater
+proportion of potash than phosphoric acid, and hence farmyard manure may
+be regarded as fairly rich in potash.
+
+
+_Occurrence of Potash._
+
+Of all sources of potash the ocean must be regarded as the chief.
+Millions and millions of tons are present in a state of solution in the
+salt water of the ocean.[126] Like phosphoric acid, its occurrence in
+the rocks forming the earth's crust may be said to be practically
+universal. Many of the commonly occurring rocks and minerals are
+extremely rich in it, and by their disintegration furnish large
+quantities to the soil. Some of these rocks contain it in such abundance
+that they have been tried as potash manures; and were other more
+valuable sources less available than they actually are, such a practice
+might well be recommended. A volcanic rock known as _palagonite_, and
+that most commonly occurring of all potash minerals--viz., felspar--have
+both been experimented with in this way with considerable success.
+
+
+_Felspar and other Potash Minerals._
+
+That felspar should prove, when finally ground, a valuable source of
+potash, is not to be wondered at when we remember that some varieties of
+it contain over 16 per cent. It has been calculated that a single cubic
+foot of this mineral is sufficient to supply an oak-wood, covering a
+surface of 26,910 square feet, with potash for a period of no less than
+five years.[127] Some idea of the enormous _potential_ fertility of a
+soil containing felspar, so far as potash is concerned, may be obtained
+from this statement. It must be remembered, however, that it is only the
+orthoclase or potash felspars which contain large quantities of
+potash--other felspathic rocks, such as oligoclase and labradorite,
+being comparatively poor in it. Another commonly occurring mineral which
+is rich in potash is mica, which has been found to contain from 5 to 13
+per cent. From this it follows that rocks which have large amounts of
+these minerals in their composition--such as granite, for example, which
+often contains 5 or 6 per cent of potash--form by their disintegration
+soils rich in this ingredient.
+
+
+_Stassfurt Salts._
+
+But in addition to the sources of potash already mentioned, it exists in
+other forms in the earth's surface. Till within recent years it was
+obtained for commercial purposes from the ashes of plants, which, as we
+shall immediately see, are extremely rich in this ingredient; from salt
+water--this source giving rise to the so-called "salt gardens" on the
+coast of France; and from nitre soils in different parts of India,
+referred to already at considerable length. Large mineral deposits,
+however, have been recently discovered in the neighbourhood of Stassfurt
+in Germany, and have since their discovery supplied all the potash
+required for manurial and other purposes. In these deposits (similar
+ones have also been found at Kalusz in the Carpathian Mountains) there
+are no less than five different minerals which contain potash. The form
+in which it is present is as sulphate or chloride, so that it is readily
+available for plants, and is of altogether very much greater value than
+the form in which it occurs in the minerals already mentioned--viz., as
+an insoluble silicate. Of the Stassfurt potash salts, the best known as
+a manure is _kainit_, which contains about 32 per cent of sulphate of
+potash. A list of the other potash minerals, with the particulars of
+their composition and the percentage of potash they contain, will be
+found in the Appendix.[128]
+
+
+_Occurrence of Saltpetre._
+
+We have already had occasion, in Chapter IV., when discussing the
+question of nitrification, to refer to the occurrence of nitrate of
+potash in certain soils in India, which have formed a large source of
+saltpetre used in commerce in the past.
+
+
+_Occurrence of Potash in the Soil._
+
+From what has been said regarding the richness in potash of certain
+commonly occurring minerals, such as felspar, it is only natural to
+infer that most soils must contain large quantities of this substance;
+and this is so. The wonder is that potash, when applied as an artificial
+manure, should have such a marked effect in increasing the fertility of
+the soil, as is often the case. We must remember, however, that although
+a soil may contain large quantities of potash, there may be a very small
+percentage of the whole in an available form for the plant's needs.
+
+
+_Potash chiefly in insoluble Condition in Soils._
+
+Potash occurs almost entirely in soils in a very insoluble form--viz.,
+combined with silica as a silicate of potash. It is only by the slow
+disintegration of potash rocks that the potash they contain is set free
+for plant uses. When it is applied as an artificial manure, on the other
+hand, it is in a soluble form. In most soils the amount soluble in water
+probably lies between .001 and .009 per cent; that soluble in dilute
+acid solutions from .1 to .5 per cent; and that insoluble from .2 to 3.5
+per cent of the soil. It is highly probable that a certain quantity of
+potash in the soil may exist in combination with humic and ulmic acids,
+forming insoluble potassium humates and ulmates.
+
+
+_Potash in Plants._
+
+Of all the ash ingredients of plants, potash is the most abundant, as it
+forms on an average about 50 per cent of the total ash of plants--about
+90 per cent of the alkalies. The ash of plants, indeed, was for long
+the chief source of potash. Certain plants remove very large quantities
+from the soil. Of these roots, potatoes, the vine, the tobacco-plant,
+and hops may be mentioned as examples. It is present in large quantities
+in the grain of cereals, although, as we have already pointed out, not
+to the same proportional extent as phosphoric acid. It is found in the
+plant's extremities, such as twigs and new leaves, in greatest
+abundance.[129]
+
+
+_Potash in the Animal Tissue._
+
+It is also found in all parts of the animal body. Especially rich in
+potash salts are the blood corpuscles, which contain about ten times the
+amount contained in the serum. It is found in especial abundance in the
+fleece of sheep, which may contain more potash than that in the whole
+body of the sheep. Animal urine also contains potash in considerable
+quantities.
+
+
+_Sources of Loss of Potash._
+
+The capacity of the soil to retain soluble potash compounds, while not
+equal to its capacity for retaining phosphoric acid, is yet very much in
+excess of its capacity for retaining nitrates. The result is, that
+potash is only found in comparatively minute traces in drainage
+water.[130] Taking the same example as we already cited in illustration
+of the loss of phosphoric acid, we find that the amount carried away in
+the course of a year in the waters of the Elbe from Bohemia is
+97,000,000 lb. (43,300 tons).
+
+
+_Potash removed in Crops._
+
+The amount of potash removed by the different crops from the soil will
+be considered in a subsequent chapter. We need only say here that the
+class of crops which remove the largest quantity are the root crops,
+especially mangels. The loss is least in the case of the cereals. The
+amount of potash contained in the straw of cereals is about three times
+the amount of that removed in the grain.
+
+
+_Potash removed in Milk._
+
+Lastly, we may refer to the potash removed in milk, which, on an
+average, may be taken at 10 lb. per annum for each cow.
+
+
+_Potash Manures._
+
+Of potash manures the chief are the sulphate and the chloride, or, as it
+is commercially known, the "muriate." The chief source of potash manures
+are the Stassfurt deposits already referred to. Wood-ashes have also
+been used in large quantities in the past (chiefly as a potash manure),
+and in some parts of the world are still used. A considerable source of
+artificial potassic manures is the refuse manufacture of sugar-beet,
+such a large industry in Germany. Potash occurs as a constituent of
+certain other manures, more valuable for nitrogen and phosphoric acid,
+such as guano and dried blood.
+
+
+FOOTNOTES:
+
+[126] According to Boguslawski and Dittmar, the total amount of potash
+calculated as sulphate of potash in salt water equals 1141 × 10^{12}
+tons.
+
+[127] See Storer's 'Agricultural Chemistry,' vol. ii. p. 291.
+
+[128] See Appendix, Note I., p. 220.
+
+[129] See Appendix, Note II., p. 220.
+
+[130] According to Way, different samples of drainage waters were found
+only to contain from .00003 to .00031 per cent.
+
+
+
+
+APPENDIX TO CHAPTER VI.
+
+
+NOTE I. (p. 215).
+
+AMOUNT OF POTASH IN DIFFERENT MINERALS.
+
+Felspars--
+ Percentage of potash.
+ (_a_) Orthoclase { 9.11 10.28 11.07 12.12 12.47
+ { 13.49 14.35 15.21 16.7
+ (_b_) Oligoclase 0.50
+ (_c_) Labradorite 0.33
+Mica { 5.61 6.20 7.23 8.26 8.95
+ { 9.00 10.25 12.40 13.15
+Amphibole 0.25 2.96
+Pyroxene 0.34 2.48
+Leucite 13.60 18.61
+Zeolites 0.30 9.35 0.98 4.93
+
+Stassfurt potash salts-- Per cent.
+ (_a_) Polyhallite, _potassium sulphate_ 28
+ (_b_) Karnallite (KCl.MgCl_{2}6H_{20}), _potassium chloride_ 24 to 27
+ (_c_) Sylvin, pure _potassium chloride_.
+ (_d_) Kainit (K_{2}SO_{4}MgSO_{4}MgCl_{2}6H_{2}O), _potassium
+ sulphate_ 32
+ (_e_) Schoenite (K_{2}SO_{4}, MgSO_{4}, 6H_{2}O), pure
+ _potassium magnesium sulphate_.
+
+
+NOTE II. (p. 217).
+
+The quantity of potash obtainable from various plants in the manufacture
+of potashes on a large scale is illustrated by the following statements.
+1000 lb. of the following vegetative products yield the following
+quantities of potashes:--
+
+ lb.
+Old spruce-wood 1/2
+Old poplar-wood 3/4
+Old oak-wood 1-1/2
+Corn-stalks 17-1/2
+Bean-stalks 20
+Grape-vine twigs 40
+
+(Storer, 'Agricultural Chemistry,' vol. ii. p. 108.)
+
+
+
+
+PART III.
+
+MANURES
+
+
+
+
+CHAPTER VII.
+
+FARMYARD MANURE
+
+
+Farmyard manure is the oldest, and is still undoubtedly the most
+popular, of all manures. It has stood the test of long experience, and
+has proved its position as one of the most important of all our
+fertilisers. It is highly desirable, therefore, to make a somewhat
+detailed examination of its composition, and to see on what the
+variation in this depends; and, finally, to examine into the mode of its
+action as a manure.
+
+That it should prove a valuable manure is scarcely to be wondered at, as
+it is originally formed from vegetable substance, and as it therefore
+contains all the elements present in the plant itself.
+
+Its composition is very variable, and probably no two samples would
+yield exactly similar analyses. In this fact lies one of the chief
+difficulties of the treatment of the subject, and all statements made
+in the following pages as to its chemical composition must be taken as
+only _approximate_.
+
+We may divide its constituents into three classes.
+
+1. That portion due to _solid excreta_.
+
+2. The liquid portion, largely made up of dilute _urine_.
+
+3. The _straw_, or other material, which is used as litter.
+
+The composition of the manure will vary according to the proportion in
+which these three substances are present, as well as according to the
+composition of the substances themselves. It will consequently tend to a
+clearer apprehension of the subject if we first examine briefly the
+chemical composition of the solid excreta and urine of the farm animals.
+
+
+1. _Solid Excreta._
+
+The manurial value of the solid excreta of animals--_i.e._, the
+proportion they contain of _nitrogen_, _phosphoric acid_, and
+_potash_--depends on a variety of conditions.
+
+The solid excreta of horses, sheep, cows, and pigs, are well known to
+possess different properties, as well as to vary in their composition.
+
+What, however, has a still greater influence is the nature of the food.
+This is owing to the fact that the solid excreta are made up of
+undigested food. We can scarcely expect the same quality of solid
+excreta from an animal fed on poor diet as from an animal fed on very
+much richer diet. Again, the percentage of the food voided in the solid
+excreta varies in the case of different animals.[131]
+
+Another consideration which enters into the question is the age, as well
+as the treatment, of the animal. A young animal, during the period of
+its growth, absorbs from its food into its system a larger quantity of
+the three fertilising substances, nitrogen, phosphoric acid, and potash,
+than is the case with an adult animal whose weight is neither increasing
+nor diminishing. A working horse, similarly, will return more of the
+nitrogen, phosphates, and potash in its dung than one not at work and
+which is permitted to gain in weight. The nature of the composition of
+the solid excreta, therefore, will depend on the nature of the _food_,
+_age_, _breed_, _condition_, and _treatment_ of the animal.
+
+Let us now investigate shortly the influence of the above
+considerations. The solid excrements of the common farm animals are
+generally distinguished from one another according to the rate at which
+they decompose or ferment on keeping. Thus horse-dung is generally known
+as a "hot" dung; while cow-dung, on the other hand, is known as "cool."
+Why this should be so is not absolutely clear. Probably it is owing to
+the fact that the former contains less water, as well as to the fact
+(and this probably has more to do with it) that it contains a larger
+percentage of fertilising matter, especially nitrogen, thus affording
+conditions more favourable for rapid fermentation than in the case of
+the more moist and less rich cow-dung.
+
+The composition of the solid excreta of various animals, as we have just
+said, varies with the nature of their food; so that it is impossible to
+take any analyses as absolutely representing its composition. It may be
+interesting, however, to compare the analyses of samples of horse-dung
+with those of some other of the commoner farm animals, with a view to
+obtaining an _approximate_ idea of this difference.
+
+Stoeckhardt has found that in 1000 lb. of the fresh solid excreta of the
+animals below mentioned, there were the following amounts of _nitrogen_,
+_phosphoric acid_, and _alkalies_:--
+
+-----------------------+----------+-------------+-------------+-----------
+ | | | PHOSPHORIC |
+ | | NITROGEN. | ACID. | ALKALIES.
+ | WATER. |-----+-------+-----+-------+---+-------
+ | | |Reduced| |Reduced| |Reduced
+ | | | to | | to | | to
+-----------------------+----+-----+-----+-------+-----+-------+---+-------
+ |lb. | per | lb. | per | lb. | per |lb.| per
+ | |cent.| | cent. | | cent. | | cent.
+Horses (winter food) |760 |76 |5 | .50 |3-1/2| .35 | 3 | .30
+Cows (winter food) |840 |84 |3 | .30 |2-1/2| .25 | 1 | .10
+Swine (winter food) |800 |80 |6 | .60 |4-1/2| .45 | 5 | .50
+Sheep (2 lb. hay per | | | | | | | |
+ diem) |580 |58 |7-1/2| .75 |6 | .6 | 3 | .30
+-----------------------+----+-----+-----+-------+-----+-------+---+-------
+
+From the above table it will be seen that the sheep's dung contains the
+least percentage of _water_, and is richer in _nitrogen_ and _phosphoric
+acid_ than any of the other three. The percentage of alkalies, of which
+the most important is potash, is, however, not so large. This may be
+accounted for by the interesting and well-known fact that a large
+percentage of potash is to be found in the wool of sheep.[132]
+
+The solid excrement of the sheep is, therefore, weight for weight, the
+most valuable as a manure, as it contains more nitrogen and phosphates
+than the others, and at the same time is much drier.
+
+If, however, we compare the composition of the solid excreta in a dry
+state, we shall find that the following are the results (basing our
+calculation on Stoeckhardt's analyses):--
+
+ Nitrogen, Phosphoric acid, Alkalies,
+ per cent. per cent. per cent.
+
+Horse 2.08 1.45 1.25
+Cow 1.87 1.56 0.62
+Pig 3.00 2.25 2.50
+Sheep 1.78 1.42 0.71
+
+It will be seen from the above that the dry substance of the solid
+excreta of the pig is richest in fertilising substances. Too much
+stress, however, as has already been pointed out, must not be put on any
+single analysis, as so much depends on various conditions, especially
+the food.[133] The most reliable method of studying this question,
+therefore, is to study it in its relation to the food consumed. Wolff
+has calculated from numerous investigations that, with regard to the
+amount of solid excreta produced by the food, the following percentage
+of _organic matter_, _nitrogen_, and _mineral substances_, originally
+present in the dry matter of the food, is voided in the dung:--
+
+ Cow. Ox. Sheep. Horse. Average.
+
+Organic matter 39.5 42.5 44.0 44.1 42.5
+Nitrogen 47.5 33.9 46.7 32.4 40.1
+Mineral substances 53.9 64.6 57.9 62.5 59.7
+
+There is one fact to be borne in mind in estimating the manurial value
+of the dung of different animals--viz., that the quantity of dung voided
+by one animal is much greater than that voided by another. Thus the
+amount voided by the cow, for example, is much greater than that voided
+by the horse; so that, in this way, the inferior quality of the former
+is, to some extent, compensated for by its greater quantity.
+
+
+2. _Urine._
+
+The solid excreta possess, however, very much less manurial value than
+the urine. The former, as already stated, are undigested
+food-substances: any fertilising matters which they contain are such as
+have failed to be digested or absorbed into the animal system. The
+urine, on the other hand, contains those fertilising substances which
+have been digested.
+
+The amount of nitrogen and mineral matter, however, in the urine, does
+not represent necessarily the total amount of these substances. Thus, in
+the case of a growing or fattening animal, there is always a certain
+amount of these substances being absorbed to build up the animal tissue
+and put on flesh.
+
+In this respect it will be seen that the composition of urine will vary
+in the same way as that of the dung. In the case of the urine, however,
+there is a compensating influence to be taken into account. Urine is a
+waste product, and there is more waste in a young than in an adult
+animal.
+
+Another very important condition which determines the composition of
+urine is the nature of the food, especially the quantity of water drunk.
+This, of course, is obvious: the more water drunk, the poorer must the
+composition of the urine be. But here again, as in the case of the dung,
+this is largely compensated for by the total quantity voided--the more
+dilute the urine, the larger will its quantity be; so that the inferior
+quality is in this way made up for by its increased quantity.
+
+Keeping in mind, then, the fact we have just stated--viz., that the
+composition of urine will vary according to different conditions--we may
+obtain an approximate idea of what its composition is from the following
+results of analyses by Stoeckhardt. In 1000 parts the following
+quantities of _water_, _nitrogen_, _phosphoric acid_, and _alkalies_
+were found to be present.
+
+From the following table it will be seen that the urine of swine
+(containing 97 per cent of water) is much poorer in nitrogen and
+alkalies than is the case with the urine of the sheep, horse, or
+cow.[134] While this is the case, the amount of phosphoric acid it
+contains is greater than that contained in the sheep's urine.
+
+-------------------+------------+-------------------------+------------
+ | | | Phosphoric |
+ | Water. | Nitrogen. | Acid. | Alkalies.
+ +------+-----+------+-----+------+-----+------+-----
+ | Per | Per | Per | Per | Per | Per | Per | Per
+ | 1000 |cent.| 1000 |cent.| 1000 |cent.| 1000 |cent.
+ |parts.| |parts.| |parts.| |parts.|
+-------------------+------+-----+------+-----+------+-----+------+-----
+Sheep (2 lb. hay }| 865 | 86.5| 14 | 1.4 | .5 | .050| 20 | 2.0
+ per diem) }| | | | | | | |
+ | | | | | | | |
+Swine (winter food)| 975 | 97.5| 3 | .3 | 1.25 | .125| 2 | .2
+ | | | | | | | |
+Horses (hay and }| 890 | 89.0| 12 | 1.2 | - | - | 15 | 1.5
+ oats) }| | | | | | | |
+ | | | | | | | |
+Cows (hay and }| 920 | 92.0| 8 | .8 | - | - | 14 | 1.4
+ potatoes) }| | | | | | | |
+-------------------+------+-----+------+-----+------+-----+------+-----
+
+Phosphoric acid is present in the urine of the farm animals in the most
+minute traces: practically, it may be considered to be wanting in the
+urine of the horse and the cow, and is present only in small quantities
+in sheep's urine. The pig's urine, indeed, contains it in larger
+quantities; but the percentage is still so small as to justify the
+statement that the urine of the common farm animals is not a complete
+manure, and must be supplemented by phosphates, if it is to be used
+alone. The incomplete nature of urine as a manure constitutes a strong
+argument in favour of its being applied along with the solid excreta,
+which contain, as we have seen, considerable quantities of phosphoric
+acid. It is on this account that the drainings of rotten manure-heaps
+are more valuable, from a manurial point of view, than urine itself,
+since these contain the soluble portion of the phosphates in the solid
+excreta.[135] The urine of all animals, however, is not equally poor in
+phosphates. In the case of flesh-eating animals, such as the dog, the
+urine is found to contain them in considerable quantities.
+
+The above tables show that the most valuable urine, weight for weight,
+is that of the sheep, as it contains the largest amount of alkalies
+(including potash) and nitrogen; that the urine of the horse comes next;
+then that of the cow; while, as has already been pointed out, that of
+the pig is the poorest.
+
+In order to make our survey of the composition of urine uniform with
+that of the dung, let us see how the urine of the common farm animals
+compares in the matter of the composition of its dry substance. The
+following results (basing our calculations on Stoeckhardt's figures,
+previously given) show this:--
+
+ Nitrogen, Phosphoric acid, Alkalies,
+ per cent. per cent. per cent.
+
+Pig 12.0 5 8
+Horse 10.9 trace 13.6
+Sheep 10.4 3.7 14.9
+Cow 10.0 trace 17.5
+
+From these figures we see that the dry substance of the urine of the pig
+is richest in nitrogen and phosphoric acid, but poorest in alkalies, of
+the four common farm animals; that of the horse comes next in the amount
+of nitrogen it contains, but that, on the whole, there is very little
+difference between the horse, cow, and sheep in this respect.[136]
+
+As in the case of the dung, this subject is best studied in relation to
+the food consumed. We are again indebted to Wolff's investigations for
+valuable information on this point. He has found that the following
+percentages of _organic matter_, _nitrogen_, and _mineral substances_,
+originally present in the dry matter of the food, are voided in the
+urine:--
+
+ Cow. Ox. Sheep. Horse. Average
+
+Organic matter 4.0 4.4 2.0 3.3 3.4
+Nitrogen 31.0 54.8 42.3 60.7 47.2
+Mineral substances 43.1 34.3 41.0 37.5 39.0[137]
+
+We have now considered briefly the composition of the solid excrements
+and urine of the common farm animals, and have also enumerated some of
+the principal causes of the variation in their composition.
+
+The solid excreta consist, as we have seen, of _undigested_ food, while
+the urine contains the manurial ingredients of the food which have been
+_digested_ by the animal system.[138] The latter is, weight for weight,
+as a rule, very much more valuable as a manure than the former. From
+the table given in the Appendix[139] it will be seen that the
+proportions of the nitrogen and ash-constituents originally present in
+the food consumed, which are voided in the excrements, vary with
+different circumstances. Wolff, in summarising his results, points out
+that, as a rule, the solid and liquid excrements will contain about 46
+per cent of the organic matter, 87.3 of the nitrogen, and 98.7 of
+mineral matter; while the experiments of Lawes and Gilbert at Rothamsted
+show that, with fattening oxen and sheep and with horses, more than 95
+per cent of the nitrogen and 96 per cent or more of the ash-constituents
+are voided in the manure. The pig retains a larger proportion of the
+nitrogen--about 85 per cent appearing in the manure--while in the
+milking-cow only about 75 per cent is returned in the excrements.
+Generally speaking, we may say that the nitrogen originally present in
+the food suffers very little loss in passing through the animal system,
+and that, practically speaking, the ash-constituents suffer no loss
+whatever.
+
+As to the distribution of the manurial ingredients, much will depend on
+the nature of the food. Almost invariably more than a _half_ of the
+total nitrogen excreted will be found in the urine, in many cases very
+much more.[140] Of the mineral constituents, about a third on the
+average may be said to be excreted in the urine. Of this mineral matter
+it may be noted that nearly all the alkalies (potash and soda), or about
+98 per cent, are found in the urine. Of phosphoric acid and lime, on the
+other hand, there are the merest traces in the urine. Horse-urine,
+however, is an exception with regard to lime, as it contains about 60
+per cent of the lime consumed in the food. For information on the
+subject of pig-manure the reader is referred to Appendix, Note V.[141]
+
+Before passing from this part of the subject, it may be desirable to
+place before our readers the composition of the dung and urine taken
+together, so that we may be able to form some idea of their relative
+value, weight for weight. As the nitrogen constitutes by far the most
+valuable portion of the manurial ingredients, it will be sufficient if
+we compare them as to their percentage of this ingredient.
+
+ Water, Nitrogen, Calculated on
+ per cent. per cent. dry substance, Analyses by
+ per cent.
+Sheep 67 .91 2.7 Jürgensen.
+Horse 76 .65 2.7 Boussingault.
+Pig 82 .61 3.4 Boussingault.
+Cow 86 .36 2.6 Boussingault.
+
+From these figures we see that, in their natural condition, the excreta
+of the sheep are the most valuable; those of the horse and pig coming
+next; while those of the cow are the poorest, containing one-third as
+much nitrogen as those of the sheep, and one-half as much as those of
+the horse and pig. This difference, however, is due almost entirely to
+the different percentage of water the excreta of the various animals
+contain in their natural state; for in the dry state they are seen to
+contain, with the single exception of the pig, practically the same
+amount.
+
+In conclusion, then, the important points to be noticed are--
+
+1. That in the passage of the food through the system of the common farm
+animals, only a very small percentage of the fertilising substances,
+nitrogen, phosphoric acid, and potash, is assimilated and retained in
+the animal body; and that, therefore, theoretically at least, the
+excreta should contain nearly the same amount of fertilising matter as
+the food originally did.
+
+2. That even in the case of a fattening animal, the loss of fertilising
+matter sustained by the food in passing through the system is not great.
+
+3. That with regard to the total amount of solid excreta and urine
+voided, the latter contains, as a rule, more nitrogen than the former;
+the nitrogen in the urine, further, being more valuable, as it is in a
+soluble condition.
+
+4. That as regards the distribution of the ash-constituents, _lime_,
+_phosphoric acid_, and _magnesia_ are almost entirely found in the solid
+excrements; while the urine contains nearly all the _potash_.
+
+5. That the best results can be expected only when the liquid and solid
+excreta are used together as a manure.
+
+As the composition of the manure depends so largely on the nature of the
+food, a table will be found in the Appendix, Note VI.,[142] containing
+the manurial composition of some of the commoner feeding-stuffs.
+
+
+3. _Litter._
+
+We have now to consider the third constituent of farmyard manure--viz.,
+the _litter_, which generally consists of straw.
+
+The uses of the litter, in addition to providing a dry and comfortable
+bed for the animal, may be briefly summed up as follows:--
+
+1. To absorb and retain the liquid portion of the excreta.
+
+2. To increase the quantity of the manure, and thus secure its more
+equal distribution when applied to the field than could otherwise be
+done.
+
+3. To add to its value as a manure, both physically and chemically.
+
+4. To retard and regulate the decomposition of the excreta.
+
+Of course litter also performs a very useful function sanitarily,
+inasmuch as it serves to keep the stall or byre fresher and cleaner, and
+more free from noxious gases, which it absorbs, than would otherwise be
+the case.
+
+_Straw_ is almost universally used for this purpose. Besides being one
+of the bye-products of the farm, it is admirably suited in many ways,
+both owing to its peculiar shape--its tubular structure being
+excellently adapted for this purpose--as well as on account of its
+composition, being largely composed of cellulose, a very absorptive
+substance. Straw thus possesses considerable absorptive power. In
+manurial ingredients it is not very rich; for, of the various parts of
+the ripened plant, straw contains the least percentage of nitrogen and
+phosphates. This is due to the fact that, as the straw ripens, a
+considerable proportion of these ingredients passes up from the stalk to
+the seeds, where they are retained.
+
+Generally speaking, straw may be said to contain not more than _a half
+per cent_ of nitrogen--_i.e._, 11.2 lb. per ton. Its percentage of
+nitrogen varies, of course; the recorded analyses[143] for wheat-straw
+ranging from .22 to .81 per cent, or furnishing an average of .48 per
+cent--_i.e._, 10.75 lb. per ton. Barley-straw is somewhat richer in
+nitrogen, the recorded analyses ranging from .41 to .85 per cent, or
+giving an average of .57 per cent--_i.e._, 12.76 lb. per ton; while
+oat-straw is the richest of the commoner straws, ranging from .32 to
+1.12 per cent, an average of .72 per cent--_i.e._, 16.12 lb per ton.
+
+Of mineral matter, however, straw contains a very much larger
+percentage, proportionally, than of nitrogen; for, with the exception of
+phosphates, there is a considerable quantity of inorganic fertilising
+matter, in the shape of potash, lime, &c., present in
+
+ Composition of Straw.[144]
+-----------------+---------------+------------------------+--------
+ | Ash. | Composition of Ash. |
+ +------+--------+------------------------+
+ | | | Lb. per ton. |
+ | | Lb. |-------+----------+-----| Number
+ | Per | per |Potash.|Phosphoric|Lime.| of
+ | cent.| ton. | | Acid | |Analyses
+-----------------+------+--------+-------+----------+-----+--------
+Wheat (winter) | 5.54 | 124.09 | 18.61 | 5.05 | 7.18| 8
+Wheat (summer) | 5.14 | 115.13 | 25.76 | 6.47 | 7.12| 6
+Rye (winter) | 5.33 | 119.39 | 20.61 | 5.89 | 9.73| 8
+Rye (summer) | 6.14 | 137.53 | 42.41 | 6.73 |10.53| 1
+Barley | 4.90 | 109.76 | 26.83 | 5.75 | 8.73| 8
+Oats | 5.09 | 114.01 | 26.22 | 4.17 | 9.12| 4
+-----------------+------+--------+-------+----------+-----+--------
+
+it. Of total ash ingredients, on an average, there are generally about 5
+per cent--or 112 lb. per ton. The largest percentage of the fertilising
+matter in this 5 per cent is potash, which varies in the ashes of the
+straws of the commoner crops from 30 to 15 per cent. The above table
+will show the variation in composition of the straws of some of the
+commoner farm crops, and may be valuable for purposes of reference. The
+crops are wheat (winter and summer), barley, oats, and rye (winter and
+summer), and the amount is also calculated in lb. per ton. The results
+represent the average of a number of analyses.[145] From the table it
+will be seen that the percentage of phosphates is, as has already been
+noticed, very small.
+
+But while straw is well adapted for the purposes for which litter is
+used, it is not the only substance. Its almost exclusive use as litter
+is largely owing to the fact that it is a bye-product of the farm.
+
+_Loam as Litter._--Generally speaking, any substance which has great
+absorptive as well as retentive powers for nitrogen and the soluble
+fertilising matters present in farmyard manure, and whose price is
+nominal, is well suited for acting as litter. Ordinary loamy soil
+possesses the above qualifications, and is, besides, a substance to be
+had for nothing, and, under certain circumstances and in certain
+countries, is actually used for this purpose, often along with straw. A
+great objection against loam, however, is that it forms a dirty litter.
+Moreover, it possesses a very small percentage of fertilising matter.
+The tendency, consequently, in using ordinary loam, would be to dilute
+the manure too much, besides retarding fermentation to an undesirable
+extent. Except, therefore, under very exceptional circumstances, loam is
+not to be regarded as a good litter.
+
+_Peat as Litter._--Some kinds of soil, however, are well suited for this
+purpose. Of these, the best are those rich in organic matter, the
+so-called peaty soils. Peat, when dried and freed from any earthy
+matter, forms an excellent absorbent of the liquid portion of the
+manure, surpassing in this respect straw itself. It is, further,
+generally very much richer in nitrogen--some peats having been found to
+contain between 4 and 5 per cent of nitrogen. In some thirty samples of
+peat analysed by Professor S. W. Johnson, the percentage of nitrogen
+varied from .4 to 2.9, giving an average of 1.5 per cent.
+
+While it has a very great capacity for absorbing liquids, it possesses
+in an unequalled degree the power of retaining the soluble nitrogen
+compounds. This is undoubtedly one of the most important properties
+which recommend peat for the purposes of litter.[146]
+
+Some interesting experiments on the value of peat-moss as a litter have
+been recently carried out by Dr Bernard Dyer.[147] From these
+experiments Mr Dyer has found that both its liquid-absorbing and
+liquid-retaining powers are very much greater than those of straw. While
+straw was only able to absorb three times its weight of water, peat-moss
+was found to absorb nearly ten times its weight. With regard to its
+water-retaining power, this was also found to be in excess of that of
+straw. Both these properties are, it need scarcely be pointed out, of
+very great value in a litter. Another point of interest in these
+experiments was the respective amounts of nitrogen absorbed and retained
+by the peat-moss and the straw. It was found that, in this respect, the
+peat-moss had again an advantage over the straw. Lastly, the manure
+produced by the peat-moss was shown to be richer in fertilising matter
+than that produced by the use of straw.[148] These experiments are
+interesting as demonstrating the fact that in peat-moss we have a
+substance which is capable of acting as an excellent substitute for the
+more costly straw, and which might increasingly be used as a fodder with
+great benefit to the farmer.
+
+Another substance which has been suggested as an excellent litter is the
+common _bracken-fern_. According to some analyses made by Mr John
+Hughes, the bracken, especially if cut in a young state, is a substance
+of considerable manurial value. When dried, it is very much richer in
+nitrogen, potash, and lime than straw. Its absorbent properties,
+however, are probably not so great. Where it can easily and cheaply be
+had, as in many parts of Scotland and Ireland, it might well be used for
+littering purposes.[149]
+
+_Dried leaves_ have also been used as a litter. Autumn leaves, however,
+contain a very small percentage of fertilising matter. This is due to
+the fact that the most of their potash, phosphoric acid, and nitrogen
+pass into the body of the trees at the approach of winter. According to
+Professor Storer, dried leaves only contain from .1 to .5 per cent
+potash,.006 to .3 per cent phosphoric acid, and about .75 per cent of
+nitrogen. Leaves, however, besides being poor in manurial ingredients,
+make a bad litter, as they ferment but slowly. There is in this
+fermentation a large quantity of cold sour humic acid formed, which
+seriously impairs the value of the manure.[150]
+
+Having now considered the composition of the three separate ingredients
+of farmyard manure--viz., the _dung_ or _solid excreta_, the _urine_,
+and the _litter_--we are in a position to consider the composition of
+farmyard manure. In this connection it will be well to consider
+separately the manures produced by the different farm animals.
+
+
+1. _Horse-manure._
+
+The composition of horse-manure is perhaps the most uniform of all the
+manures produced by the different farm animals. This is due to the fact
+that the food of the horse is generally of the same kind, consisting of
+oats, hay, and straw.
+
+The total excrements voided by a horse in a day have been calculated,
+according to the average of experiments by Boussingault and Hofmeister,
+at 28.11 lb., of which only 6.37 lb. consisted of dry matter.[151] These
+28.11 lb. contained .18 lb. of nitrogen and .92 lb. of mineral matter.
+The amount of straw necessary to absorb this amount of excrement may be
+stated at from 4 to 6 lb. The amounts of nitrogen and mineral matter in
+4 lb. of straw are .01 and .23 lb. respectively. The total amount of
+nitrogen and ash, therefore, in the farmyard manure produced by a horse
+in one day, would be .19 lb. nitrogen and 1.15 lb. mineral matter; or,
+if we take the larger quantity of straw, somewhat more.
+
+Taking these figures, we find that the amount of manure produced by a
+horse in a year will be from 11,720 to 12,450 lb. (_i.e._, from 5-1/4
+to 5-1/2 tons),[152] containing from 69 to 73 lb. nitrogen, and from 420
+to 460 lb. mineral matter.[153]
+
+A word or two may be of value regarding the treatment in the stable of
+horse-manure. The great object to be aimed at is the prevention of loss
+of valuable fertilising constituents. This loss may be due to two
+causes. It may be, in the first place, caused by drainage of the soluble
+matter of the manure; or secondly, it may be due to volatilisation of
+the volatile constituents.
+
+The first of these two sources of loss depends on the precautions taken
+in the way of providing a proper impervious flooring to the stable. This
+source of loss is extremely difficult to prevent, inasmuch as nearly all
+materials used for flooring absorb a certain percentage of urine. The
+judicious use of litter, however, will minimise this loss to within a
+trifling extent.
+
+Dr Heiden states that the amount of straw used as litter for the horse
+in Germany is from 4 to 6 lb. per day. The quantity should be regulated
+according to the percentage of water the excreta contain; the more
+watery excreta requiring naturally a larger quantity of litter. The most
+eminent authorities on this subject recommend that the amount of litter
+should equal one-fourth of the food in its natural state, or about
+one-third of its dry substance.
+
+The second source of loss, which is due to volatilisation of the
+volatile ingredients, may be largely prevented by the use of certain
+preservatives.
+
+Horse-dung being, comparatively speaking, of a dry nature, it is
+extremely difficult to effect its thorough mixture with the litter. For
+this reason the manure formed from horse excreta is particularly liable
+to rapid fermentation.[154] In the process of fermentation, as will be
+seen more in detail further on, the nitrogen is converted into carbonate
+of ammonia. As nitrogen in this form is of an extremely volatile nature,
+the risks of loss from this source are considerable. As illustrating
+this fact, it may be mentioned that Boussingault has found by experiment
+that the total percentage of nitrogen contained by fresh horse-manure
+might be reduced in the process of fermentation to one-half of its
+original amount by loss from this source.
+
+The preservatives used to prevent this volatilisation are technically
+known as "fixers." This they do by chemically combining with the
+volatile ammonia and forming non-volatile compounds with it.
+
+Of the acid fixers, hydrochloric and sulphuric acids have been
+recommended. The former, however, is not well suited for this purpose.
+It is a strongly fuming acid, and when brought into contact with
+ammonia forms dense white fumes. The use of sulphuric acid is not open
+to this objection. Sulphate of ammonia, the salt formed in this case, is
+one of the most stable (or least volatile) of the compounds of ammonia.
+If used, it should be largely diluted with water, and the whole mixed
+with sand. Such a mixture, when sprinkled over the stable-floor in even
+very small quantities, has been found to effectually prevent any loss of
+the volatile carbonate of ammonia.
+
+It is not, however, on the whole advisable to use an acid substance as a
+fixer, since such a substance may act deleteriously on the horses'
+hoofs.
+
+Such substances as _gypsum_, _copperas_, and _sulphate of magnesia_,
+while equally efficient, are not open to this objection. The
+above-mentioned substances owe their efficacy to the fact that they are
+compounds of sulphuric acid, which, by combining with the volatile
+ammonia and forming sulphate of ammonia, prevent its escape.
+
+Gypsum, or sulphate of lime, although, comparatively speaking, an
+insoluble substance, when brought in contact with carbonate of ammonia
+has been proved to effect the conversion of the ammonia into sulphate of
+ammonia. It is also believed to retard the decomposition of the
+manure.[155] Copperas, or ferrous sulphate, while a soluble salt, and
+while thus acting in a more speedy manner in fixing the ammonia, is not
+so well suited, owing to the hurtful influence it is well known to
+possess on plant-life. It is only right to remember that there may be
+circumstances in which copperas may, in small quantities, act even
+beneficially as a manure, as Griffiths' experiments would seem to
+indicate. The above objection, however, cannot be urged against sulphate
+of magnesia. In addition to fixing the ammonia, sulphate of magnesia may
+very probably fix the soluble phosphoric acid. Kainit, which consists of
+a mixture of sulphates and chlorides of potassium and magnesium, has
+also been suggested for this purpose. By using such a fixer, the value
+of the resulting manure would be much enhanced. In conclusion, it must
+be remembered that all the above-named fixers act very much in the same
+way--viz., by converting the volatile carbonate of ammonia into sulphate
+of ammonia.[156]
+
+
+2. _Cow-manure._
+
+The composition of the manure formed from the excrementitious matter of
+the cow is very much less constant than is the case in the horse-manure.
+An average statement of that composition is therefore very much more
+difficult to obtain. The number of analyses available for the purpose of
+forming this average is, however, very large. The manure produced by
+cows contains a large percentage of water. This is due to the large
+quantity of water they drink. It has been estimated that milch-cows
+drink along with their winter food, for every pound of dry substance, 4
+lb. of water, and in summer about 6 lb.
+
+According to some experiments by Boussingault, the excrements of a cow
+in a day amounted to 73.23 lb., of which only 9.92 lb. were dry
+matter.[157] These excrements contained .256 lb. of nitrogen and 1.725
+lb. of mineral matter. The amount of straw necessary to use as litter
+for this amount of excrements may be taken at 6 to 10 lb. The manure,
+therefore, formed by a cow per day, would contain from .274 to .286 lb.
+of nitrogen, and from 2.046 to 2.278 lb. of mineral matter. In a year
+this would amount to from 100 to 104.4 lb. of nitrogen, and from 746.8
+lb. to 831.5 lb. of mineral matter; or from 6 cwt. 75 lb. to 7 cwt. 47
+lb.
+
+Cow-dung is, owing to its more watery nature and poorer quality, very
+much slower in its fermentation than horse-dung. When applied alone,
+cow-manure is very slow in its action, and makes its influence felt for
+at least three or four years. It is difficult to spread it evenly over
+the soil, owing to the fact that, when somewhat dried, it has a tendency
+to form hard masses, which, when buried in the soil, may resist
+decomposition for a very long period. The cause of this is due to the
+presence of a considerable amount of mucilaginous and resinous matter in
+the solid excreta, which prevents the entrance of moisture and air into
+the centre of the mass. This tendency of cow-manure to resist
+decomposition will be greatly lessened in the case of the excrements of
+a cow richly fed.
+
+The risks of loss of volatile ammonia are, therefore, in its case not so
+great as we have seen them to be in the case of the "hot" horse-dung.
+Notwithstanding this fact, much of what has been said on the use of
+preservatives for horse-manure may be also applied to the cow-dung. This
+is owing to the fact that the dung is allowed to accumulate in the court
+for some time. The amount of straw it is advisable to use as litter
+varies, as has been said, from 6 to 10 lb. per day. The best method of
+calculating this amount, according to Dr Heiden, is by taking one-third
+of the total weight of the dry substance of the food. The above
+authority also recommends that the straw is best applied in blocks of
+about one foot in length; and this for the following reasons:--
+
+1. The strewing of it is more convenient.
+
+2. The absorption of the fluid portion is more complete.
+
+3. The cleaning out of the manure from the byre is easier.
+
+4. The manure is more easily distributed when applied to the field.
+
+Among the advantages incidental to allowing the manure to accumulate in
+the court may be mentioned the following:--
+
+1. The more thorough absorption of the urine by the straw, and,
+consequently, the more uniform mixture which will be thus effected of
+the more valuable urine with the less valuable solid excreta.
+
+2. A certain retardation of decomposition effected by the treading under
+foot of the manure.
+
+3. The protection of the manure from rain and wind, and the securing of
+a uniform temperature.
+
+Against those advantages must be placed the risk of seriously affecting
+the health of the animal. Although this is a point of very great
+importance, it scarcely falls within the scope of this work. It may be
+pointed out, however, that the judicious use of some of the chemical
+fixers previously referred to may do much to keep the air of the byre or
+court free of noxious gases.[158]
+
+
+3. _Pig-manure._
+
+The food of the pig is so very variable in its character that it is
+wellnigh impossible to obtain anything like an average analysis of its
+excrements. When the food of the pig is rich, then the manure may be
+quite equal in quality to the other manures. According to Boussingault,
+the total amount of excrements, on an average, voided by a pig in
+twenty-four hours is about 8.32 lb., of which 1.5 lb. is dry
+matter.[159] The amount of nitrogen these excrements contain is only .05
+lb., and of mineral ingredients .313 lb. If we take the amount of straw
+most suitable for absorbing this quantity of excrementitious matter at
+from 4 to 8 lb., then we shall find that the manure produced by a pig
+will contain from .06 to .074 lb. nitrogen and .545 to .772 lb. mineral
+matter. These quantities, calculated for a year, give from 22 to 27 lb.
+of nitrogen, and from 1 cwt. 87 lb. to 2 cwt. 57 lb. of mineral matter.
+That is about as much nitrogen as would be contained in 1-1/4 to 1-1/2
+cwt. of nitrate of soda (95 per cent purity); or from slightly less than
+1 cwt. to slightly over 1 cwt. of sulphate of ammonia (97 per cent
+purity).
+
+As has already been pointed out, the excrements of the pig are, as a
+rule, very poor in nitrogen. This accounts for the fact that pig-manure
+is a "cold" manure, slow in fermenting.[160]
+
+
+4. _Sheep-manure._
+
+The dung and the urine of the sheep, as we have already seen, are,
+weight for weight, the most valuable of any of the common farm animals.
+The total weight of the excrements voided by a sheep in a day may be
+taken, on an average,[161] at 3.78 lb., of which .97 lb. is dry matter.
+These excrements contain .038 lb. of nitrogen and .223 lb. mineral
+matter. Taking the amount of straw most suitable for absorbing this
+quantity of excrementitious matter at three-fifths of a pound, then the
+manure produced by a sheep in a day will contain .0429 lb. nitrogen and
+.264 lb. mineral matter. That is, in a year the quantities of nitrogen
+and mineral matter in the manure produced by a sheep would be 15.66 lb.
+of nitrogen and 96.36 lb. of mineral matter.
+
+From its richness in nitrogen, and from its dry condition, sheep-dung is
+peculiarly liable to ferment. While richer in fertilising substances
+than horse-manure, it is not so rapid in its fermentation. This is due
+to the harder and more compact physical character of the solid excreta.
+The risks of loss of volatile ammonia are, in its case, exceptionally
+great. The use of artificial "fixers" is therefore to be strongly
+recommended.[162]
+
+
+_Fermentation of Farmyard Manure._
+
+Having now considered the nature of the different manures produced by
+the four common farm animals separately, it is of importance to consider
+the exact nature of the fermentation, decomposition, or putrefaction
+which takes place in the manure-heap.
+
+It is now more than thirty years since Pasteur showed that the
+fermentation which ensued on keeping a sample of urine was due to the
+action of a minute organism, for the propagation of which a certain
+amount of warmth, air, and moisture, as well as the presence of certain
+food-constituents, especially nitrogenous bodies, were necessary.
+
+Subsequent researches by Pasteur and others have conclusively
+demonstrated that the micro-organic life instrumental in effecting the
+putrefaction or decay of organic matter of any kind, may be divided into
+two great classes:--
+
+1. Those which require a plentiful supply of oxygen for their
+development, and which, when bereft of oxygen, die--known as _aerobies_.
+
+2. Those which, on the contrary, develop in the complete absence of
+oxygen, and which, when exposed to oxygen, die--known as _anaerobies_.
+
+In the fermentation of the manure-heap, therefore, we must conceive of
+the two classes of organisms as the active agents. In the interior
+portion of the manure-heap, where the supply of oxygen is necessarily
+limited, the fermentation going on there is effected by means of the
+anaerobic organism--_i.e._, the organism which does not require oxygen;
+while on the surface portion, which is exposed to the air, the aerobic
+(or oxygen-requiring) organism is similarly active. Gradually, as decay
+progresses, the aerobic organisms increase in number. It is through
+their instrumentality that the final products of decomposition are
+largely produced. The functions of the anaerobic organisms may be, on
+the contrary, regarded as largely preparatory in their nature. By
+breaking up the complex organic substances in the manure into new and
+simpler forms, they advance the process of putrefaction through the
+initial stages; and when this is accomplished, they die and give place
+to the aerobic, which, as we have just seen, effect the final
+transformation of the organic matter into such simple substances as
+_water_ and _carbonic acid gas_.
+
+The conditions influencing the fermentation of farmyard manure may be
+summed up as follows:[163]--
+
+1. _Temperature._--The higher the temperature the more rapidly will the
+manure decay.
+
+2. _Openness to the Air._--Of course it will be seen that the effect of
+exposing the manure to the action of the air is to induce the
+development of the aerobic type of organism, and thus to promote more
+rapid fermentation. If, on the other hand, the manure be impacted, the
+slower but more regular fermentation, due to the anaerobic type of
+organism, will be chiefly promoted. It must be remembered that in the
+proper rotting of farmyard manure both kinds of fermentation should be
+fostered. It is, in fact, on the careful regulation of the two classes
+of fermentation that the successful rotting of the manure depends. It
+must further be remembered that, even with a certain amount of openness
+in a manure-heap, anaerobic fermentation may take place. This is due to
+the fact that the evolution of carbonic acid gas, in such a case, is so
+great as to exclude the access of the atmospheric oxygen into the pores
+of the heap.
+
+3. The _dampness_ of the manure-heap is another important influence.
+This, of course, will act in two ways. First, by lowering the
+temperature. Where the manure-heap is found to be suffering from
+"fire-fang," the common method in practice is to lower the temperature
+by moistening the heap with water. Secondly, it acts as a retarder of
+fermentation by limiting the supply of atmospheric oxygen, and thus
+preventing, as we have just seen, aerobic fermentation.
+
+4. The fourth chief influence in regulating fermentation of the
+manure-heap is its _composition_, and more especially the amount of
+nitrogen it contains in a soluble form. The rate at which fermentation
+takes place in any organic substance may be said chiefly to depend on
+the percentage of soluble nitrogenous matter it contains: the greater
+this is in amount, the more quickly does fermentation go on. There are
+always a number of soluble nitrogenous bodies in farmyard manure. These
+are chiefly found in the urine, such as _urea_, _uric_ and _hippuric
+acids_, and _ammonia_ salts.
+
+
+_Products of Decomposition of Farmyard Manure._
+
+The most important of the changes which take place in the rotting of
+farmyard manure may be briefly enumerated as follows:--
+
+1. The gradual conversion into gases of a large portion of the organic
+elements in the manure. Of these gaseous products the most abundant is
+_carbonic acid gas_ (CO_2). It is in this form that the carbonaceous
+matter which constitutes the chief portion of the manure escapes into
+the air. Carbon also escapes into the air, combined with hydrogen, in
+the form of _carburetted hydrogen_ or _marsh-gas_ (CH_4), a product of
+the decomposition of organic matter in the presence of a large quantity
+of water. This gas is consequently found bubbling up through stagnant
+water. Next to carbonic acid gas, _water_ (H_2O) is the most abundant
+gaseous product of decomposition. The nitrogen present in the manure, in
+different forms, is converted by the process of decomposition chiefly
+into _ammonia_, which, combining with the carbonic acid, forms carbonate
+of ammonia, a very volatile salt. It is to this fact that one of the
+great sources of loss in the decomposition of farmyard manure is due. If
+the temperature of the manure-heap be permitted to rise too high, the
+carbonate of ammonia volatilises. It is probable, also, that a not
+inconsiderable portion of the nitrogen escapes into the air in the free
+state. The last of the most important gaseous products of decomposition
+are _sulphuretted_ and _phosphoretted hydrogen_. It is to these gases
+that much of the smell of rotting farmyard manure is due.
+
+2. The second class of substances formed are _soluble organic acids_,
+such as _humic_ and _ulmic acids_. The function performed by these acids
+is a very important one. They unite with the ammonia and the alkali
+substances in the mineral portion of the manure, forming humates and
+ulmates of ammonia, potash, &c. It is these ulmates that form the black
+liquor which oozes out from the manure-heap.
+
+In very rotten farmyard manure traces of _nitric acid_ may be found; but
+it must be remembered that the formation of nitrates is practically
+impossible under the ordinary conditions of active fermentation of
+farmyard manure, except perhaps in its very last stages.
+
+3. The third class of changes taking place have to do with the mineral
+portion of the manure. The result of the formation of so much carbonic
+and other organic acids is to increase the amount of _soluble_ mineral
+matter very considerably.
+
+
+_Analyses of Farmyard Manure._
+
+It is chiefly to the valuable researches of the late Dr Augustus
+Voelcker that we owe our knowledge of the composition of old and fresh
+farmyard manure. All interested in this important question should peruse
+the original papers on this subject contributed to the 'Journal of the
+Royal Agricultural Society' by Dr Voelcker. Typical analyses
+illustrating the variation in the composition of farmyard manure at
+different stages of decomposition will be found in the Appendix.[164]
+From what has been already said, it is obvious chat the composition of
+farmyard manure is of a very variable nature.
+
+The quantity of moisture naturally varies most, and this variation will
+depend on the age of the manure, and the conditions under which it is
+permitted to decay. It may be taken at from a minimum of 65 per cent in
+fresh to 80 per cent in well-rotted manure. The total organic matter may
+be taken at from 13 to 14 per cent, containing nitrogen .4 to .65 per
+cent. The total mineral matter will range from about 4 to 6.5 per cent,
+containing of potash from .4 to .7 per cent, and of phosphoric acid from
+.2 to .4 per cent.[165]
+
+As Mr Warington[166] has pointed out, one ton of farmyard manure would
+thus contain 9 to 15 lb. of nitrogen, about the same quantity of potash,
+and 4 to 9 lb. of phosphoric acid. These quantities of nitrogen and
+phosphoric acid, calculated to (95 per cent) nitrate of soda, and (97
+per cent) sulphate of ammonia, and (25 per cent) superphosphate, give
+respectively 57.25 to 96 lb. nitrate of soda, 45 to 75 lb. sulphate of
+ammonia, and 35 to 79 lb. superphosphate. That is, in order to apply as
+much nitrogen to the soil as is contained in one ton of nitrate of soda,
+we should require to use from 23 to 41 tons of farmyard manure:
+similarly one ton of sulphate of ammonia contains as much nitrogen as 30
+to 50 tons farmyard manure. In the same way one ton of superphosphate
+of lime contains as much phosphoric acid as 28 to 64 tons farmyard
+manure.
+
+The value of rotten manure is, weight for weight, greater than that of
+fresh manure. This is due to the fact that, while the water increases in
+amount, the loss of organic matter of a non-nitrogenous nature more than
+counterbalances the increase in water. The manure, therefore, becomes
+more concentrated in quality. The loss on the total weight, according to
+Wolff, in the rotting of farmyard manure, should not exceed in two or
+three months' time 16 to 20 per cent--viz., a sixth to a fifth of its
+entire weight. Not only, however, does the manure become richer in
+manurial ingredients, but the forms in which the manurial ingredients
+are present in rotten manure are more valuable, as they are more
+soluble. These statements must not be taken as proving that it is more
+economical to apply farmyard manure in a rotten condition than in a
+fresh one. The distinction must not be lost sight of which exists
+between relative increase--increase in the percentage of valuable
+constituents--and absolute increase. The increase in the value of the
+manure by the changes of the manurial ingredients from the insoluble to
+the soluble condition may be effected at the expense of a considerable
+amount of absolute loss of these valuable ingredients. This is a point
+which is probably too often left out of account in discussing the
+relative merits of fresh and rotten farmyard manure; and it is
+important that it should be clearly understood. In the words of the late
+Dr Voelcker: "Direct experiments have shown that 100 cwt. of fresh
+farmyard manure are reduced to 80 cwt. if allowed to lie till the straw
+is half rotten; 100 cwt. of fresh farmyard manure are reduced to 60 cwt.
+if allowed to ferment till it becomes 'fat or cheesy'; 100 cwt. of fresh
+farmyard manure are reduced to 40-50 cwt. if completely decomposed. This
+loss not only affects the water and other less valuable constituents of
+farmyard manure, but also its most fertilising ingredients. Chemical
+analysis has shown that 100 cwt. of common farmyard manure contain about
+40 lb. of nitrogen, and that during fermentation in the first period 5
+lb. of nitrogen are dissipated in the form of volatile ammonia; in the
+second, 10 lb.; in the third, 20 lb. Completely decomposed common manure
+has thus lost about one-half of its most valuable constituent."[167]
+While, of course, a very great amount of absolute loss of the valuable
+constituents--the nitrogen and ash-constituents--of farmyard manure may
+take place through volatilisation and drainage, by taking requisite
+precautions this loss may be very much minimised. As regards the total
+loss, this, in two or three months' time, should only amount to 16 to 20
+per cent--or one-sixth to one-fifth of the weight.[168] The use of
+fixers, to which reference has already been made, will greatly minimise
+this loss. The application of fixers is best made to the manure when
+still in the stall or byre. The health of the animal benefits by so
+doing, while the manure is at once guarded against loss from this
+source.
+
+As to the relative merits of covered and uncovered manure-heaps, much
+difference of opinion exists. It is one of those questions which does
+not admit of final decision one way or another, as it depends so largely
+on the individual circumstances of each case. That manure produced under
+cover is more valuable than manure made in the open is readily granted.
+The question, however, is as to whether the increase in its value is
+sufficiently great to warrant the extra expense involved in building
+covered courts. This depends on the individual circumstances of each
+case, and cannot be decided in a general way. For experiments on the
+relative value of manure made under cover and in the open, see
+Appendix.[169]
+
+The method of applying farmyard manure to the field is a question which
+belongs more to the practical farmer than, to the scientist, and must be
+largely decided by economic considerations. There is an aspect, however,
+of the question which may well be treated here. The first point in the
+production of good manure is in connection with its even distribution.
+It is of great importance that the excrements of the different farm
+animals be thoroughly mixed together. By the intimate incorporation of
+the "hot" horse-dung with the "cold" cow and pig dung, uniform
+fermentation is secured. Fire-fang--or too rapid fermentation--may occur
+from this not being properly done, and from the manure becoming too dry.
+It is important, also, as we shall see immediately, to have the manure
+uniform in quality when applied to the field. The manure ought to be
+firmly trodden down, to moderate the rate of fermentation. Where the
+manure-heap is exposed to rain, the quantity of water it will naturally
+receive will probably be quite sufficient, if indeed not too much, to
+ensure a proper rate of fermentation--except, perhaps, in very warm
+weather. The great point to be aimed at is to ensure regular
+fermentation. What has to be especially avoided is any sudden exposure
+of the manure to large quantities of water. The result of such a
+washing-out of the soluble nitrogen is to retard fermentation, besides
+incurring the risk of great actual loss by drainage.[170]
+
+
+_Application of Farmyard Manure to the Field._
+
+In applying the manure to the field, and before ploughing it in, two
+methods of procedure may be pursued. First, the manure may be set out in
+heaps, larger or smaller, over the field, and be allowed to remain in
+these heaps some time before being spread; and secondly, it may be
+directly spread broadcast over the field, and thus allowed to lie for
+some time. Lastly, the manure may be ploughed in immediately; and it may
+be stated that such a method is, where circumstances permit, the safest
+and most economical method.[171]
+
+In discussing the merits and demerits of these two methods, Dr Heiden
+points out, first, with regard to the distribution of the manure in
+small heaps over the field, that this is not to be recommended, on the
+following grounds:--
+
+1. Because the chances of loss by volatilisation are thereby increased.
+The manure is distributed several times instead of only once or twice.
+
+2. It is apt to ensure unequal distribution. The separate heaps run the
+risk of losing their soluble nitrogenous matter, which soaks into the
+ground beneath the heaps. The other portions of the field not covered by
+the manure-heaps are thus manured with washed-out farmyard manure,
+bereft of its most valuable constituents. The result is, that while
+certain portions of the field are too strongly manured, other portions
+are too weakly manured.
+
+3. The proper fermentation of the manure is apt to be interfered with by
+the loss of that which is its most important agent--viz., the soluble
+nitrogenous matter--and also by the drying action of the wind.
+
+The same objections hold good to a large extent with regard to the
+setting out in the fields of the manure in large heaps. The risks of
+loss, in one respect, may be said to be less, owing to the smaller
+surface presented. On the other hand, they may be greater, owing to
+fermentation taking place more quickly. Agricultural practice, however,
+often renders this custom necessary; and if precautions are taken not to
+let the heap lie too long, and to cover it over with earth, the risk of
+serious loss may be rendered inconsiderable.
+
+With regard to the second method of procedure--viz., the spreading of
+the manure broadcast over the field, and allowing it thus to lie--Dr
+Heiden is of opinion that this should only be done when the field is
+level. In the case of uneven ground the risks are, of course, obvious.
+It has been affirmed that, by allowing farmyard manure thus to lie
+exposed for some time, an important loss of volatile ammonia--carbonate
+of ammonia--is apt to take place. This could only take place where the
+former treatment of the farmyard manure had been bad. Hellriegel has
+shown that in the case of properly prepared farmyard manure there is no
+danger of loss in this way. The absorptive power of the soil for
+ammonia, it must be remembered, is very great, and the amount of
+volatile ammonia in farmyard manure is relatively so small that it is
+scarcely possible that any could escape in this way. Hellriegel's
+experiments have demonstrated this in a very striking way. He has found
+that in the case of a chalky soil, and during the summer and autumn
+months, practically no loss of ammonia takes place. The following
+considerations may be further urged in support of this method of
+application, as against immediately ploughing in the manure, viz.:--
+
+1. That fermentation takes place more quickly.
+
+2. That it results in a more equable distribution of the manurial
+constituents in the dung, by gradually and thoroughly incorporating the
+liquid portion of the manure with the soil-particles.
+
+Against, however, these undoubted advantages, one serious disadvantage
+may be urged--viz., that the manure, before being ploughed in, becomes
+robbed to a large extent of its soluble nitrogenous compounds, which, as
+we have repeatedly observed, are so necessary for fermentation; and
+that, therefore, when it is ploughed in, it does not so readily ferment.
+This being so, it is highly advisable, in the case of light or sandy
+soils, not to follow such a practice, but to plough the manure directly
+in.
+
+As to the depth to which it is advisable to plough the manure in, it may
+be here noticed that it should not be too deep, so as to permit of the
+access of sufficient moisture to ensure proper fermentation, and to
+prevent rapid washing down of nitrates to the drains. Lastly, it need
+scarcely be pointed out that it is highly important to have the manure
+evenly and thoroughly incorporated with the soil-particles. Where the
+manure is permitted to cake together in lumps, it may successfully
+resist the action of fermentation for several years.
+
+
+_Value and Function of Farmyard Manure._
+
+Practical experience has long demonstrated the fact that farmyard manure
+is, taking it all round, the most valuable, and admits of the most
+universal application, of all manures; and science has done much to
+explain the reason of this. The influence of farmyard manure is so
+many-sided that it is difficult even to enumerate its different
+functions. As has already been pointed out, its indirect value as a
+manure is probably as great as, if indeed even not greater than, its
+direct value. In concluding our study of farmyard manure, we shall
+endeavour to summarise, in as brief a manner as possible, its chief
+properties.
+
+First, as to its value as a supplier of the necessary elements of
+plant-food. This, there can be little doubt, has been, and still is,
+grossly exaggerated by the ordinary farmer. Much has been claimed for it
+as a "general" manure. How far it merits pre-eminence on this score
+among other manures will be seen in the sequel. It is true that, since
+it is composed of vegetable matter, it contains all the necessary plant
+ingredients.[172] As has been shown in the Introduction, there is
+practically in the case of most soils no necessity to add to a manure
+any more than the three ingredients, _nitrogen_, _phosphoric acid_, and
+_potash_. Its value, then, as a direct manure, must depend on the
+quantity and proportion in which these three ingredients are present.
+These substances, as we have already seen, it contains only in very
+small quantities. It is, judged from this point of view, a comparatively
+poor manure. Furthermore, only a certain percentage of these substances
+is in a soluble or immediately available condition,--in this respect the
+rotten manure being very much more valuable than the fresh manure.
+
+Again, a point of great importance in a universal manure is the
+proportion in which the necessary plant-foods are present. If it be
+asked, Are the nitrogen, phosphoric acid, and potash in farmyard manure
+present in the proportion in which crops require these constituents? the
+answer must be in the negative. Heiden[173] has very strikingly
+illustrated this point, in so far as the relations between the two ash
+ingredients are concerned, by some computations as to the amount which
+would be removed from the soil in the course of different
+rotations.[174] In the case of five different rotations it was found
+that the ratio between the potash and phosphoric acid removed was as
+follows:[175] (1) 2.96 to 1; (2) 2.76 to 1; (3) 2.95 to 1; (4) 4.13 to
+1; (5) 3.78 to 1. This would give a mean of 3.32 to 1. This is not the
+ratio in which these ingredients are generally present in farmyard
+manure. Farmyard manure may be said to be much richer in the mineral
+constituents of plants than in nitrogen. Professor Heiden found that in
+the case of a farm at Waldau, the crops in the course of ten years
+removed from a _morgen_ (.631 of an acre) the following quantities:--
+
+ lb.
+Nitrogen 329
+Potash 263
+Phosphoric acid 121
+
+In order to supply these amounts the following quantities of manure
+would require to be supplied:--
+
+1. For the nitrogen, 26 or 27 tons (manure containing .606 per cent
+nitrogen).
+
+2. For the potash, 20 to 25 tons (manure containing .672 per cent
+potash).
+
+3. For the phosphoric acid, 13 to 19 tons (manure containing .315 per
+cent phosphoric acid).
+
+From the above it will be seen that farmyard manure contains too little
+nitrogen in proportion to its ash ingredients.
+
+It is not merely the amount of fertilising ingredients removed by the
+crop we have to take into account in estimating the value of certain
+manurial ingredients for the different crops. Two other considerations
+have to be remembered--viz., the amount of the constituents already
+present in the soil, and the ability of the different crops to obtain
+the ingredients from the soil. If we take into account these two
+considerations in estimating the value of farmyard manure as a general
+manure, we shall find that they accentuate the inadequacy of the ratio
+existing between the nitrogen and the mineral ingredients. Messrs Lawes
+and Gilbert have found in the Rothamsted experiments with farmyard
+manure, that while it restored the mineral ingredients, it was
+inadequate as a sufficient source of nitrogen. Nitrogen is, of all
+manurial ingredients, in least abundance in soils. It is consequently
+found that the ingredient in which farmyard manure requires to be
+reinforced is nitrogen. With regard to phosphoric acid and potash, it
+has already been shown that the ratio between them is probably greater
+than that in a good average manure. We should, arguing from this alone,
+be inclined to think that farmyard manure would be best reinforced with
+potash. The reverse is the case, however, as every farmer knows. This is
+due, first, to the fact that the potash, unlike the phosphoric acid, is
+entirely of a soluble nature, and therefore immediately available for
+the plant's needs; and secondly, to the fact that the necessity for the
+application of potash as a manure is generally not nearly so great as in
+the case of phosphoric acid. The result is, that farmyard manure will
+be, as a rule, more valuably supplemented by phosphoric acid than by
+potash.
+
+Another point of great importance, in estimating the value of farmyard
+manure as a chemical manure, is the inferior value possessed by much of
+the nitrogen it contains, as compared with the nitrogen in such
+artificial manures as nitrate of soda and sulphate of ammonia. According
+to the Rothamsted experiments, weight for weight, the nitrogen in
+farmyard manure is not half so valuable as it is in sulphate of ammonia.
+Much of the nitrogen becomes only very slowly available; not a little of
+it perhaps actually takes years to be converted into nitrates.[176]
+
+Thus, with regard to the direct value of farmyard manure as a manure, we
+have seen--
+
+1. That it contains a very small quantity of the three fertilising
+ingredients.
+
+2. That the proportion in which these three ingredients are present is
+not the best proportion for the requirements of crops.
+
+3. That the form in which a portion of these ingredients--nitrogen and
+phosphoric acid--is present is not of the most valuable kind.
+
+It is consequently not as a direct chemical manure that farmyard manure
+is pre-eminently valuable. We must seek for perhaps its most valuable
+properties in its indirect influence.
+
+It adds to the soil a large quantity of organic matter. Most soils are
+improved by the addition of _humus_. The water-absorbing and retaining
+powers of a soil are increased by this addition of _humus_, while it
+enables the soil to attract an increased amount of moisture from the
+air. This is often of great importance, as in the period of germination
+of seed.[177] The influence it exerts on the texture of the soil in the
+process of fermentation is also very great. This is especially so in
+soils whose texture is too close, such as heavy clayey soils. It opens
+up their pores to the air, and renders them more friable. Where such an
+influence is most required, as in clayey soils, the manure ought to be
+applied in a fresh condition, so that the maximum influence exerted by
+the manure in this direction may be experienced. On light soils, on the
+contrary, whose friability and openness are already too great, and which
+do not require to be increased, the manure will be best applied in a
+rotten condition. It adds, further, greatly to the heat of the soils by
+its decomposition. Thus on cold damp soils it effects one very marked
+benefit. The influence it exerts in its decomposition upon the
+fertilising ingredients present in the soil is also by no means
+inconsiderable. In the process of its fermentation large quantities of
+carbonic acid gas are generated. This carbonic acid probably acts in a
+double capacity. It will, in the first place, greatly increase the
+solvent power of the soil-water, and thus enable it to set free an
+increased amount of mineral plant-food; and secondly, it will help to
+conserve a certain quantity of the soil-nitrogen, by preventing its
+conversion into nitrates.
+
+As its indirect and mechanical properties are greatest when in its fresh
+condition, it will be better to apply it in that condition to soils most
+lacking in these mechanical properties. We may therefore say that
+farmyard manure is best applied in a rotted condition to light sandy
+soils, and to soils in a high state of cultivation, where its mechanical
+properties are not so much required.
+
+An important point still remains to be discussed--viz., the rate at
+which the farmyard manure should be applied. This, of course, should
+naturally depend on a variety of circumstances--the amount of artificial
+manures used as supplementary to the farmyard manure, the frequency of
+its application, and the nature of the soil.
+
+These considerations naturally vary so much, that the quantities of
+farmyard manure it is advisable to apply in different cases are widely
+different. There is a strong probability that the rate at which farmyard
+manure has been applied in the past has been grossly in excess of what
+could be profitably employed. Opinion is gaining ground among practical
+farmers, that smaller and more frequent applications of farmyard manure
+to the soil would be fraught with better results than the older custom
+of applying a large dressing at a time. This is an opinion in the
+support of which science can urge strong arguments. It is only of late
+years that we have come to recognise sufficiently the various risks
+which all fertilisers are subject to in the soil, and the importance,
+therefore, of minimising these risks as much as possible by putting into
+the soil at one time only as much manure as it is safely able to retain.
+
+"The famous old German writer Thaer regarded 17 or 18 tons as an
+abundant dressing; 14 tons he called good, and 8 or 9 tons light. Other
+German authorities speak of 7 to 10 tons as light, 12 to 18 tons as
+usual, 20 or more tons as heavy, and 30 tons as a very heavy
+application."[178]
+
+In the new edition of Stephens' 'Book of the Farm,'[179] from 8 to 12
+tons per acre for roots, and from 15 to 20 tons for potatoes, along with
+artificials, which may cost from 25s. to 60s. per acre additional, are
+quoted as general dressings.
+
+The majority of recent experiments with farmyard manure would seem to
+indicate that, even in the case of what are considered small dressings,
+the extra return in crop the first year after application is not such as
+to cover the expense of the manure. Of course, as is commonly pointed
+out, the effect of farmyard manure is of a lasting nature, and is
+probably felt throughout the whole rotation, or even longer. This, to a
+certain extent, is no doubt true; still it may be strongly doubted
+whether farmyard manure is, after all, an economical manure, as compared
+with artificial manures. The desirability of manuring the soil and not
+the crop is, in this age of keen competition, no longer believed in; and
+the Rothamsted experiments have shown that it is highly doubtful whether
+even the soil benefits to anything like a commensurate extent by the
+application of large quantities of farmyard manure. This is of course
+assuming for farmyard manure the value that it would fetch when sold,
+or, to put it rather differently, the price it would cost if the farmer
+had to purchase it. Farmyard manure is a necessary bye-product of the
+farm, and can scarcely be regarded, therefore, in the same light as the
+artificial manures which the farmer buys.[180]
+
+
+FOOTNOTES:
+
+[131] See Appendix, Note I., p. 279.
+
+[132] "The large amount of potash in unwashed wool is very remarkable: a
+fleece must sometimes contain more potash than the whole body of the
+shorn sheep."--Warington's 'Chemistry of the Farm,' p. 78.
+
+[133] See Appendix, Note II., p. 279.
+
+[134] The urine of the pig, from the nature of its food, is, as a
+general rule, a very poor nitrogenous manure.
+
+[135] See Appendix, Note XV., p. 290.
+
+[136] See Appendix, Note III., p. 280.
+
+[137] See Appendix, Note XVIII., p. 291.
+
+[138] The nitrogen present in the urine, it may be well to point out, is
+derived from the waste of nitrogenous tissue as well as from nitrogenous
+matter of the food digested.
+
+[139] Note IV., p. 281.
+
+[140] Warington puts this matter admirably in the following words: "If
+the food is nitrogenous and easily digested, the nitrogen in the urine
+will greatly preponderate. If, on the other hand, the food is one
+imperfectly digested, the nitrogen in the solid excrement may form the
+larger quantity. When poor hay is given to horses, the nitrogen in the
+solid excrement will exceed that contained in the urine. On the other
+hand, corn, cake, and roots yield a large excess of nitrogen in the
+urine." ('Chemistry of the Farm,' p. 137).
+
+[141] See p. 281.
+
+[142] See p. 282.
+
+[143] See Heiden's 'Düngerlehre,' vol. ii. p. 58.
+
+[144] Heiden's 'Düngerlehre,' vol. i. p. 404.
+
+[145] The following quantities of nitrogen are found in rye, pea, and
+bean straw:--
+
+ Ranging from Average Lb.
+ per cent. per cent. per ton.
+
+Rye-straw .30 to .73 .57 12.76
+Pea-straw .76 to 1.61 1.21 27.10
+Bean-straw 1.15 to 2.62 1.92 43.00
+
+[146] Dr J. M. H. Munro recommends the sprinkling of a little finely
+sifted peat-powder in addition to straw, as an excellent means of
+preventing loss of volatile ammonia in the fermentation of manure.
+
+[147] See 'Mark Lane Express,' October 7, 1889, p. 475.
+
+[148] See Appendix, Note VII., p. 283.
+
+[149] For analyses see Appendix, Note VIII., p. 283.
+
+[150] According to Storer, in a ton of autumn leaves of the best quality
+there would be 6 lb. of potash, less than 3 lb. of phosphoric acid, and
+10 or 15 lb. of nitrogen. Another substance that may be used as a litter
+is sawdust. This substance is a good absorbent, but is of little value
+as a manurial substance.
+
+[151] Heiden's 'Düngerlehre,' vol. ii. pp. 34, 66. In Boussingault's
+experiments the food consisted of 15 lb. _hay_, 4.54 lb. _oats_, and 32
+lb. water; the total excrements amounting to 31.16 lb., containing 7.42
+lb. dry matter. In Hofmeister's experiments the food consisted of 5.23
+lb. _hay_, 6.18 lb. _oats_, 1 lb. _chopped straw_, and 25.57 lb. water;
+the excrements amounting to 25.07 lb., containing 5.32 lb. dry matter.
+
+[152] This is taking no account of the amount of water which the manure
+will absorb, and which will probably double the quantity.
+
+[153] See Appendix, Note IX., p. 283.
+
+[154] The rapid fermentation of horse-manure is due to its mechanical as
+well as its chemical nature. The horse does not reduce its food to such
+small pieces, and its urine is rich in nitrogen.
+
+[155] Schulze recommends one-third of a pound per day of sulphate of
+lime for each horse.
+
+[156] See Appendix, Note X., p. 284.
+
+[157] The food consisted of 30 lb. _potatoes_, 15 lb. _hay_, and 120 lb.
+_water_.
+
+[158] For further analyses of cow-manure, see Appendix, Note XI., p.
+286.
+
+[159] This is for a pig of six to eight months old, and fed on potatoes.
+
+[160] It has been asserted that the use of pig-manure, when applied
+alone, is apt to give an unpleasant taste to the produce grown.
+
+[161] Taken from a very large number of analyses by a number of
+experimenters. See Heiden's 'Düngerlehre,' vol. i. p. 99.
+
+[162] See Storer, 'Agricultural Chemistry,' vol. ii. p. 96.
+
+A question of great importance is as to the amount of farmyard manure
+produced on a farm in a year, and its value. This is a question which is
+extremely difficult to satisfactorily deal with. Various methods of
+calculating this amount have been resorted to. It may be well to state
+these pretty fully. Some practical authorities estimate the amount by
+calculating that every ton of straw should produce 4 tons of manure.
+Another method consists in estimating the amount from the size of the
+farm. Sir John Lawes has calculated the composition of farmyard manure
+which should be produced in the case of a farm of 400 acres, farmed on
+the four-course system. He assumes that half of the roots and 100 tons
+of hay are consumed at the homestead; that the whole of the straw of the
+corn crops is retained at home as food and litter; that twelve horses
+have corn equal to 10 lb. of oats per head per day; and that about ten
+shillings per acre are expended in the purchase of cake for feeding
+stock. Under these conditions the amount of farmyard manure should be
+855 tons (or an average of 8-1/2 tons for each of the 100 acres of
+root-crop) of _fresh undecomposed dung_. (For composition, see Appendix,
+Note XVII., p. 291.) Another method is by taking, as the data of
+calculation, the number of cattle, horses, sheep, &c., producing the
+manure. Lloyd considers that a fattening animal requires 3 tons of straw
+in the year, and makes about 12 tons of manure. A farmer, therefore,
+should make 8 tons of manure for every acre of that part of his land
+which, in the four-course rotation, is put down to turnips.
+
+The last method consists in taking as the data the amount of food
+consumed and litter used in the production of the manure. Of these
+methods Heiden considers the last as alone satisfactory and trustworthy.
+Applying this method to the horse, he shows, from experiments, that a
+little over 47 per cent of the dry matter of its food has been proved to
+be voided in the solid and liquid excreta. Taking the average percentage
+of water in the excreta as about 77.5, the percentage of dry matter in
+the excreta will be 22.5. That is, every pound of dry matter in the food
+eaten by the horse yields a little over 2 lb. of excrementitious matter.
+To this of course must be added the amount of straw used as litter,
+which may be taken at 6.5 lb.
+
+From these data we may calculate the amount of manure produced in a year
+by a horse, making certain assumptions as to the amount of work
+performed. This Heiden does by assuming that a horse works 260 days, of
+twelve hours each, in the course of a year, or 130 whole days, spending
+235 days in the stall. Calculating from the above data, he estimates
+that a well-fed working horse will produce about 50 lb. of manure in a
+day, or 6.5 tons in a year. Of course this does not necessarily
+represent all the manure actually produced by the horse, but how much of
+the remaining portion of the manure actually finds its way to the farm
+it is impossible to say. According to the 'Book of the Farm,' Division
+III. p. 98, a farm-horse makes about 12 tons of manure in a year.
+
+It has been calculated that cows void about 48 per cent of the dry
+matter of their food in the solid and liquid excreta, which contain of
+water, on an average, 87.5 per cent. That is, every pound of dry matter
+will furnish 3.84 lb. of total excreta. By adding the necessary amount
+of straw for litter (which may be taken at one-third the weight of the
+dry matter of the fodder), Heiden calculates that an ox weighing 1000
+lb. should produce 113 lb. of manure in a day, or 20 tons in a year. The
+'Book of the Farm,' Division III. p. 98, gives the annual amount at from
+10 to 14 tons. According to Wolff, one may assume that on an average the
+fresh excrements (both liquid and solid) of the common farm animals
+(with the exception of the pig) contain of every 100 lb. of dry matter
+in the food consumed about 50 lb., or a half. Estimating the dry matter
+in the litter used at equal to about 1/4 of the dry matter of the food,
+this would mean that for every 100 lb. of dry matter consumed in food
+there would be 75 lb. of dry manure (viz., 50 lb. dry excrements + 25
+lb. dry litter), which would yield 300 lb. of farmyard manure in the wet
+state--_i.e._, with 75 per cent water. The amount of food daily required
+per every 1000 lb. of live-weight of the common farm animals may be
+taken, roughly speaking, at 24 lb. dry food material and 6 lb. of straw
+as litter. The daily production of manure for 1000 lb. of live-weight
+would amount, therefore, to 18 lb. of dry, or 72 lb. wet manure. (See
+Appendix, Note XVII., p. 291.) According to J. C. Morton and Evershed,
+oxen feeding in boxes require 20 lb. of straw per head per day as
+litter. An ox, therefore, will make 8 tons of fresh dung in six months,
+using 32 cwt. of litter. This means that each ton of litter gives 5 tons
+of fresh dung. It is calculated that nearly twice as much litter must be
+used in open yards.
+
+[163] It has been calculated that under ordinary circumstances
+sheep-dung, when allowed to ferment by itself, should do so in about
+four months, horse-dung in six months, and cow-dung in eight months.
+
+[164] See Appendix, Note XII., p. 286.
+
+[165] See Heiden's 'Düngerlehre,' vol. ii. p. 156.
+
+[166] Warington, 'Chemistry of the Farm,' p. 33.
+
+[167] Recent experiments by Müntz and Girard in France have shown that
+the loss in sheep excreta from volatilisation of the carbonate of
+ammonia amounted to over 50 per cent. By the use of straw litter this
+was reduced to about a half less, and with earth litter one quarter
+less.
+
+[168] See Appendix, Note XIII., p. 288.
+
+[169] See Appendix, Note XIV., p. 289.
+
+[170] See Appendix, Note XV., p. 290.
+
+[171] For spring application rotten farmyard manure is generally used,
+because in this condition its fertilising matter is more quickly
+available. On light land it is best to apply it in the rotten condition
+shortly before it is likely to be used. (See p. 261.)
+
+[172] The total amount of plant-food in a ton of farmyard manure is
+together less than 1/20th of its total weight.
+
+[173] See Heiden's 'Düngerlehre,' vol. ii. p. 171.
+
+[174] For full details see Appendix, Note XVI., p. 290.
+
+[175] Storer reproduces these results in his 'Agricultural Chemistry,'
+vol. ii. p. 21.
+
+[176] This aspect of farmyard manure has been ably stated by Mr F. J.
+Cooke, a well-known Norfolk farmer. In commenting on the results of the
+Rothamsted experiments, he says: "It is clear enough that the faith of
+the farmer in the soil-enriching character of his home-made manure is
+amply justified; the only question being, indeed, if this quality be not
+too highly appreciated. It is not, after all, so much by the fattening
+of our land as by the bounty of the crop grown upon it that we reap the
+fruit of our exertions. The man of scientific mind keeps his purpose
+fixed on the _production of good crops_ mainly, and the cheapest way to
+grow them. The experiments under consideration show that richness of
+land may be purchased much too dearly, and that richness of crop by no
+means bears the necessary relation to richness of soil which has
+sometimes been imagined. We may boast of the 'lasting qualities' of our
+dung, but the answer of science by these experiments is, that so great
+is the last that the life of one man may not be long enough to exhaust
+it. In the extravagant use of dung, therefore, such considerations,
+amongst many others, as length of purse, as well as length and character
+of tenure, must clearly be taken into account."
+
+[177] See paper on "Manurial Experiments with Turnips" by author, in
+'Transactions of the Highland and Agricultural Society of Scotland;'
+1891.
+
+[178] Storer's 'Agricultural Chemistry,' vol. i. p. 498.
+
+[179] Division III. p. 130.
+
+[180] Mr F. J. Cooke, who has already been quoted, has kindly furnished
+the author with his views on the peculiar functions of farmyard manure
+as a manure. He says: "I look upon it, broadly speaking, as chiefly of
+value in restoring to good land, after cropping, those particular
+advantages which good land alone can give, and in helping better than
+any other manure, when applied to poor land, to bring it up to the level
+of good land in those particular merits which belong alone to fine
+soils. I speak now of an inherent value in good soils, beyond that
+attaching to them as mere reservoirs of abundant plant-food. For
+instance, one may supply a poor soil by artificial manure with much more
+food--and in a highly soluble condition--than is needed by the crop to
+be grown upon it, and yet not get so good a crop as upon a naturally
+richer but otherwise similar soil less abundantly filled with
+immediately available food. This may arise from a more perfect
+distribution of the plant-food in the rich soil, or from the steady way
+in which it becomes available to the crop, as well as for other reasons.
+But whatever the cause, there, I think, is the broad fact of the power
+of farmyard manure to enrich poor soils, so to speak, more
+naturally--that is, in a way which makes them more nearly correspond to
+better soils than artificial manures can."
+
+Hence the indirect benefit to the farmer from farmyard manure is
+probably greater than its direct value as a mere manure. And the usual
+provision and use of it amongst all straw-growing farmers is
+sufficiently justified. The extent, however, to which that course may be
+beneficially carried, is one of the most important of the many difficult
+economic and scientific problems which the farmer has to face.
+
+On the economic side must of course be considered the cost of
+manufacture in individual instances, as ruled by the market value of the
+straw, and the different circumstances and conditions under which the
+various farm animals are kept and fed (I have the figures by me of one
+well-known farmer, which show the cost to him of every ton of home-made
+manure to be 20s. or more); the price the resultant crops may be
+expected to command; the cost at the moment of artificial manures, &c.,
+&c. Whilst on the scientific side must be considered the nature of the
+soil, the particular rotation of crops, &c.
+
+It was, amongst others, just these scientific and yet very definite and
+practical problems we have tried to throw light on in the series of
+field experiments conducted for several years by the Norfolk Chamber of
+Agriculture. (See reprint of summary of same in last year's Report of
+the Board of Agriculture.)
+
+
+
+
+APPENDIX TO CHAPTER VII.
+
+
+NOTE I. (p. 225).
+
+DIFFERENCE IN AMOUNT OF EXCRETA VOIDED FOR FOOD CONSUMED.
+
+With regard to the difference in the composition of the solid excreta
+voided by different fattening animals fed on the same amount of food,
+see Warington's 'Chemistry of the Farm,' p. 125, where it is shown that
+for equal amount of live-weight, the sheep produces on the same weight
+of dry food very much more manure than the pig, while the ox produces
+even more than the sheep. Of course this does not refer to the total
+amount of manure produced by the different animals, but only to the
+amount of manure produced from the consumption of equal quantities of
+food. This would seem to be owing to the greater capacity the pig has
+for assimilating its food.
+
+
+NOTE II. (p. 227).
+
+SOLID EXCRETA VOIDED BY SHEEP, OXEN, AND COWS.
+
+To contrast with the analyses given by Stoeckhardt, it may be well to
+cite those based on Lawes and Gilbert's experiments, and quoted by
+Warington ('Chemistry of the Farm,' p. 138):--
+
+I.--SHEEP (fed on _meadow-hay_).
+
+ SOLID EXCREMENT.
+ Fresh. Dry.
+Water 66.2 -
+Organic matter 30.3 89.6
+Ash 3.5 10.4
+ ---- ----
+Nitrogen .7 2.0
+
+II.--OXEN (fed on _clover-hay_ and _oat-straw_, with 8 lb.
+_beans_ per day).
+
+ Fresh. Dry.
+Water 86.3 -
+Organic matter 12.3 89.7
+Ash 1.4 10.3
+ ---- ----
+Nitrogen .3 1.9
+
+III.--COWS (fed on _mangels_ and _lucerne hay_).
+
+ Mangels. Lucerne hay.
+Water 83.00 79.70
+Nitrogen .33 .34
+Phosphoric acid .24 .16
+Potash .14 .23
+
+
+NOTE III. (p. 232).
+
+URINE VOIDED BY SHEEP, OXEN, AND COWS.
+
+The following are the results for urine, the animals being fed as in
+Note II.:--
+
+ Sheep. Oxen.
+ Fresh. Dry. Fresh. Dry.
+Water 85.7 - 94.1 -
+Organic matter 8.7 61.0 3.7 63.0
+Ash 5.6 39.0 2.2 37.0
+ ---- ---- ---- ----
+Nitrogen 1.4 9.6 1.2 20.6
+
+ Cows.
+ Mangels. Lucerne hay.
+Water 95.94 88.25
+Nitrogen .12 1.54
+Phosphoric acid .01 .006
+Potash .59 1.69
+
+
+NOTE IV. (p. 233).
+
+PERCENTAGE OF FOOD VOIDED IN THE SOLID AND LIQUID EXCREMENTS.
+
+According to Wolff, the following table shows the percentage of the dry
+substance of the food which is voided in the solid and liquid excrements
+of the cow, ox, sheep, and horse:--
+
+ Cow. Ox. Sheep. Horse. Average.
+Solid excreta 38.0 44.0 42.6 46.7 42.8
+Urine 5.8 6.3 6.8 5.7 6.2
+ ---- ---- ---- ---- ----
+Total 43.8 50.3 49.4 52.4 49.0
+
+
+NOTE V. (p. 234).
+
+PIG EXCREMENTS.
+
+The excrements voided by pigs are poor in manurial constituents, because
+the food on which they are fed is generally of a very poor nature. In
+their case the urine is always very much richer in manurial ingredients
+than the solid excreta. The relative composition of the solid excreta
+and the urine will be best illustrated by quoting some experiments
+carried out by Wolff on this subject. The experiments were carried out
+with two pigs nine and a half months old, and each 121.9 kilogrammes (a
+kilogramme is equal to about 2-1/4 lb.) in weight. The first consumed
+daily 1000 grammes of barley, 5000 grammes of potatoes, and 2572 grammes
+of sour-milk. The second one consumed the same quantities of potatoes
+and sour-milk as the first, and 1000 grammes of peas. The following
+table gives the results of excreta and urine daily voided, in grammes:--
+
+ Dry Nitrogen. Ash. Potash. Lime. Magnesia. Phosphoric
+ substance acid.
+Solid { I. 217.7 8.7 28.6 7.3 4.4 3.0 10.3
+excreta { II. 161.1 9.1 31.1 5.9 4.9 2.8 11.1
+
+Urine { I. 112.8 19.3 56.2 33.0 0.4 0.9 6.7
+ { II. 137.7 30.6 62.2 37.1 0.2 1.1 7.1
+
+
+NOTE VI.(p. 236).
+
+MANURIAL CONSTITUENTS IN 1000 PARTS OF ORDINARY FOODS.
+
+Based on Lawes and Gilbert's Analyses.
+
+(Warington's 'Chemistry of the Farm,' p. 139.)
+
+-----------------------------+---------+-----------+---------+------------
+ | Dry | Nitrogen. | Potash. | Phosphoric
+ | matter. | | | acid.
+-----------------------------+---------+-----------+---------+------------
+ Cotton-cake, decorticated | 918 | 70.4 | 15.8 | 30.5
+ Rape-cake | 887 | 50.5 | 13.0 | 20.0
+ Linseed-cake | 883 | 43.2 | 12.5 | 16.2
+ Cotton-cake, undecorticated | 878 | 33.3 | 20.0 | 22.7
+ Linseed | 882 | 32.8 | 10.0 | 13.5
+ Palm-kernel meal, English | 930 | 25.0 | 5.5 | 12.2
+ Beans | 855 | 40.8 | 12.9 | 12.1
+ Peas | 857 | 35.8 | 10.1 | 8.4
+ Malt-dust | 905 | 37.9 | 20.8 | 18.2
+ Bran | 860 | 23.2 | 15.3 | 26.9
+ Oats | 870 | 20.6 | 4.8 | 6.8
+ Rice-meal | 900 | 19.1 | 6.1 | 23.8
+ Wheat | 877 | 18.7 | 5.2 | 7.9
+ Rye | 857 | 17.6 | 5.8 | 8.5
+ Barley | 860 | 17.0 | 4.7 | 7.8
+ Maize | 890 | 16.6 | 3.7 | 5.7
+ Brewers' grains | 234 | 7.8 | 0.4 | 3.9
+ Clover-hay | 840 | 19.7 | 18.6 | 5.6
+ Meadow-hay | 857 | 15.5 | 16.0 | 4.3
+ Bean-straw | 840 | 13.0 | 19.4 | 2.9
+ Oat-straw | 857 | 6.4 | 16.3 | 2.8
+ Barley-straw | 857 | 5.6 | 10.7 | 1.9
+ Wheat-straw | 857 | 4.8 | 6.3 | 2.2
+ Potatoes | 250 | 3.4 | 5.8 | 1.6
+ Swedes | 107 | 2.2 | 2.0 | 0.6
+ Carrots | 140 | 2.1 | 3.0 | 1.1
+ Mangels | 120 | 1.8 | 4.6 | 0.7
+ Turnips | 80 | 1.6 | 2.9 | 0.8
+-----------------------------+---------+-----------+---------+------------
+
+
+NOTE VII. (p. 241).
+
+ANALYSES OF STABLE-MANURE, MADE RESPECTIVELY WITH PEAT-MOSS LITTER
+AND WHEAT-STRAW (by BERNARD DYER, B.Sc.)
+
+ Peat-moss litter. Wheat-straw.
+ Per cent. Per cent.
+Total nitrogen 0.88 0.61
+Equal to ammonia 1.07 0.74
+Phosphoric acid 0.37 0.43
+Equal to Tribasic phosphate of
+ lime (or Tricalcic phosphate) 0.80 0.94
+Potash 1.02 0.59
+
+
+NOTE VIII. (p. 242).
+
+ANALYSES OF BRACKEN (by J. HUGHES, F.C.S.)
+
+ No. 1 No. 2
+ Young fern. Old fern.
+ Per cent. Per cent.
+
+ Water 11.66 14.90
+ * Organic matter 83.38 80.54
+ + Mineral matter 4.96 4.56
+ ------ ------
+ 100.00 100.00
+ ------ ------
+Containing--
+ * Nitrogen 2.42 0.90
+ + Silica 1.60 2.81
+ Potash 1.15 0.10
+ Soda 0.64 0.26
+ Lime 0.44 0.62
+ Magnesia 0.13 0.47
+ Phosphoric acid 0.60 0.30
+
+
+NOTE IX. (p. 244).
+
+ANALYSES OF HORSE-MANURE.
+
+For a fuller discussion of this question, the reader is referred to
+Heiden's 'Düngerlehre,' vol. ii. p. 185, and also to Storer's
+'Agricultural Chemistry,' vol. i. p. 575. The statements in the
+different text-books as to the quantity of manure produced by the horse
+are such as naturally to perplex the student. This discrepancy is due,
+however, to the different methods adopted by different writers of
+calculating this amount. The subject is further discussed in the
+footnote to p. 252. The following analyses of horse-manure may be
+valuable for reference. They are taken from Storer's 'Agricultural
+Chemistry,' vol. i. p. 496:--
+
+----------------+-------+-------+-------+-------+-------+---------
+ | 1. | 2. | 3. | 4. | 5. | Average.
+----------------+-------+-------+-------+-------+-------+---------
+Water | 75.76 | 69.30 | 67.23 | 72.13 | 71.30 | 71.15
+Dry matter | 24.24 | 24.82 | 32.72 | 27.87 | 28.70 | 27.67
+Ash ingredients | 5.07 | 5.05 | 6.49 | 3.37 | 3.30 | 4.65
+Potash | 0.51 | 0.63 | 0.22 | 0.59 | 0.53 | 0.49
+Lime | 0.30 | 0.74 | 0.17 | 0.41 | 0.21 | 0.36
+Magnesia | 0.19 | 0.29 | 0.20 | 0.17 | 0.14 | 0.20
+Phosphoric acid | 0.41 | 0.67 | 0.35 | 0.12 | 0.28 | 0.36
+Ammonia | 0.26 | 0.12 | 0.15 | 0.44 | - | 0.24
+Total nitrogen | 0.53 | 0.69 | 0.47 | 0.67 | 0.58 | 0.59
+----------------+-------+-------+-------+-------+-------+---------
+
+
+NOTE X. (p. 247).
+
+THE NATURE OF THE CHEMICAL REACTIONS OF AMMONIA "FIXERS."
+
+For the student, the exact nature of the chemical reactions taking place
+may be of interest.
+
+In the first place, it must be distinctly understood that the form in
+which ammonia escapes from the manure-heap is not, as is so commonly
+erroneously stated in agricultural text-books, as "free" ammonia.
+Whenever ammonia is brought into contact with carbonic acid, carbonate
+of ammonia is formed. When it is remembered that carbonic acid is by far
+the most abundant of the gaseous products of the decomposition of
+organic matter, it will be at once seen that free ammonia could not
+exist under such circumstances.
+
+1. In the case of _hydrochloric acid_, the following chemical equation
+will represent the nature of the reaction--
+
+2HCl + (NH_{4})_{2}CO_{3} = 2NH_{4}Cl + H_{2}O+CO_{2}
+(Hydrochloric (carbonate of ammonia,) (sal-ammoniac,) (carbonic acid.)
+ acid,)
+
+2. In the case of _sulphuric acid_, the equation will be--
+
+H_{2}SO_{4} + (NH_{4})_{2}CO_{3} = (NH_{4})_{2}SO_{4} + H_{2}O+CO_{2}
+(Sulphuric (carbonate of (sulphate of ammonia,) (carbonic acid.)
+ acid,) ammonia,)
+
+3. With _gypsum_ (CaSO_{4})--
+
+CaSO_{4} + (NH_{4})_{2}CO_{3} = CaCO_{3} + (NH_{4})_{2}SO_{4}
+(Gypsum,) (carbonate of (calcium (sulphate of ammonia.)
+ ammonia,) carbonate,)
+
+4. With _copperas_ (FeSO_{4})--
+
+FeSO_{4} + (NH_{4})_{2}CO_{3} = FeCO_{3} + (NH_{4})_{2}SO_{4}
+(Sulphate of (carbonate of (ferrous (sulphate of ammonia.)
+iron,) ammonia,) carbonate,)
+
+5. With _sulphate of magnesia_ (MgSO_{4})--
+
+MgSO_{4} + (NH_{4})_{2}CO_{3} = MgCO_{3} + (NH_{4})_{2}SO_{4}
+(Sulphate of (carbonate of (carbonate of (sulphate of
+ magnesia,) ammonia,) magnesia,) ammonia.)
+
+Reference has been made to the fact that magnesium sulphate may probably
+not only fix the ammonia, but the phosphoric acid. When magnesium
+sulphate, soluble phosphoric acid, and ammonia are brought in contact
+with one another, the double insoluble phosphate of ammonium and
+magnesium (MgNH_{4}PO_{4}6Aq) is formed. While such a reaction is
+possible, it is highly improbable that it takes place to any extent. The
+double phosphate is a crystalline salt which only separates after a
+considerable time, and in the presence of a large excess of ammonia.
+
+
+NOTE XI. (p. 250).
+
+ANALYSES OF COW-MANURE.[181]
+
+----------------+-------+-------+-------+-------+-------+-------+--------
+ | 1. | 2. | 3. | 4. | 5. | 6. |Average.
+ +-------+-------+-------+-------+-------+-------+--------
+Water | 85.30 | 77.71 | 74.02 | 72.87 | 75.00 | 77.50 | 77.06
+Dry matter | 14.70 | 22.30 | 25.98 | 27.13 | 25.00 | 22.50 | 22.93
+Ash ingredients | 2.04 | 4.71 | 3.94 | 6.70 | 6.22 | 2.20 | 4.30
+Potash | 0.36 | 0.46 | 0.56 | 1.69 | 0.39 | 0.40 | 0.64
+Lime | 0.29 | 0.37 | 0.58 | 0.41 | 0.24 | 0.31 | 0.48
+Magnesia | 0.19 | 0.11 | 0.13 | - | 0.18 | 0.11 | -
+Phosphoric acid | 0.16 | 0.13 | 0.07 | 0.20 | 0.14 | 0.16 | 0.14
+Ammonia | 0.06 | 0.16 | 0.07 | - | 0.27 | - | 0.14
+Total nitrogen | 0.38 | 0.54 | 0.41 | 0.79 | 0.46 | 0.34 | 0.48
+----------------+-------+-------+-------+-------+-------+-------+--------
+
+
+NOTE XII. (p. 259).
+
+COMPOSITION OF FRESH AND ROTTEN FARMYARD
+MANURE (VOELCKER).
+
+Composition of fresh manure, composed of horse, cow,
+and pig dung, about fourteen days old:--
+
+ Water 66.17
+ * Soluble organic matter 2.48
+ Soluble inorganic matter 1.54
+ + Insoluble organic matter 25.76
+ Insoluble inorganic matter 4.05
+ ------
+ 100.00
+ ------
+ * Containing nitrogen .149
+ Equal to ammonia .181
+ + Containing nitrogen .494
+ Equal to ammonia .599
+ Total percentage of nitrogen .643
+ Equal to ammonia .780
+ Ammonia in a volatile state .034
+ Ammonia in form of salts .088
+
+Composition of the whole ash:--
+
+ Soluble in water, 27.55 per cent:--
+ Soluble silica 4.25
+ Phosphate of lime 5.35
+ Lime 1.10
+ Magnesia 0.20
+ Potash 10.26
+ Soda 0.92
+ Chloride of sodium 0.54
+ Sulphuric acid 0.22
+ Carbonic acid and loss 4.71
+
+ Insoluble in water, 72.45 per cent:--
+ Soluble silica 17.34
+ Insoluble silicious matter 10.04
+ Oxide of iron and alumina with phosphates 8.47
+ (Containing phosphoric acid, 3.18 per cent.)
+ (Equal to bone-earth, 6.88 per cent.)
+ Lime 20.21
+ Magnesia 2.56
+ Potash 1.78
+ Soda 0.38
+ Sulphuric acid 1.27
+ Carbonic acid and loss 10.40
+ ------
+ 100.00
+ -------
+
+Composition of rotten dung, six months old, is as
+follows:--
+
+ Water 75.42
+ * Soluble organic matter 3.71
+ Soluble inorganic matter 1.47
+ + Insoluble organic matter 12.82
+ Insoluble inorganic matter 6.58
+ ------
+ 100.00
+ ------
+
+ * Containing nitrogen .297
+ Equal to ammonia .360
+ + Containing nitrogen .309
+ Equal to ammonia .375
+ Total amount of nitrogen .606
+ Equal to ammonia .735
+ Ammonia in a volatile state .046
+ Ammonia in form of salts .057
+Composition of the whole ash:--
+
+Soluble in water, 18.27 per cent:--
+
+Soluble silica 3.16
+Phosphate of lime 4.75
+Lime 1.44
+Magnesia 0.59
+Potash 5.58
+Soda 0.29
+Chloride of sodium 0.46
+Sulphuric acid 0.72
+Carbonic acid and loss 1.28
+
+Insoluble in water, 81.73 per cent:--
+Soluble silica 17.69
+Insoluble silica 12.54
+Phosphate of lime -
+Oxides of iron alumina with phosphates 11.76
+ (Containing phosphoric acid, 3.40 per cent.)
+ (Equal to bone-earth, 7.36 per cent.)
+Lime 20.70
+Magnesia 1.17
+Potash 0.56
+Soda 0.47
+Chloride of sodium -
+Sulphuric acid 0.79
+Carbonic acid and loss 16.05
+ ------
+ 100.00
+ ------
+
+
+NOTE XIII. (p. 263).
+
+COMPARISON OF FRESH AND ROTTEN MANURE (WOLFF).
+
+ Fresh. Moderately rotten
+ (Taking the quantity of dry matter
+ as the same.)
+Dry matter 25.00 25.00
+Ash 3.81 4.76
+Nitrogen 0.39 0.49
+Potash 0.45 0.56
+Lime 0.49 0.61
+Magnesia 0.12 0.15
+Phosphoric acid 0.18 0.23
+Sulphuric acid 0.10 0.13
+Silica 0.86 1.08
+
+
+NOTE XIV. (p. 263).
+
+LORD KINNAIRD'S EXPERIMENTS.[182]
+
+"Lord Kinnaird has given the particulars of a very careful experiment.
+He tried to test the comparative value of manure kept in an open court
+with that kept under cover. He selected the same kind of cattle, gave
+them the same kind and quantity of food, and bedded them with the same
+kind of straw. A field of 20 acres of uniform land was selected. This
+having been equally divided, 2 acres out of each 10 gave the following
+results:--
+
+_Potatoes grown with Uncovered Manure._
+
+ Tons. cwt. lb.
+First measurement--1 acre produced. 7 6 8
+Second do. do. do. 7 18 99
+
+_Potatoes grown with Covered Manure._
+
+First measurement--1 acre produced. 11 17 56
+Second do. do. do. 11 12 26
+
+This shows an increase of about 4 tons of potatoes per acre with the
+covered manure.
+
+"The next year the weather was wet, grain soft and not in very good
+order, but the following was the amount of produce:--
+
+_Wheat grown with Uncovered Manure._
+
+ Weight per
+ Produce in grain. bushel. Produce in straw.
+ Acre. bushels. lb. lb. stones. lb.
+First 41 19 61-1/2 152 of 22
+Second 42 38 61-1/2 160 of 22
+
+_Wheat grown with Covered Manure._
+
+First 53 5 61 220 of 22
+Second 53 47 61 210 of 22"
+
+
+NOTE XV. (pp. 231, 264).
+
+DRAININGS OF MANURE-HEAPS.
+
+The importance of not separating the liquid portion from the solid
+portion has already been pointed out in dealing with the composition of
+the solid excreta and the urine. These two constituents of the manure
+are complementary to one another, and the value of farmyard manure as a
+general manure is very much impaired if the liquid portion is not
+applied along with the solid. In one important respect do the drainings
+of manure-heaps differ from urine--that is, in the percentage of
+phosphates they contain, the latter being practically devoid of
+phosphoric acid.
+
+The following is an analysis of drainings from a manure-heap (Wolff):--
+
+Dry substance 18.0 | Magnesia 0.4
+Ash 10.7 | _Phosphoric acid_ 0.1
+Nitrogen 1.5 | Sulphuric acid 0.7
+Potash 4.9 | Silica 0.2
+Lime 0.3 |
+
+
+NOTE XVI. (p. 270).
+
+AMOUNTS OF POTASH AND PHOSPHORIC ACID REMOVED BY THE FOLLOWING
+ROTATIONS FROM A PRUSSIAN MORGEN (.631 ACRE).
+
+ Potash. Phosphoric acid.
+ lb. lb.
+1. Wheat 16.40 10.67
+ Oats 10.47 4.59
+ Potatoes 66.41 18.33
+ Hay 39.54 11.32
+ ------ -----
+ 132.82 44.91
+ ------ -----
+The ratio of potash to phosphoric acid is 2.96 to 1.
+
+2. Wheat 16.90 10.67
+ Barley 17.44 10.65
+ Potatoes 66.41 18.33
+ Hay 39.54 11.32
+ ------ -----
+ 140.29 50.97
+ ------ -----
+The ratio of potash to phosphoric acid is 2.76 to 1.
+
+3. Rye 20.03 12.15
+ Oats 10.97 4.59
+ Potatoes 66.41 18.33
+ Hay 39.54 11.32
+ ------ -----
+ 136.95 46.39
+ ------ -----
+The ratio of potash to phosphoric acid is 2.95 to 1.
+
+4. Wheat 16.90 10.67
+ Oats 10.97 4.59
+ Mangels 148.54 25.62
+ Hay 39.54 11.32
+ ------ -----
+ 215.95 52.20
+ ------ -----
+The ratio of potash to phosphoric acid is 4.13 to 1.
+
+5. Rye 20.03 12.15
+ Barley 17.44 10.65
+ Mangels 148.54 25.62
+ Hay 39.54 11.32
+ ------ -----
+ 225.55 59.74
+The ratio of potash to phosphoric acid is 3.78 to 1.
+
+
+NOTE XVII. (pp. 253, 254).
+
+COMPOSITION OF FARMYARD MANURE (FRESH), (calculated by SIR
+JOHN LAWES).
+
+ Phosphoric acid
+ Total dry Total mineral calculated as Potash. Nitrogen.
+ matter. matter. phosphate of
+ lime.
+Percent 30.0 2.77 .50 .53 .64
+Per ton (in lb.) 67.2 62.0 11.1 12.0 14.3
+
+
+NOTE XVIII. (p. 232).
+
+THE URINE.
+
+An important consideration we have omitted to take note of in the text
+is the quantity of the urine voided. It is this consideration that
+renders the urine so much more valuable than the solid excreta. In the
+case of a man it has been estimated that the urine voided is fifteen
+times as much, is twelve times as rich in nitrogen, three times in
+potash, and two in phosphoric acid, as the solid excreta (Munro). The
+relation of solid matter in the case of the farm animals is not exactly
+similar. The urine of the ox is about twice the weight of its solid
+excreta. Both the horse and the sheep, however, void as a rule more
+solid excreta than urine. Munro, in his work on 'Soils and Manures,'
+contrasts the composition of the urine and solid excreta of the
+different farm animals by the following statement:--
+
+ 1 ton of urine contains 1 ton of solid excreta
+ in lb.: contains in lb.:
+
+ Nitrogen. Potash. Nitrogen.
+Cow 30 20 9
+Horse 36 22 12
+Sheep 38 30 16
+
+
+FOOTNOTES:
+
+[181] Storer's 'Agricultural Chemistry,' vol. I. p. 496.
+
+[182] Scott's 'Manures and Manuring,' p. 19.
+
+
+
+
+CHAPTER VIII.
+
+GUANO.
+
+
+_Importance in Agriculture._
+
+In the consideration of _artificial_ manures, guano deserves the first
+place. This it does mainly on historical grounds, as it is now largely a
+manure of the past. Not merely has it been used in agriculture to an
+extent to which no other artificial manure has as yet ever approximated,
+but its influence on agricultural practice has been enormous. Introduced
+into this country about the middle of the present century, it was the
+first of artificial manures to be used in large quantities.[183] It may
+be thus described as having introduced the modern system of _intensive_
+cultivation, and given rise to the now almost universal practice of
+artificial manuring.
+
+
+_Influence on British Farming._
+
+It is, indeed, difficult to over-estimate the important influence which
+the introduction of this most valuable fertiliser has exercised on
+British as well as, to a large extent, on European husbandry. Before its
+introduction the farmer was almost completely dependent on his farmyard
+manure. He was tied down to a great extent, by the exigencies of the
+then prevailing agricultural customs, to certain rotations of crops. He
+could do little in the way of enriching barren soils or of ensuring a
+heavy yield of crop. By the use of this very potent fertiliser, he
+quickly discovered that the most wonderful results ensued--results which
+must have seemed to him at first little short of miraculous. He found
+that by the application of a few hundredweights per acre, poor soils
+could be made to yield large returns, and that barren patches in a field
+could be brought up to the average of the surrounding portions by
+sprinkling merely a few handfuls of it; that by its means a good start
+could be ensured to every crop, and one slow of coming away could be
+hastened on. In short, in this wonderful brown powder, with such a
+characteristic odour, the astonished farmer discovered a manure which,
+for the speed of its action, and for the increase of crop it gave,
+completely threw into the shade both farmyard manure and bones. What
+wonder, then, that its fame as a manure should have become so quickly
+known and its use so extensive! It thus gave a most powerful impetus to
+intelligent farming by bringing home to the minds of those who used it
+the important position nitrogen and phosphates occupied as constituents
+of the soil, and the influence they exercised on plant-growth. It
+furnished, in fact, on an enormously large scale, a practical
+demonstration of the principles of manuring. The educational value which
+the use of guano thus exercised may be said to have been very great. It
+also led the way to the use of the various artificial manures so much
+used during the last fifty years. Impressed by the value of guano,
+farmers were favourably disposed towards the use of other fertilisers;
+and, largely owing to its widespread popularity, the new practice
+speedily gained ground.
+
+
+_Influence not wholly for Good._
+
+But its influence, it must be admitted, was not wholly for good. In its
+very popularity lay the danger of its abuse. Had its value and the
+method of its action been more widely understood, and had the principles
+upon which the practice of artificial manuring depends been better
+realised, agriculturists would have been spared much of the needless
+pecuniary losses they sustained by being imposed upon by unscrupulous
+manure-dealers. Among the farming community the word guano soon became a
+name to conjure with, and under this title many spurious and worthless
+manures were attempted to be palmed off on the unwary farmer. Even the
+genuine article, there can be little doubt, was at one time largely
+adulterated; and as the farmer was almost invariably content to purchase
+the article not on any guaranteed chemical analysis, but simply on the
+ground of its appearance, colour, and more especially smell, every
+facility was given for the successful perpetration of such fraudulent
+imposition. Guano, it was very soon found, varied in its composition,
+but this variation in quality the farmer did not recognise. In the early
+days of its use all guano was in his eyes of the same value. Too often,
+as we have just pointed out, provided it had a good colour and a strong
+odour, it was all right. Under such conditions, it can scarcely be
+wondered at that its introduction should have proved not an unmixed
+blessing to agriculture.
+
+
+_Its Value as a Manure._
+
+Guano derives its value as a manure from the nitrogen, phosphates, and
+the small amount of potash it contains. This at any rate is true of the
+great bulk of guano which has been used in the past. There are, as we
+shall immediately see, certain kinds of guano, known as phosphatic
+guanos, which only contain phosphates. The amount of such purely
+phosphatic guano directly used as a manure in this country is, however,
+inconsiderable, and guano may truly be described as owing its value
+chiefly to its nitrogen. Not a little of its value and popularity as a
+manure may be said to be due to the fact that it contains all of the
+three important manurial constituents, and that in this respect it may
+be regarded in a sense as a _general_ manure, thus resembling most
+nearly, of all artificial manures, farmyard manure. Although its sources
+are now, to a very large extent, exhausted, and its total annual imports
+into this country are at present considerably less than what they were
+thirty or forty years ago,[184] it may be well, on account of its
+historical importance, to give a somewhat detailed account of its
+origin, occurrence, and value as a manure.
+
+
+_Origin and Occurrence._
+
+Guano (which means _dung_)--or huano, as it is spelt in the Spanish
+language--was first used in Peru. It seems to have been used there long
+before that country was discovered by the Spaniards--probably as early
+as the twelfth century. Regarding its origin there can be little doubt.
+It is almost entirely derived from the excrements of sea-birds, such as
+pelicans, penguins, and gulls, as well as from the remains of the birds
+themselves, and of seals, walruses, and various other animals.[185]
+Under the influence of a tropical sun, and in a region in which rain
+scarcely ever falls, these excrements are soon dried, and remain little
+changed in their composition through centuries. Many of the Peruvian
+deposits must be extremely old, as they are covered up with sand and
+other _débris_, and are of considerable depth. Especially is this the
+case with deposits occurring on the mainland, such as those at Pabellon
+de Pica, where the layer of sand or conglomerate covering up the deposit
+varies in depth from a few feet to over a hundred. The effect of this
+superficial covering has been to protect the guano, to a certain extent,
+from loss of nitrogen.
+
+Although guano of the best class has been derived from the neighbourhood
+of Peru, deposits have also been found in many other parts of the
+world--viz., in North America, West Indies, Australia, Asia, Africa, and
+among the islands of the Pacific.[186]
+
+
+_Variation in the Composition of different Guanos._
+
+The guano found in these different deposits varies very considerably in
+composition. This is due to the difference in the nature of the
+prevailing climate of the places where these deposits occur. Where the
+climate is dry and warm, as is the case in Chili and Peru, the
+excrements dry quickly and remain very little changed, as one very
+important condition of fermentation--viz., moisture--is absent.[187] In
+a damp climate, on the other hand, speedy fermentation ensues, resulting
+in the loss of nearly all the organic matter, including nitrogen, in
+such volatile forms as carbonate of ammonia, carbonic acid gas, water,
+&c. The soluble alkalies, the most important of which is potash, as well
+as the soluble phosphates, are also, under such conditions, lost to the
+guano by being washed out by the rain. We have thus a wide difference in
+the quality of the different deposits, depending on the extent to which
+decomposition has taken place. Guano thus ranges from the rich
+nitrogenous Peruvian kind, which has undergone little or no change from
+the time of its deposit, to the purely phosphatic kind (such as those of
+Malden and Baker islands), in which everything of manurial value has
+been lost except the insoluble phosphate of lime. Even among the
+nitrogenous guanos we find a considerable difference in quality, some
+deposits being partially impoverished by the action of the atmospheric
+moisture, dew, spray or sea-water, but still containing a considerable
+proportion of their nitrogen. Other deposits, again, are largely admixed
+with sand, which has been blown in upon them to such an extent as to
+make them unsaleable. We can divide guano, therefore, into two great
+classes--viz., _nitrogenous_ and _phosphatic_.
+
+
+I.--NITROGENOUS GUANOS.
+
+(_a_) PERUVIAN.
+
+By far the most valuable and abundant deposits as yet discovered have
+been those on the Peruvian and Chilian coasts. As already pointed out,
+guano seems to have been used in this country from a very early period;
+and so impressed were the Incas with its importance as a manure, that
+the penalty of death was imposed on any one guilty of killing the
+sea-fowl during the breeding season in the vicinity of the deposits.
+
+The occurrence of guano in Peru seems first to have been made known in
+Europe in the beginning of the eighteenth century. It was not, however,
+till the beginning of the present century--viz., 1804--that A. Humboldt,
+the great German traveller, brought some of the wonderful fertiliser
+home with him, and that its composition was able to be investigated by
+chemical analysis. Shortly afterwards, its practical value was
+demonstrated by experiments carried out on potatoes by General Beatson
+in St Helena. To Lord Derby is due the credit of having first introduced
+it into this country, the earliest importation into Liverpool being in
+1840. Experiments were shortly afterwards instituted in different parts
+of the country, prominent among which were those by Sir John Lawes and
+Sir James Caird; and so striking were the results obtained, that the
+manure rapidly found favour with the farming community--so much so, that
+ten years later the importations into this country amounted to no less
+than 200,000 tons, while in 1855 the total exports from the west coast
+of South America reached the enormous amount of 400,000 tons. In all, it
+has been estimated that since the year 1840 over 5,000,000 tons of
+Peruvian guano have been imported into this country.
+
+
+_Different Deposits._
+
+Peruvian guano has been derived from various deposits occurring in
+different parts of the coast, and from a number of small adjacent
+islands. The richest of these was that found on Angamos, a rocky
+promontory on the coast of Bolivia. Samples of this guano contained as
+high as 20 per cent of nitrogen (equal to 24 per cent ammonia).[188]
+Unfortunately, however, the quantity of this deposit was extremely
+limited, and became rapidly exhausted. Next to this deposit in quality
+was the guano found on the Chincha islands, three little islands off the
+coast of Peru. These deposits were the largest which have ever been
+discovered, and for a period of nearly thirty years were almost the sole
+source of the Peruvian guano sold in commerce, over 10,000,000 tons
+having been exported from them alone. Some of this guano contained 14
+per cent of nitrogen (equal to 17 per cent ammonia); and although part
+of the guano shipped from these islands was not quite so rich, yet it
+was all of a high-class order. The deposits on these islands were in
+many cases 100 to 200 feet in depth, and rested on rocks of granite. The
+lower layers were consequently found to be poorer in quality, and mixed
+with pieces of granite. The Chincha island deposits have been long
+exhausted,[189] and the chief deposits of Peruvian guano since worked
+have been those on Guanape and Macabi islands--a considerably inferior
+guano, containing only 9 to 11 per cent of nitrogen (equal to 11 to 13
+per cent of ammonia)--which in their turn have become exhausted; from
+Ballestas, almost as rich as the Chincha island guano, also now
+exhausted; and from Pabellon de Pica, Punta de Lobos, Huanillos,
+Independence Bay, and Lobos de Afuera. Quite recently a deposit of very
+high-class guano was discovered in Corcovado, and a good many cargoes
+have already been shipped to this country. It is found to contain
+nitrogen equal to from 10 to 13 per cent ammonia, 30 to 35 per cent
+phosphates, and some potash, being thus a most valuable guano.
+
+
+_Appearance, Colour, and Nature._
+
+In colour it varies from a very light to a very dark brown, the richer
+samples being generally lighter. Samples taken from even the same
+deposit have been found to differ very considerably in appearance, those
+taken from the lower and older layers being usually darker than those
+taken from the more recent upper layers. It was soon found also to vary
+very much in composition. After a deposit had been worked for some time,
+the quality of guano it yielded was found to be inferior and coarser,
+and in many cases mixed with pebbles or pieces of granite, porphyry, &c.
+This led to the custom of screening it on arrival in this country,
+before it was used as a manure. In the richer qualities--_e.g._, in the
+Chincha guano--little round concretionary nodules, varying in colour
+from pure white to dark brown, were occasionally found. Analysis showed
+these nodules[190] to be composed chiefly of potash salts. Sometimes,
+also, little crystals of almost pure ammonia salts were found. It soon
+became customary, therefore, to prepare guano for the market by
+separating the stones and reducing the whole to a fine uniform powder.
+One of its most characteristic properties, and the one which seems to
+have impressed the public most, was its pungent odour. Undue importance
+was attached to this property, in the belief that it was caused by the
+ammonia it contained. It may be doubted, however, whether the
+characteristic smell of guano is due so much to its ammonia as to
+certain fatty acids.
+
+
+_Composition._
+
+In composition it is of a most complex nature. It contains its nitrogen
+in a great variety of forms, the chief of these being urate, oxalate,
+ulmate, humate, sulphate, phosphate, carbonate, and muriate of ammonia;
+and also in a rare form of organic nitrogen peculiar to guano, called
+guanine. According to Boussingault, some guanos contain small quantities
+of nitrates. Its phosphoric acid is present both in the soluble
+state--viz., as phosphates of the alkalies (ammonia and potash)--and in
+the insoluble state as phosphate of lime; and lastly, its potash is
+present as sulphate and phosphate. The proportion in which these
+different forms of nitrogen and phosphoric acid are present varies
+considerably in different samples. The richer a sample, as a rule, the
+more nitrogen in the form of uric acid it contains. The most of the
+nitrogen is present as uric acid and ammonia. Damp guanos contain more
+of their nitrogen as ammonia than dry ones, this being due to the
+fermentation which goes on in the former. On an average, about a third
+of its total nitrogen is soluble in water. Of its phosphates, on the
+other hand, only about a fourth are soluble in water.
+
+The following analyses of a sample of Chincha island guano by
+Karmrodt[191] will illustrate this. (Sample dried at 212° Fahr.):--
+
+1. _Constituents easily soluble in Water._
+
+Urate of ammonium 12.74
+Oxalate of ammonium 13.60
+Nitrogenous and sulphurous organic substances 3.61
+Ammonium-magnesium phosphate 4.00
+Ammonium phosphate .90
+Ammonium sulphate 1.82
+Ammonium chloride 1.55
+Potassium sulphate 3.30
+Sodium chloride 2.44
+ -----
+ 43.96
+ -----
+
+2. _Difficultly soluble in Water, soluble in Acids,
+Alcohol, and Ether._
+
+Uric acid 21.14
+Resin 1.11
+Fatty acids 1.60
+Nitrogenous and sulphurous organic substances 2.29
+Calcium phosphate 18.22
+Phosphate of iron 1.04
+Silica .64
+ -----
+ 46.04
+ -----
+
+In the above analysis it will be noticed that none of the ammonia is
+present as carbonate. In most samples, however, of Peruvian guano, the
+ammonia in this form amounted to from 1 to 2 per cent. In the inferior
+qualities, chiefly those which had been subjected to the action of
+water, and consequently of fermentation, to a certain extent, this form
+of ammonia was found to be most abundant. Such guanos were most liable
+to loss of nitrogen by volatilisation.
+
+The older Peruvian guano contained as high as 14 per cent of nitrogen
+(equal to 17 per cent of ammonia), and of phosphoric acid 12 to 14 per
+cent (equal to 26 to 28 per cent of phosphate of lime). It, however,
+gradually deteriorated in quality as the deposits became worked out, the
+percentage of nitrogen becoming year by year less, until latterly
+Peruvian guano, as imported, contains only from 3 to 4 per cent of
+nitrogen (equal to 4 to 5 per cent of ammonia). This guano is, however,
+richer in phosphates, containing often 50 to 60 per cent of phosphate of
+lime, and 3 to 4 per cent of potash.[192]
+
+
+(_b_) OTHER NITROGENOUS GUANOS.
+
+The guanos, other than those which come from Peru, are chiefly purely
+phosphatic guanos, so that the term Peruvian has not unfrequently in the
+past been used as a generic term synonymous with the term nitrogenous,
+and consequently applied to all nitrogenous guanos independent of their
+source. There are, however, a few deposits other than the Peruvian
+which have yielded considerable quantities of valuable nitrogenous
+guano. Of those, the richest in quality--in fact, the richest of any
+deposits hitherto discovered--was the Angamos guano, which came from a
+rocky promontory on the coast of Bolivia. The few samples of this which
+have been analysed showed over 20 per cent of nitrogen. Unfortunately,
+the deposit proved to be comparatively insignificant in amount, and has
+long been exhausted.
+
+Poorer in quality, but more abundant in quantity, were the deposits
+found on the Ichaboe and other islands off the south-west coast of
+Africa. These deposits were discovered shortly after the introduction of
+Peruvian guano, and for a few years supplied considerable quantities of
+valuable manure. The deposits first discovered were soon exhausted, so
+that for a number of years Ichaboe guano ceased to be procurable. Fresh
+deposits, however, were subsequently found, and considerable quantities
+have of late years been used in agriculture.[193] Ichaboe guano is
+inferior in value to Peruvian. It exemplifies the influence of small
+quantities of rain on guano deposits in impoverishing them in their
+nitrogen. In much of the Ichaboe guano imported into this country a
+large amount of feathers is found. It also contains an abnormally large
+quantity of insoluble matter.
+
+Among the other nitrogenous guanos may be mentioned the Patagonian,
+Falkland, and Saldanha Bay. They are, like the Ichaboa, of comparatively
+recent origin, and are collected in small quantities after the breeding
+season every year.
+
+
+II.--PHOSPHATIC GUANOS.
+
+Phosphatic guanos, as already pointed out, are similar in origin to
+nitrogenous guanos. In their case, however, the nitrogen, alkalies, and
+soluble phosphates which they originally contained have been almost
+entirely lost by the decomposition of their organic matter and the
+action of water.[194] Most of them still contain very small quantities
+of nitrogen, amounting to a fraction of a per cent. Of these deposits
+there are very many occurring on islands in different parts of the
+world. In appearance the guano obtained from them is very different from
+nitrogenous guano, being much lighter in colour, and of a fine powdery
+nature. It forms a very rich phosphatic guano, containing in many cases
+between 70 and 80 per cent of insoluble phosphate of lime. Such guanos
+are largely used in the manufacture of high-class superphosphates, by
+treating them with sulphuric acid. Being of an insoluble nature, they
+are not very suitable for direct application to the soil. Of these
+phosphatic guanos the following are the chief--those marked in italics
+being still unexhausted:--
+
+1. _Baker_, Jarvis, Howland, Starbuck, Flint, _Enderbury_, _Malden_,
+Lacepede, _Browse_, _Huon_, _Chesterfield_, _Sydney_, _Phoenix_,
+_Arbrohlos_, _Shark's Bay_, and _Timor_--all found on islands in the
+Pacific Ocean.
+
+2. _Mejillones_, on the coast of Bolivia.
+
+3. Aves, _Tortola_, _Mona_, and other deposits in the West Indies.
+
+4. _Kuria Muria_ islands, in the Arabian Gulf.
+
+For further particulars as to the composition of these different guanos,
+the reader is referred to the Appendix, Note V., p. 329.
+
+
+_Inequality in Composition._
+
+That guano was a substance of by no means uniform composition was a fact
+early recognised in the history of the trade. Not only did guano from
+different deposits show on analysis different percentages of the
+manurial ingredients, but different samples of guano from the same
+deposit were often found to differ very considerably from one another.
+It soon became the custom, therefore, to sell it on chemical analysis,
+each separate cargo being carefully analysed. But this custom did not
+wholly obviate the difficulty, as the guano in even one cargo might
+differ. In the case of the older and richer guanos, there was certainly
+more uniformity in quality, but they were liable to differ in their
+percentage of nitrogen.[195] As, however, the deposits became gradually
+worked out, their lower layers were found more or less largely admixed
+with stony and earthy matter, and their composition was naturally
+rendered very variable. This state of matters was unsatisfactory to
+buyers and sellers, and led to much friction between the two, as it was
+found wellnigh impossible on the part of the seller to guarantee the
+composition of his manure. The custom of preparing the material by
+reducing it to a fine powder before sending it into the market, and the
+custom, subsequently introduced, of treating it with sulphuric acid,
+have done away with this difficulty to a large extent.
+
+
+_"Dissolved" Guano._
+
+The treatment of guano with sulphuric acid was first had recourse to in
+the case of cargoes damaged with water. In such guano, as has been
+already pointed out, fermentation has been permitted to take place, with
+the result of the formation of volatile carbonate of ammonia in greater
+or less quantity. By the addition of sulphuric acid the ammonia was
+fixed, and the guano was prevented from losing its most valuable
+constituent. It was soon found, however, that guano so treated possessed
+greater activity as a manure. The result of the sulphuric acid was to
+increase very materially the amount of its soluble phosphates, and also
+its soluble nitrogen compounds.[196] It had, moreover, the effect of
+producing a guano of uniform composition. The custom, first introduced
+in 1864 by Messrs Ohlendorff & Co., was soon largely practised. The
+guano is treated with 25 to 30 per cent sulphuric acid (sp. gr. 1.73).
+After a short time the resulting hard mass is, by means of
+disintegrators, reduced to a uniform powder.
+
+
+_"Equalised" or "Rectified" Guano._
+
+As guano decreased in its quality the demand for a high-class article
+became more and more difficult to meet. This led to the custom of
+"fortifying" or "rectifying"--as it is variously called--the natural
+material with sulphate of ammonia. A manure closely resembling in the
+percentage of its manurial constituents the older rich guanos is thus
+obtained. Of these so-called "equalised" guanos, two qualities are at
+present sold, the first being guaranteed to contain nitrogen equal to 8
+to 9 per cent ammonia, 30 to 35 per cent phosphates, and 2 to 3 per cent
+of potash; the second quality containing only about half as much
+nitrogen, but more phosphates.
+
+However valuable this fortified guano may be--and it is, undoubtedly, a
+most valuable manure--its action cannot be supposed to be exactly
+similar to the old Peruvian guano, which it resembles in the percentage
+of its nitrogen, phosphates, and potash. Much of the distinctive value
+of guano as a manure, as will be pointed out immediately, lies in the
+fact that it contains its manurial ingredients in a variety of
+differently soluble compounds, which are gradually rendered available in
+the soil for the plant's needs. This undoubtedly is one of the reasons
+why the action of guano among manures is quite unique; and there are
+other reasons which we probably do not clearly understand. However
+skilfully the composition of the guano may be artificially simulated, it
+still remains an undoubted fact that the "equalised" guano is not
+exactly similar in its action to the genuine article. Nevertheless, that
+it is superior in its results to the poorer classes of guano at present
+available, and to ordinary compound manures, there can be little doubt.
+A great merit of the equalised guano is, however, that it is sold at a
+lower price than guano as imported; and as the guano is sold on a
+guaranteed analysis, the practice has done much to advance the true
+interests of agriculture.
+
+
+_Its Action as a Manure._
+
+Next to farmyard manure, guano may be regarded as the most "general" of
+all the commonly used manures; for in addition to nitrogen, phosphoric
+acid, and potash, it contains nearly all the other plant ingredients,
+such as lime, magnesia, &c. Its special value as a manure, however, does
+not merely consist in the amount of valuable plant-food it contains.
+Like farmyard manure, it owes much of its characteristic action to the
+state of the intimate mixture of its manurial constituents, and also, as
+has already been pointed out, to the fact that it contains those
+constituents in a great variety of chemical forms, each of which differs
+in its solubility, and consequently availability for the plant's needs.
+Take, for example, the great number of different forms of nitrogen it
+contains. Some are in the condition in which plants can immediately
+absorb them, while the rest are in a series of less and less available
+forms, which, however, are gradually converted into available forms as
+the plant requires them. Like farmyard manure, again, it may be applied
+with almost equally good results to all kinds of crops and on all kinds
+of soils. We have in guano, in short, an admirable example of the value
+of applying our manurial ingredients in different forms. That this is no
+mere theory is abundantly proved by the large number of different
+experiments which have in the past been carried out with guano, more
+especially the well-known experiments made by Grouven, the German
+chemist. In those well-known experiments, guano was tested against a
+large variety of different fertilisers, and the tests were so arranged
+that in most cases the amounts of nitrogen, phosphoric acid, and potash
+were the same in the other manures used. In short, these experiments
+prove in a very striking manner that a manure artificially made up out
+of most valuable fertilisers, such as nitrate of soda, sulphate of
+ammonia, superphosphate, &c., so as to closely resemble in its
+composition guano, is by no means similar in its effects to the genuine
+article. As in farmyard manure, so in guano: we must look to the
+complexity of the composition of both these fertilisers in order to
+fully estimate their worth. There is in the action of both manures much
+that we cannot explain, or even, as yet, understand. The action of guano
+is merely one of many problems in the science of manuring which
+illustrate how unsatisfactory, despite the great amount of research
+already carried out, is our knowledge of this most important department
+of agriculture.[197]
+
+
+_Proportion of fertilising Constituents in Guano._
+
+Guano must be regarded as a nitrogenous and phosphatic manure, as the
+quantity of potash it generally contains is small. In many soils, more
+especially in such a country as Scotland, this deficiency in potash is
+not of so much importance, as the value of potash as an artificial
+manure is less than is the case with the other two ingredients. In
+soils, however, lacking potash, guano ought to be supplemented with some
+potash manure. With regard to the nitrogen and phosphoric acid, we may
+ask if these two constituents are in the best proportions. This question
+does not admit of a direct answer. In the first place, the proportion
+in which these two ingredients are present is variable. In the old rich
+Peruvian guanos, as we have above shown, the nitrogen was more abundant
+than is the case at present. Such guanos, it was found, were best
+supplemented with phosphatic manure when applied to the field. In the
+"equalised" and "dissolved" guanos, which are now so largely sold,
+manufacturers attempt to adjust the percentage of nitrogen and
+phosphoric acid to what is considered the best proportion in most cases.
+As, however, we have again and again to point out, regard must be had
+both to the soil and the crop in determining what is the best proportion
+of the manurial ingredients in a manure. For cereals it may be well
+supplemented by nitrogenous manures, while for roots it may be well
+supplemented by phosphatic manures.
+
+
+_Mode of Application._
+
+Like all manures, it is desirable to apply it in as fine a condition as
+possible, so as to ensure as thorough a mixture with the soil-particles
+as practicable. In order, furthermore, to prevent any risk of loss
+through volatilisation of the ammonia, as well as to ensure even
+distribution, it is best applied mixed with dry earth, ashes, sand, or
+some other substance,--not lime, however. The custom of applying along
+with the guano common salt, has been proved by numerous experiments to
+be highly beneficial to the action of the guano as a manure. The exact
+nature of the action of salt as an adjunct to manures is a point which
+has elicited much discussion. Its action is probably to be ascribed to a
+number of causes. For one thing, it probably acts as an antiseptic in
+retarding the fermentative action which has a tendency to go on so
+rapidly in such manures as guano. It further increases the power of the
+manure to attract moisture from the air--a most important property in
+the case of drought. Some experiments by Dr Voelcker illustrate this in
+a striking manner. Two lots of guano--one pure and one mixed with
+salt--were exposed to the action of the air for a month, and were then
+tested as to the amount of water they contained, when it was found that
+the lot containing the salt had absorbed 2 per cent more water than the
+other.
+
+Much stress has been laid on the importance of having the guano buried a
+certain depth in the soil; and many experiments have been carried out to
+prove how much better it acts when so applied. This is probably due to
+the prevention of any loss of volatile ammonia, and the mixture of the
+manure with the soil-particles before it comes in contact with the
+plant-roots. This last precaution is an important one, for it has been
+found that the raw material is apt to have a bad effect on the seed or
+the plant's roots. This has been found to be especially the case in
+regard to potatoes, the quality of which has been found to suffer when
+the guano is brought into direct contact with the tubers. As guano is a
+manure which is speedily available, it is desirable to apply it as
+shortly before it is required by the plant as possible. It is therefore
+generally best applied in spring, shortly before seed-time, or indeed at
+the same time. Where farmyard manure is used, the guano has been
+recommended to be used as a top-dressing in small quantities. In the
+majority of cases it will be advisable, however, not to apply it as a
+top-dressing, for the various reasons above-mentioned.
+
+
+_Quantity to be used._
+
+As to the quantity to be used, this of course will depend on the soil,
+the crop, and the amount and nature of the other manures employed: 1 to
+4 cwt. per acre have been the usual limits, but even heavier dressings
+have been commonly resorted to, especially in Scotland, where 6 to 8 or
+even 9 cwt. for turnips are often used. Sir J. B. Lawes and Sir James
+Caird long ago, shortly after the introduction of guano, estimated, from
+the experiments they carried out, that the application of 2 cwt. per
+acre to the wheat crop gave an increase of 8 to 9 bushels in grain, and
+added a fourth to the quantity of straw. The former authority recommends
+2 to 3 cwt. per acre for wheat, to be sown broadcast and harrowed into
+the land before sowing the seed. We have already stated that it may be
+used in all soils and for all kinds of crops. While this is so, it has
+been found to have specially favourable results when applied to the
+turnip crop, when it may be used in larger quantities than in the case
+of cereals. When applied to the turnip crop, it is well to use the more
+phosphatic guanos or to supplement it with superphosphates. By applying
+it in two lots, the larger portion before seed-time and the rest between
+the drills after the turnips are up, excellent results have been
+obtained. It has also proved an admirable manure for mangels. On the
+whole, it gives best results on heavy soils and in a dampish climate.
+
+
+_Adulteration of Guano._
+
+Probably no artificial manure has been subjected to greater adulteration
+in the past than guano. This has been due to the fact that the practice
+of selling guano on analysis--especially among retail buyers--did not
+largely obtain in the early years of the trade. A good deal of this
+adulteration was probably caused by ignorant prejudice on the part of
+the farmer, to whom the pungency of its smell and its colour were too
+apt to be ranked as its most important properties. The variation in the
+quality of different kinds of guano was too often not sufficiently
+realised by the buyer, who not unfrequently was made to pay as high a
+price for guano of an inferior quality as he ought to have paid for that
+of the best quality. Indeed no manure illustrates the importance of
+chemical analysis more than guano. Among the different forms of
+adulteration practised may be mentioned the addition of such substances
+as sawdust, rice-meal, chalk, sulphates of lime and magnesia, common
+salt, sand, earth, peat, ashes of various kinds, and water. There can be
+no doubt, however, that such adulteration has now long ceased to be
+practised to any extent. Nevertheless, it may be of use to draw
+attention to one or two of the tests by means of which some of the
+commoner forms of adulteration may be detected. One or two are extremely
+easily detected--as, for example, adulteration with sand or other
+mineral substances. In such a case, the percentage of ash left on
+burning a small portion of the guano will be found to be excessive. The
+percentage of ash in a sample of genuine Peruvian guano should not
+exceed from 50 to 60 per cent. The colour of the ash is another
+important point, and may serve as a further indication of adulteration.
+In the case of genuine guano, this should be whitish or greyish.
+Red-coloured ash generally points to the adulteration of the guano with
+some mineral substance containing iron--such, _e.g._, as Redonda
+phosphate, a mineral phosphate of iron and alumina. Where the ash is
+white, but excessive in quantity, adulteration with common salt,
+sulphate of magnesia, gypsum, or chalk, may be suspected. The last-named
+substance is easily detected by treating it with any of the common
+acids, when brisk effervescence, due to the liberation of the carbonic
+acid, will ensue.[198] A further point of importance with regard to the
+ash is its solubility in water and in acids. A large insoluble residue
+may be taken as indicating adulteration with sand. Adulteration with
+water is also easily detected by heating a sample to the boiling
+temperature and determining the loss it sustains. Of course the amount
+of water varies in different samples. The appearance of the guano will
+serve fairly well to detect whether it is abnormally moist. It may be
+added, in conclusion, that Peruvian guano is extremely light; and while
+this by itself is not a sufficient test of genuineness, it may serve to
+confirm other tests.
+
+
+III.--SO-CALLED GUANOS.
+
+Before concluding this chapter, reference may be made to certain manures
+which are commonly known under the name of guanos--such as "fish-guano,"
+"flesh-guano," "meat-meal-guano," and "bat-guano,"--as well as to
+manures which may more conveniently be described here--viz., "fowl and
+pigeon dung."
+
+
+_Fish-Guano._
+
+The application of fish, not suited for other purposes, to the fields
+as a manure is a practice which has obtained in certain parts of the
+country for a number of years. In many districts on the sea-coast, where
+fishing is the chief industry, the only way in the past of disposing of
+a superabundant catch of herrings, for example, has been to utilise them
+as a manure. From such a practice has sprung up what is now an important
+and ever-increasing trade--viz., the manufacture of fish-guano.
+
+This manufacture was first started, and is still most largely practised,
+in Norway. The guano obtained varies very considerably in quality
+according to the nature of the process employed, and as to whether the
+guano is made from whole fish or merely from fish-offal. The latter
+source is the common one. The manufacture is carried on at the
+fish-curing stations, and the quality of the guano made from this source
+is somewhat different from that made from whole fish, as a large
+proportion of the fish-offal is made up of bones and heads. Large
+quantities of Norwegian fish-guano are exported to various parts of
+Europe.
+
+The best quality of this guano may contain as much as 10 per cent of
+nitrogen, but as a rule it is nearer 8 per cent. A very considerable
+variation in the amount of phosphoric acid occurs for the reason above
+stated, the guano made from fish-scrap being naturally much richer in
+this ingredient than whole-fish guano. The phosphoric acid may be said
+to range from 4 to 15 per cent, and there is also a small quantity of
+potash present.
+
+Guano is also manufactured in Norway from the carcasses of whales. Such
+guano contains from 7-1/2 to 8-1/2 per cent of nitrogen, and about
+13-1/2 per cent of phosphoric acid.
+
+In America fish-guano is manufactured to a considerable extent--one
+important source being the menhaddo, a coarse sort of herring. This fish
+is caught for the sake of its oil, which is extracted by boiling, the
+residue being manufactured, after pressing and drying, into guano.
+
+In this country the manufacture of fish-guano is carried out to a
+considerable and increasing extent. Formerly it was imported from Norway
+to a larger extent than is now the case, the present annual imports
+amounting only to 1000 or 2000 tons. The total annual production in the
+United Kingdom is probably 7000 or 8000 tons.
+
+
+_Value of "Fish-Guano."_
+
+That fish-guano is a valuable manure there can be no doubt. What,
+however, impairs its value is the fact that, as a rule, it contains a
+certain amount of oil. The effect of this oil is to retard fermentation
+and decomposition when the guano is applied to the soil, and thus render
+its action slower than would otherwise be the case.
+
+When applied to the soil, therefore, every opportunity ought to be
+given to promote its fermentation. It is best applied some time before
+it is likely to be used. It ought to be well mixed with the
+soil-particles, and not allowed to lie on the top of the soil. Its best
+effect will be on light well-cultivated soils, which permit of the
+access both of sufficient moisture and of sufficient air for rapid
+fermentation. Its value as a manure for hops, vines, grass, and
+strawberries has been found to be considerable. It has been recommended
+to be applied along with farmyard manure; and such a mode of application
+is no doubt well suited to promote its decomposition. It has also been
+used for mixing with superphosphate of lime. Professor Storer has
+advocated a more general use of fish as a manure than is at present the
+case. He suggests that even fish not suitable for edible purposes might
+be caught for the purpose of conversion into manure. The difficulty of
+preserving fish, however, is considerable; and he suggests the use of
+potash salts, such as muriate of potash, or lime for this purpose. The
+benefit of using potash would be twofold. In addition to acting as a
+preservative, it would considerably enhance the value of the resulting
+guano as a manure. There is much truth in Professor Storer's views; and
+no doubt, as our sources of artificial nitrogenous manures grow more
+limited, the manufacture of fish-guano will be carried on in the future
+on a larger and more systematic scale than hitherto.
+
+
+_Meat-meal Guano._
+
+What is called "meat-meal guano" is generally that made from the refuse
+of the carcasses of cattle after they have been treated for their
+meat-extract according to Liebig's process. The meat-meal is used both
+for feeding and manurial purposes. Considerable quantities[199] of this
+guano are imported annually into this country from South America,
+Queensland, and New Zealand,--that coming from Frey Bentos, in Uruguay,
+being best known. It is a valuable manure, especially so for its
+nitrogen, which varies from 4 to 8 per cent, while it contains of
+phosphoric acid from 13 to 20 per cent. Some meat-meal guanos contain as
+much nitrogen as 11 per cent.
+
+In some parts of the world, more especially in Germany, the carcasses of
+horses, as well as cattle, dogs, pigs, &c., which have died of disease,
+are converted into a guano. They are subjected to treatment by steam in
+digestors, by which means the fat and gelatine are separated and
+utilised, while the remaining portion of the animal is converted into
+guano. Other processes are also employed. The resulting manure contains
+from 6 to 10 per cent of nitrogen, and from 6 to 14 per cent of
+phosphoric acid.
+
+
+_Value of Meat-meal Guano._
+
+Meat-meal guano is a valuable nitrogenous manure. The same remarks
+apply to it as to fish-guano, although it ferments probably very much
+more quickly than the latter, and is undoubtedly a more valuable manure.
+
+
+_Bat Guano._
+
+In conclusion, we may consider bat guano. Bat guano, which is really a
+very rare curiosity, has been found accumulated in hot climates in
+caves.
+
+The samples which have been analysed have differed very much in quality,
+some containing as much as 9 per cent of nitrogen and 25 per cent of
+phosphoric acid. Provided it could be obtained in any quantity, and of a
+quality even approximating to the above analysis, it need scarcely be
+pointed out that bat guano would be a most valuable manure.
+
+A singular point about its composition is, that it has been found to
+contain a considerable proportion of its nitrogen (as much as 3 per
+cent) in the form of nitrates.
+
+
+_Pigeon and Fowl Dung._
+
+Pigeon dung is a manure which historically is of great importance. The
+dung of pigeons was used as a manure by the ancient Romans; and even in
+modern times, more especially in France, it was considered a most
+important fertiliser. Despite these facts, pigeon dung is by no means a
+rich manure, and its composition compares most unfavourably with that of
+the guanos we have just been considering. According to Storer,[200] it
+only contains from 1-1/4 to 2-1/2 per cent of nitrogen, and from 1-1/2
+to 2 per cent of phosphoric acid, and a little over 1 per cent of
+potash.
+
+The dung of poultry is just about as poor, fowl dung containing from .8
+to 2 per cent of nitrogen, 1-1/2 to 2 per cent of phosphoric acid, and a
+little under 1 per cent of potash; while that of ducks and geese is even
+poorer.[201]
+
+From these statements it will be seen that the excrements of pigeons,
+hens, and ducks do not form a rich manure. One thing about pigeon dung
+which is to be noticed, is the fact that it ferments very quickly.
+
+None of the pseudo-guanos, however rich they may be in manurial
+ingredients, can be regarded as equal in their action to the genuine
+article, for reasons which we have gone into already when considering
+the action of guano.
+
+
+FOOTNOTES:
+
+[183] Bones, it is true, were in use long before guano; but popular as
+they deservedly were, they had not been used, at the time of the
+importation of guano, to any very considerable extent.
+
+[184] The total annual imports at present may be taken at under 30,000
+tons, whereas in 1855 they amounted to over 200,000 tons. For statistics
+on this point the reader is referred to the Appendix, Note I., p. 327.
+
+[185] With regard to the origin of certain guano deposits, which are of
+very recent date--_e.g._, _Angamos_ and _Ichaboe_--there can be no doubt
+whatever, because we can witness the process of formation still taking
+place. It is not so, however, with regard to older deposits, for which
+some have been inclined to claim mineral origin. The best proof that
+such deposits owe their origin mainly to bird excrements is the
+comparatively large quantity of _uric acid_ they contain. On the other
+hand, the evidence in support of the belief that they are also formed
+from the remains of the birds themselves and other animals, is to be
+found in the large proportion of phosphates they contain, and the
+presence in the deposits of feathers and the fossilised skeletons of the
+animals above mentioned.
+
+[186] A complete list of the various deposits will be found in the
+Appendix, Note II., p. 327. It may be noticed that nearly all the
+deposits lie within 10° to 20° north and south of the Equator.
+
+[187] See Chapter on Farmyard Manure, p. 257.
+
+[188] According to Nesbit, some of the cargoes of this guano contained
+hard saline lumps of very little manurial value--over 50 per cent being
+common salt.
+
+[189] The salt exports were made in 1868.
+
+[190] For analyses of these nodules and crystals, see Appendix, Note
+III., p. 328.
+
+[191] See Heiden, vol. ii. p. 356.
+
+[192] See Appendix, Note IV., p. 329.
+
+[193] The Ichaboe guano at present exported is a fresh deposit, and is
+annually collected for shipment.
+
+[194] Further chemical changes have occurred in certain cases between
+the guano and the limestone rock beneath, resulting in the formation of
+what is called a "crust" guano. Such guanos form a soft phosphatic rock,
+and are extremely rich in phosphates. As examples of these "crust"
+guanos may be mentioned Sombrero, Curaçao, Aruba, Mexico, and Navassa
+phosphates.
+
+[195] The presence in the old Peruvian guano of concretionary nodules
+has already been referred to.
+
+[196] According to Vogel the nitrogen as urates is converted by the
+sulphuric acid into ammonia salts.
+
+[197] See Appendix, Note VI. p. 330.
+
+[198] It must be remembered, however, that even genuine guano contains a
+certain quantity of carbonate of lime, and will give a slight amount of
+effervescence when so treated.
+
+[199] The annual imports may be stated at from 3000 to 4000 tons.
+
+[200] Agricultural Chemistry, vol. i. p. 367.
+
+[201] See Appendix, Note VII., p. 331.
+
+
+
+
+APPENDIX TO CHAPTER VIII.
+
+
+NOTE I. (p. 297).
+
+PERUVIAN GUANO IMPORTED INTO THE UNITED KINGDOM, 1865-1893.
+
+Year. Tons. | Year. Tons.
+1865 213,024 | 1881 33,393
+1870 247,028 | 1882 27,382
+1871 144,735 | 1883 36,713
+1872 74,964 | 1884 15,802
+1873 135,895 | 1885 -
+1874 94,346 | 1886 28,733
+1875 86,042 | 1887 5,784
+1876 158,674 | 1888 16,446
+1877 111,835 | 1889 17,000
+1878 127,813 | 1890 19,000
+1879 45,475 | 1891 11,000
+1880 58,631 | 1892 14,000
+
+
+NOTE II. (p. 298).
+
+GUANO DEPOSITS OF THE WORLD.
+
+SOUTH AMERICA--
+
+_Peru._--In various islands off the coast--viz., Chincha, Guanape,
+Ballestas, Macabi, Lobos, and Patillos; and on different parts of the
+coast--viz., Pabellon de Pica, Chipana, Huanillos, Punta de Patillos,
+Independence Bay, and Lobos de Afuera.
+
+_Columbia._--In different parts of the States of Venezuela, New Granada,
+and Ecuador. Guano coming from these parts is often known as Columbian
+guano, or according to the name of the State in which it is found.
+Maracaïbo and Monks guanos come from the coast of Venezuela. Deposits
+are also found on the Galapagos Islands, to the west of Ecuador.
+
+_Bolivia._--Mejillones, Patagonia, Leon's.
+
+NORTH AMERICA--Deposits have been found on the coasts of Mexico and
+California; on the Raza and Patos Islands; and on the coasts of
+Labrador. They have also been found on the Islands of Curaçao, Aruba,
+and Navassa in the Gulf of Mexico.
+
+AFRICA--On the west coast deposits have been found at Algoa
+Bay, Saldanha Bay, and on the Island of Ichaboe.
+
+AUSTRALIA--Shark's Bay and Swan Island.
+
+WEST INDIES--Sombrero, Aves, and Cuba.
+
+PACIFIC OCEAN--On the Islands of Baker, Jarvis, Howland,
+Malden, Starbuck, Fanning, Enderbury, Lacepede, Browse, Huon, and
+Surprise.
+
+ASIA--Deposits at Kuria Muria on the Arabian coast, and on the
+Sandwich Islands. (See Heiden's 'Düngerlehre,' vol. ii. p. 349.)
+
+
+NOTE III. (p. 303).
+
+COMPOSITION OF CONCRETIONARY NODULES.
+
+(_Analyses by Karmrodt._)
+
+No. 1.
+
+Potassium sulphate 7.49
+ " phosphate 9.52
+Sodium " 9.08
+Ammonium " 7.57
+Calcium sulphate 3.40
+Ammonium urate 4.09
+ " oxalate 41.28
+Nitrogenous organic matter 10.17
+Water 7.40
+ -----
+ 100.00
+ ------
+ Nitrogen 14.84
+
+No. 2.
+
+Potassium sulphate 45.64
+Sodium " 13.22
+Ammonium " 10.23
+ " oxalate 9.14
+Basic ammonium phosphate 12.09
+Precipitated ammonium phosphate 4.78
+Organic matter .94
+ Insoluble 1.90
+ Water 2.06
+ ------
+ 100.00
+ ------
+
+
+NOTE IV. (p. 306).
+
+The following analyses, being the average of a large number of different
+samples analysed from time to time in the chemical laboratory of the
+Pommritz Agricultural Experimental Station, show the gradual
+deterioration of Peruvian guano, as regards its percentage of nitrogen,
+during the years 1867-81:--
+
+ Nitrogen. Nitrogen.
+1867 13.16 | 1873 9.16
+1868 11.98 | 1874 9.83
+1869 13.66 | 1878 7.10
+1870 12.37 | 1879 6.95
+1871 10.04 | 1880 7.07
+1872 10.72 | 1881 6.93
+
+
+NOTE V. (p. 309).
+
+COMPOSITION OF DIFFERENT GUANOS.
+
+The following is a list of the more common nitrogenous and phosphatic
+guanos which have been used in the past or are at present in use. Those
+printed in italics are still being worked. As their value depends on
+their nitrogen and phosphoric acid, these alone have been given. The
+percentages must be taken as mere approximations, as the quality of
+different cargoes from the same deposits varies very much. The table may
+be found useful for reference.
+
+_Nitrogenous Guanos._
+ Phosphoric } { Tricalcic
+ Nitrogen = Ammonia. acid } = { phosphate.
+ per cent. per cent. per cent. per cent.
+Angamos 20 24 5 11
+Chincha 14 17 13 28
+Ballestas 12 15 12 26
+Egyptian 11 13 19 41
+Guanape 11 13 - -
+Macabi 11 13 12 26
+Corcovado 11 13 15 33
+_Saldanha Bay_ 9 11 9 20
+_Ichaboe_ 8 10 9 20
+Independence Bay 7 9 12 26
+_Pabellon de Pica_ 7 9 14 31
+_Punta de Lobos_ 4 5 15 33
+_Huanillos_ 6 7 18 28
+Penguin 5 6 11 24
+Patagonian 4 5 18 39
+Falkland Islands 4 5 14 31
+
+_Phosphatic Guanos._
+
+ Phosphoric } { Tricalcic
+ acid } = { phosphate.
+ per cent. per cent.
+Maracaïbo, or Monks 42 92
+Raza Island 40 87
+Curaçao 40 87
+_Baker Island_ 39 85
+Starbuck 38 83
+_Enderbury_ 37 81
+Californian 35 76
+_Aves_ 34 74
+Fanning Island 34 74
+Howland 34 74
+_Sidney Island_ 34 74
+Mejillones 33 72
+Lacepede Island 33 72
+_Malden Island_ 32 70
+Sombrero 32 70
+_Browse Island_ 31 68
+_Huon Island_ 28 61
+Patos Island 24 52
+Jarvis Island 20 44
+Cape Vert 11 24
+
+
+NOTE VI. (p. 314).
+
+It may be of interest to refer to a theory put forward by Liebig as to
+the action of oxalic acid in guano. This, he considered, had the effect
+of gradually rendering the insoluble calcium phosphate soluble, and
+giving rise to the formation of ammonium phosphate and calcium oxalate.
+Such an action would probably take place were the guano allowed to
+ferment by itself. We know, however, that when it is brought in contact
+with the soil-particles, all its soluble phosphate is converted into
+precipitated phosphate.
+
+
+NOTE VII. (p. 326).
+
+ANALYSES OF DUNG OF FOWLS, PIGEONS, DUCKS, AND GEESE. (Storer's
+'Agricultural Chemistry,' vol. i. p. 367.)
+
+ Fowls. Pigeons. Ducks. Geese.
+Water 56.00 52.00 56.60 77.10
+Organic matter 25.50 31.00 26.20 13.40
+Nitrogen 1.60 1.75 1.00 .55
+Phosphoric acid 1.5-2.00 1.5-2.00 1.40 .54
+Potash .80-.90 1.0-1.25 .62 .95
+Lime 2.00-2.50 1.5-2.00 1.70 .84
+Magnesia .75 .50 .35 .20
+
+According to a computation by a Belgian farmer, a pigeon yields about 6
+lb. of dung in a year, a hen about 12 lb., a turkey or goose about 25
+lb., and a duck 18 lb.
+
+
+
+
+CHAPTER IX.
+
+NITRATE OF SODA.
+
+
+Nitrate of soda,[202] or, as it is more correctly designated from a
+chemical point of view, sodium nitrate, now forms the chief artificial
+nitrogenous manure in use. Along with sulphate of ammonia, it has taken
+the place once held in the manure markets by the older Peruvian guano,
+and may without doubt be reckoned, at present prices, one of the
+cheapest and most valuable of the artificial sources of nitrogen for the
+plant. It is some sixty-two years ago since it was first exported from
+South America into this country. The total exports in that year amounted
+to about 800 tons, and some indication of the enormous extent to which
+the use of this valuable fertiliser has been developed since then will
+be obtained from the statement that the total exports at present amount
+to little less than 1,000,000 tons per annum, representing a monetary
+value of 6 to 7 millions sterling. Of this quantity about 120,000 tons
+are imported into Britain.[203] While its chief use is for manurial
+purposes, it must not be imagined that it is only used for this purpose.
+A certain amount is used in connection with various chemical
+manufactures--for instance, that of nitric and sulphuric acid--and also
+in the manufacture of saltpetre, the chief constituent of gunpowder.
+
+
+_Date of Discovery of Nitrate Deposits._
+
+The exact date of the discovery of the nitrate deposits seems to be a
+point of considerable dubiety. The earliest published description of
+them was written by Bollaert about the year 1820, in which year, it is
+stated, the first shipment was made to England. It was not, however,
+till some ten or twelve years later that the Peruvian Government, to
+whom they then belonged,[204] seems to have recognised their value. The
+most important deposits are found in the vicinity of the town of
+Iquique, which is the chief nitrate port of South America. It is a
+somewhat striking fact that this substance, which has conclusively
+proved itself to be the most potent of all known artificial agents in
+the promotion of vegetable growth, should be found in a district utterly
+lacking the slightest traces of vegetation of any kind. Lest such a
+statement should seem to savour of irony, we hasten to explain that the
+singular barrenness of this part of the country is largely due to the
+character of its climate, the deposits occurring in the midst of sandy
+deserts,[205] on which rain never falls.
+
+
+_Their Origin._
+
+The origin of these nitrate-fields is a geological problem of very
+considerable interest, the difficulty of which is greatly enhanced by
+their altitude--3000 to 4000 feet above the sea-level--and their
+distance inland, which amounts in some cases to eighty or ninety miles
+from the sea-coast. The nitrate deposits are not the only saline
+deposits found in Chili. According to the late David Forbes,[206] they
+are not to be confused with other saline formations, which appear at
+intervals scattered over the whole of that portion of the western coast,
+on which no rain falls. The latter stretch from north to south for a
+distance of more than 550 miles--their greatest development being
+between latitudes 19° and 25° south. The depth to which they extend
+downwards varies considerably. Most of them, however, are of a very
+superficial character, and "they always show signs of their existence by
+the saline efflorescence seen on the surface of the ground, which often
+covers vast plains as a white crystalline incrustation, the dust from
+which, entering the nostrils and mouth of the traveller, causes much
+annoyance, whilst at the same time the eyes are equally suffering from
+the intensely brilliant reflection of the rays of a tropical sun." These
+saline incrustations, or _salinas_, as they are generally called, are
+chiefly composed of salts of lime, soda, magnesia, alumina, and of
+boracic acid. Their composition would lead one to attribute their origin
+to the evaporation of salt water; for, with the single exception of
+boracic acid,[207] all the mineral substances are such as would be
+obtained by the evaporation of sea-water, or by the mutual reactions of
+its salts with the constituents of the adjacent rocks. As there is
+"indisputable evidence of the recent elevation of the whole of this
+coast," volcanic upheaval might be reasonably held to explain their
+altitude. Their comparative proximity to the coast would seem further to
+favour this theory. On these grounds, therefore, Forbes is inclined to
+think that they owe their origin to the evaporation, under the influence
+of a tropical sun, of lagoons of salt water, the communication of which
+with the sea had been cut off by the rising of the land.
+
+
+_Forbes and Darwin on the Theory of their Origin._
+
+The obvious difficulty of accounting for the formation of the larger
+deposits by such a theory he meets by saying that it is only necessary
+to suppose that, even after the partial isolation of the lagoons by the
+elevations of the coast, they might still have maintained tidal or
+occasional communication with the sea by means of lateral openings in
+the chain of hills separating them from the ocean. In such cases there
+would be a gradual accumulation of salts, very much greater in amount
+than that due simply to the evaporation of the water originally
+contained in the lagoons. The above theory of the origin of the lower
+saline deposits may go to explain the mode of formation of the
+nitrate-fields; but in this case several difficulties present
+themselves. One is the much greater altitude of the latter, as well as
+their greater distance inland. This difficulty, however, may be met by
+assuming that they are of older origin than the lower deposits, and have
+been subjected to a correspondingly greater amount of volcanic upheaval.
+There is abundance of proof that this part of the continent has been the
+scene in the past of such volcanic upheaval. Forbes is of opinion that
+there is the fullest evidence to prove that, even since the arrival of
+the Spaniards, a very considerable elevation of the land has taken place
+over the greater part, if not the whole extent, of the line of coast;
+while Darwin states that he has convincing proof that this part of the
+continent has been elevated from 400 to 1200 feet since the epoch of
+existing shells. Furthermore, elevations of the coast-line, amounting in
+many cases to several feet, are known to have happened within recent
+times, while earthquakes and volcanic disturbances of a less striking
+nature are still of common occurrence. Successive lines, indicative of
+old sea-beaches, can be distinctly traced stretching inland, one behind
+the other; and patches of sea-sand and water-worn stone, found at a
+great distance from the coast, both in valleys and at altitudes much
+greater even than 4000 feet, point to the same conclusion.[208] The
+difficulty, therefore, of altitude and distance from the coast cannot be
+regarded as insuperable.
+
+
+_Source of Nitric Acid._
+
+A difficulty, however, which is not so easily met, is afforded by the
+presence of the nitric acid which, in combination with the soda, forms
+the nitrate of soda. It is scarcely necessary to inform our readers that
+nitrogen--except, of course, in small quantities in the free state--is
+not a normal constituent of salt water. The question, therefore, of
+greatest interest in connection with the formation of these nitrate-beds
+is, Whence has the nitric acid been derived? Several theories have been
+put forward to account for it.
+
+
+_Guano Theory._
+
+One is to the effect that it owes its origin to huge guano deposits,
+originally covering the shores of the large salt lakes which, by the
+subsequent overflowing of their shores, effected the mixture of the
+guano with the salts. In this way, by a slow process of decomposition,
+nitrate of soda would be ultimately formed.[209] This theory, apart from
+other considerations, seems at first sight extremely plausible, more
+especially when we remember that it is on this very coast that the
+greatest guano deposits have been found, and that the famous Chincha
+Islands, which alone have yielded over 10 million tons of this valuable
+fertiliser, are comparatively near the scene of the nitrate deposits.
+What seems further to support this theory, is the actual occurrence in
+the nitrate-fields themselves of small quantities of guano. But however
+plausible it may appear at first sight, it does not bear closer
+criticism. One very serious objection is the absence in these deposits
+of phosphate of lime, which is the largest constituent of guano. If they
+were really due to guano, how does it happen that the insoluble
+phosphate of lime should have disappeared, while the easily soluble
+nitrate of soda should alone be preserved? Again, assuming this theory
+to be correct, we should naturally expect to be still able to find
+evidence of the chemical changes which would under such circumstances
+have taken place, in the shape of portions of the guano in the
+transition stage. Such evidence, however, the most careful
+investigations have failed to detect. Apart, however, from the above
+objections, there seems to be little doubt, from evidence afforded by
+traces of birds' nests, &c., that the guano found in the nitrate-beds
+was deposited subsequent to the formation of the nitrate of soda.
+
+
+_Nitric Acid derived from Sea-weed._
+
+The most probable theory seems to be that put forward by Nöllner. The
+origin of the nitric acid is, according to him, to be ascribed to the
+decay of great masses of sea-weed, which, by means of hurricanes such as
+are still prevalent in these districts, were driven into the lagoons.
+The chief difficulty in the way of accepting this theory is the enormous
+quantity of sea-weed required to produce the millions of tons of nitric
+acid these deposits contain. It must be remembered, however, as bearing
+upon this point, that the occurrence of gigantic masses of sea-weed in
+the Pacific Ocean[210] is by no means uncommon even at the present time.
+If, to understand the formation of coal, we must suppose the
+Carboniferous period to be one during which exceptionally luxuriant
+growth of vegetation took place, we may be permitted to suppose a
+similar luxuriant growth of sea-weed during the formation of the nitrate
+deposits. Very strong confirmation of the truth of this theory is
+further afforded by the presence in large quantities, in the raw nitrate
+of soda, of iodine, a substance characteristic of sea-weed; while pieces
+of sea-weed still undecomposed are met with here and there. On the
+whole, therefore, this theory, while not free from difficulties, seems
+to be the most worthy of acceptance as regards the origin of the nitrate
+deposits.[211]
+
+
+_Appearance of Nitrate-fields._
+
+Having thus discussed the origin of the nitrate-fields, we may now give
+a more detailed description of their appearance. The chief deposits at
+present being worked are those lying in the Pampa de Tamarugal, in the
+province of Tarapaca. They stretch to a distance of thirty or forty
+miles inland, from Pisagua southwards to somewhat beyond the town of
+Iquique. This huge desert, as has been already indicated, seems to be
+entirely destitute of all vegetation and animal life. Even in the
+immediately adjoining country the only kind of vegetation that seems to
+grow is a species of _acacia_. The few streams that are found in this
+neighbourhood are entirely fed by the melting snow from the Cordilleras.
+Darwin describes the appearance presented by these pampas as resembling
+"a country after snow, before the last dirty patches are thawed." The
+_caliche_, or raw nitrate of soda, is not equally distributed over the
+pampas. The most abundant deposits are situated on the slopes of the
+hills which probably formed the shores of the old lagoons. An expert can
+tell from the external appearance of the ground where the richest
+deposits are likely to be found. The _caliche_ itself is not found on
+the surface of the plain, but is covered up by two layers. The
+uppermost, known technically as _chuca_, is of a friable nature, and
+consists of sand and gypsum; while the lower, the _costra_, is a rocky
+conglomerate of clay, gravel, and fragments of felspar. The _caliche_
+varies in thickness from a few inches to 10 or 12 feet, and rests on a
+soft stratum of earth called _cova_.
+
+
+_The Method of mining the Nitrate._
+
+The mode in which the _caliche_ is excavated is as follows: A hole is
+bored through the _chuca_, _costra_, and _caliche_ layers till the
+_cova_ or soft earth is reached below. It is then enlarged until it is
+wide enough to admit of a small boy being let down, who scrapes away the
+earth below the _caliche_ so as to form a little hollow cup. Into this a
+charge of gunpowder is introduced, and subsequently exploded. The
+_caliche_ is then separated by means of picks from the overlying
+_costra_ and carried to the refinery.
+
+
+_Composition of Caliche._
+
+Both in appearance and composition it varies very much. In colour it may
+be snow-white, sulphur, lemon, orange, violet, blue, and sometimes brown
+like raw sugar.
+
+The _caliche_ found in the Pampa de Tamarugal contains generally about
+30 to 50 per cent pure nitrate of soda; that in the province of Atacama
+contains from 25 to 40 per cent. The subsequent refining processes,
+which consist in crushing it by means of rollers and then dissolving it,
+need not here be described. It may be sufficient to mention that the
+process used is that known as systematic lixiviation, and is analogous
+to the method introduced by Shanks in the manufacture of soda. The chief
+impurity in the raw material is common salt: gypsum, sulphates of
+potassium, sodium, and magnesium, along with insoluble matters, are the
+other impurities. The manufacture of iodine, which, as has been already
+noticed, is found in the nitrate-beds, is also carried on at these
+_oficinas_.
+
+
+_Extent of the Nitrate Deposits._
+
+The question of the extent of the nitrate of soda deposits is naturally
+one of very great interest, especially from the agricultural point of
+view. M. Charles Legrange, a French writer, estimated a few years ago
+that they still contained about 100,000,000 tons of pure nitrate of
+soda. Opinions on this point differ very considerably, and it seems
+wellnigh impossible to arrive at any very accurate estimate.
+
+The number of years they will last will depend, of course, on the amount
+of annual exportation. This, at present, falls little short of 1,000,000
+tons. If this amount is maintained, they should last, according to
+experts, some twenty or thirty years at least. A consideration which has
+an important influence on this question, is the price obtained for the
+article. If this should be increased, it may be possible to treat the
+larger quantities of the inferior raw material (which at present prices
+are allowed to accumulate) at a profit. Undoubtedly this is what will
+ultimately take place, when the richer quality of the _caliche_ has been
+exhausted.
+
+
+_Composition and Properties of Nitrate of Soda._
+
+As has already been pointed out, commercial nitrate of soda contains
+about 95 per cent of pure nitrate of soda, or about 15-1/2 per cent of
+nitrogen, which, if calculated as ammonia, would equal 19 per cent. It
+is, next to sulphate of ammonia (which contains 24-1/2 per cent of
+ammonia), the most concentrated nitrogenous manure, and further,
+contains its nitrogen in the form most readily available for the plant's
+use. Its most characteristic property is its great solubility, and
+consequent speedy diffusion in the soil, and the inability of the
+soil-particles to fix its nitrogen. In the latter respect it differs
+very considerably from other forms of nitrogen. Ammonia salts, though
+practically quite as soluble, do not diffuse in the soil so rapidly as
+nitrate of soda does; for the ammonia is more or less tenaciously fixed
+by the soil-particles, and retained till converted by the process of
+_nitrification_ into nitrates.
+
+
+_Nitrate of Soda applied as a Top-dressing._
+
+On this account nitrate of soda is chiefly employed--and rightly so--as
+a top-dressing. The risk of loss by drainage is thus minimised, and the
+valuable nitrogen finds its rightful destination--viz., in the plant's
+roots.
+
+
+_Encourages deep Roots._
+
+A special benefit which the diffusibility of nitrate of soda has been
+held to confer on the plant, is to encourage the growth of deep roots,
+by inducing the growing plant to send down its roots into the lower
+layers of the soil after the nitrate of soda. The benefit of deep roots
+is, of course, very great. They enable the plant to withstand the action
+of drought, and at the same time increase the area whence the plant may
+derive its nourishment. Although the value of the manure is practically
+entirely due to the nitrogen it contains, it has been urged that the
+soda exercises a beneficial effect on the mechanical properties of the
+soil, by increasing its power of absorbing moisture, and in also
+rendering it more compact. This would partly explain how its results in
+dry seasons are so much better than those obtained from sulphate of
+ammonia. This mechanical action of nitrate can scarcely be very great
+when we remember the comparatively small quantity applied. Even in the
+driest of seasons there will always be sufficient moisture to secure the
+diffusion of the nitrate of soda, while the risk of loss by drainage
+will be reduced to a minimum. Much ignorance, as well as prejudice, has
+existed in the past as to the true nature of the action of nitrate of
+soda. Nor is this prejudice even yet entirely dispelled.
+
+
+_Is Nitrate an exhausting Manure?_
+
+The common charge brought against it is, that it is what has been termed
+an exhausting manure. This objection, to have any weight, must mean that
+nitrate of soda produces a crop which takes out of the soil an
+_abnormal_ quantity of fertilising matter. But, so far as the writer is
+aware, no scientific evidence has ever been brought forward to support
+this contention. That the indiscriminate use of a manure may produce a
+crop in which the stem and leaves are unduly developed at the expense of
+the grain, or in which the quality of the crop may suffer from too rapid
+growth, is, of course, a well-known fact. But as this could also be
+produced by an overdose of soluble phosphoric acid as well as ammonia
+salts, it is not a property that belongs exclusively to nitrate of soda.
+Probably nitrate of soda has in the past been often used in this
+indiscriminate way so as to produce such results. The fault, therefore,
+lies not in the manure, but in the mode of its application. A few
+remarks, therefore, on this most important subject may prove
+serviceable.
+
+
+_Crops for which it is suited._
+
+Opinions will naturally differ as to the crops to which it is profitable
+to apply nitrate of soda. Its value as a manure for cereals is pretty
+generally admitted. Its value as a manure for roots is not, however, so
+universally admitted. Experiments would seem to show that such a crop as
+the mangold derives just as much benefit as do the cereals; while in
+Germany practical experience on a very large scale has demonstrated its
+value as a manure for beetroots. It may be generally recommended as a
+manure for all crops, except, perhaps, the so-called leguminous crops,
+such as clover, beans, peas, &c, whose ability to obtain nitrogen for
+themselves renders the application of expensive artificial nitrogenous
+manures unadvisable.
+
+An interesting point with regard to nitrate of soda is the curious
+effect it seems to have on the colour of the leaves of plants. This
+interesting fact has been strikingly demonstrated at the Rothamsted
+Experimental Station, in the contrast in the colour of the leaves of
+different experimental grass-plots, manured with nitrate of soda and
+sulphate of ammonia respectively--the plots manured with nitrate of soda
+being distinctly darker in hue, obviously owing to the greater
+production of chlorophyll or green matter. Such a depth of colour would
+seem to indicate a more healthy development.
+
+
+_Method of Application._
+
+While opinions, therefore, will naturally differ as to the crops to
+which nitrate of soda will be most profitably applied, little difference
+of opinion exists as to the method of its application. The inability of
+the soil-particles to retain it, the frequency of rain, the costly
+nature of the manure itself, and its immediate availability as a
+plant-food, all point to the extreme advisability of using it as a
+top-dressing. Even when used as a top-dressing, it may be advisable not
+to apply the entire quantity all at one time. By applying it in
+instalments, little risk is run that, through inclemency of weather, the
+manure will be lost. Another point of importance in applying nitrate of
+soda is to secure uniform distribution. This of course is applicable to
+all artificial manures, but in a very special degree to nitrate of soda,
+because of its great value and the comparatively small quantity
+applied.
+
+As the uniform distribution of one cwt. of any material over an acre of
+soil is by no means an easy task, the mixing of nitrate of soda with
+some diluent, such as dry loam, is consequently highly advisable. Common
+salt is often applied along with nitrate of soda. The indirect value of
+salt as a manure is considerable, and when applied along with nitrate,
+ensures its more speedy diffusion in the soil, by increasing the soil's
+capacity for absorbing moisture from the air.
+
+
+_Must be a Sufficiency of other Fertilising Constituents._
+
+A third point of importance in applying nitrate of soda, is to see that
+the soil is sufficiently supplied with the other plant-foods--phosphates
+and potash. This is a _sine qua non_, if the nitrate is to get a fair
+chance. If it is desired to apply nitrate of soda along with
+superphosphate of lime, a word of caution is necessary against making
+the mixture long before it is used. The reason of this is, that a
+chemical action is apt to ensue, resulting in the loss of the nitric
+acid in the nitrate of soda. The nature of the soil is another important
+consideration to be taken into account. In the case of extremely loose
+and sandy soils, it is scarcely to be recommended as the most suitable
+form in which to apply nitrogen. If applied to such soils, especial care
+ought to be taken to minimise risk of loss. No hard-and-fast rules can
+be laid down as to the quantity in which it ought to be applied. This
+must be regulated very much by the crop, the nature of the soil, and
+the quantity of other manures employed. From 1 to 1-1/4 cwt. may be
+recommended as a suitable quantity for corn crops which are otherwise
+liberally manured. On strong clay soils this quantity may be judiciously
+increased up to 2 cwt. Dr Bernard Dyer, who has experimented largely on
+its use as a manure for mangolds, is of opinion that an application of
+from 3 to 4 cwt. an acre is likely to prove thoroughly profitable; and
+the present writer has found in his experiments with turnips that a
+top-dressing of 1 cwt. amply repaid itself.
+
+
+_Conclusions drawn._
+
+In conclusion, the nature and characteristics of nitrate of soda as a
+manure may be briefly summed up as follows:--
+
+1. It is a whitish, crystalline salt, extremely soluble, and is quickly
+diffused in the soil. It should contain 95 per cent of pure nitrate of
+soda--_i.e._, 15-1/2 per cent of nitrogen, equal to about 19 per cent of
+ammonia.
+
+2. Next to sulphate of ammonia, it is the most concentrated nitrogenous
+manure; the relative quantities of nitrogen these two manures contain
+being as three is to four.
+
+3. It contains its nitrogen in the most valuable and readily assimilable
+form--_i.e._, as _nitric acid_, the form into which all other forms of
+nitrogen have first to be converted before they become available for
+the plant's uses.
+
+4. That, at present market prices, nitrate of soda may be safely
+affirmed to be the cheapest form of nitrogenous manure.
+
+5. That nitrate of soda, in addition to its direct value as a manure,
+probably exercises a slight influence on the mechanical properties of
+the soil, by increasing its compactness and water-absorbing capacities;
+that it further tends to promote deep roots, and thus to increase the
+soil area whence the plant may derive its nourishment, at the same time
+rendering the plant more able to withstand the injurious influence of
+drought.
+
+6. That a plentiful supply of the other manurial constituents should be
+present in the soil, if nitrate of soda is to exercise its full value.
+
+7. That it may be profitably applied in the case of nearly all kinds of
+crops, but that great care should be taken as to the mode of its
+application. That this should be almost invariably as a top-dressing,
+and that it should be applied in several doses if possible.
+
+8. That its effects can be regarded as lasting only during the first
+year after application.
+
+
+FOOTNOTES:
+
+[202] This substance is also largely known under the name Chili
+saltpetre, to distinguish it from potassium nitrate or common saltpetre.
+
+[203] See Appendix, p. 351.
+
+[204] We may remind our readers that these nitrate deposits were largely
+the cause of the late war between Chili and Peru, which resulted in the
+cession to Chili by Peru of the province of Tarapaca, where the most
+important deposits are situated.
+
+[205] The other nitrate deposits are found in the provinces of
+Antofagasta and Atacama, and a certain amount of the refined article is
+exported from these places. The amount, however, is inconsiderable as
+compared with that which comes from the province of Tarapaca.
+
+[206] See his elaborate article on the Geology of Bolivia and Peru,
+published in the 'Quarterly Journal of the Geological Society' for
+November 1860.
+
+[207] The source of the boracic acid is probably volcanic.
+
+[208] A friend of the present writer, who has visited this part of the
+west coast of South America, informs him that at one point of the coast
+at Mejillones (in Bolivia) he could trace the remains of no fewer than
+twelve distinct sea-beaches, situated at different distances from the
+sea, and rising to an altitude of 2500 feet.
+
+[209] In this change, lime derived from the sea-shells would play an
+important part. Modern researches have shown, as we have already said in
+a previous chapter, that, in the conversion of organic nitrogen into
+nitrates, the presence of carbonate of lime is a necessary condition.
+
+[210] The Gulf weed is an instance in point. Huge masses of floating
+sea-weed are sometimes found, 500 to 600 miles in length, forming the
+so-called Saragossa Sea.
+
+[211] A difficulty which has not been referred to is the belief
+entertained by geologists that "there has been a change of climate in
+Northern Chili, and that there must have been more rain there formerly
+than there is at present. Traces of human habitations are found high up
+in the Cordilleras to-day. Cobs of Indian corn, axes and knives of
+copper tempered to exceeding sharpness, arrow-heads of agate, even
+pieces of cloth, are dug up in arid plains now without any trace of
+water for many leagues in or around them" (Russell, 'The Nitrate-Fields
+of Chili,' p. 290).
+
+
+
+
+APPENDIX TO CHAPTER IX.
+
+
+NITRATE OF SODA.
+
+_Total Shipments from South America, 1830-1892._
+
+Year. Tons. | Year. Tons. | Year. Tons.
+1830 800 | 1870 131,400 | 1886 437,500
+1835 6,200 | 1875 321,000 | 1887 680,600
+1840 10,100 | 1880 217,300 | 1888 745,700
+1845 16,800 | 1881 344,600 | 1889 930,000
+1850 22,800 | 1882 477,800 | 1890 1,030,000
+1855 41,800 | 1883 572,400 | 1891 790,000
+1860 55,200 | 1884 540,900 | 1892 790,000
+1865 109,000 | 1885 423,100 |
+
+The following tables exhibit the total imports into Europe, and into the
+United Kingdom from the years 1873-92:--
+
+NITRATE OF SODA, 1873-1892.
+
+_Imports into Europe._ _Imports into United Kingdom._
+
+Year. Tons. | Year. Tons.
+1873 225,000 | 1873 124,000
+1874 230,000 | 1874 108,200
+1875 280,000 | 1875 164,900
+1876 300,000 | 1876 166,800
+1877 208,000 | 1877 69,600
+1878 250,000 | 1878 104,400
+1879 205,000 | 1879 55,300
+1880 140,000 | 1880 48,300
+1881 230,000 | 1881 54,800
+1882 335,000 | 1882 96,000
+1883 440,000 | 1883 103,700
+1884 505,000 | 1884 103,700
+1885 380,000 | 1885 109,400
+1886 330,000 | 1886 75,100
+1887 440,000 | 1887 83,100
+1888 640,000 | 1888 103,100
+1889 760,000 | 1889 120,000
+1890 784,000 | 1890 114,000
+1891 851,000 | 1891 121,000
+1892 795,000 | 1892 115,000
+
+
+
+
+CHAPTER X.
+
+SULPHATE OF AMMONIA.
+
+_Value of Ammonia as a Manure._
+
+
+The value of ammonia salts as a manure has been long recognised; indeed
+till recently ammonia was thought to be the most valuable form in which
+nitrogen could be applied as a plant-food--a view, we may mention, held
+by Liebig. While the plant, no doubt, can absorb its nitrogen in the
+form of ammonia,[212] as well as in other forms, as we have already
+pointed out in previous chapters, it is now fully recognised that
+ammonia salts, when applied to the soil, are converted into nitrates.
+Nitric acid, then, must be regarded as the most valuable, inasmuch as it
+is the most rapidly assimilated form of nitrogen for the plant; but
+next to nitric acid in value comes ammonia. Of the different forms of
+ammonia available for manurial purposes, the only one used to a large
+extent is sulphate.
+
+
+_Sources of Sulphate of Ammonia._
+
+The oldest, and what is still the chief source of this valuable salt, is
+the gas-works, where it is obtained as one of the bye-products in the
+manufacture of gas. It is also obtained to a lesser extent from shale,
+iron, coke, and carbonising works. Bones, horn, leather, and certain
+other animal substances rich in nitrogen, when subjected to dry
+distillation, as is the case in certain manufactures, such as the
+manufacture of bone-charcoal for use in sugar-refineries, and the
+distillation of horn, &c., in the manufacture of prussiate of potash,
+also constitute less abundant sources.
+
+
+_Ammonia from Gas-works._
+
+Coal contains on an average from a half to one and a half per cent of
+nitrogen. When it is subjected to dry distillation, as is done in the
+gas-works, the nitrogen which it contains is chiefly converted into
+ammonia, and, in the process of purification of the gas, is removed in
+the "gas-liquor,"[213] which contains about one per cent of ammonia.
+The ammonia recovered from this liquor by distillation is then absorbed
+in sulphuric acid. It may be pointed out that nothing like all the
+nitrogen contained in the coal is recovered as sulphate of ammonia. It
+has been calculated that only from a fifth to a tenth is actually
+recovered, and many processes have been patented with a view to
+increasing the yield of ammonia in gas manufacture. The total production
+of ammonia from gas-works may be placed at little over 100,000 tons per
+annum for Great Britain. Mr L. Mond, F.R.S., recently drew attention to
+the possibility of largely increasing our supply of sulphate of ammonia
+from coal. As indicating what an enormous source of sulphate of ammonia
+we have in coal, Mr Mond calculated that its annual consumption in this
+country (estimated at 150,000,000 tons) would yield as much as 5,000,000
+tons of sulphate of ammonia.
+
+
+_Other Sources._
+
+While the ammonia produced in the manufacture of gas has long been
+collected, it is only of recent years that the other sources of ammonia
+have been developed. Next to the gas-works, the shale-works of Scotland
+form in this country the chief source of this valuable manure. In these
+works the ammonia is obtained in distilling the paraffin shale by a
+method somewhat similar to that in use in the gas-works. The amount of
+sulphate of ammonia obtained from this source is between 20,000 and
+30,000 tons per annum. Recently the ammonia has been recovered from the
+blast-furnace gases in iron-works--some 6000 tons being annually
+obtained in this way; while from coke and carbonising works the annual
+production is about half that amount. The combined annual production
+from all these sources may be put down at 140,000 tons, the total
+production in Europe being probably little more than 200,000 tons. In
+the Appendix further statistics will be found.[214]
+
+
+_Composition, &c., of Sulphate of Ammonia._
+
+Pure sulphate of ammonia is a whitish crystalline salt, extremely
+soluble in water. The commercial article, however, is generally greyish
+or brownish in colour, owing to the presence of slight quantities of
+impurities. The pure salt should contain 25.75 per cent of ammonia; but
+the commercial article is generally sold on a basis of 24.5 per cent. A
+useful test of its purity is the fact that when subjected to a red-heat
+it should almost entirely volatilise, leaving very little residue. The
+chief impurities which it is likely to contain are an excess of
+moisture, free acid, or the presence of insoluble matter. Certain
+samples contain small quantities of ammonium sulphocyanate, an extremely
+poisonous substance for plants. The presence of this dangerous impurity
+is easily detected by adding ferric chloride, which, in presence of the
+sulphocyanate, produces a blood-red colour. Sulphate of ammonia is thus
+the most concentrated of all nitrogenous manures in common use, and is
+for that reason the most expensive.
+
+
+_Application._
+
+For this reason, as well as from the fact that it contains a speedily
+available form of nitrogen, sulphate of ammonia should only as a rule be
+applied in comparatively small quantities--100 to 125 lb. per acre.[215]
+It should also be applied before, but not too long before, the crop is
+likely to require it. The reason of this is to give it time to be
+converted into nitrates. The ability of the soil to retain ammonia has
+already been pointed out. It is not safe, however, to rely too much on
+the retentive power of the soil for ammonia, the conversion of ammonia
+into nitrates going on very quickly under favourable circumstances. It
+is most profitably used as a manure for cereals, and it has been found
+by Lawes and Gilbert in their experiments, that an increase of one
+bushel of wheat and a corresponding increase of straw have been obtained
+for every 5 lb. of ammonia added to the soil. As has been pointed out in
+the previous chapter, the respective merits of sulphate of ammonia and
+nitrate of soda depend largely on the nature of the season during which
+they are used. In wet seasons the sulphate is rather more favourable
+than the nitrate, but, on an average, nitrate of soda is probably the
+more valuable manure--_i.e._, due regard being had to the quantity of
+nitrogen the two manures respectively contain. In one respect sulphate
+of ammonia is a much more useful manure than nitrate of soda, as the
+nature of its action when applied to the soil permits of it being used
+as an ingredient of mixed manures.
+
+Like nitrate of soda, but even to a greater extent, its most favourable
+action is obtained when it is applied along with other manurial
+ingredients. It should be applied at least a month earlier than nitrate.
+It has been shown that in the case of chalky soils a certain loss of
+ammonia in sulphate of ammonia is apt to take place, due to the action
+of the lime; and this leads us to point out that, in preparing mixed
+manures, care ought to be taken that it is not mixed with any compound
+containing free lime or caustic alkali, as otherwise loss of ammonia
+will ensue. It should never, for example, be used along with basic slag.
+
+
+FOOTNOTES:
+
+[212] From experiments by Lehmann and others with buckwheat and maize,
+it would seem that certain plants may prefer, at certain stages of their
+growth, ammonia to nitrates. In the case of maize, ammonia may be
+preferred in the early stages of growth, while nitrates are preferred as
+it becomes more mature. In view, however, of our present knowledge of
+nitrification, it may well be doubted whether the conclusions arrived at
+from Lehmann's experiments can be accepted.
+
+[213] As the expense of converting the ammonia present in the ammoniacal
+liquor is considerable, the practice of using the liquor itself as a
+manure has been advocated; but as an objection to this it must be urged
+that, besides being so bulky a manure, the liquor contains various
+substances poisonous to plant-life.
+
+[214] See Appendix, p. 358.
+
+[215] Some crops, however, may with advantage be treated with larger
+quantities of sulphate of ammonia, such as mangels and potatoes.
+
+
+
+
+APPENDIX TO CHAPTER X.
+
+
+NOTE (p. 355).
+
+The following table will exhibit the production of sulphate of ammonia
+in this country from 1870 to 1892:--
+
+Year. Tons. | Year. Tons.
+1870 40,000 | 1882 72,000
+1871 41,000 | 1883 75,000
+1872 42,000 | 1884 87,000
+1873 43,000 | 1885 97,000
+1874 45,000 | 1886 106,500
+1875 46,000 | 1887 113,700
+1876 48,000 | 1888 122,800
+1877 52,000 | 1889 132,000
+1878 55,000 | 1890 140,000
+1879 57,000 | 1891 143,500
+1880 60,000 | 1892 157,000
+1881 65,000
+
+The following table exhibits the sources, and the respective quantities
+from each source, of the last seven years' production:--
+
+ 1886. 1887. 1888. 1889. 1890. 1891. 1892.
+
+Gas-works 82,500 85,000 93,000 100,000 102,150 107,950 112,000
+Iron-works 4,000 5,000 5,300 6,000 5,050 6,300 12,000
+Shale-works 18,000 21,000 22,000 23,000 24,750 26,600 28,000
+Coke and
+ carbonising
+ works 2,000 2,700 2,500 3,000 2,300 2,800 5,000
+
+
+
+
+CHAPTER XI.
+
+BONES
+
+
+_Early Use of Bones._
+
+A most important manure, and one to the history of which very peculiar
+interest attaches, is Bones. Employed first in 1774, their use has
+steadily increased ever since, and their popularity as a phosphatic
+manure is among farmers in this country quite unrivalled. Like guano,
+although to a less extent, the early practice of using bones has done
+much to arouse interest in the problems of manuring, and to bring home
+to farmers the principles underlying that practice. It was from bones
+that Liebig first made superphosphate of lime, and the distinguished
+veteran experimenter, Sir John Bennet Lawes, has told us that the
+benefit accruing from the use of bones on the turnip crop first drew his
+attention to the interesting problem connected with the application of
+artificial manures. Bones were first used in Yorkshire. Shortly
+afterwards they were applied to exhausted pastures in Cheshire. Soon
+their use became so popular that the home supply was found inadequate;
+and they were imported from Germany and Northern Europe, Hull being the
+port of disembarkation. So largely were they used by English farmers,
+that Baron Liebig considered it necessary to raise a warning protest
+against their lavish application. "England is robbing all other
+countries of the condition of their fertility. Already, in her eagerness
+for bones, she has turned up the battle-fields of Leipzig, of Waterloo,
+and of the Crimea; already from the catacombs of Sicily she has carried
+away the skeletons of many successive generations. Annually she removes
+from the shores of other countries to her own the manurial equivalent of
+three millions and a half of men, whom she takes from us the means of
+supporting, and squanders down her sewers to the sea. Like a vampire,
+she hangs upon the neck of Europe--nay, of the entire world!--and sucks
+the heart-blood from nations without a thought of justice towards them,
+without a shadow of lasting advantage to herself."[216]
+
+
+_Different Forms in which Bones are used._
+
+It may be pointed out that bones have done much to alter our system of
+farming, by helping to develop turnip culture. Used at first in
+comparatively large pieces, experience gradually showed that a finer
+state of division facilitated their action. Yet it was long before the
+prejudice in favour of rough bones disappeared; and it was not till 1829
+that Mr Anderson of Dundee introduced machinery for preparing 1/2-inch
+and 1/4-inch bones and bone-dust. In the early days of their use, bones
+were fermented before being used, in order to render their action more
+speedy when applied to the soil; and this practice still obtains to the
+present day in some parts of the country among farmers. This
+fermentation was often effected simply by mixing the bones with water,
+and allowing the heap to lie for a week or two. In other cases the bones
+were mixed with urine or other refuse matter. The most important step,
+however, in the history of the treatment of bones for manure was the
+discovery in 1840, by Liebig, of the action of sulphuric acid on them--a
+discovery which led to the institution of the manufacture of
+superphosphate of lime by Sir John Lawes. The nature of this action will
+be explained in the following chapter, so that we need only say here
+that the efficacy of the manure by treatment with sulphuric acid is more
+than doubled. Bones have thus been used, and still are used, in a
+variety of conditions, such as in the raw or green state, bruised,
+boiled, steamed, fermented, burned, dissolved, and broken or ground into
+various states of fineness, to which the names of 1/2-inch, 1/4-inch
+bones, bone-meal, bone-dust, and floated bones are given. We shall now
+proceed to discuss the composition of bones, and investigate more
+exactly the nature of their action.
+
+
+_Composition of Bones._
+
+The composition of bone-tissue varies considerably, and depends on the
+age and kind of animal to which it belongs, as well as to the part of
+the animal frame from which it is taken. Bones are made up of an organic
+and an inorganic part. By steeping a piece of bone in a dilute acid
+solution, the inorganic portion of the bone is dissolved out, and the
+organic portion, which forms the framework of the bone, is alone left.
+On the other hand, by submitting a bone to the action of great heat, the
+organic portion of the bone is driven off, and all that remains is a
+quantity of ash. The proportion of the organic to the inorganic matter
+varies considerably in different bones. The bones of young animals
+contain more organic matter than those of old animals. In compact bones,
+also, the organic matter is greater than in spongy bones. The
+thigh-bone, of all the bones, contains most inorganic matter. In short,
+bones which have to bear the greatest strain are richest in inorganic
+matter. Of the bones of animals, fish-bones exhibit the greatest variety
+of composition, some being almost entirely made up of organic matter,
+while others are similar in their composition to the bones of
+quadrupeds.
+
+
+_The Organic Matter of Bones._
+
+The organic portion of bones is almost entirely made up of a substance
+to which the name _ossein_ has been given, and which, when boiled for a
+long time, is converted into gelatine. This ossein, which forms on an
+average from 25 to 30 per cent of the weight of bones, is extremely rich
+in nitrogen, containing over 18 per cent.
+
+
+_Inorganic Portion of Bones._
+
+The inorganic portion, which forms about 70 per cent, is made up chiefly
+of phosphate of lime. The dry leg-bones of oxen and sheep, according to
+Heintz, have the following percentage composition:--
+
+ Per cent.
+Phosphate of lime 58 to 63
+Carbonate of lime 6 to 7
+Phosphate of magnesia 1 to 2
+Fluoride of calcium 2
+Organic matter 25 to 30
+
+According to Payen and Boussingault, raw bones contain 6-1/4 per cent of
+nitrogen and 8 per cent of water. Pure bones are thus seen to contain
+about 29 per cent of phosphoric acid and 6-1/4 per cent of nitrogen. The
+composition of the commercial article, however, differs very widely.
+This is due to the fact that bones collected from India and America,
+where they have been long exposed to atmospheric influences, have lost
+much of their organic matter. The amount of sand and earthy impurities
+also varies very considerably.
+
+
+_Treatment of Bones._
+
+Bones are used for the manufacture of glue and gelatine. These are
+extracted from them by steaming the bones. The bones after treatment are
+used as a manure. The improvement noted in the action of the bones thus
+treated led to the introduction of the use of steamed bones as a manure.
+Raw bones are now rarely used. The fat present in raw bones retards
+their decomposition in the soil. Probably, as has been suggested, it
+forms along with lime an insoluble soap which prevents the mineral
+matter in the bone being dissolved by the carbonic acid of the soil. In
+the process of boiling or steaming a certain loss of nitrogen takes
+place, greater or less, according to the length of time they are boiled
+or steamed, and in the latter case the pressure applied. A more
+economical method for extracting the fat has been introduced by using
+benzine, but this process is not used to any extent. The loss of
+nitrogen in the former case is more than compensated for by their more
+speedy action as a manure when applied to the soil. Bone-meal of good
+quality contains from 45 to 55[217] per cent of phosphate of lime, and
+3-1/2 per cent of nitrogen. Our present total consumption of bones is
+probably little less than 100,000 tons per annum, of which about half is
+obtained from home collections, over 20,000 tons being annually
+collected in and around London alone.
+
+
+_Action of Bones._
+
+It is well known that bones are a slow-acting manure. They may be said
+to possess both a mechanical and chemical action when applied to the
+soil. When they putrefy, their nitrogen is slowly converted into
+ammonia, and carbonic acid as well as various organic acids are formed,
+which, acting upon the insoluble mineral matter in the bones, renders it
+available for plant uses. Bones thus, when applied in large quantities,
+may not merely act directly as suppliers of plant-food, but in the
+course of their putrefaction may act upon a certain amount of the inert
+fertilising matter of the soil and render it available. The more
+readily, then, bones putrefy, the more speedy will be their effect. As
+we have already pointed out, bones, in order to increase their
+efficiency, are often fermented before application. The removal of the
+fat is another means of increasing the rate of their action, but the
+fineness to which they are ground determines this more than anything
+else. Much ingenuity has been expended in perfecting machinery for
+grinding bones. At one time in Germany they were pounded in stamps
+similar to those used for ore. In America what has been called "floated
+bone" has been prepared. This bone is so fine that it actually floats in
+the air like flour-dust, and is made by whirling the bones against one
+another. The action of bones prepared in this way is of course very
+speedy, but the difficulty of applying a manure in such a fine state of
+division to the soil is great. The expense of the process also is
+considerable.
+
+The ease with which bones when ground into a fine state of division
+putrefy, is evidenced by the fact that bone-flour has to be salted in
+order to enable it to keep. Another condition which determines the rate
+at which the fertilising matters in bones become available is the nature
+of the soil. Fermentation, as we have already seen, requires a plentiful
+supply of air, and a certain amount, but not too much, of moisture.
+Consequently bones act best in medium soils--soils which are "neither
+too light and dry, nor too close and wet." There can be no doubt that
+what gives to bones a peculiar value in the eyes of the farmer is the
+fact that they form a manure of a lasting character. They give what has
+been termed backbone to a soil. But the tendency of modern agricultural
+practice is to use quick-acting manures rather than slow. This has been
+admirably put by Professor Storer in the following words: "The old
+notion, that those manures are best which make themselves felt through a
+long series of years, is now recognised to be an error. The adage, that
+'one cannot eat the cake and have the cake' is conspicuously true in
+agriculture; and just as it is the part of prudence in household or
+maritime economy to abstain from laying in at any one time more
+provisions than can be properly disposed of in a year or during a
+voyage, so should the farmer refrain from bringing to the land an
+unnecessary excess of plant-food. Such food is liable to spoil withal
+in the soil, as well as other kinds of provisions that are kept too long
+in store. A just proportion of food, properly prepared, is the point to
+be aimed at always."
+
+In view, therefore, of what has just been said, it might seem best to
+use bones in the form in which they are most speedily available--viz.,
+as dissolved bones. This would be so if bones were the only source we
+possessed for the manufacture of superphosphate of lime; but we now
+have, in the various mineral phosphates, abundant and cheaper sources of
+this valuable manure. The opinion of leading agriculturists and
+agricultural chemists is rather in favour of applying bones in the
+undissolved condition. For one thing, it seems far from economical to
+utilise an expensive material such as bones for manufacturing an article
+which can be equally well manufactured from cheaper materials; for once
+the phosphate of lime is dissolved, it is equally valuable from whatever
+source it may be derived. Of course this is not tantamount to saying
+that dissolved bones as a manure are no more valuable than
+superphosphate. In dissolved bones we have, in addition to soluble
+phosphate, a considerable proportion of undissolved bone-tissue,
+containing a certain quantity of nitrogen and organic matter; but so far
+as the soluble phosphate is concerned, it seems only rational to
+conclude that its efficacy is equally great, whether it be derived from
+bone or mineral phosphate. Another reason is, that much of the
+characteristic action of bones is lost by treating them with sulphuric
+acid. As Dr Aitken has pointed out, the germ life in the soil and in the
+bones gradually converts them into a form available for the nourishment
+of plants; but to dissolve bones with sulphuric acid is to kill out the
+germ life and retard the decay of any nucleus of bone in the dissolved
+manure.
+
+
+_Dissolved Bones._
+
+Dissolved bones, however, are still manufactured. Formerly the manure
+called dissolved bones was often a mixture of mineral superphosphate
+along with undissolved bone-meal, but recent legislation has stopped the
+continuance of this practice. The composition of dissolved bones varies
+somewhat, the percentage of soluble phosphate being about 20 to 23 per
+cent, the insoluble amounting to from 9 to 10 per cent, and the nitrogen
+from 2-1/2 to 3-1/2 per cent.[218] Another reason against dissolving
+bones is to be found in the difficulty experienced in dissolving their
+phosphate. Bones, especially when raw, are not easily acted upon by
+acids.
+
+
+_Crops suited for Bones._
+
+Bones are commonly regarded as being specially beneficial to
+pasture-land, to which they are applied as a top-dressing. Turnips,
+tobacco, potatoes, vines, and hops are also much benefited by the
+application of bones. In America, mixed with wood-ashes (the chief
+manurial constituent of which is potash), they have been extensively
+used as a substitute for farmyard manure, and have been applied at the
+rate of 5 to 6 cwt. per acre. In Saxony, according to Professor Storer,
+1 cwt. of fine bone-meal is worth as much as 25 to 30 cwt. of farmyard
+manure.
+
+
+_Bone-ash._
+
+The ash which is left on burning bones used to be an article of
+considerable manurial importance. It is still imported from South
+America in some quantity, and is used chiefly in the pottery industry.
+It is occasionally still used to a limited extent for the manufacture of
+high-class superphosphates. It is extremely rich in phosphate of lime,
+of which it contains between 70 and 80 per cent; but of course it is
+devoid of nitrogen.[219] Bone-ash is best used in the dissolved form, as
+it possesses no characteristic action such as is possessed by bones.
+
+
+_Bone-char or Bone-black._
+
+When heated in a closed retort, bones are not converted into bone-ash,
+but into a body called bone-char. This body is similar in composition to
+bone-ash, except for a certain percentage of charcoal--amounting, on an
+average, to 10 per cent. It contains but little nitrogen and other
+organic matter. Bone-black or bone-char is an article which is prepared
+in enormous quantities for use in sugar-refineries, where it is used in
+the purification of sugar. After use it may be renovated by submitting
+it to heat; but as this process gradually lessens the percentage of
+carbon it contains, after a certain period it becomes too poor in this
+substance for efficiently acting as a filter. When this takes place it
+is technically known as spent char, and is used for the manufacture of
+superphosphates. Spent char is a highly phosphatic substance, being very
+little poorer than bone-ash, and containing about 70 per cent of
+phosphate of lime.[220]
+
+
+FOOTNOTES:
+
+[216] It is only fair to Liebig to say that when he wrote these words
+the practically boundless supply of mineral phosphates which we now know
+to exist in many parts of the world was little dreamt of.
+
+[217] See Appendix, Note I., p. 371.
+
+[218] See Appendix, Note II., p. 371.
+
+[219] See Appendix, Note III., p. 372.
+
+[220] See Appendix, Note IV., p. 372.
+
+
+
+
+APPENDIX TO CHAPTER XI.
+
+
+NOTE I. (p. 364).
+
+The following analysis will serve to show the composition of
+bone-meal:--
+
+ Moisture 10.43
+*Organic matter 32.30
+ Phosphate of lime 48.40
+ Carbonate of lime, magnesia, &c. 7.20
+ Insoluble siliceous matter 1.67
+ ------
+ 100.00
+ ------
+*Containing:--
+ Nitrogen 3.71
+ Equal to ammonia 4.51
+
+
+
+NOTE II. (p. 368).
+
+COMPOSITION OF DISSOLVED BONES.
+
+The accompanying analysis may be taken as representing the average
+composition of dissolved bones:--
+
+ Moisture 10.10
+*Organic matter and water of combination 29.34
+ Monobasic phosphate of lime 11.23
+(Equal to tricalcic phosphate rendered "soluble" 17.58)
+ Phosphate soluble in ammonium citrate 14.02
+ Insoluble phosphate of lime 1.88
+ Calcium sulphate, magnesia, alkalies, &c. 30.23
+ Sand 3.20
+ ------
+ 100.00
+ ------
+*Containing:--
+ Nitrogen 2.62
+ Equal to ammonia 3.18
+
+
+COMPOSITION OF COMPOUND BONES.
+
+The following analysis illustrates the composition of compound bones:--
+
+ Moisture 8.10
+*Organic matter and water of combination 37.22
+ Monobasic phosphate of lime 13.68
+(Equal to tricalcic phosphate rendered "soluble" 21.42)
+ Insoluble phosphate of lime 10.48
+ Calcium sulphate, magnesia, alkalies, &c. 26.02
+ Sand 4.50
+ ------
+ 100.00
+ ------
+*Containing:--
+ Nitrogen 1.90
+ Equal to ammonia 2.30
+
+
+NOTE III. (p. 369).
+
+As showing the composition of bone-ash, the following analysis may be
+quoted:--
+
+ Moisture .25
+ Organic matter .85
+*Phosphoric acid 35.56
+ Lime 47.09
+ Magnesia, alkalies, &c. 9.80
+ Sand 6.45
+ ------
+ 100.00
+ ------
+*Equal to tricalcic phosphate 77.63
+
+
+NOTE IV. (p. 370).
+
+Composition of bone-char (on dry sample):--
+
+Carbon 10.51
+Calcium and magnesium phosphates, calcium fluoride, &c. 80.21
+Calcium carbonate 8.30
+Calcium sulphate .17
+Ferric oxide .12
+Silica .34
+Alkaline salts .35
+ ------
+ 100.00
+ ------
+
+
+
+
+CHAPTER XII.
+
+MINERAL PHOSPHATES.
+
+
+In this chapter we shall give an account of the more commonly occurring
+mineral phosphates. In Chapter V., where we discussed the position of
+phosphoric acid in agriculture, it was pointed out that mineral
+phosphates were very abundant, and that large deposits of them were
+found in many parts of the world.
+
+
+_Coprolites._
+
+Reference may first be made to the so-called coprolites or phosphatic
+nodules which have been found in great abundance in the greensand
+formation, in the crag of the eastern counties, and in the chalk
+formation of the southern counties. These coprolites are rounded
+nodules, and are composed of the fossil excrements and remains of
+ancient animals. They are found in large quantities in Cambridgeshire,
+and were discovered by Dr Buckland many years ago. The history of their
+discovery is not a little curious. The manurial properties of
+road-scrapings in parts of Cambridgeshire were noticed, and on being
+examined were found to be in part composed of phosphate of lime, derived
+from phosphatic nodules dug out of the underlying greensand, and used
+for the purpose of repairing roads. Professor Henslow first drew
+attention to them at a meeting of the British Association held in
+Cambridge in 1845, and pointed out that they contained about 60 per cent
+of phosphate of lime. They were also found in enormous quantities in
+Suffolk, Norfolk, Bedfordshire, and Essex, and were for a long time
+largely used in the manufacture of superphosphate, but of late years
+have not been used to anything like the same extent, owing to the fact
+that there are richer and cheaper sources of phosphate of lime
+available. In 1887 about 20,000 tons of coprolites were raised. The
+richest were those obtained in Cambridge, while those got from
+Bedfordshire were about the poorest. Deposits have also been found in
+France and other countries. The average amount of phosphate of lime in
+English coprolites is between 50 and 60 per cent, while the French
+contain about 45 per cent.
+
+
+_Canadian Apatite or Phosphorite._
+
+We have already referred in Chapter V. to large deposits of apatite or
+phosphorite found in Canada. The Canadian mines commenced to be worked
+about fifteen years ago, and the output now amounts to nearly 25,000
+tons per annum.[221] A portion of this goes to the United States; the
+rest, amounting to about 20,000 tons, being shipped to England, whence
+it is again exported to Hamburg and other places.[222] It contains from
+70 to 80 per cent of phosphate. Deposits are also found at Estremadura
+in Spain, and in Norway.
+
+
+_Estremadura or Spanish Phosphates._
+
+Large deposits of phosphate have long been known to exist at Estremadura
+in Spain, and the mines at Caceres have been worked on a large scale for
+seventeen years, and about half a million tons have been raised. In 1882
+the imports into this country amounted to over 56,000 tons; but latterly
+they have only been about a fourth of this amount. Dr Dauberry visited
+the deposits in 1843, and wrote a most interesting account of them. They
+do not seem, however, to have been imported for purposes of
+superphosphate manufacture till a number of years afterwards. Of
+Estremadura phosphate there are three classes, containing respectively
+50, 60, and 70 per cent of phosphate of lime, the lowest quality being
+the commonest.[223]
+
+
+_Norwegian Apatite._
+
+This apatite has ceased to be imported of late years, owing to a duty on
+exportation.
+
+
+_Charleston or South Carolina Phosphate._
+
+For a number of years these deposits have formed the chief source of
+phosphate of lime used in the manufacture of mineral superphosphates in
+this country (in fact they have furnished two-thirds of our phosphate
+supply during recent years). Discovered twenty-five years ago, some four
+to five million tons have already been shipped. About half a million
+tons were raised in 1886 from these mines, which are the most abundant
+in the world. There are two kinds--the so-called "land" and "river"
+phosphates. The former contains more oxide of iron and alumina, and is
+therefore less pure than the latter, in which the iron and alumina do
+not exceed 2 per cent. The river phosphate is dredged from the Bull,
+Coosaw, and Beaufort rivers. Of phosphate of lime it contains from 50 to
+60 per cent. It is generally sold in three grades--50 to 52 per cent, 55
+to 56 per cent, and 58 to 60 per cent of phosphate of lime. It will thus
+be seen to be incapable of producing very high-class superphosphates
+--_i.e._, containing more than 30 per cent "soluble" phosphate.
+This point will be more intelligible when we describe the manufacture of
+superphosphate. The demand for these phosphates in the United States has
+increased enormously in recent years, owing to the increase in the
+quantity of manure used.
+
+
+_Belgian Phosphate._
+
+Another very important source of mineral phosphates are deposits
+discovered some years ago in Belgium near Mons. These phosphates are of
+different qualities, and are found, some in layers near the surface in
+pockets forming the richest class, and containing from 45 to 65 per cent
+of phosphate, and some in the form of a friable phosphatic rock, the
+so-called _craie-grise_ (phosphatic chalk), containing from 25 to 35 per
+cent of phosphate of lime. The higher quality of Belgian phosphate is
+pretty well exhausted, and it is the second class that forms the bulk of
+the ordinary Belgian phosphate at present exported. The commercial
+article contains about 35 to 40 per cent of phosphate, and about 45 per
+cent of carbonate of lime. The fact of its poor quality, together with
+the large percentage of carbonate of lime it contains, renders its
+adoption alone in the manufacture of superphosphate unsuitable. Attempts
+have been made to get rid of a portion of this carbonate of lime and to
+raise the percentage of phosphate. For this purpose the phosphate has
+been calcined, but this was soon found to be a great mistake. Other
+means have been adopted, with the result that the percentage has been
+increased to 50 per cent. It is consequently used in small quantities
+as a drier, for which it is peculiarly suited on account of its
+carbonaceous nature, along with the higher-class phosphates. In the year
+1886 about 145,000 tons of this phosphate were raised, of which about
+45,000 tons were imported into the United Kingdom.
+
+
+_Somme Phosphate._
+
+Still more recently a discovery of phosphate deposits has been made in
+the Somme and Pas de Calais departments in the north of France,
+adjoining, and similar in character to, the Belgian deposits. The only
+difference between Belgian and French phosphates is, that the latter is
+of a higher quality, and contains from 50 to 80 per cent of phosphate of
+lime. A very large demand for these phosphates sprang up, and in 1888,
+although they had only been worked for some two years, no less than
+150,000 tons had been raised, of which about one-half contained from 70
+to upwards of 75 per cent. There are four grades in the market,
+containing 55 to 60, 60 to 65, 70 to 75, and 75 to 80 per cent of
+phosphate of lime. The highest quality furnishes the chief material for
+the manufacture of high-grade superphosphates.
+
+
+_Florida Phosphate._[224]
+
+During the last few years large quantities of phosphates have been
+imported from Florida. These are of different qualities, the land rocks
+now imported containing from 70 to 80 per cent of phosphate of lime, and
+the river phosphate about 60 per cent. The latter class are similar in
+composition to the best South Carolina river-phosphates, which they much
+resemble.
+
+
+_Lahn Phosphate._
+
+Phosphate deposits were found at Nassau in Germany in 1864; but as the
+phosphate contained a considerable proportion of iron and alumina, they
+are not used in this country now, although they are in Germany for
+double superphosphate manufacture.
+
+
+_Bordeaux or French Phosphate._
+
+Similar in quality to Lahn phosphate is that obtained in the
+neighbourhood of Bordeaux.
+
+
+_Algerian Phosphate._
+
+Excellent phosphates are now being sent from Algeria--some cargoes being
+as rich as 70 per cent.
+
+
+_Crust Guanos._
+
+We have already referred to the guanos in the chapter on Guano. They are
+also known under the name of Caribbean phosphates, and come from the
+West India Islands. The chief kinds are Aruba, Curaçao, Sombrero, and
+Navassa, the Great Cayman, Redonda, and Alta Vela. Most of them are of
+high quality, containing from 60 to 80 per cent of phosphate, and are
+thus suited for the manufacture of high-class superphosphates. Some of
+them, however, contain a considerable proportion of iron and alumina,
+and are not suitable for this purpose. The Redonda and Alta Vela
+phosphates consist chiefly of phosphate of alumina.
+
+
+_Value of Mineral Phosphates as a Manure._
+
+While it is commonly regarded as unadvisable to use mineral phosphates
+directly as phosphatic manures, it may well be questioned how far such
+an opinion is warranted by actual experience. Professor Jamieson of
+Aberdeen, in his interesting and valuable experiments, has drawn
+attention to the fact that coprolites in a fine state of division are an
+extremely valuable source of phosphoric acid for crops, and are a more
+quickly available source than is commonly supposed. Experiments
+conducted elsewhere with ground coprolites and other mineral phosphates
+corroborate Professor Jamieson's conclusions. The successful use of
+Thomas-phosphate has drawn attention to the possibility of profitably
+applying undissolved mineral phosphate to the soil; and no doubt the
+practice may in future years be increased. At present, however, with the
+exception of Thomas-phosphate, mineral phosphates alone are used for
+conversion into superphosphate.
+
+
+FOOTNOTES:
+
+[221] Since the discovery of the Florida deposits of phosphate, the
+working of the Canadian mines has been practically abandoned.
+
+[222] See Appendix, p. 381.
+
+[223] These phosphates are now no longer worked.
+
+[224] These deposits were discovered a few years ago; and as they are of
+considerable extent and high quality, have entirely revolutionised the
+phosphate market. About 300,000 tons are now annually raised in
+Florida.
+
+
+
+
+APPENDIX TO CHAPTER XII.
+
+
+NOTE (p. 375).
+
+THE FOLLOWING TABLE SHOWS THE IMPORTS OF PHOSPHATES INTO THE UNITED
+KINGDOM, AND THE COUNTRIES OF PRODUCTION, DURING THE YEARS 1885-92.
+
+-----------------------+---------+---------+---------+---------+---------+
+ | 1885. | 1886. | 1887. | 1888. | 1889. |
+-----------------------+---------+---------+---------+---------+---------+
+ | Tons. | Tons. | Tons. | Tons. | Tons. |
+ United States | 138,844 | 144,623 | 165,275 | 111,369 | 122,554 |
+ Canada | 21,484 | 18,069 | 19,194 | 12,423 | 23,297 |
+ Dutch West Indies | | | | | |
+ (Curaçao, Aruba) | 11,588 | 12,581 | 9,505 | 10,736 | 14,730 |
+ British West Indies | | | | | |
+ (Sombrero, &c.) | 7,727 | 3,351 | 6,451 | 11,010 | 1,880 |
+ Spain and Portugal | 19,282 | 5,825 | 15,612 | 6,978 | 1,326 |
+ Belgium | 35,405 | 31,551 | 45,322 | 54,261 | 64,643 |
+ Holland | 865 | 2,194 | 4,778 | 4,137 | 2,270 |
+ France | 2,276 | 1,503 | 11,140 | 39,059 | 65,490 |
+ Australia | - | 200 | 350 | - | 1,250 |
+ Germany | 704 | - | - | - | - |
+ Hayti (San Domingo) | - | 2,175 | 3,044 | 6,238 | 4,094 |
+ Brazil | - | - | 1,200 | - | - |
+ Venezuela and Guiana | - | - | 405 | - | - |
+ Norway | - | - | - | - | - |
+ Other countries | 397 | 1,039 | 1,139 | 1,675 | 390 |
+ | | | | | |
+ *Florida phosphate. | - | - | - | - | - |
+ Carolina phosphate. | - | - | - | - | - |
+-----------------------+---------+---------+---------+---------+---------+
+
+-----------------------+---------+----------+----------
+ | 1890. | 1891. | 1892.
+-----------------------+---------+----------+----------
+ | Tons. | Tons. | Tons.
+ United States | 177,283 | *131,084 | *201,465
+ Canada | 21,089 | 15,918 | 7,814
+ Dutch West Indies | | |
+ (Curaçao, Aruba) | 14,763 | 8,851 | 6,648
+ British West Indies | | |
+ (Sombrero, &c.) | 3,970 | 1,960 | 2,473
+ Spain and Portugal | - | 320 | 971
+ Belgium | 82,096 | 70,723 | 65,079
+ Holland | 2,428 | 3,434 | 6,627
+ France | 35,659 | 18,325 | 18,239
+ Australia | - | - | -
+ Germany | - | - | -
+ Hayti (San Domingo) | 992 | 1,639 | 2,965
+ Brazil | - | - | -
+ Venezuela and Guiana | - | 540 | -
+ Norway | 4,151 | 1,495 | 305
+ Other countries | 1,070 | 1,483 | 1,594
+ | | |
+ *Florida phosphate. | - | 35,203 | 66,327
+ Carolina phosphate. | - | 96,881 | 135,138
+-----------------------+---------+----------+----------
+
+
+
+
+CHAPTER XIII.
+
+
+SUPERPHOSPHATES.
+
+As was mentioned in the chapter on Bones, Liebig in the year 1840
+discovered that the effect of adding oil of vitriol, or sulphuric acid,
+to bones was to render the phosphate they contain soluble. This
+discovery marked an epoch in the history of artificial manures, and laid
+the foundation of the now enormous manufacture of superphosphate. In
+1862 the juries of the London International Exhibition published an
+elaborate report containing an interesting article on the manure trade
+of Great Britain, in which it was stated that the annual quantity of
+superphosphate then made amounted to from 150,000 to 200,000 tons. Now
+it may be placed not far short of a million tons. Probably that made in
+the United States is considerably more. In the first instance,
+superphosphate was manufactured by Sir John Lawes from spent bone-char.
+This was superseded by coprolites and Estremadura phosphorite, Suffolk
+coprolites being for many years the chief material employed. This in
+turn was succeeded by the richer Cambridge coprolites, but of late years
+coprolites have practically ceased to be a source of superphosphate, the
+other mineral phosphates mentioned in the previous chapter--such as the
+South Carolina, Belgian, Somme, &c., phosphates--taking their place.
+
+
+_Manufacture of Superphosphate._
+
+The manufacture of superphosphate is of too technical a nature to permit
+of discussion in a work of this kind. It is important, however, that the
+general principles underlying the process of manufacture and the
+chemical changes in the phosphate taking place during the process be
+clearly understood. In the first place, great importance attaches in the
+manufacture of the superphosphate to the fineness of division of the raw
+material, and much ingenuity has been spent on apparatus designed for
+this purpose. The difficulty of grinding the phosphate varies, of
+course, with the nature of the material used--apatite, for example,
+being much more difficult to reduce to the necessary fineness than
+phosphatic guano. The finer the state of division, the more complete
+will be the decomposition of the phosphate by the acid. Mr Warington
+recommends that for first-class work the powder should be so fine as to
+admit of it passing through a sieve of eighty wires to the inch. After
+the phosphate is reduced to powder, it is mixed with acid. This takes
+place in the mixer, which is generally in the form of an iron cylinder
+furnished in the centre with a revolving shaft, the sulphuric acid used
+being the ordinary chamber acid (sp. gr. 1.57). Whatever strength of
+acid is used, there must be a certain quantity of water present to form
+gypsum. It is to the formation of gypsum in the resulting product that
+the dryness of the superphosphate is due. The proportion of sulphuric
+acid used depends on the composition of the phosphate; and here it may
+be pointed out that the presence of much carbonate of lime is a most
+important factor in determining the quantity of acid required. The
+reason of this is, that where carbonate and phosphate of lime are
+present together, sulphuric acid first acts upon the carbonate, and it
+is not till this is wholly decomposed that the phosphate can be acted
+upon. Hence mineral phosphates with a large percentage of carbonate of
+lime do not constitute such an economical material for the manufacture
+of superphosphate as those in which the percentage of carbonate is
+small.[225] A certain amount of heat is necessary for the purpose of
+enabling a quick decomposition to take place. For this purpose the
+sulphuric acid added has been previously heated. In the ordinary
+manufacture of superphosphate, however, this is not considered
+necessary, as the heat developed by the chemical action between the
+phosphate and the acid is sufficiently great. The phosphate, after being
+thoroughly mixed with the acid, is discharged into what is technically
+known as the pit, a chamber built of brick or concrete. The mixture,
+which is in a fluid state when it enters the pit, very soon hardens, and
+is dug out in a day or two. It is next reduced to powder in a
+disintegrator, and is then ready for use as a manure.
+
+
+_Nature of the Reaction taking place._
+
+In order to clearly understand the nature of the reaction which takes
+place when sulphuric acid is added to a phosphatic material, it may be
+well to say a word or two on the composition of the different compounds
+of lime and phosphoric acid.
+
+
+_Phosphates of Lime._
+
+In the various phosphatic manures used in agriculture there are four
+different kinds of phosphates. In the commonest form, popularly called
+bone-phosphate, which is the form in which lime and phosphoric acid are
+combined in bones, guano, and the ordinary mineral phosphates, the lime
+and phosphoric acid are combined in the form of what is known as
+tribasic phosphate of lime, or tricalcic phosphate--that is to say, for
+every equivalent of phosphoric acid there are three equivalents of lime.
+This may be represented as follows:--
+
+Lime }
+Lime > Phosphoric acid.
+Lime }
+
+Or we may also say that for every 142 parts by weight of phosphoric acid
+there are 168 parts by weight of lime in this form of phosphate. This is
+the least soluble form of phosphoric acid,[226] and is the form
+generally referred to in commercial analyses as insoluble phosphate.
+When this phosphate is acted upon with sulphuric acid, a soluble
+phosphate is formed, as Liebig first showed, to which the name
+superphosphate has been given, and which is also known as monobasic
+phosphate of lime, or monocalcic phosphate. This compound may be
+represented as containing, instead of three equivalents of lime, only
+one, the other two equivalents being replaced by water. This compound
+may be represented as follows:--
+
+Lime }
+Water > Phosphoric acid.
+Water }
+
+In it, for every 142 parts of phosphoric acid, there are only 56 parts
+of lime. It is soluble in water, and gives to the commercial article
+known as superphosphate of lime its value. Intermediate in composition
+between these two phosphates there is another known as precipitated
+phosphate of lime, or dicalcic phosphate (the same as reverted
+phosphate), which contains two equivalents of lime and one equivalent of
+water as follows:--
+
+Lime }
+Lime > Phosphoric acid.
+Water }
+
+This compound contains, for every 142 parts of phosphoric acid, 112
+parts of lime; and in solubility occupies an intermediate position.
+Lastly, there is a fourth compound of lime and phosphoric acid, which
+only occurs in one phosphatic manure--viz., phosphatic slag, in which
+indeed it was first discovered--which consists of four equivalents of
+lime to one of phosphoric acid, to which the name tetrabasic phosphate
+of lime or tetracalcic phosphate has been given. Its composition may be
+illustrated as follows:--
+
+Lime }
+Lime > Phosphoric acid.
+Lime >
+Lime }
+
+Or, for every 142 parts of phosphoric acid, there are 224 parts of lime.
+Contrary to what we might expect, this phosphate is less insoluble than
+the ordinary tribasic or bone phosphate. This may be owing to the fact
+that, in the tetrabasic phosphate, there is more lime present than that
+which the phosphoric acid can retain with strong chemical affinity.[227]
+In the manufacture of superphosphate the tribasic phosphate is converted
+into the soluble phosphate--the lime, which was formerly in combination
+with the phosphoric acid, uniting with the sulphuric acid, and forming
+gypsum.[228] It was till recently supposed that soluble phosphate and
+gypsum were the only two resulting products of this decomposition. It
+has been recently shown, however, by Ruffle and others, that this is
+not, strictly speaking, the case, and that probably a large proportion
+of free phosphoric acid is formed; in fact, it seems probable that in
+the first stage of the reaction, only phosphoric acid is produced, and
+that this subsequently acts upon the undecomposed phosphate, with the
+production of monocalcic phosphate.[229] The amount of sulphuric acid
+which experience has shown it is necessary to add for the successful and
+economical manufacture of superphosphate, depends on the composition of
+the raw material employed. The larger the percentage of tribasic
+phosphate, the larger the quantity of sulphuric acid required for its
+decomposition; but sometimes even a poor phosphate consumes a large
+amount of sulphuric acid. This is the case where much calcium carbonate
+or fluoride is present in the raw phosphate, as both of these compounds
+require a quantity of acid for their decomposition, which takes place
+before the decomposition of the phosphate. Hence phosphates rich in
+carbonate of lime are not well suited as economical materials from which
+to manufacture superphosphate.
+
+
+_Reverted Phosphates._
+
+A change which is apt to take place in superphosphate after its
+manufacture is what is known as reversion of the soluble phosphate. Thus
+it is found that on keeping superphosphate for a long time the
+percentage of soluble phosphate becomes less than it was at first. The
+rate at which this deterioration of the superphosphate goes on varies in
+different samples. In a well-made article it is practically
+inappreciable, whereas in some superphosphates, made from unsuitable
+materials, it may amount to a considerable percentage. The causes of
+this reversion are twofold. For one thing, the presence of undecomposed
+phosphate of lime may cause it. This source of reversion, however, is
+very much less important than the other, which is the presence of iron
+and alumina in the raw material. When a soluble phosphate reverts, what
+takes place is the conversion of the monocalcic phosphate into the
+dicalcic. Now in the first case, where reversion is due to the presence
+of undecomposed phosphate, the action taking place may be represented as
+follows:--
+
+Lime } } { lime } }
+Lime } phosphoric acid } { water} phosphoric acid }
+Lime } } + { water} } =
+(One molecule of insoluble } { (One molecule of soluble}
+ phosphate) } { phosphate) }
+
+Lime } } { lime }
+Lime } phosphoric acid } { lime } phosphoric acid.
+Water} } + { water}
+(One molecule of reverted } { (One molecule of reverted
+ phosphate) } { phosphate.)
+
+It may be mentioned, however, that reversion from this cause probably
+takes place to a very slight extent in practice.[230] Where reversion is
+due to the presence of iron and alumina in the raw material, the nature
+of the reaction is not well understood, and is consequently not so
+easily demonstrated as in the former case. Where iron is present in the
+form of pyrites, or ferrous silicate, it does not seem to cause
+reversion. It is only when it is present in the form of oxide--and in
+most raw phosphatic materials it is generally in this latter
+form[231]--that it causes reversion in the phosphate.
+
+
+_Value of reverted Phosphate._
+
+The value of reverted phosphate is a subject which has given rise to
+much dispute among chemists. That it has a higher value than the
+ordinary insoluble phosphate is now admitted; but in this country, in
+the manure trade, this is not as yet recognised. At first it was thought
+that it was impossible to estimate its quantity by chemical analysis.
+This difficulty, however, has been overcome, and it is generally
+admitted that the ammonium citrate process furnishes an accurate means
+of determining its amount. Both on the Continent and in the United
+States reverted phosphate is recognised as possessing a monetary value
+in excess of that possessed by the ordinary insoluble phosphate. The
+result is, that raw phosphates containing iron and alumina to any
+appreciable extent are not used in this country, although they do find a
+limited application in America and on the Continent.
+
+
+_Composition of Superphosphates._
+
+Superphosphates as manufactured may be divided, generally speaking, into
+three classes--viz., low class, medium, and high class. The ordinary or
+medium class contains from 25 to 27 per cent of soluble phosphate; and
+here it may be pointed out that by soluble phosphate is meant the
+percentage of tribasic phosphate which has been dissolved--not, as might
+at first sight be supposed, the percentage of monocalcic phosphate. The
+lower-class superphosphates are those containing less than 25 per cent,
+generally 23 to 25 per cent, of soluble phosphate; while the high-class
+superphosphate may contain from 30 to 45 per cent. For the manufacture
+of high-class superphosphate only a certain number of raw phosphates are
+available, such as Curaçao and Somme phosphates, phosphatic guanos,
+bone-char, &c. Certain processes have been patented for the manufacture
+of even more concentrated superphosphates, and by them phosphates
+containing as much as 40 per cent of soluble phosphoric acid--_i.e._,
+equal to 87 per cent of soluble phosphate--have been prepared. To this
+class belongs the so-called double superphosphate, manufactured at
+Wetzlar in Germany. Such a concentrated form of manure is naturally very
+expensive to manufacture, and is hardly to be recommended for home
+consumption. Where, however, manures have to be conveyed long distances,
+and the freight is consequently very high, such a concentrated article
+may be found most economical.
+
+
+_Action of Superphosphates._
+
+When superphosphate is applied to the soil it is converted into an
+insoluble state. In short, the process of reversion is carried on on a
+wholesale scale. This is due to the lime, iron, and alumina salts which
+the soil contains. In all probability the phosphate is finally converted
+into a hydrated ferric or aluminic phosphate, in which form it is
+gradually acted upon by the sap of the plant-roots as required. This
+being the case, it may be asked, Why is superphosphate so much more
+rapid in its action than insoluble phosphate; or why should we be at the
+trouble and expense of dissolving the phosphate if it has to become
+insoluble again in the soil? This question is one of very great
+importance, for the answer to it furnishes, in our opinion, the key to
+the whole phosphate question. When superphosphate is added to the soil,
+being soluble in water, it is soon dissolved and carried down by the
+rain into its pores, and becomes thoroughly mixed with the
+soil-particles. It is thus soon fixed in the soil, beyond the risk of
+being washed away. The result is, that the phosphate is obtained in a
+state of division infinitely more minute than could ever be obtained by
+mechanical grinding, and is, further, most intimately mixed with the
+particles of the soil. It is this intimate mixture of the phosphate with
+the particles of the soil, and its minute state of division, that
+constitute the only reason for rendering superphosphate superior in its
+action to even the most finely ground insoluble phosphates. This opinion
+is supported by the fact, that although the chemist has imitated nature
+in this matter so far as to manufacture precipitated phosphate, he has
+failed, as a rule, in getting as favourable results with it as with
+superphosphate. Although the mechanical state of division of the
+manufactured precipitated phosphate is probably as fine as that
+obtained by nature from the superphosphate, it is impossible to obtain
+so intimate a mixture with the soil-particles, and hence the results
+obtained are different. For these reasons it will be easily seen that
+the rate of action of the superphosphate must always be quicker than
+that of any other form of phosphatic manure. The phosphate is everywhere
+distributed in the soil. The plant-roots are thus furnished with a
+continuous supply throughout their growth, and micro-organisms, which
+require for their development a supply of this necessary plant-food, are
+propagated. A regularity in the plant's growth is thus secured, which is
+of great importance. But while admitting this, there are many cases in
+which this greater quickness of action does not render soluble phosphate
+the most economical form. The nature of the crop, as well as the nature
+of the soil, may in many cases be such as to render the application of
+the cheaper insoluble phosphate more economical. It is imperative that
+the early growth of some crops be hastened as much as possible by a
+ready supply of easily assimilable plant-food, in order to enable them
+to successfully sustain the attack of certain pests to which they are
+liable to succumb. This, for example, is notably the case with turnips.
+In such a case there can be no doubt that the value of soluble phosphate
+to the young plants is very great, as it enables them to survive this
+critical period.
+
+
+_Action of Superphosphate sometimes unfavourable._
+
+But even in this case there may be other conditions which render
+insoluble phosphate a preferable manure. Such a case is where the soil
+is of a very light nature and is deficient in lime. In this case the
+acid superphosphate, not having the necessary base to combine with, may
+prove even hurtful to the young plants. According to the late Dr
+Voelcker, a concentrated superphosphate may produce a smaller crop than
+a fertiliser containing only a quarter as much soluble phosphoric acid,
+when applied to root-crops on sandy soils, greatly deficient in lime.
+Cases such as the above, however, are extremely rare; and we may say
+that, in the case of root-crops generally, superphosphate must be
+regarded as of special value.
+
+
+_Application of Superphosphate._
+
+In any case, superphosphate ought to be applied to a soil some time
+before it is likely to be assimilated by the plant, in order to allow
+neutralisation of its acid character to be fully effected before the
+plant's roots come in contact with it. Thus Professor S. W. Johnson, one
+of the greatest living American authorities, states it as his opinion
+that recent investigations tend to show that soluble and reverted (or
+precipitated) phosphates are, upon the whole, about equally valuable as
+plant-food, and of nearly equal commercial value. But as Sir John Lawes,
+in quoting Professor Johnson to the above effect, remarks, this opinion
+is based on an experience of American agriculture, in which country
+soluble phosphate is chiefly applied to cereal crops, while in this
+country it is chiefly applied to turnips. In the case of cereal crops,
+the importance of a speedy early growth is not so great, as we have
+already pointed out, as it is in turnips, where the danger to the young
+plants from the ravages of the turnip-fly is such that the growth of
+even a day or two may make a very considerable difference.
+
+
+_Value of Insoluble Phosphate._
+
+A consideration of the action of superphosphate, then, throws a good
+deal of light on the conditions which determine the value of insoluble
+phosphates when applied to the soil, and shows that the state of
+division, intimacy of mixture with soil-particles, and the nature of the
+soil, are the determining factors. Insoluble phosphates, as we shall
+have occasion to see when discussing basic slag, have their best action
+on soils poor in lime and rich in organic matter. Tables have been drawn
+up with a view to furnishing a guide for the value of phosphoric acid in
+different manures. In the Appendix[232] we give those of Wolff for 1893,
+and an American table, drawn up for 1892. The comparative values of
+mineral phosphates, as well as Peruvian guano and bone-dust, will be
+further referred to in the following chapter.
+
+
+_Rate at which Superphosphate is applied._
+
+The rate at which superphosphate is applied to the soil varies in
+different parts of the country. In England 2 to 3 cwt. per acre is
+considered an average dressing; whereas in many parts of Scotland it is
+applied in as large quantities as 6 to 8 cwt. per acre to the turnip
+crop. The reason why so much heavier dressings can be advantageously
+given in northern parts of this country is owing to the much longer
+period of unchecked growth. In the more southern districts, where the
+rainfall is less, mildew is almost certain to appear when the sowing is
+as early as required for a maximum crop. With it, as with other manures,
+the quantity must be determined by the conditions of its application,
+and the amount of other manure applied.
+
+
+FOOTNOTES:
+
+[225] This holds true, it may be mentioned, with regard to the
+application of certain manures, such as bone-char, to the soil.
+Bone-char was for a long time used in France as a manure without being
+dissolved. The action of such a manure, containing a considerable
+percentage of carbonate of lime, is slower than its action would be were
+it pure phosphate of lime, as the carbonate of lime is first acted upon
+(as in the case of superphosphate manufacture) by the soil acids.
+
+[226] The solubility of tribasic phosphate, of course, is not always
+equal in different manures. For example, the phosphate in apatite, owing
+to the crystalline structure of that mineral, is not nearly so soluble
+as the phosphate in phosphatic guanos, although in both cases its
+chemical composition is practically the same.
+
+[227] For formulæ of the different phosphates, see Appendix, Note I., p.
+398.
+
+[228] For chemical formulæ, showing reaction, see Appendix, Note II., p.
+398.
+
+[229] Of course it is well known that free phosphoric acid is obtained
+by acting upon phosphate of lime with an excess of sulphuric acid; but
+the point above referred to as having been recently discovered is, that
+when phosphate of lime is acted upon, even by a small quantity of
+sulphuric acid, free phosphoric acid is formed.
+
+[230] For chemical formulæ showing this reversion, see Appendix, Note
+III., p. 399.
+
+[231] For chemical theories on reversion of soluble phosphate by iron
+and alumina, see Appendix, Note IV., p. 399.
+
+[232] See Appendix, Note V., p. 400.
+
+
+
+
+APPENDIX TO CHAPTER XIII.
+
+
+NOTE I. (p. 388).
+
+The formulæ, and molecular and percentage composition, of the different
+phosphates, are given in the following table:--
+
+----------------------------------------------------------------------------
+ | Composition in terms of--
+ +--------------------------+-------------------
+ | Molecular weight. | Per cent.
+---------------+-------------+-----+------+------+------+-----+------+------
+ | | | |Phos- | | | |Phos-
+ Name. | Symbol. |Lime.|Water.|phoric|Total.|Lime.|Water.|phoric
+ | | | |acid. | | | |acid.
+---------------+-------------+-----+------+------+------+-----+------+------
+Tri- or bone- |3CaO, | | | | | | |
+ phosphate. | P_{2}O_{5} | 168 | 0 | 142 | 310 |54.19| 0.00| 45.81
+Bi- or di- |2CaO, H_{2}O,| | | | | | |
+ phosphate. | P_{2}O_{5} | 112 | 18 | 142 | 272 |41.18| 6.61| 52.21
+Mono- or super-|CaO, 2H_{2}O,| | | | | | |
+ phosphate. | P_{2}O_5 | 56 | 36 | 142 | 234 |23.93| 15.39| 60.68
+---------------+-------------+-----+------+------+------+-----+------+------
+
+
+NOTE II. (p. 388).
+
+When sulphuric acid is added to tricalcic phosphate, the following
+reaction takes place:--
+
+(1.) 3CaO, P_{2}O_{5} + 2(H_{2}O, SO_{3})
+ (Tricalcic phosphate), (Sulphuric acid),
+
+ = 2(CaO, SO_3) + CaO, 2H_{2}O, P_{2}O_{5}
+ (Gypsum), (Monocalcic phosphate).
+
+(2.) 3CaO, P_{2}O_{5} + 3(H_{2}O, SO_{3}) = 3CaO, SO_{3} +
+ 3H_{2}O, P_{2}O_{5}, or 2H_{3}PO_{4}.
+
+
+NOTE III. (p. 390).
+
+This equation gives the chemical reaction taking place when soluble
+phosphate is reverted, owing to the presence of undissolved
+phosphate:----
+
+ 3CaO, P_{2}O_{5} + CaO, 2H_{2}O, P_{2}O_{5}
+(Tricalcic phosphate), Monocalcic phosphate,
+
+= 2CaO, H_{2}O, P_{2}O_{5} + 2CaO, H_{2}O, P_{2}O_{5}
+ (Dicalcic phosphate), (Dicalcic phosphate).
+
+
+NOTE IV. (p. 390).
+
+"Just what the reactions are which are produced by the iron and alumina
+compounds has never been made out very clearly. But some idea of them
+may be gained from the following suggestions, which were thrown out by
+the English chemist Patterson. Suppose the sulphuric acid has dissolved
+a quantity of iron or alumina, then we may have the reaction:----
+
+Fe_{2}O_{3}, 3SO_{3} + CaO, 2H_{2}O, P_{2}O_{5} = Fe_{2}O_{3},
+P_{2}O_{5} + CaO, SO_{3} + 2(H_{2}O, SO_{3}),
+
+and the free acid thus formed would proceed to dissolve more iron or
+alumina from the rock that had previously escaped decomposition, and the
+reaction here formulated would occur again and again. Here we have a
+cumulative process continually increasing the quantity of insoluble
+Fe_{2}O_{3}, P_{2}O_{5}, and diminishing in the same proportion the
+soluble P_{2}O_{5}. Again, we may have simply----
+
+2Fe_{2}O_{3} + 3(CaO, 2H_{2}O, P_{2}O_{5}) = 2(Fe_{2}O_{3}, P_{2}O_{5})
++ 3CaO, P_{2}O_{5};
+
+where three molecules of the soluble phosphoric acid are made to revert
+to the insoluble state at one blow.
+
+"In case the iron in the original rock were in the state of ferrous
+oxide, perhaps the following reaction might occur:----
+
+4(FeO, SO_{3}) + 2O + CaO, 2H_{2}O, P_{2}O_{5} + 3CaO, P_{2}O_{5} =
+2(Fe_{2}O_{3}, P_{2}O_{5}) + 4(CaO, SO_{3}).
+
+In all these equations, except the last, alumina would serve as well as
+oxide of iron."--(_Vide_ Storer's 'Agricultural Chemistry,' vol. i. pp.
+276, 277.)
+
+
+NOTE V. (p. 396).
+
+The following table shows the relative trade values of phosphoric acid
+in different manures:--
+
+
+I.--WOLFF, 1893.
+
+Phosphate soluble in water (as in super) 100
+Precipitated phosphate, Peruvian guano 92
+Reverted phosphate, finest steamed bone-dust
+ fish-guano, poudrette 83
+Phosphatic guanos (Baker Island), wood-ashes 75
+Coarser bone-dust, powdered animal charcoal, bone-ash 67
+Coarse fragments of bone, powdered phosphorite and
+ coprolite, Thomas-slag, farmyard manure 33
+
+
+II.--AMERICAN, 1892.
+
+Phosphate soluble in water 100
+Phosphate soluble in ammonium citrate 94
+Fine bone-dust, powdered fish 94
+Fine medium bone 74
+Medium bone 60
+Coarse bone 40
+
+
+
+
+CHAPTER XIV.
+
+THOMAS-PHOSPHATE OR BASIC SLAG.
+
+
+In this substance we have a most important addition to our phosphatic
+manures. It has been in the market since 1886, and the consumption alone
+in Germany in 1887 amounted to nearly 300,000 tons. In this country it
+is only now beginning to be used to any extent.
+
+
+_Its Manufacture._
+
+_Thomas-slag_ is a bye-product obtained in the manufacture of steel by
+what is known as the "basic" process. In the year 1879 an improvement in
+the well-known "Bessemer" process was patented by Messrs Gilchrist &
+Thomas. It must be explained that in the manufacture of steel from
+pig-iron certain impurities in the raw material have to be got rid of in
+order to produce a good steel. Among these impurities one of the most
+important is _phosphorus_. This is owing to the fact that even a very
+small percentage of phosphoric acid in steel has the effect of
+rendering it brittle. The extraction of the phosphorus from the raw
+material was formerly, however, attended with very serious difficulties,
+and had the effect naturally of rendering steel a costly article,
+inasmuch as only the purer kinds of pig-iron could be used for the
+purpose.
+
+By the introduction in 1879, however, of the "Thomas-Gilchrist" or
+"basic" process, these difficulties were very largely overcome, and the
+employment of even such impure irons as the Cleveland (containing
+comparatively a large percentage of phosphorus) was rendered possible,
+and the price of steel consequently generally very much reduced. The
+process consists of submitting the molten pig-iron to a very great heat
+in a pear-shaped vessel (known technically as the "converter"). This is
+open at the top, and is supported on hinges, which permit of its being
+moved so as to pour off the scum which rises to the surface at the end
+of the operation, and which, we may explain, consists of "basic slag."
+In the original process the sides of the "converter" were lined with
+fire-bricks, consisting largely of silica. This process was known as the
+"acid" process. In the "Thomas-Gilchrist" process, however, the sides of
+the "converter" are lined with _lime_ (dolomitic limestone being largely
+used), lime being also added to the pig-iron. An air-blast is injected
+through the molten mass, and the impurities are burnt, or oxidised as it
+is chemically termed. The phosphorus in the iron is thus converted into
+phosphoric acid, and, uniting with the lime, forms phosphate of lime,
+which rises, as we have already said, to the surface in the form of a
+scum, and is separated from the steel by being poured off.
+
+
+_Not at first used._
+
+This, then, is how the _Thomas-slag_ is obtained. It did not seem,
+however, for some years after the introduction of this ingenious
+process, to have struck any one that this rich phosphatic bye-product
+might prove a valuable addition to our artificial fertilisers. The
+result was, that the Thomas-slag was treated as another of the only too
+numerous valueless bye-products which seem to be necessarily incidental
+to most of our chemical and other manufactures, and was allowed to
+accumulate in large quantities without being used for any purpose.
+
+
+_Discovery of its Value._
+
+In 1883 some short articles published in Germany on the subject were the
+means of first drawing the attention of the public to its importance as
+a manure. During the years 1884 and 1885 numerous experiments were
+carried out on the subject in the same country; and from then up till
+the present hour it has become more and more extensively used in
+Germany, till in 1887, as already stated, its consumption amounted to
+nearly 300,000 tons.
+
+
+_Composition._
+
+It consists mainly of phosphate of lime, silicate of lime, free lime,
+free magnesia, and oxides of iron and manganese. Its composition, of
+course, naturally varies; but the following may be taken as an average
+analysis:[233]--
+
+ Per cent.
+*Phosphoric acid 17
+ Lime in combination with phosphoric, silicic,
+ sulphuric, and carbonic acids 40
+ Free lime 15
+ Oxides of iron 12
+*Equal to tricalcic phosphate 37
+
+As a rule, the phosphoric acid varies considerably, ranging from 10 to
+20 per cent--that is, from 22 to 44 per cent tricalcic phosphate. This
+is owing to the difference in the percentage of phosphorus in the raw
+material and the quantity of lime added. Attempts have been made in
+Germany during the last two or three years to obtain a slag richer in
+phosphoric acid than that obtained heretofore, and a process for this
+purpose has been patented by Professor Scheibler. This consists of a
+slight modification in the ordinary process. Instead of treating the
+pig-iron with an excessive quantity of lime, the amount added is not
+sufficient to effect the complete dephosphorisation of the iron. The
+resulting slag is very rich in phosphoric acid, and is correspondingly
+poor in iron. The iron is then again treated with fresh lime, and the
+phosphorus completely removed, while the same lime may be used over
+again. Such slag forms a very much more concentrated phosphatic manure
+than the ordinary slag, and is known as _patent phosphate meal_.
+
+A point which not only renders the slag a product of peculiar interest
+from a chemical point of view, but has a most important bearing on its
+value as a manure, is the nature of the compound formed by the union of
+the lime with the phosphoric acid.
+
+In the ordinary so-called raw phosphates, such as bone-meal, bone-ash,
+coprolites, &c., the lime and phosphoric acid are combined in the form
+of what is known, in chemical phraseology, as _tribasic phosphate of
+lime_. That is to say, that for every equivalent of phosphoric acid
+there are three equivalents of lime. Now it was naturally concluded at
+first that the tribasic phosphate was the form in which these two
+substances existed in the slag. This, however, was found out not to be
+the case, in the following way. On allowing the slag to cool, it was
+found that small but perfectly defined crystals were formed. These
+crystals, by careful analysis, were shown, first by Hilgenstock, to
+consist of a form of phosphate of lime hitherto unknown, in which four
+equivalents of lime were combined with one equivalent of phosphoric
+acid, and which was therefore called "tetrabasic phosphate."
+
+
+_Processes for preparing Slag._
+
+As soon as the idea of utilising the slag as a manure was suggested,
+various plans for extracting its phosphoric acid, and rendering it
+available as plant-food, were devised. These were deemed necessary, it
+was thought, by the very insoluble nature of the phosphates in the slag,
+as well as by the supposed injurious action which would be exerted on
+plant-life by the protoxide of iron it contained. Accordingly, a large
+number of patents were taken out, "covering almost every conceivable
+method for treating the slag, whether practicable or not. They all in
+the main are combinations or variations of the following processes:--
+
+"1. _Preliminary preparation of the Slag._
+
+ (_a_) By treating molten, or otherwise, with superheated steam, or
+ cooling when hot with water, to reduce it to small pieces or
+ to a fragile state.
+
+ (_b_) Grinding.
+
+ (_c_) Treating with water to wash out free lime, or with sugar
+ solution.
+
+ (_d_) Roasting in the air, or with some oxidising agent.
+
+"2. _Solution of the Slag._
+
+ (_a_) _Completely_ in weak or strong acids (hydrochloric, sulphuric,
+ &c.)
+
+ (_b_) _Partially_, so as to dissolve the phosphates and silicates of
+ lime, and leave most of the iron and manganese oxides.
+
+"3. _Precipitation_ of the phosphoric acid, with lime
+or iron salts: or,
+
+"Processes in which the slag is smelted with charcoal,
+to reduce phosphates to phosphides, treated with
+acid, and the phosphuretted hydrogen burnt to phosphoric
+acid; and,
+
+"Processes in which the slag is fused with soda or
+potash salts,--caustic, chlorides, sulphates, carbonates,--with
+or without steam being forced through, to form soluble alkaline
+phosphates."[234]
+
+Many of these processes were tried; but it was found by experiment that
+the best and most economical way was by applying the slag direct to the
+ground in a state of very fine powder. Experiments further showed that
+it had _not_ the injurious effect on vegetation which it was feared it
+would have from the protoxide of iron it contained. The discovery that
+its phosphoric acid existed, as has been already explained, as a
+tetrabasic phosphate of lime, has strengthened the opinion that this is
+the best method of application.
+
+A good deal has been found to depend upon the fineness of the ground
+slag, with the result that it is now commonly sold on a mechanical as
+well as a chemical analysis--_i.e._, the slag is guaranteed to pass
+through a sieve of a certain fineness.
+
+
+_Solubility of Slag._
+
+Professor Wagner of Darmstadt has carried out some extremely interesting
+experiments on the solubility of slag. He found that very finely
+powdered slag was dissolved in carbonic acid water to the extent of 36
+per cent, while, similarly treated, phosphorite only dissolved to the
+extent of 8 per cent.[235] Another very important solvent is _citrate of
+ammonia_. Reverted (or precipitated) phosphate is entirely soluble in
+it, and phosphate soluble in it ought to be valued as worth more than
+that which is not. Now, the solubility of Thomas-slag in citrate of
+ammonia was found by Professor Wagner to be no less than 74 per cent,
+while that of phosphorite only amounted to 4 per cent. These results
+were corroborated by Professor S. W. Johnson, who found that of the
+19.87 per cent of phosphoric acid contained in a sample of basic slag,
+no less than 19.57 per cent was soluble in ammonium citrate, while a
+finely ground sample of phosphatic rock yielded, on analysis, only 1.81
+per cent soluble in citrate of ammonia, of a total of 29.49 per cent
+phosphoric acid which it contained. Professor Fleischer has also tested
+the comparative solubility of basic slag and phosphorite, by boiling
+them in a solution of acetic acid. The former was found to have been
+dissolved to the extent of 19 per cent, while the latter to only 5 per
+cent. A highly interesting and most important experiment was performed
+by Mr Heinrich Albert, of Biebrich. One gramme of basic slag and 100
+grammes of peat were mixed together in a litre of water, and it was
+found that, after standing for fourteen days, 79 per cent of the
+phosphoric acid contained in the slag was rendered soluble.
+
+In the above experiments it was found that the _fineness of grinding_
+had a marked effect on the solubility of the slag, and that the finer it
+was ground the greater was its solubility. This has been further
+demonstrated in Professor Wagner's practical experiments. From these it
+was found that finely ground slag has an action _four times_ as quick as
+coarse slag; but that, as far as practical results were concerned, there
+seemed to be a limit to the fineness to which it was advisable to grind
+the slag, as slag above a certain fineness did not give better results
+than a coarser slag. At any rate, he found that slag of a fineness so
+great that it all passed through a gauze sieve, gave no better results
+in his experiments than slag which left 17 per cent behind. We may say,
+however, that the _finer the slag is ground, the greater will its
+activity as a manure be_; and that a certain degree of fineness is
+absolutely necessary to constitute it an active fertiliser. As
+Professor Wagner's experiments are among the most valuable and complete
+carried out on basic slag, we shall give a somewhat detailed account of
+them.
+
+
+_Darmstadt Experiments._
+
+Professor Wagner's experiments were carried out on such different kinds
+of crops as flax, rape, wheat, rye, barley, peas, and white mustard, and
+the object of the experiments was to ascertain the comparative activity
+as fertilisers of superphosphate, basic slag of different degrees of
+fineness, Peruvian guano, damped bone-meal, and very finely ground
+coprolites. In order to obtain a correct estimate of the relative value
+of these different forms of phosphatic manures, it was necessary to
+render the nitrogen in the bone-meal and the nitrogen and potash
+contained by the Peruvian guano inactive--_i.e._, to limit the test
+strictly to phosphoric acid. This was done by adding to the super, basic
+slag, and coprolites, quantities of nitrogen and potash equal to those
+contained by the other manures. There was further added to all the
+experiments (the unmanured ones, of course, as well) an excess of
+nitrogen and potash. In this way the increase in returns could only be
+due to the phosphoric acid.
+
+The general results obtained from these experiments may be summed up as
+follows: Taking the activity of "super" to be represented by 100, then
+the relative activity of--
+
+Basic slag of No. 1[236] fineness is 61
+Basic slag, No. 2[237] 58
+Peruvian guano 30
+Basic slag, No. 3[238] 13
+Bone-meal 10
+Coprolites 9
+
+From these results the value of the commercial article has been
+attempted to be ascertained. As it contains 80 per cent or thereby of
+fine meal and 20 per cent of coarse, its activity may be stated to be
+50, or half as active as super. Thus 2 cwt. of basic slag is equal to 1
+cwt. of super. This only refers to the first year's effect. Professor
+Wagner has made further experiments as to the after-effects of the
+different manures, with the result that he has found that the
+after-effects of the basic slag are even _better_ than those of the
+"super." This stands to reason, for if twice as much phosphoric acid be
+added in the form of basic slag as is added in the form of "super," and
+the effect of the first year is similar--that is, the same quantity of
+phosphoric acid is assimilated by the plant from the soil in both
+cases--there is naturally more phosphoric acid left behind in the soil
+manured with basic slag than in that manured with superphosphate of
+lime. For example, if 100 lb. of super has the same effect in the first
+year as 200 lb. of basic slag, and it is found that only 60 lb. of the
+super and the basic slag have been assimilated the first year by the
+plant, it is only natural to conclude that the remaining 140 lb. of the
+basic slag will have a better after-effect than the remaining 40 lb. of
+super. This has been actually proved to have been the case in
+Professor's Wagner's experiments. The following are the results of some
+experiments which Professor Wagner has carried out on the after-effects
+of different manures:--
+
+Out of 100 parts of phosphoric acid, there was removed by the first
+year's crop--
+
+Super 63
+Peruvian guano 22
+Bone-meal 7
+Coprolites 6
+Thomas-meal--
+ No. 1 fineness 39
+ No. 2 " 43
+ No. 3 " 15
+
+Out of 100 parts of phosphoric acid left by the first crop, there was
+removed by the three succeeding crops--
+
+Super 30
+Peruvian guano 9
+Bone-meal 13
+Coprolites 6
+Thomas-meal--
+ No. 1 fineness 14
+ No. 2 " 29
+ No. 3 " 24
+
+Numerous other experiments have been carried out by various
+experimenters in different parts of Germany which it is unnecessary to
+cite here. None, however, are so complete as those of Professor Wagner.
+
+
+_Results of other Experiments._
+
+In this country experiments have been carried out at Rothamsted,
+Cirencester, Downton, Bangor, and by Dr Aitken at the Highland and
+Agricultural Society's stations, as well as elsewhere. The results of
+these various experiments naturally differ considerably, this being
+owing to the difference in the nature of the soils upon which the
+experiments were carried out, as well as the different degrees of
+fineness of the slag used. They all, however, serve to confirm Professor
+Wagner's general results. The results obtained in Scotland by Dr Aitken
+at the Highland Society's stations were especially favourable to basic
+slag as a phosphatic manure. The experiments were carried out on
+turnips, and it was found that the Thomas-slag was, weight for weight,
+superior to superphosphate. It may be added that the slag used in these
+experiments was rich in phosphoric acid, and was in an unusually fine
+state of division. Experiments carried out by the author have proved
+slag to be, on various Scottish soils, one of the most economical
+phosphatic manures to apply to turnips.[239]
+
+We will sum up, in conclusion, the deductions which may be fairly drawn
+from the results of all the above-mentioned experiments as to the value
+of basic cinder as a manure.
+
+
+_Soils most suited for Slag._
+
+Although its action is undoubtedly more favourable on some soils than
+others, it may be broadly stated that generally its phosphoric acid is
+_half as valuable_ as that in soluble phosphate. The soils on which it
+will have the most marked effect will be those of a _peaty_ nature,
+_poor_ in lime, but _rich_ in _organic matter_. The beneficial results
+obtained by an application of lime to peaty soils are well known. As the
+slag contains a large percentage of free lime, it thus performs on such
+soils a double function. On meadow-lands, all kinds of pasture-lands (if
+not of too dry a character), and clay soils poor in lime, its action has
+been shown to be especially favourable. Of different kinds of crops,
+those best suited to benefit from the slag as a phosphatic manure are
+those of the leguminous kind. This arises from the fact that their
+period of growth is longer than that of most other crops.
+
+
+_Rate of Application._
+
+As to the rate per acre at which the slag ought to be applied, there
+will naturally be a difference of opinion. Professor Wrightson, of
+Downton Agricultural College, recommends that it should be applied at
+the rate of from 6 to 10 cwt. per acre. This, of course, is very
+liberal manuring. We must remember, however, that phosphatic manures,
+unlike nitrogenous manures, and to some extent potash manures, may be
+applied in even excessive quantities without any risk of loss. It is
+impossible to measure out our phosphate manures in the same accurate
+manner as we measure out our nitrogen. It is safer, therefore, and on
+that account more economical in the long-run, to apply our phosphate in
+excessive quantity than the reverse. The reason of this may be shortly
+explained. The phosphoric acid which is naturally present in most soils
+is with difficulty soluble. Only a small quantity is yielded daily to
+the plant. This quantity may, under favourable climatic conditions, be
+sufficient; but these favourable influences never last very long at a
+time.
+
+For three weeks, perhaps, the plant may experience drought, and during
+this period it takes up no phosphoric acid, and its growth practically
+comes to a standstill; but this period of drought is followed by rain
+and warm weather, and the plant, if it is to be ripe by harvest-time,
+must make up for lost time. It must grow as much the next few days under
+these favourable climatic conditions as it would have grown under normal
+conditions in double or treble the time. In order to do so, however, it
+must be able to obtain plenty of phosphoric acid, and this is only
+possible where there is a decided excess of phosphoric acid present in
+the soil.
+
+The richness of a soil, therefore, in phosphoric acid, must be such
+that it is not only able to supply the ordinary wants of the plant, but
+to provide an excess when such an excess will be needed; for one must
+remember that the amount of plant-substance formed in the course of a
+few days under favourable conditions is very great, and that the amount
+consequently of phosphoric acid which plants assimilate during that
+period must also be very considerable.
+
+
+_Method of Application._
+
+In conclusion, as to the method of application of the slag,
+agriculturists must be _warned against mixing it with sulphate of
+ammonia_; for if this is done, a _considerable loss of ammonia_ will
+ensue, set free from the sulphate by the action of the free lime which
+the Thomas-slag contains. With nitrate of soda and potash salts it may
+be freely mixed. Such mixtures, however, are apt to form themselves into
+little balls, which soon become very hard. They should therefore only be
+mixed shortly before use. To overcome this difficulty, Professor Wagner
+recommends the mixture of a little peat or sawdust with the slag.
+
+
+FOOTNOTES:
+
+[233] See Appendix, p. 417.
+
+[234] _Vide_ paper on "Basic Slag: Its Formation." By Stead and
+Ribsdale. 'Journal of the Iron and Steel Institute,' 1887, p. 230.
+
+[235] _Vide_ Professor Wagner's pamphlet, 'Der Düngewerth und die
+rationelle Verwendung der Thomas Schlacke,' Darmstadt, 1888.
+
+[236] No. 1 fineness was such as passed entirely through a fine gauze
+sieve of 250 wires to the linear inch.
+
+[237] No. 2 fineness was such as passed entirely through the regular
+standard sieve--_i.e._, containing 120 wires to the linear inch.
+
+[238] No. 3 was what would not pass through the standard sieve.
+
+[239] 'Transactions of the Highland and Agricultural Society,' 1891;
+'Chemical News,' 1893.
+
+
+
+
+APPENDIX TO CHAPTER XIV.
+
+
+NOTE (p. 404).
+
+For those more particularly interested, we append a full analysis of the
+slag, taken from Messrs Stead and Ribsdale's paper in the 'Journal of
+the Iron and Steel Institute,' 1887, vol. i. p. 222:--
+
+Lime 41.58
+Magnesia 6.14
+Alumina 2.57
+Peroxide of iron 8.54
+Protoxide of iron 13.62
+Protoxide of manganese 3.79
+Protoxide of vanadium 1.29
+Silica 7.38
+Sulphur } .23
+Calcium } .31
+Sulphuric anhydride .12
+Phosphoric acid 14.36
+ -----
+ 99.93
+
+
+
+
+CHAPTER XV.
+
+POTASSIC MANURES.
+
+_Relative Importance._
+
+
+In Chapter VI. we pointed out that of the three manurial ingredients
+potash was the one most abundantly occurring, and that, consequently,
+the necessity of adding it in the form of an artificial manure existed
+less frequently than in the case of nitrogen or phosphoric acid. It was
+further pointed out that, under the ordinary conditions of agriculture,
+a greater restoration to the soil of the potash removed in the crops was
+made in the straw used in farmyard manure than was the case with regard
+to the other two ingredients. Despite these facts, there are many cases
+where the addition of potassic manures is of the highest importance in
+increasing plant-growth. It will be well, therefore, to devote a little
+space to considering our different potassic manures and their respective
+action.
+
+
+_Scottish Soils supplied with Potash._
+
+Potassic manures are not so valuable in this country since experience
+has shown that most Scottish soils are abundantly supplied with this
+manurial ingredient. Moreover, under the conditions of most European
+farming, there seems to be a steady gain to the soil of potash. In
+America, however, the action of potash as a manure seems to be more
+strikingly illustrated. Indeed, wherever forage crops or straw are sold
+off the farm in large quantities, or where beets, cabbages, carrots,
+potatoes, onions, &c., are also grown in large quantities, the necessity
+for potash manuring generally arises.
+
+
+_Sources of Potassic Manures._
+
+The value of potash as a manure first came to be recognised from the
+favourable action of wood-ashes. Of course their favourable action is
+not due solely to potash, as they contain, in addition to the other ash
+ingredients of the plant, phosphates; and their value as a manure may
+also be said to depend not a little on their indirect action. They
+contain a certain percentage of caustic alkali, which promotes the
+decomposition of the nitrogenous matter of the soil. But making due
+allowance for these other valuable properties, the chief value of
+wood-ashes is undoubtedly due to the potash they contain. Hence the use
+of the commercial article called _potash_, which is a mixture of
+potassium carbonate and hydrate, and which is obtained from wood-ashes,
+was formerly common to a considerable extent as a manure, especially for
+clover. _Barilla_, a rich potassic manure prepared by burning certain
+strand plants, especially the saltwort, was also in the past largely
+exported from Sicily and Spain. _Kelp_, a product got by burning
+sea-weed in Scotland, is also a rich potassic manure. Since, however,
+the discovery of the Stassfurt mines, all potassic manures have come
+from these.
+
+
+_Stassfurt Potash Salts._
+
+Huge salt deposits exist at Stassfurt in Germany. They have been formed
+by the evaporation of an inland sea. Salt was first discovered in these
+deposits in 1839, but for long the presence of potash salts was little
+suspected, and it was not until 1862 that the potash salts were worked.
+We have already, in the Appendix to Chapter VI., given a list of the
+chief potash minerals occurring in the Stassfurt deposits. These
+minerals are found in layers, the lowest layer consisting of almost pure
+salt; while immediately above this we have a layer of salt mixed with
+the mineral polyhallite (containing potassium sulphate) of about 100
+feet thick. Above this last layer there is a layer of about 90 feet,
+containing kieserite (magnesium sulphate) mixed with potassium and
+magnesium chlorides; and above this again is a layer (90 feet) of
+carnallite, which furnishes the chief source of the potash salts used
+for manurial purposes.
+
+At first the crude salts, as obtained direct from the deposits, were
+sold as manures under the name of _Abraum_ salts. Now, however, they are
+purified. Of potash salts in 1888 some 25,000 tons were exported from
+Stassfurt for manurial purposes. Of these salts there may be mentioned,
+viz., kainit, an impure form of the sulphate, containing on an average
+about 12 per cent of potash, and the muriate and the sulphate--both
+salts, in a more or less pure form, being used. A word or two may be
+added on the effect of the two forms of potash--viz., as the sulphate
+and as the muriate.
+
+
+_Relative Merits of Sulphate and Muriate of Potash._
+
+It is a well-known fact that muriate of potash, far from having a
+beneficial effect on certain crops, is actually harmful. Of these,
+sugar-beets, potatoes, and tobacco may be mentioned. In the case of
+beets it seems to have an effect in lessening the percentage of
+crystallisable sugar, while potatoes are rendered waxy. With regard to
+the tobacco-plant, it seems to impair the value of the leaf from the
+smoker's point of view. That this deleterious action is due to the form
+in which the potash is present, and not to the potash itself, seems to
+be pretty clear, since potash in the form of sulphate has not this
+deleterious effect on these plants. Another objection which has been
+urged against muriate of potash is that, when applied as a manure, it
+is apt to give rise to the formation of calcium chloride,--a compound
+which is distinctly hurtful to many plants. A similar charge cannot be
+brought against sulphate of potash, since gypsum, which is the chief
+compound it is likely to give rise to, is of much value, as we have
+already pointed out, as an indirect manure. On the whole, therefore,
+sulphate of potash seems to be the safest form in which to add potash.
+Unfortunately, however, most of the commercial sulphates are very
+impure, and contain generally considerable quantities of muriate. In
+favour of the muriate, it may be said that it is the more concentrated
+manure, and that it diffuses better in the soil than the sulphate--a
+point of great importance. It has, moreover, been used without any bad
+effect for clover, corn, grass, and some root crops.
+
+
+_Application of Potash Manures._
+
+The extreme tenacity with which the soil-particles fix potash salts,
+when applied as manures, is a point which ought to be borne in mind in
+their application. This, as we have just noticed, is greater in the case
+of the sulphate than in the case of muriate, and it has been observed
+that certain other fertilisers seem to exercise a considerable influence
+in hindering their fixation. Among these may be mentioned bone-meal and
+farmyard manure. Nitrate of soda also seems to increase the
+diffusibility of potash salts. Conversely, potash salts seem to help to
+fix ammonia.
+
+For the above reasons potash manures ought to be applied to the soil a
+considerable period before they are likely to be used by the crop. There
+is little risk of any serious loss taking place owing to rain. Autumn
+application is generally recommended. Even in very light soils it has
+been proved in the Norfolk experiments that autumn application has an
+immense advantage over spring application. It has been found that where
+potash is applied as sulphate, little sulphuric acid is absorbed by the
+plant.
+
+
+_Soils and Crops suited for Potash Manures._
+
+Of soils best suited for potash manures, it has been found that light
+soils, and those largely charged with peaty organic matter (such as the
+moorland soils of Germany), are most benefited; while on heavy clayey
+soils the percentage of potash which these latter contain is already
+sufficiently abundant for the needs of plants. At Flitcham the value of
+potash on chalk soils has been strikingly demonstrated. Of crops, it is
+now pretty generally acknowledged that those of the leguminous order are
+most benefited by potash. Especially in the case of clover has potash
+always proved itself a manure worth applying.
+
+
+_Rate of Application._
+
+Potash is best applied in small quantities. From 1 to 2 cwt. of the
+muriate or sulphate is a common amount, and from 6 to 8 cwt. of kainit.
+
+
+
+
+CHAPTER XVI.
+
+MINOR ARTIFICIAL MANURES.
+
+
+In addition to the manures which have been discussed in previous
+chapters, there are a number of minor manures which are used to a very
+much smaller extent--dried blood, hoofs, horns, &c.
+
+Among these one of the most valuable is dried blood. Fresh blood,
+containing 80 per cent of water, has from 2.5 to 3 per cent of nitrogen,
+about .25 per cent of phosphoric acid, and about .5 per cent of
+alkalies. When dried it forms a very concentrated and valuable
+nitrogenous manure, which has long been used in France. The commercial
+article contains, on an average, about 12 per cent of nitrogen, and
+slightly over 1 per cent of phosphoric acid. When mixed with the soil it
+ferments, and the nitrogen it contains is converted into ammonia.
+Although not so quick-acting a manure as nitrate of soda or sulphate of
+ammonia, it can by no means be described, as is done in ordinary
+agricultural text-books, as a slow-acting manure. Its nitrogen may be
+regarded as of equal value to that in Peruvian guano. It is peculiarly
+suited for horticulture, and is chiefly used in this country as a manure
+for hops. It has also been used with beneficial results for wheat,
+grass, and turnips. As a manure it is best suited for sandy or loamy
+soils. Considerable quantities are exported to the sugar-growing
+colonies as a manure for sugar-cane. Manures are made from other animal
+refuse. It may be mentioned that lean flesh (containing 75 per cent of
+water) has about 3 to 4 per cent of nitrogen,.5 per cent of alkalies,
+and .5 per cent of phosphoric acid; that is to say, a ton of lean flesh
+would contain about 70 lb. of nitrogen and 10 lb. of phosphoric acid. In
+air-dried flesh, according to Payen and Boussingault (containing 8-1/2
+per cent of moisture), there is 13 per cent of nitrogen. Flesh,
+therefore, is, when properly composted, a valuable nitrogenous manure.
+Dried flesh is generally made into a manure called meat-meal guano, the
+composition of which we have already referred to in the chapter on
+Guano.[240]
+
+Hoofs, horns, hair, bristles, and wool, wool-waste and the intestines of
+animals, have been used as manures. Hoofs and horns form a regular
+source of artificial nitrogenous manure; the latter being obtained as a
+bye-product in the manufacture of combs and other articles. They are in
+the form of a fine powder; and in order to increase their rate of
+action, which is very slow, they are often composted in America with
+horse-manure before use. They have also been composted with slaked lime.
+There can be no doubt that such treatment increases very considerably
+their value. Their percentage of nitrogen seems to vary very much
+according to the kind of animal from which they are derived. In nine
+samples of horn the nitrogen was found to vary from 7-1/2 to 14-1/4 per
+cent; giving an average of 11-1/3 per cent. The nitrogen seems rarely to
+exceed 15 per cent. The amount of phosphoric acid they contain has been
+found by various investigators to range from 6 to 10 per cent. S. W.
+Johnson found only from .08 to .15 per cent in buffalo-horn shavings. In
+France what is known as "torrefied" horn has been used. This is horn
+which has been subjected to the action of steam. The nitrogen in this
+material is considered to be more active than in ordinary horn.
+According to Way, horns have been used for the hop crop with good
+results. Ground hoof is very similar in composition to horn, and
+contains about 14 to 15 per cent of nitrogen. Considerable quantities
+are now used. It must be remembered, however, that horns, hoofs, hair,
+bristles, &c., although rich in nitrogen, possess a comparatively low
+manurial value. The home production of these articles may be estimated
+at 6000 to 7000 tons.
+
+
+_Scutch._
+
+Scutch is the name given to a manure made from the waste products
+incidental to the manufacture of glue and the dressing of skins. It
+contains about 7 per cent of nitrogen, and is manufactured in London to
+the extent of several thousand tons annually.
+
+
+_Shoddy and Wool-waste._
+
+Shoddy, which is a manure made from waste-wool products, is a material
+largely manufactured in this country, and which was formerly (it is now
+used to a considerably less extent) used to a large extent as a manure.
+Its annual production amounts to about 12,000 tons. There are three
+qualities,--the first containing 8 to 12 per cent of nitrogen; the
+second, 6 to 8 per cent; and the third, 5 to 8 per cent. Shoddy is by no
+means a very valuable manure. Woollen-waste products were formerly much
+richer in nitrogen than is now the case. This is due to the fact of the
+adulteration with cotton, now so prevalent in the manufacture of woollen
+goods. Pure woollen rags should contain 17 to 18 per cent of nitrogen.
+It has been strongly recommended to treat woollen waste with caustic
+alkali before being used as a manure, in order to render their nitrogen
+more quickly available; and there is a good deal to recommend this
+treatment. When wool-waste is applied as a manure, it should in every
+case be in autumn, so as to allow as long a period as possible to elapse
+before it is required for the plant's growth.
+
+Leather has also been used as a manure. Its nitrogen may be stated at
+from 4 to 6 per cent; and it may safely be described as of all materials
+used as nitrogenous manures the least valuable. Leather is, from its
+very nature, admirably adapted to resist decomposition when applied to
+the soil, and unless it is reduced to a very fine condition, might be
+trusted to remain undecomposed for a long period. Torrefied leather,
+however, is probably of greater value. It is obtained in the same way as
+torrefied horn, already referred to--namely, by treatment with steam.
+The grease and fatty matters which so largely aid it in resisting
+decomposition being extracted, it is much better suited for manurial
+purposes than ordinary leather. Torrefied leather contains from 5 to 8
+per cent of nitrogen.
+
+
+_Soot._
+
+A manure which has long been used and highly esteemed is soot. Obtained
+in the usual way, it generally contains some 3 per cent of nitrogen,
+chiefly in the form of sulphate of ammonia, and small quantities of
+potash and phosphates. A varying proportion of the nitrogen is present
+in the form of ammonia salts; and this undoubtedly confers upon soot its
+manurial value. It has long been used as a top-dressing for young grain
+and grass, and has been applied at the rate of from 40 to 60 bushels per
+acre. It has an indirect value as a slug-destroyer.
+
+Many of the above-mentioned manures, of comparatively low value, will
+probably be less used in the future than they have been in the past,
+owing to the more abundant supplies of nitrate of soda and ammonia salts
+which are now available. Many of these substances have probably been
+used in mixed manures.
+
+
+FOOTNOTES:
+
+[240] See p. 324.
+
+
+
+
+CHAPTER XVII.
+
+SEWAGE AS A MANURE.
+
+
+The value of sewage as a manure has been in the past enormously
+overrated, and much misunderstanding has existed on the part of the
+public on the question of the profitableness of the disposal of town
+sewage as an agricultural manure. Not a few of the erroneous opinions
+prevalent in the past regarding sewage have been due to statements made
+by scientific and other writers as to the enormous wealth lost to the
+world by many of the present methods of sewage disposal. Fortunately,
+however, the sewage question is now increasingly regarded as a question,
+in the first instance, of sanitary interest. As much has been written on
+the subject, and many schemes have been devised, at the expense of much
+ingenuity, for utilising its manurial properties, it may be desirable
+here to say a few words on the purely agricultural side of the question.
+
+The two most important points about sewage are its enormous abundance
+and its extremely poor quality. If the most important consideration
+were not the sanitary one, but its manurial value, then indeed our water
+system, so universally used in towns, must be regarded as a most
+wasteful one; for by its means the value of the excrementitious matter
+from which it derives its manurial ingredients is tremendously lessened.
+When we reflect that a ton of sewage, such as is produced in many
+European cities, contains only 2 or 3 lb. of dry matter, and that the
+total amount of nitrogen in this is only an ounce or two, while the
+phosphoric acid is considerably less, and that it is on those two
+ingredients that its value as a manure entirely depends, we see very
+strikingly how poor a manurial substance sewage is. Various methods have
+been devised and experimented with for extracting these manurial
+ingredients, and many methods are in operation in different parts of the
+world. The methods of utilising sewage for agricultural purposes may be
+broadly divided into two classes.
+
+
+_Irrigation._
+
+One of these, which may be classed under the heading of irrigation,
+consists in pouring the sewage on to certain kinds of coarse green
+crops. Sometimes the land is made to filter large quantities of sewage
+by special arrangements of drains and ditches. The land is first
+carefully and evenly graded down a gentle incline. At the top of the
+field the sewage is conducted along an open ditch from which it is
+permitted to escape, by the force of gravity, by several smaller
+ditches running at right angles from the main ditch. By means of stops
+which may be shifted at will, the sewage can be directed to flow over
+different parts of the field. Modifications in this plan may be made so
+as to suit the nature of the ground. In the case, for example, of a
+steep incline, the field may be sewaged by means of what are known as
+"catch-work" trenches running horizontally along the hill. In this way
+the sewage is allowed to pass over the whole of the field, and is caught
+at the bottom in a deep ditch, whence it is allowed to flow into the
+nearest river or stream. This is the system which has been employed at
+the famous Beddington Meadows, near Croydon.
+
+Another method of distributing the sewage is by means of underground
+pipes, which are laid in a sort of network over the ground to be
+manured. At certain intervals pipes with couplings for hose are fitted
+on, and by keeping a certain amount of pressure on the main pipes the
+sewage may be distributed over the different parts of the field as it is
+required.
+
+A third modification is subsoil irrigation. This resembles the
+last-named system, with this difference, that the pipes used are either
+porous or perforated with small holes.
+
+Total submersion can only be applied in the case of absolutely level
+lands, and is practised to an enormous extent in Piedmont and Lombardy.
+
+There has been little dispute as to the thorough efficiency of
+irrigation--when conducted under favourable conditions--as a method of
+purifying sewage and utilising to the full its constituents of manurial
+value. It is the only method which has been conclusively shown to
+extract from sewage that to which it owes most largely its value as a
+manure--viz., ammonia; and from this fact it deserves a first place in
+the consideration of agriculturists. For however admirable other methods
+may be from a sanitary point of view, it is obvious that a method which
+would allow the ammonia in sewage wholly, or at least to over 90 per
+cent, to be lost, cannot claim the same place in the judgment of
+agriculturists as a method which can extract for the soil not only the
+whole of this valuable constituent, but all else in the sewage which in
+any way is of value to plant-life.
+
+
+_Effects of continued Application of Sewage._
+
+When sewage is continuously applied to the same land, what generally
+takes place is this: At first the sewage is purified, and the soil
+derives corresponding benefit from the valuable fertilising ingredients
+it thus extracts. After a time, however, the land becomes what has been
+termed "sewage-sick." The pores in the soil become choked up by the
+slimy matter the sewage contains in suspension; the aeration of the
+soil, which, as we have already mentioned, is so necessary, is
+consequently to a large extent stopped; and the result is, that the land
+rapidly deteriorates, and the sewage is no longer purified.
+
+
+_Intermittent Irrigation._
+
+This is obviated to some extent by intermittent irrigation. The land,
+instead of receiving sewage continuously, only receives it at intervals,
+and is allowed some time to recover between each dose. It is, however,
+the opinion of those who have given the subject much attention, that
+land, even although intermittently sewaged, never recovers its original
+efficacy.
+
+Irrigation, therefore, under favourable conditions, is a most successful
+method of utilising the manurial value of sewage; but the great
+difficulty in practice is to obtain those favourable conditions. It has
+long been known that if soil is properly to discharge its function as a
+purifier of sewage water, it must be properly aerated; and we now know
+that in every fertile soil the process of nitrification must be
+permitted free development. Now the application of large quantities of
+sewage to a soil is apt to prevent this free development. As we have
+already seen, absence of air and the lowering of the temperature of the
+soil distinctly tend to retard nitrification; and these two conditions
+accompany the application of large quantities of sewage.
+
+
+_Crops suited for Sewage._
+
+Another objection to irrigation has been found in the alleged limited
+number of crops sewaged land is suited to yield. It has been repeatedly
+stated that rye-grass is about the only crop it is profitable to grow
+on it. In opposition to this statement, however, is the opinion
+expressed in the conclusions arrived at by the committee appointed by
+the British Association for the consideration of the sewage question. A
+vast number of experiments were carried out by them between the years
+1868-72, and the result they arrived at was as follows: "It is certain
+that all kinds of crops may be grown with sewage, so that the farmer can
+grow such as he can best sell; nevertheless, the staple crops must be
+cattle food, such as grass, roots, &c., with occasional crops of kitchen
+vegetables and of corn." While, therefore, it is probably a mistake to
+say that rye-grass is the only crop sewaged land is capable of growing
+profitably, the bulk of experience goes to show that such a crop is best
+suited for such land. This being so, the question naturally arises, What
+is the farmer who uses sewage as a manure to do with the large green
+crops he obtains from his land? He is, in most cases, unable to use them
+himself or dispose of them at the time. And while this has hitherto
+proved to be a most important drawback, now that we have in ensilage a
+means of preserving our green crops in a condition suitable as fodder
+for as long a time as is necessary, the grounds on which this objection
+rests are almost entirely removed.
+
+It will be obvious, of course, that some soils are naturally much better
+fitted to perform purification of sewage than others; but it must be
+frankly admitted that even the best of soils can only deal with a
+certain quantity of sewage. Various calculations have been indulged in
+as to the amount of sewage an acre of land can successfully deal with.
+According to one of these, an acre can purify some 2000 gallons per day,
+or that produced by 100 persons; while other calculations estimate it at
+60 persons; and others, again, at 150. The capacity of a sandy soil in
+this respect will be much greater than that of a heavier soil; and at
+Dantzic an acre of the sand-dunes is regarded as being capable of
+purifying the sewage of 600 persons. The late Dr Wallace has calculated
+that, in order to treat the sewage of Glasgow, over twelve square miles
+of land would be required. Of course, if the sewage is subjected to
+previous treatment, which is often the case, by the method immediately
+about to be described--namely, precipitation--the amount of sewage the
+soil is capable of purifying will be correspondingly increased. A
+difficulty which may also be pointed out in connection with irrigation
+as a means of disposing of sewage, is the impossibility of carrying it
+on during frosty weather, when the land is frost-bound. In warm climates
+irrigation has much to recommend it as a means of sewage disposal. In
+damp and cold climates, on the other hand, there are many objections.
+
+
+_Treatment of Sewage by Precipitation, &c._
+
+We now come to consider the methods grouped under this second heading.
+Mechanical filtration, of course, only aims at purifying sewage to the
+extent of removing all insoluble suspended matter which it contains.
+Different substances have been used as filters, the most generally used
+being charcoal. Charcoal mixed with burnt clay, gravel, sand, &c., has
+also been used.
+
+In chemical precipitation, however, we have a method which claims to do
+more. Beyond the extracting of all solid matters in suspension, it
+removes (at any rate most chemical precipitants do) nearly all the
+phosphoric acid, which, next to the ammonia, is the most valuable
+constituent the sewage contains. Of all precipitants, lime has been the
+most universally used; and on the whole, it is perhaps the best, for it
+is both cheap and obtainable almost anywhere. According to an analysis
+by the late Professor Way, the difference in the percentages of
+phosphoric acid, potash, and ammonia, before and after treatment with
+lime, in a sample of sewage, was as follows:--
+
+ _Grains per Gallon._
+
+ Before. After.
+Phosphoric acid 2.63 .45
+Potash 3.66 3.80
+Ammonia 7.48 7.50
+
+From the above we see that while sludge caused by lime as a precipitant
+contains nearly all the phosphoric acid, there is not a trace of the
+potash or ammonia removed. Sulphate of alumina has also been used, both
+alone and in conjunction with lime. The advantage claimed by it over
+lime is, that the resulting precipitate is much less bulky. In other
+respects, however, it does not seem to be any more efficient as a
+precipitant. In the well-known A, B, C process, a mixture of alum, clay,
+lime, charcoal, blood, and alkaline salts, in different proportions, has
+been used. This mixture is said to extract, in addition to the
+phosphoric acid, a certain proportion of the ammonia; but the amount is
+so small as scarcely to be worth considering.
+
+Numerous other chemical substances have been used, alone and also in
+conjunction with one another, such as perchloride of iron, copperas,
+manganese, &c. All alike, however, have failed to do more than effect
+partial purification,--the best results, it may be added, being obtained
+when the sewage thus treated was fresh. With regard to the manurial
+value of the resulting sludges, much difference of opinion has existed.
+The small percentage of phosphoric acid and nitrogen they contain has
+prevented them from being used to any extent as a manure, as their value
+did not admit of carriage beyond the distance of a few miles. By the
+introduction a few years ago of the filter-press, their value has been
+considerably enhanced. The old method of dealing with the sludge at
+precipitation-works was to allow it to dry gradually by exposure to the
+atmosphere. The result, however, of leaving sewage-sludge with over 90
+per cent of water in it to dry in the air, was to encourage the rapid
+decomposition and putrefaction of its organic matter, so that in many
+cases the decomposing sludge proved to be as great a nuisance as the
+unpurified sewage itself would have been. By the use of Johnson's
+filter-press, however, a sludge containing 90 per cent of water was at
+once reduced to 50 per cent or even less. By this means the percentage
+of its valuable constituents was very much increased, and the
+sludge-cake, besides being much more portable, was neither so
+objectionable nor so liable to decomposition as before.
+
+
+_Value of Sewage-sludge._
+
+As to the value of this sludge-cake as a manure, we are happily in
+possession of some very interesting and valuable experiments by
+Professor Munro of Downton Agricultural College. The sludge experimented
+upon was that produced by sulphate of alumina, lime, and sulphate of
+iron, and contained, after being subjected to Johnson's filter-press,
+from .6 to .9 per cent of nitrogen, and over 1 per cent of phosphoric
+acid. It was found that the benefit resulting from the application of
+the sludge was far from what in theory might have been expected. The
+experiments were made with turnips; and the results obtained with
+superphosphate and farmyard manure respectively, in the same field and
+under exactly the same conditions, were contrasted with those obtained
+with sludge. Thus it was found that 53 lb. of phosphoric acid as
+superphosphate, or 60 lb. as farmyard manure, produced a considerably
+larger crop than 240 lb. of phosphoric acid in the sludge. That is to
+say, that the phosphoric acid in the sludge did not exert more than
+one-fifth of its theoretical effect. The explanation of this somewhat
+strange result Dr Munro finds in the unsuitable physical character of
+the sludge-cakes. In farmyard manure we have a loose texture and a large
+amount of soluble constituents when well rotted. It thus quickly
+distributes its fertilising elements throughout the soil. In the case of
+the sludge, on the other hand, its composing particles are closely
+compacted together, and thus offer the greatest resistance to mechanical
+and chemical disintegration. "As a matter of fact," says Dr Munro, "the
+sludge-plots in my experimental series were all readily identified, when
+the roots were pulled, by the presence of unbroken and undecomposed
+clods of cake, which had evidently given up, at most, a small portion of
+their valuable ingredients to the soil."
+
+Briefly stated, therefore, the objections to chemical precipitation as a
+means of dealing with sewage are these--viz., that while it relieves
+sewage of all its organic matter, and to a large extent of its
+phosphoric acid, it fails to extract any ammonia, which is thus lost;
+that the resulting sludge is consequently so poor in fertilising matters
+as scarcely to make it worth while to remove it any distance for
+manuring purposes; and that, further, owing to its unfavourable
+physical character, as at present made, even the small percentage of
+plant-food it contains is not realisable, within, at any rate, anything
+like a reasonable time, to its full theoretical extent.
+
+The most profitable method of treating sewage must be determined by
+various local conditions; and it must be clearly understood that the
+question of sewage disposal is primarily a sanitary one, and that it
+must be dealt with from the sanitary aspect. The most profitable way of
+applying sewage as a manure, however, will doubtless be found by
+combining chemical precipitation and land irrigation.
+
+
+
+
+CHAPTER XVIII.
+
+LIQUID MANURE.
+
+
+The adoption of irrigation as a means of utilising sewage, suggests a
+short consideration of the value of liquid manures. It has been a custom
+on many farms to apply the liquid manure got from the oozings of
+manure-heaps, the drainings of the farmyard, byres, stables, piggeries,
+&c., directly to the soil. Indeed, so strongly has the belief in the
+superiority of liquid manure over other manure been held by certain
+farmers, that they have washed the solid animal excreta with water, in
+order to extract from it its soluble fertilising constituents. The late
+Mr Mechi was one of the foremost exponents of the value of liquid
+manure. His farm of Tiptree Hall was fitted up with iron pipes for the
+distribution of the manure over the different fields. Superphosphate, it
+may also be added, as first made from bones by Baron Liebig, was applied
+in a liquid form. As to the general merits of liquid manure, there can
+be no doubt that it is the most valuable form in which to apply manure.
+It secures for the manurial ingredients it contains a speedy and uniform
+diffusion in the soil; but, on the other hand, the expense of
+distributing it makes its application far from economical. The chief
+ingredient in liquid manure is urine. Now the removal of urine from the
+farmyard manure-heap entails a severe loss of the ingredient which is
+most potent in promoting fermentation. Separation of the urine from the
+solid excreta is on this very account not to be recommended. Urine, when
+applied alone, is lacking in phosphoric acid, of which it contains mere
+traces. It is not, therefore, suitable as a general manure. It has to be
+pointed out, however, that the drainings from a manure-heap in this
+respect are superior to pure urine, since they contain the soluble
+phosphates washed out of the solid excreta. The objections against using
+liquid manure may be summed up as follows:--
+
+First, it is too bulky a form in which to apply the manure, and hence
+too expensive; secondly, it is not advisable to deprive the solid
+excreta of the liquid excreta, as the one supplements the other;
+thirdly, fermentation is largely fostered in the solid excreta by the
+presence of the liquid excreta--hence fermentation will not take place
+properly in the solid excreta when deprived of the liquid excreta.
+
+If, however, the production of liquid manure on the farm is in excess
+of what can be used for the proper fermentation of farmyard manure, it
+will be best to utilise it for composts. No better addition to a compost
+can be made than liquid manure, as it induces speedy fermentation in
+nearly all kinds of organic matter.
+
+
+
+
+CHAPTER XIX.
+
+COMPOSTS.
+
+
+The use of composts is an old one. Before artificial manures were so
+plentiful as they are at present, much attention was paid by farmers to
+their preparation. A compost is generally made by mixing some substance
+of animal origin which is rich in manurial ingredients with peat or
+loam, and often along with lime, alkali salts, common salt, and indeed
+any sort of refuse which may be regarded as possessing a manurial value.
+Composting, in short, may be looked upon as a useful method of turning
+to profitable use refuse of various kinds which accumulate on the farm.
+The object of composting is to promote fermentation of the materials
+forming the compost, and to convert the manurial ingredients they
+contain into an available condition for plant needs. Composts often
+serve a useful purpose in retaining valuable volatile manurial
+ingredients, such as ammonia, formed in easily fermentable substances
+like urine. In fact, we may say that farmyard manure is the typical
+compost, and its manufacture serves to illustrate the principles of
+composting.
+
+
+_Farmyard Manure a typical Compost._
+
+Farmyard manure as ordinarily made is not generally regarded as a
+compost, but in the past it has been widely used for the purpose of
+making composts. Thus the practice of mixing farmyard manure with large
+quantities of peat has been in some parts of the world a common one.
+Peat, as has already been pointed out in a previous chapter, is
+comparatively rich in nitrogen. When it is mixed with urine or some
+other putrescible substance, the peat undergoes fermentation, with the
+result that its nitrogen is to a greater or less extent converted into
+ammonia. The effect, therefore, of mixing peat with farmyard manure is
+beneficial to both substances mixed: the escape of ammonia is rendered
+impossible by the fixing properties of the peat, while the inert
+nitrogen of the peat is largely converted by fermentation into an
+available form. The proportion of peat which it is advisable to add in
+composting farmyard manure will depend on the richness of the quality of
+the manure: the richer the quality of the manure, the greater the amount
+of peat it will be able to ferment. Composts of this kind are generally
+made by piling up the manure in heaps, consisting of alternate layers of
+peat and farmyard manure. From one to five parts of peat to every one
+part of farmyard manure is a common proportion. The use of such a
+manure, containing so much organic matter, will exercise its best effect
+on light sandy soils.
+
+
+_Other Composts._
+
+But instead of farmyard manure, or in addition to farmyard manure,
+various other substances may be added, as bones, flesh, fish-scrap, and
+the offal of slaughter-houses. Sometimes leaves and the dried
+bracken-fern are used for the manufacture of composts. Some of these
+substances contain much nitrogen or phosphoric acid, but in their
+natural condition ferment when applied to the soil at a slow rate. If
+mixed together before application in pits with peat, leaves,
+bracken-fern, or some other absorbent material, fermentation proceeds
+evenly and rapidly. The addition of lime, potash, and soda salts has
+been found to have a most beneficial effect in promoting fermentation.
+These substances, as is well known, hasten putrefaction of organic
+matter. Lime seems especially to be valuable in composting. This is no
+doubt due to the fact that lime plays a valuable part in promoting the
+action of various ferments, as has already been illustrated in the case
+of nitrification. The effect of large quantities of sour organic acids
+(humic and ulmic), which are the invariable products of the
+decomposition of organic matter like peat, leaves, &c., is inimical to
+micro-organic life. The action of lime is to neutralise these acids.
+There can be no doubt that composting is a useful process for increasing
+the fertilising properties of different more or less inert manurial
+substances. But in view of the abundant supply of concentrated
+fertilisers, the use of composts may considerably decrease in future.
+
+
+
+
+CHAPTER XX.
+
+INDIRECT MANURES.
+
+LIME.
+
+
+We now come to discuss those manures which we may class under the term
+_Indirect_, because their value is due, not to their direct action as
+suppliers of plant-food--like those manures we have hitherto been
+engaged in discussing--but to their indirect action. Of these by far the
+most important is lime.
+
+
+_Antiquity of Lime as a Manure._
+
+Lime is one of the oldest and one of the most popular of all manures. It
+is mentioned, and its wonderful action commented on, in the works of
+several ancient writers, more especially Pliny. Of late years, perhaps,
+its use has become restricted; and, as we shall point out by-and-by, it
+is well that it is so.
+
+
+_Action of Lime not thoroughly understood._
+
+Despite the fact of the long-established and almost universal use of
+lime, it can scarcely be said that we as yet clearly understand the
+exact nature of its action. Much light, however, has been thrown of late
+years on the subject by the great advance which has been made in our
+knowledge of agricultural chemistry. Nevertheless, there are many points
+connected with the action of lime on the soil which are still obscure.
+Perhaps one reason for the conflicting ideas prevalent with regard to
+the value of this substance in agriculture is to be found in the fact
+that it acts in such a number of different ways, and that the nature of
+the changes it gives rise to in the soil is most complicated. The
+experience of agriculturists with lime in one part of the country often
+seems contradictory to the experience of those in other parts of the
+country. Its action on different soils is very dissimilar. For these
+reasons, therefore, the discussion of the value of lime as a manure is
+by no means an easy one.
+
+
+_Lime a necessary Plant-food._
+
+Lime, as we have already pointed out in a former chapter, is a necessary
+plant-food, and were it present in the soil to a less extent than is
+actually the case, would be just as valuable a manure as the different
+nitrogenous and phosphatic manures; and in certain circumstances this is
+the case. There are soils, though they are by no means of common
+occurrence, which actually lack sufficient lime for supporting
+plant-growth, and to which its addition directly promotes the growth of
+the crop. Poor sandy soils are often of this nature. Another class of
+soils are also apt to be lacking in lime--at any rate their surface-soil
+is. These are permanent pasture-soils. Originally there may have been an
+abundance of lime in the surface portion of the soil; but, as is well
+known to every practical farmer, lime has a tendency to sink down in the
+soil. This tendency in ordinary arable soils is largely counteracted by
+ordinary tillage operations, such as ploughing, &c., by means of which
+the lime is again brought to the surface. In permanent pasture-soils,
+however, no such counteracting action takes place, hence impoverishment
+of the surface-soil in lime eventually results. It is for this
+reason--partly at any rate--that permanent pasture benefits in an
+especial degree by the application of lime. We say _partly_, for there
+are other important reasons. One is, that lime seems to have a striking
+effect in improving the quality of pastures by inducing the finer
+grasses to predominate. It has also a very favourable action in
+promoting the growth of white clover. Another reason for the favourable
+effect of lime on pasture-soils is doubtless on account of the action it
+has in setting potash free from its compounds. Soils, however, which
+directly benefit from the application of lime in the same way as they
+benefit from the application of nitrogenous manures, may be safely said
+to be rare. In the great majority of soils lime exists, so far as the
+demands of plant-life are concerned, in superabundance.
+
+
+_Lime of abundant Occurrence._
+
+Indeed limestone is one of the most abundant of all rock substances, and
+it has been calculated that it forms not less than one-sixth of the
+rock-mass of the earth's crust. Nearly all the commonly occurring
+minerals contain it, and in the course of their disintegration furnish
+it to the soil. Vast tracts of country are composed of nothing but
+limestone; and we have examples, even in this country, of so-called
+chalk-soils, where it is the most abundant constituent. Nor can it be
+classed amongst the insoluble mineral constituents of the soil; for
+although insoluble in pure water, it is soluble in water--such as the
+soil-water--which contains carbonic acid. This is proved by the fact
+that it is the chief dissolved mineral ingredient in all natural waters.
+
+
+_Lime returned to the Soil in ordinary Agricultural Practice._
+
+It may be further pointed out, as bearing upon the true function of lime
+when applied as a manure, that in ordinary agricultural practice nearly
+all the lime removed from the soil in crops finds its way back again to
+the farm in the straw of the farmyard manure. For these reasons, then,
+it is clear that the true function of lime is as an indirect manure.
+
+Let us now proceed to discuss its action. Before doing so, however, it
+is important that we should clearly understand the different chemical
+forms in which it occurs.
+
+
+_Different Forms of Lime._
+
+Lime occurs chiefly as carbonate of lime in the forms of limestone,
+marble, or chalk, which are all chemically the same. It occurs also as
+sulphate of lime or gypsum, as well as in the forms of phosphate and
+fluoride. In agriculture it is only used--if we except the phosphate,
+which is applied not on account of its lime, but its phosphoric acid--in
+the form of the carbonate or _mild_ lime as it is commonly called,
+burnt, caustic, or quick lime, and as gypsum. As the value of gypsum as
+a manure is of such importance, and depends not entirely on its being a
+compound of lime, we shall consider it by itself. Hence we have only to
+consider here the action of mild and caustic lime.
+
+
+_Caustic Lime._
+
+When limestone or mild lime is submitted to a great heat, such as is
+practically done on a large scale in lime-kilns, it is converted into
+caustic lime or lime proper. Limestone is made up, as we have just
+mentioned, of lime and carbonic acid. The latter ingredient is expelled
+in the form of a gas, and the lime is left behind. Lime never occurs
+naturally as caustic lime, for the simple reason that it is impossible
+for it to remain in this state, owing to the great affinity it has both
+for water and carbonic acid.
+
+When lime is burnt, and before it is applied to the field, some time is
+allowed to elapse in order to permit of its absorbing moisture--or
+becoming slaked, as it is technically called. This it does more or less
+slowly by absorbing moisture from the air. As, however, the process
+would take too long, and as, moreover, the absorption of carbonic acid
+gas would also take place at the same time, lime is generally slaked in
+another way. This can be done by simply adding water. An objection to
+this method is, that the lime is not so uniformly slaked as is
+desirable. It becomes gritty. The usual method is to cover it up with
+damp earth in heaps, and allow the moisture of the earth to effect the
+slaking. When lime absorbs water a new chemical compound is formed,
+known as lime hydrate; and so rapidly does the lime unite with water,
+that a great deal of heat is evolved in the operation, the temperature
+produced being considerably above that of boiling-water. The conversion
+of slaked lime into carbonate of lime or mild lime is a slower process.
+Sooner or later, however, it takes place, whether the lime is left on
+the surface of the soil or buried in it.
+
+A knowledge of these elementary chemical facts is necessary in order
+clearly to understand the nature of the action of lime in agriculture.
+
+The respective action of quicklime and mild lime is, on the whole,
+similar, although the former is in every case very much more powerful
+in its effects than the latter.
+
+
+_Lime acts both mechanically and chemically._
+
+Lime may be said to act on the soil both mechanically and chemically. It
+alters the texture of the soil, and affects its mechanical properties,
+such as its absorptive, retentive, and capillary powers with regard to
+water. It acts upon its dormant fertility, and decomposes its mineral
+substances as well as its organic matter. Lastly, its influence on the
+micro-organic life of the soil, which plays such an important part in
+the preparation and elaboration of plant-food, is of the highest
+importance. We cannot do better, therefore, than discuss its properties
+under the headings _mechanical_, _chemical_, and _biological_.
+
+
+I. MECHANICAL FUNCTIONS OF LIME.
+
+
+_Action on Soil's Texture._
+
+The effect of lime upon the texture of a soil is among its most striking
+properties. Every farmer knows well what a transformation is effected in
+the texture of a stiff clay soil by the application of a dressing of
+lime. The adhesive property of the soil--its objectionable tendency to
+puddle when mixed with water--is greatly lessened, and the soil is
+rendered very much more friable when it becomes dry. Several reasons
+exist for this change. In the first place, the tendency to puddle in a
+clayey soil is due to the fine state of division of the soil-particles.
+The way in which lime counteracts this adhesive property is by causing a
+coagulation of the fine soil-particles. This flocculation or aggregation
+of the fine clay-particles, when mixed with water by lime, is strikingly
+demonstrated by adding to some muddy water a little lime-water. The
+result will be that the water will speedily be rendered clear, the fine
+clay-particles coming together and sinking to the bottom of the vessel.
+Even a very small quantity of lime will effect this change. This
+property possessed by lime, we may mention, is utilised in the treatment
+of sewage. As it is the fine clay-particles that are the chief cause of
+the puddling of clay soils, their flocculation does much to destroy this
+objectionable property. Another reason why lime renders a clay soil more
+friable when dry is, that lime does not undergo any shrinkage in dry
+weather. As clay soils shrink very much in drying, the mixture with such
+a substance as lime tends to minimise this tendency to cake in hard
+lumps. The effect of even a very small addition of lime to a clay soil,
+in the way of increasing its friable nature, is very striking, and can
+be easily illustrated by taking two portions of clay, into one of which
+a small percentage of lime is introduced, and working both into a
+plastic mass with water, and then allowing them to dry. It will be found
+that while the one is hard and resists disintegration, that portion to
+which the lime has been added crumbles away easily to a powder. This
+effect which lime has in "lightening" heavy soils has been known to last
+for years. The disintegrating effect of quicklime when applied to heavy
+soils is also due, it may be added, to the change undergone by the lime
+itself from the caustic state to the mild state.
+
+
+_Lime renders light Soils more cohesive._
+
+Although it may seem somewhat paradoxical, lime, it would appear, in
+some cases exercises an effect upon the soil exactly the reverse of what
+has just been stated. That lime should act as a binding agent is only
+natural when we reflect on the way in which it acts when used as mortar.
+It is quite to be understood, therefore, that its action on light
+friable soils should be to increase their cohesive powers, and at the
+same time to increase the capillary power of the soil to absorb water
+from the lower layers. The extent of this action, of course, would
+depend on the form in which the lime is applied, and the amount. A
+striking example of the binding power of lime is to be found in certain
+soils extremely rich in lime, in which what is known as a lime-pan has
+been formed at some distance from the surface.
+
+
+II. CHEMICAL ACTION OF LIME.
+
+But more important probably than even its mechanical action is the
+chemical action of lime. It is a most important agent in unlocking the
+inert fertility of the soil. This it does by decomposing different
+minerals and setting free the potash they contain. The disintegrating
+power of lime in this respect depends, of course, on its chemical
+condition, the caustic form being much more potent than the other forms.
+Its action in decomposing vegetable matter and rendering the inert
+nitrogen it contains available for the plant's use, is also one of its
+most important properties, and accounts for its beneficial action when
+applied to soils, such as peaty soils, rich in organic matter. Again,
+its use as a corrective for sour lands has long been practically
+recognised. The presence of acidity in a soil is hurtful to vegetable
+life. Lime, by neutralising this acidity, removes the sourness of the
+land, and does much to restore it to a condition suitable for the growth
+of cultivated crops. The generation of sourness in a soil is almost sure
+to give rise to certain poisonous compounds. Lime, therefore, in
+sweetening a soil, prevents the formation of these poisonous compounds.
+Badly drained and sour meadow-lands, as every farmer knows, are
+immensely benefited by the application of this useful manure; for not
+merely is their sourness removed and their general condition
+ameliorated, but many of the coarser and lower forms of plant-life,
+which alone flourish on such soils, are killed out, and the more
+nutritive grasses are allowed to flourish instead. The action of lime in
+promoting the formation of a class of compounds of great importance in
+the soil--viz., hydrated silicates--is worthy of notice. According to
+the commonly accepted theory, much of the available mineral fertilising
+matter of the soil is retained in the form of these hydrated silicates.
+Hence lime, by increasing these compounds, not merely adds to the amount
+of the available fertility in the soil, but also increases its
+absorptive power for food-constituents.
+
+
+III. BIOLOGICAL ACTION OF LIME.
+
+The last way in which lime acts is what we have termed biological. By
+this we mean the important _rôle_ lime plays in promoting or retarding,
+as the case may be, the various kinds of fermentative action which go on
+so abundantly in all soils. The presence of carbonate of lime in the
+soil is a necessary condition for the process of nitrification. Lime is
+the base with which the nitric acid, when it is formed, combines; and as
+we have seen, when discussing nitrification, soils of a chalky nature
+are among those best suited to promote the natural formation of
+nitrates. This is one of the reasons for the beneficial effects produced
+by lime when applied to peaty soils. Not merely does it help to
+decompose the organic matter so abundant in such soils, but it also
+furnishes the base with which the nitric acid may combine when it is
+formed. But while the action of lime is to promote fermentation, it must
+not be forgotten that there may be cases in which its action is rather
+the reverse of this. Fermentation of organic matter goes on when there
+is a certain amount of alkalinity present; while, on the other hand, the
+presence of acidity seems to retard and check it. Too great an amount of
+alkalinity, however, would, in the first instance, retard fermentation
+as much as too great acidity. It has been claimed that the addition of
+caustic lime to fresh urine may act in this way; and if this were so,
+the addition of lime to farmyard manure might, to a certain extent, be
+defended. The experiment, however, would be a hazardous one and not to
+be recommended, as loss of ammonia would most likely ensue.
+
+
+_Action of Lime on Nitrogenous Organic Matter._
+
+The action of lime on nitrogenous organic matter is of a very striking
+kind, and is by no means very clearly understood. As we have pointed
+out, it sometimes acts as an antiseptic or preservative; and this
+antiseptic or preservative action has been explained on the assumption
+that insoluble albuminates of lime are formed. Its action in such
+industries as calico-printing, where it has been used along with casein
+for fixing colouring matter; or in sugar-refining, where it is used for
+clarifying the sugar by precipitating the albuminous matter in solution
+in the saccharine liquor; or lastly, in purifying sewage,--has been
+cited in support of this theory. While, however, there may be
+circumstances in which lime, especially in its caustic form, acts as an
+antiseptic, its general tendency is to promote these fermentative
+changes, such as nitrification, so important to plant-life.
+
+An important use of lime in agriculture is in preventing the action of
+certain fungoid diseases, such as "rust," "smut," "finger-and-toe," &c.,
+as well as in killing, as every horticulturist and farmer knows, slugs,
+&c.
+
+
+_Recapitulation._
+
+We may, in conclusion, sum up in a single paragraph the different ways
+in which lime acts. Its action is mechanical, chemical, and biological.
+It acts on the texture of the soil, rendering clay soils more friable,
+and exerting a certain binding effect on loose soils. It decomposes the
+minerals containing potash and other food-constituents, and renders them
+available for the plant's needs. It further decomposes organic matter,
+and promotes the important process of nitrification. It increases the
+power of a soil to fix such valuable food-constituents as ammonia and
+potash. It neutralises sourness, and prevents the formation of poisonous
+compounds in the soil. It increases the capillary condition of the soil,
+prevents fungoid diseases, and promotes the growth of the more nutritive
+herbage in pasture-land.
+
+
+
+
+CHAPTER XXI.
+
+INDIRECT MANURES--GYPSUM, SALT, ETC.
+
+
+GYPSUM.
+
+In the previous chapter mention was made of gypsum as a compound of
+lime, but no reference to its action as a manure was made. In the past,
+gypsum was used extensively and highly valued. It was found to be of
+especial value for clover; and there is a story told of Benjamin
+Franklin which illustrates the very striking nature of its action on
+this crop. It is related that he once printed with gypsum the words
+"This has been plastered" on a field of clover, and that for a long time
+afterwards the legend was plainly discernible on account of the
+luxuriance of the clover on the parts of the field which had been thus
+treated.
+
+
+_Mode in which gypsum acts._
+
+Despite the fact that gypsum is a most ancient manure, it is only of
+late years that we have come to understand the true nature of its
+action. For long it was believed that the reason of its striking effect
+in promoting clover was due to the fact that, as clover was a
+lime-loving plant, the action of gypsum was owing to the lime it
+contained. That, however, the action of gypsum is not due to the fact
+that it supplies lime to the plant, seems evident when it is stated that
+were this so, any other form of lime would have the same beneficial
+effect. It is well known, however, that this is not so. Besides, as we
+have already pointed out, lime is not a constituent which most soils
+lack, so far as the needs of the crop are concerned. There is a certain
+amount of truth in the old belief that gypsum enriches the soil in
+ammonia by fixing it from the air. The power that gypsum has as a fixer
+of ammonia has already been referred to in the chapter on Farmyard
+Manure; but in this case the gypsum is brought in contact with the
+ammonia. The origin of this old belief was due to a misconception as to
+the amount of ammonia in the atmosphere. No doubt gypsum greatly
+increases the power of a soil to absorb ammonia from the air; but the
+quantity of ammonia in the air is so very trifling, that its action in
+this respect is hardly worth considering. The true explanation of the
+action of gypsum is to be found in its effect on the double silicates,
+which it decomposes, the potash being set free. Its action is similar to
+that of other lime compounds, only more characteristic. As a manure,
+therefore, its action is indirect, and its true function is to oust the
+potash from its compounds. Its peculiarly favourable action on clover is
+due to the fact that clover specially benefits by potash, and that
+adding gypsum practically amounts to adding potash. Of course it should
+be borne in mind that the soil must contain potash compounds if gypsum
+is to have its full effect. Now, however, that potash salts suitable for
+manuring purposes are abundant, it may well be doubted whether it is not
+better to apply potash directly. Further, it must be borne in mind that
+gypsum is applied to the soil whenever it receives a dressing of
+superphosphate of lime, as gypsum is one of the products formed by
+treating insoluble phosphate of lime with sulphuric acid.
+
+It is possible that gypsum may act as an oxidising agent in the soil,
+just as iron in the ferric condition does. It has a large quantity of
+oxygen in its composition, and under certain conditions may act as a
+carrier of oxygen to the lower layers of the soil. When it is used, it
+should be applied some months before the crop is sown.
+
+Gypsum, therefore, although it contains two necessary
+plant-constituents, lime and sulphuric acid, cannot be regarded as a
+direct manure; and as its action comes to be more fully understood, its
+use, which was never very abundant in this country, will probably
+decrease. We have already, in the chapter on Nitrification, referred to
+the action of gypsum in promoting nitrification.
+
+
+SALT.
+
+The action of salt as a manure presents a problem which is at once of
+the highest interest and surrounded with the greatest difficulties. In
+view of the large quantities now used for agricultural purposes, a
+somewhat detailed examination of the nature of its action is not out of
+place in a work such as the present.
+
+
+_Antiquity of the Use of Salt._
+
+The recognition of the manurial functions of salt dates back to the very
+earliest times. Its use among the ancients is testified by numerous
+allusions in the Old Testament; while, according to Pliny, it was a
+well-known manure in Italy. The Persians and the Chinese seem also to
+have used it from time immemorial, the former more especially for
+date-trees.
+
+
+_Nature of its Action._
+
+Despite, however, the great antiquity of its use, much difference of
+opinion seems always to have existed as to the exact method of its
+action, and as to its merits as a manure in promoting vegetable growth.
+It furnishes, in fact, a good example of the difficulty which exists in
+the case of many manures, whose action is chiefly indirect, of fully
+understanding their influence on the soil and on the crop. In fact, the
+action of salt is probably more complicated than that of any other
+manurial substance.
+
+
+_Salt not a necessary Plant-food._
+
+We have already seen that neither sodium nor chlorine--the two
+constituent elements of salt--are in all probability absolutely
+necessary plant-foods. If they are necessary, the plant only requires
+them in minute quantities. Despite this fact, soda is an ash-constituent
+of nearly every plant, and in many cases one of the most abundant. In
+amount it is one of the most variable of all the ash-constituents, being
+present in some plants only in minute quantities, while in others it
+occurs in large quantities. Mangel and plants of the cabbage tribe may
+be cited as examples of plants containing large amounts of soda in their
+composition. But the plants which contain it in largest quantity are
+those which thrive on the sea-coast, and it has been thought that for
+them at least salt is a necessary manure. This, however, does not seem
+to be the case. In fact, the amount of soda in a plant seems to be
+largely a matter of accident. It may be added that the succulent
+portions of a plant are generally richest in soda.
+
+
+_Can Soda replace Potash?_
+
+Again, it has been believed that soda is capable of replacing potash in
+the plant; but this does not seem to be the case to any extent. The view
+that soda is able to replace potash, it has been thought, is supported
+by the variation which exists in the proportion of soda and potash in
+different plants. It must be remembered, however, that it is highly
+probable that most plants contain a larger quantity of ash-constituents
+than is absolutely necessary for their healthy growth. Especially is
+this the case with such a necessary plant-food as potash, of which there
+is generally present, in all likelihood, an excess. The variation in the
+quantity of potash and soda present in many plants under different
+circumstances can scarcely, therefore, be regarded as furnishing a proof
+of the replacement of potash by soda. Incidentally we may mention, as a
+fact worthy of notice, that cultivated plants have more potash and less
+soda in their composition than wild plants. What has been said of soda
+may be held to apply equally to chlorine, as it seems to be chiefly in
+the form of common salt that soda enters the plant. The amount of salt,
+therefore, present in plants must be regarded as largely accidental and
+dependent on external circumstances, such as the nature of the soil, &c.
+
+
+_Salt of universal Occurrence._
+
+But even were salt a necessary plant-food, its occurrence in the soil is
+already of sufficient abundance to obviate any necessity for its
+application. It may be said to be of almost universal occurrence. Even
+the air contains it in traces. That this is the case in the
+neighbourhood of the sea-coast is well known; but even in air far
+inland, accurate analysis of the air would probably demonstrate its
+presence in greater quantity than is commonly believed. It is a wise
+provision that plants absorb salt, for it increases their efficiency as
+food,--the function of salt as a constituent of animal food being of the
+very highest importance. It is an indispensable food-ingredient for
+animal life. With regard to ordinary farm-stock, the amount of salt
+which naturally occurs in their food is quite sufficient. In the case,
+however, of pastures in countries far removed from the sea, the custom
+of specially supplying stock with salt is common. This is done by
+placing a piece of rock-salt in the fields.
+
+
+_Special Sources of Salt._
+
+The salt of commerce is obtained from various sources. Besides the sea,
+we have ample sources of salt in the large saline deposits found in many
+parts of Europe, especially in Austria, and in England in Cheshire.
+
+
+_The Action of Salt indirect._
+
+From what has been said above, it is clear that the action of salt as a
+manure is indirect and not direct. What the nature of that indirect
+action is we shall now proceed to discuss.
+
+In considering the evidence of the manurial value of salt, we are at
+once brought face to face with the fact that the experience of its
+action in the past has as often been unfavourable as favourable. Salt,
+it is well known, is both an antiseptic and a germicide. It is, indeed,
+one of the most commonly used of preservatives. When applied in large
+quantities to the soil, it has a most deleterious action on vegetation.
+This hurtful action of salt has long been known; and it is as often
+mentioned in the writings of antiquity on account of its unfavourable as
+on account of its favourable action. Thus, for example, among the
+ancient Jews it was customary, after the conquest of a hostile town, to
+strew salt on the enemy's fields, for the purpose of rendering them
+barren and unfertile. And again, among the Romans, for the same purpose,
+salt was often spread on a spot where some great crime had been
+committed.
+
+While, therefore, its unfavourable action has long been known, the fact
+that there are circumstances under which its action is, on the contrary,
+favourable for promoting vegetable growth has also been long recognised.
+The difficulty for the agricultural student is to reconcile these two
+seemingly contradictory experiences. For the English agriculturist the
+subject possesses especial interest, since in England it has been in the
+past most generally used and its action most discussed since the time of
+Lord Bacon, who discusses in his writings the action of solutions of it
+on different plants.
+
+The true explanation of salt being so different in its action is to be
+found in the quantity applied, the nature of the soil, the crop to which
+it is applied, and the conditions under which it is applied--_i.e._,
+whether it is applied alone or along with other manures.
+
+
+_Mechanical Action on Soils._
+
+In the first place, it must be noted that salt exerts a mechanical
+action on the soil of a very similar kind to that exercised by lime.
+When applied to clay soils it causes a flocculation or coagulation of
+the fine clay-particles, and thus prevents the soil from puddling to the
+same extent as would otherwise be the case. In fact, an example of this
+action of salt when in solution causing the precipitation of fine
+suspended clayey matter, is afforded by the formation of deltas at the
+mouths of rivers. The power of clarifying muddy water is common indeed
+to saline solutions. Schloesing attributes the clarifying power of a
+soil to the presence of the saline matters it contains; and from this
+point of view it would appear that manures containing any saline
+substance may exert an important mechanical influence on the soil.
+
+
+_Solvent Action._
+
+But a much more important property of salt is its solvent action on the
+plant-food present in the soil. Its action in decomposing the minerals
+containing lime, magnesia, potash, &c., is similar to the action of
+gypsum. By acting upon the double silicates it liberates these necessary
+plant-foods. It is not only on the basic substances upon which it acts,
+but also on the phosphoric and silicic acids, which it sets free. Its
+power of dissolving ammonia from the soil is considerable. Experiments
+with a weak solution of salt on a soil by Peters and Eichhorn to test
+its solvent power, showed that the salt solution dissolved more than
+twice as much potash and nearly thirty times as much ammonia as an equal
+quantity of pure water did. When applied to the soil, it seems chiefly
+to liberate lime and magnesia. The exact nature of the chemical action
+taking place is a point of some dubiety. According to some, it is
+changed into nitrate of soda; according to others, into carbonate of
+soda. The latter theory seems to be the more probable one. Its action on
+the lime and magnesia compounds is to convert them into chlorides; and
+this chemical reaction explains the action that salt has in increasing
+the water-retaining and water-absorbing power of the soil; for the
+chlorides of magnesia and lime are salts which have a great power of
+attracting water from the air.
+
+Again, the very fact that salt acts as an antiseptic may serve to
+explain its beneficial action in certain cases where it prevents
+rankness of growth. No doubt this was its function when applied along
+with Peruvian guano. This it might do by preventing too rapid
+fermentation (nitrification) of the manure, or by actually weakening the
+plant. Its action when applied with farmyard manure may also be similar.
+But while its effect in many cases may be towards retarding
+fermentation, on the other hand its action, when applied along with lime
+to compost-heaps, is towards promoting more rapid decomposition.
+Probably a reaction takes place between the lime and the salt, the
+result of which is the formation of caustic soda.
+
+Such are some of the ways in which salt may act. It must at once be seen
+how its action in one case will be favourable and in another case
+unfavourable. There must be fertilising matter present in the soil if it
+is to act favourably. Again, it will only be under such circumstances,
+where rankness of growth is likely to ensue, that its antiseptic
+properties will act favourably and not unfavourably.
+
+
+_Best used in small Quantities along with Manures._
+
+Probably it is for these reasons that its action has been found to be
+most favourable when applied along with other manures and not alone.
+Applied along with nitrate of soda, as is commonly done, it doubtless
+increases the efficiency of the nitrate. Some plants seem to be
+undoubtedly benefited by salt: of these flax may be mentioned. The
+application of salt to plants of the cabbage tribe seems also to be
+highly beneficial. On mangels, along with other manures, it has also
+been found to have a very favourable effect. But with many crops its
+action has been proved to be less favourable.
+
+
+_Affects Quality of Crop._
+
+Although salt has often been found to increase the quantity of a crop,
+the quality of the crop has been made to suffer. Its action on beetroot
+has been more especially studied. The effect of its application is to
+lessen the total quantity of dry matter and sugar in the plant. This has
+been found to be the case both when the salt was applied alone and along
+with nitrate of soda and other manures. On potatoes, again, its action
+has been found to be deleterious, lessening their percentage of starch.
+The deleterious action of chlorides on the quality of potatoes is also
+seen when potassium chloride is applied. It is for this reason that
+potash should never be applied to the potato crop in the form of
+chloride.
+
+In the late Dr Voelcker's opinion, the conditions under which salt had
+the most favourable action on the mangel crop was in the case of a light
+sandy soil, and applied at the rate of 4 to 5 cwt. per acre. Its action
+when applied to clay soils was not so favourable.
+
+
+_Rate of Application._
+
+Lastly, the rate at which it may be applied will naturally vary. From 1
+cwt. and even less, up to 6 cwt. or even more, has been the rate at
+which it has been commonly applied in the past. From what has been said,
+it will be seen that it is more likely to exert a favourable influence
+when applied only in small quantities.
+
+
+
+
+CHAPTER XXII.
+
+THE APPLICATION OF MANURES.
+
+
+The conditions which regulate the application of manures are many and
+varied, and the subject, it must be admitted, despite the large amount
+of investigation already carried out, is most imperfectly understood.
+For these reasons it is impossible to do little more than lay down
+certain general principles which may be of service to the agriculturist
+in guiding him in carrying out the manuring of his crops.
+
+
+_Influence of Manures in increasing Soil-fertility._
+
+In the first place it may be asked, How far can what we may call the
+permanent fertility of a field be influenced by the application of
+manures? And to this question the answer must be made, that the
+influence of manuring in increasing soil-fertility is very slight and
+only very gradually felt. This is illustrated by the difficulty
+experienced in attempting to restore to a fertile condition a soil which
+has long been treated by an exhaustive system of cultivation. In such a
+case it will be found impossible to restore the fertility of the soil,
+except very gradually. Farmers who farm in new countries, and in rich
+virgin soils, little realise sometimes how quickly they may impoverish
+the fertility of their soils by exhaustive treatment, and how slow the
+process of restoration is. Nor is this strange when we reflect on the
+relatively small quantities of fertilising ingredients we are in the
+habit of adding to the soil by the application of manures, and the
+nature of their action. The small rate at which they are applied, and
+the impossibility of distributing them equally in the soil, explain how
+comparatively limited their action must necessarily be. Some manures, it
+is true--viz., those which are soluble--are more equally distributed;
+but then such manures, from their very nature, are little likely to
+affect the permanent fertility of the soil.
+
+
+_Influence of Farmyard Manure on the Soil._
+
+Of manures which have the best effect in improving a soil's permanent
+fertility, farmyard manure is undoubtedly the most important. This is
+owing partly to the fact that it is applied in such large quantities,
+and partly on account of its composition. Liberal manuring with farmyard
+manure, systematically carried out, will in time do much to build up a
+soil's fertility. But liberal manuring with artificial manures will also
+effect the same end. This it does in an indirect manner by means of the
+increased crop residues obtained under such treatment. Indeed one of the
+speediest methods of bringing a soil into good condition is by heavily
+manuring certain green crops, and then ploughing them in.
+
+
+_Farmyard Manure v. Artificials._
+
+The question how far farmyard manure may be supplanted by artificials is
+one often discussed. We have already referred to this question in the
+chapter on Farmyard Manure. It is possible that, with our increasing
+knowledge of agricultural science, we may in the future be able to
+dispense with farmyard manure, and make shift to do with artificials
+alone. At present, however, all our experience points to the fact that
+the most satisfactory results are obtained from manures by using
+artificials in conjunction with farmyard manure. It is better both for
+farmyard manure and artificial manures to be applied together,[241] so
+that they may mutually act as supplementary the one to the other. While
+this is so, there may be circumstances in which it will be best to use
+artificials alone. Where, for example, fields, owing to their situation,
+are inaccessible, and where the expense of conveying the bulky farmyard
+manure would be very considerable, it may be found more economical to
+apply the more concentrated artificial manures. With few exceptions,
+however, it will be found most desirable to use artificial manures as
+supplementary to farmyard manure, and not as substitutes for it.
+
+
+_Farmyard Manure not favourable to certain Crops._
+
+While the above is true, it may be well to point out one or two facts
+regarding the nature of the influence of farmyard manure on certain
+crops. For instance, it has long been recognised as inadvisable in
+strong rich soils to apply it directly to certain grain crops, such as
+barley and wheat, since such a practice is apt to encourage rankness of
+growth--an undue development of straw at the expense of the grain. It is
+consequently customary to apply farmyard manure to the preceding crop.
+The direct application of farmyard manure to wheat, however, according
+to Sir J. B. Lawes, is not fraught with unfavourable results where the
+soil is a light one; it is only when the soil is of a heavy nature that
+it is best to apply it to the preceding crop. Potatoes are another crop
+to which it is best not to apply it directly. On the other hand, many
+are of the opinion that mangels seem to be able to benefit from large
+applications of farmyard manure.
+
+
+_Conditions determining the Application of Artificial Manures._
+
+In the application of artificial manures a large number of
+considerations have to be taken into account. Among these may be
+mentioned the nature of the manure itself, and its mechanical and
+chemical condition; the nature of the soil and its previous treatment
+with manures, as well as the nature of the climate, the nature of the
+crop, and the previous cropping. It may be well, therefore, to examine
+somewhat in detail some of these considerations.
+
+
+_Nature of the Manure._
+
+Nitrogen, phosphoric acid, and potash exist in the common manures, as
+has already been pointed out, in different states of availability.
+Nitrogen, for example, may exist in a soluble or insoluble condition, as
+nitrates, as ammonia, or in various organic forms. Phosphoric acid,
+similarly, may exist in a soluble form, as it does in superphosphate of
+lime, or in an insoluble form, as it does in bones or basic slag.
+Potash, on the other hand, exists--or should exist--in artificial
+manures only in a soluble form. Now a correct knowledge of the behaviour
+of these different forms of the common manurial ingredients when applied
+to the soil is, in the first place, necessary for their successful and
+economical use.
+
+
+_Nitrogenous Manures._
+
+Thus our knowledge of the inability of the soil-particles to retain
+nitrogen in the form of nitric acid, as well as our knowledge of the
+fact that nitrogen is in this form immediately available for the
+plant's needs, teaches us that nitrate of soda should never be applied
+before the plant is ready to utilise it--in short, that it should only
+be applied as a top-dressing; and further, that the use of such a
+fertiliser in a damp season is less likely to be economical than in a
+dry one. Again, with regard to nitrogen in the form of ammonia salts,
+our knowledge of the fact that ammonia is retained by the
+soil-particles, and that before it becomes available for the plant's
+needs it has to undergo the process of nitrification, teaches us the
+desirability of applying it a short time before it is likely to be used.
+While, lastly, with regard to the nitrogen in the various organic forms
+in which it occurs, our knowledge of the rate at which these are
+converted into an available form in the soil will determine when they
+are best applied. Some forms of organic nitrogen are in a soluble
+condition, and are quite as speedy in their action as sulphate of
+ammonia. This is the case with a considerable proportion of the
+different organic forms of nitrogen present in guano. Other forms of
+organic nitrogen are only slightly less so--as, for example, dried
+blood, which ferments very speedily. With regard, therefore, to nitrates
+and ammonia salts, as well as the more quickly available organic forms
+of nitrogen, they should either be applied as a top-dressing after the
+plant has started growth, or only shortly before seed-time. Bones,
+shoddy, and the various so-called native guanos, should be applied a
+considerable period before they are likely to be required--not later
+than the previous autumn.
+
+
+_Phosphatic Manures._
+
+With regard to phosphatic manures the same considerations hold good.
+Inasmuch as phosphoric acid, whether applied in the soluble condition,
+as in superphosphate, or the insoluble form, as in bones, basic slag,
+&c., is not liable to be washed out of the soil, the risk of loss is
+very slight, and need not be taken into account. As we have pointed out
+in considering the action of superphosphate, phosphoric acid in this
+latter form is more speedily available to the crop, and the necessity of
+applying it much before it is likely to be used does not exist. Hence
+superphosphate and manures which contain any appreciable amount of
+soluble phosphoric acid, such as guano, should only be applied shortly
+before seed-time. Bones, basic slag, or mineral phosphate ought to be
+applied, on the other hand, a long time before they are likely to be
+used. Hence an autumn application is to be recommended in the case of
+such manures.
+
+
+_Potash Manures._
+
+Lastly, with regard to potash manures, as these are soluble, there is no
+necessity for applying them much before they are likely to be absorbed
+by the plant. Some are of the opinion that potash is, except in the case
+of sandy soils, best applied some little time before it is likely to be
+used, so as to permit of its being washed down into the soil--a process
+which takes place only comparatively slowly. As potash manures have
+often been found to give a better result on pastures during the second
+year than during the first, they are best applied in the autumn.
+
+The above statement as to the behaviour of the different fertilisers
+when applied to the soil, has a not unimportant bearing on the
+quantities in which they may safely be respectively applied. The rate at
+which manures may be applied depends, as we shall immediately see, on
+other conditions; but what it is here desirable to point out is, that it
+is not safe to apply such manures as nitrate of soda, or, for that
+matter, sulphate of ammonia, in large quantities at a time. In fact
+these manures, especially the former, will best be applied in very small
+quantities, and rather in several doses. With regard to other manures,
+more especially phosphatic manures, the same reasons for small
+application do not exist.
+
+The truth of the above statements is so obvious that it may be regarded
+as superfluous to make them. As, however, their clear apprehension is
+essential to understanding the conditions of successful manuring, no
+apology need be made for making them.
+
+
+_Nature of Soil._
+
+Another condition which has to be taken into account in considering the
+application of manures is the nature of the soil, as well as its
+previous treatment. Soils poor in organic matter are those which are
+most likely to be benefited by the application of nitrogenous manures.
+Soils of a dry light character require less phosphoric acid than they do
+of nitrogen and potash; while on a damp and heavy soil phosphatic
+manures are more likely to be beneficial than nitrogenous or potassic
+manures. Lastly, a soil rich in organic matter generally requires
+phosphates, and possibly potash. A point of considerable importance to
+notice is, that a soil rich in lime can stand a larger application of
+phosphoric acid than one poor in lime. As a rule, it will be found that
+the best results with potash will be obtained when applied to a sandy
+soil. The nature of the soil is an important consideration in
+determining how far it is advisable to apply readily soluble manures. To
+a very light and non-retentive soil the risk of loss in applying an
+easily soluble manure is considerably increased. The nature of the
+climate is also of importance. Thus, in a dry climate, manures of a
+soluble nature will have a better effect than in a wet climate, while
+the opposite will be the case with the more slowly acting manures.
+
+
+_Nature of previous Manuring._
+
+A consideration of equal importance is the previous treatment of the
+soil with manure. For example, where a soil has been liberally treated
+with farmyard manure, it has been found that mineral manures have a
+very inferior effect to that obtained by nitrogenous manure. Lawes and
+Gilbert have found this to be strikingly the case in their experiments
+on the growth of wheat. In these experiments it was found that the
+application of mineral manures was accompanied with little or no benefit
+to the crop, whereas very striking results followed the application of
+nitrogen. This they attributed to the fact that the supply of mineral
+fertilisers in the straw of the farmyard manure is largely in excess of
+the supply of nitrogen. The nature of the action of the manure
+previously applied is also to be taken into account in determining how
+long its influence may probably last. Where, for example, the manure has
+been nitrate of soda or sulphate of ammonia, it may be safely concluded
+that its direct influence is no longer felt a year after application.
+The influence of superphosphate of lime, while scarcely so temporary,
+may be said to last only for a comparatively short time.[242] On the
+other hand, when the manure applied is of a slow-acting nature, such as
+bones or basic slag, its influence will probably be felt for a number of
+years.
+
+
+_Nature of the Crop._
+
+But more important than any of the above-mentioned conditions is the
+nature of the crop itself. Our knowledge of the requirements of the
+different farm crops is still very imperfect. A very wide experience,
+however, of the effect of different manures on different crops, has
+conclusively proved that their manurial requirements differ very
+considerably. The subject is complicated by other considerations, such
+as the nature of the soil, &c.; but notwithstanding this fact, certain
+points seem to be pretty well established.
+
+In seeking to understand the respective requirements of the different
+crops for different fertilisers, two important considerations must be
+borne in mind. These are--(1) _the quantities of the three fertilising
+ingredients--nitrogen, phosphoric acid, and potash--which different
+crops remove from the soil;_ and (2) _the different power crops possess
+of assimilating these ingredients._
+
+
+_Amounts of Fertilising Ingredients removed from the Soil by different
+Crops._
+
+The most convenient way of instituting a comparison between the
+requirements of the different crops in this respect is by calculating
+the amount, in pounds, of nitrogen, phosphoric acid, and potash, which
+average amounts of the different crops remove per acre. The following
+table shows this for the common crops:--
+
+
+ FERTILISING INGREDIENTS REMOVED FROM SOIL.
+----------------------------+-----------+------------+----------
+ | Nitrogen. | Phosphoric | Potash.
+ | | Acid. |
+----------------------------+-----------+------------+----------
+Mangels {Root, 22 tons | 87 | 36.4 | 222.8
+ {Leaf | 51 | 16.5 | 77.9
+ |-----------|------------|----------
+ Total crop | 138 | 52.9 | 300.7
+ |-----------+------------+----------
+Turnips {Root, 17 tons | 63 | 22.4 | 108.6
+ {Leaf | 49 | 10.7 | 40.2
+ |-----------+------------+----------
+ Total crop | 112 | 33.1 | 148.8
+ |-----------+------------+----------
+Beans {Grain, 30 bushels | 77 | 22.8 | 24.3
+ {Straw | 29 | 6.3 | 42.8
+ |-----------+------------+----------
+ Total crop | 106 | 29.1 | 67.1
+ |-----------+------------+----------
+Red clover hay, 2 tons | 102 | 24.9 | 83.4
+ |-----------+------------+----------
+Swedes {Root, 14 tons | 70 | 16.9 | 63.3
+ {Leaf | 28 | 4.8 | 16.4
+ |-----------+------------+----------
+ Total crop | 98 | 21.7 | 79.7
+ |-----------+------------+----------
+Oats {Grain, 45 bushels | 38 | 13.0 | 9.1
+ {Straw | 17 | 6.4 | 37.0
+ |-----------+------------+----------
+ Total crop | 55 | 19.4 | 46.1
+ |-----------+------------+----------
+Meadow hay, 1-1/2 ton, | 49 | 12.3 | 50.9
+ |-----------+------------+----------
+Wheat {Grain, 30 bushels | 33 | 16.0 | 9.8
+ {Straw | 15 | 4.7 | 25.9
+ |-----------+------------+----------
+ Total crop | 48 | 20.7 | 35.7
+ |-----------+------------+----------
+Barley {Grain, 30 bushels | 35 | 16.0 | 9.8
+ {Straw | 13 | 4.7 | 25.9
+ |-----------+------------+----------
+ Total crop | 48 | 20.7 | 35.7
+ |-----------+------------+----------
+Potatoes, 6 tons | 47 | 21.5 | 76.5
+ |-----------+------------+----------
+Maize {Grain, 30 bushels | 28 | 10.0 | 6.5
+ {Stalks, &c. | 15 | 8.0 | 29.8
+ |-----------+------------+----------
+ Total crop | 43 | 18.0 | 36.3
+----------------------------+-----------+------------+----------
+
+From the table it will be seen that the crops which remove the largest
+quantities of all three fertilising ingredients are the root
+crops--mangels and turnips; that beans remove twice as much nitrogen as
+the cereals--oats, barley, and wheat--which, in this respect,
+practically differ very little from one another; while potatoes remove
+about the same quantity of nitrogen as the cereals. It will further be
+noticed that the amounts of phosphoric acid removed by the different
+crops differ very much less than those of nitrogen and potash. Mangels
+remove slightly more, and turnips slightly less, than double the amount
+removed by cereals. Meadow-hay, it will be seen, of all crops removes
+the least phosphoric acid.
+
+In looking at the amounts of potash, we are at once struck by their
+great discrepancy. Such a crop as mangels removes more than six times as
+much potash from the soil as the cereals. Turnips also make large
+demands on this ingredient, removing over four times as much as the
+cereals. Leguminous crops, such as red clover and beans, remove about
+twice as much.
+
+
+_Capacity of Crops for assimilating Manures._
+
+Instructive though these figures undoubtedly are, _they must not be
+regarded, as often erroneously they are, as furnishing by themselves
+sufficient data upon which to base the practice of manuring_. A
+consideration which is of much greater importance is the capacity that
+different crops possess for assimilating the various manurial
+ingredients from the soil. Considered from the point of view of absolute
+amount, there is in most soils an abundant supply of plant-food; but of
+this amount only a small proportion is available. Further, the amount of
+this available plant-food will vary with different crops--one crop being
+able to grow where another crop would starve. As illustrative of this,
+in the Norfolk experiments it was found that the turnip was able to
+assimilate potash from a soil on which the swede was practically
+starved. It is on this fact more than any other that the principles of
+manuring are based. Several explanations of the different capacities
+crops possess of assimilating their food may be put forward. And we may
+here point out that crops belonging to the same class exhibit, on the
+whole, a certain amount of similarity in their manurial requirements.
+Thus, for example, we may say that _gramineous crops_ so far resemble
+one another in possessing _small capacity for assimilating nitrogen_,
+_root crops for assimilating phosphoric acid_, and _leguminous crops for
+assimilating potash_, and that, consequently, these crops are generally
+most benefited by the application, respectively, of nitrogen, phosphoric
+acid, and potash. But while a certain general resemblance exists, crops
+belonging to the same class differ in many cases very considerably, as
+we shall immediately see.
+
+
+_Difference in Root Systems of different Crops._
+
+One explanation of the different capacity possessed by different crops
+for absorbing plant-food from the soil is to be found in the difference
+of their root systems. Every agriculturist knows that crops in this
+respect differ very widely. Crops having deep roots will naturally have
+a larger surface of soil from which to draw their food-supplies than
+crops having shallower roots. Such crops as red clover, wheat, and
+mangels are able to draw their food-supplies from the subsoil to an
+extent not possessed by shallower-rooted crops, such as barley, turnips,
+and grass. Crops having surface-roots, on the other hand, have often
+greater capacity for assimilating nitrogen,--this ingredient, as has
+already been pointed out, being chiefly located in the surface-soil. The
+tendency of growing shallow-rooted crops will therefore be towards
+impoverishing the surface-soil; whereas the occasional growth of a
+deep-rooted crop brings the plant-food in the subsoil into requisition.
+In this connection it may be well to draw attention to the singular
+capacity possessed by certain crops for absorbing nitrogen. Of these the
+case of clover is the most striking, and has long puzzled
+agriculturists. The discovery, which has been repeatedly referred to in
+these pages, that the leguminous order of crops, to which clover
+belongs, have the power of absorbing the free nitrogen of the air
+through the agency of micro-organic life in the plant and in the soil,
+has furnished an explanation of this long-debated problem.
+
+
+_Period of Growth._
+
+A further reason is the difference in the period of a crop's growth. A
+crop which grows quickly, and consequently occupies the ground during a
+comparatively short period, will naturally require a richer soil, and
+therefore a more liberal treatment with manure, than one whose growth is
+more gradual.
+
+Another consideration is the season of the year during which active
+growth of the crops takes place. For example, in the case of the wheat
+crop, active growth takes place in spring and ceases early in the
+summer. Since, however, nitrification goes on right through the summer,
+and nitrates are most abundant in the soil in late summer and autumn,
+such a crop as wheat is ill suited to obtain any benefit from this
+bountiful provision of nature, and is consequently particularly
+benefited by the application of nitrogenous manures. Root crops, on the
+other hand, sown in summer, continue their active growth into autumn,
+and are thus enabled to utilise the nitrates formed in the process of
+nitrification. The custom of sowing a quickly growing green crop, such
+as rye, mustard, rape, &c., after a wheat crop, is a practice which aims
+at conserving the nitrates and preventing their loss by autumn and
+winter rains. The name "catch crop" has been applied to such a crop. By
+ploughing under the green crop, the nitrogen removed from the soil in
+the form of easily soluble nitrates is restored in an insoluble organic
+form, and the soil is at the same time enriched by the addition of much
+valuable organic matter.[243]
+
+It is chiefly the above facts that form the scientific basis of the
+long-pursued practice of the rotation of crops.
+
+
+_Variation in Composition of Crops._
+
+A point of considerable interest is the influence exerted by manures on
+the composition of crops. It has been assumed in the preceding pages
+that the composition of crops of the same plant is uniform; but this is
+not strictly the case, as it has been proved that not merely the manure
+and soil have an appreciable influence on the crop's composition, but so
+also has the climate.
+
+
+_Absorption of Plant-food._
+
+The laws regulating the absorption of plant-food are most interesting,
+although, unfortunately, very imperfectly understood as yet. The
+fertilising ingredients are capable of considerable movement in the
+plant, and are only absorbed up to a certain period of growth. This in
+many plants is reached when they flower. After this period they are no
+longer capable of absorbing any more food. The popular belief that
+plants in ripening exhaust the soil of its fertilising matters is
+consequently a fallacy.
+
+
+_Fertilising Ingredients lodge in the Seed._
+
+The tendency of fertilising matters is to move upward in the plant as it
+matures, and finally to become lodged in the seed. It is for this reason
+that the cereals prove such an exhaustive crop. That nature, however,
+can in certain cases be very economical of her food-supplies, is
+strikingly illustrated by the fact that much of the fertilising matter
+contained in the mature leaves in autumn passes back into the tree
+before the leaves fall from it.
+
+
+_Forms in which Nitrogen exists in Plants._
+
+The form in which nitrogen is present in the plant is chiefly as
+albuminoids. As, however, albuminoids belong to that class of bodies
+known as colloids, which cannot easily pass through porous membranes
+like those forming the walls of plant-cells, they are changed during
+certain periods of the plant's growth into amides, which are
+crystalloids, and consequently able to move freely about in the plant.
+Amides are most abundant in young plants during the period of their most
+active growth, and as the plant ripens the amides seem to be largely
+converted into albuminoids.
+
+While the subject is not very clearly understood, it would seem to be
+pretty conclusively proved that there is a direct relation between the
+amount of the phosphoric acid and of the nitrogen absorbed.
+
+
+_Bearing of above Facts on Agricultural Practice._
+
+The bearing of these facts upon practice is obvious. In the first place,
+they show how important it is that plants should be well fed when they
+are young, and that in the practice of green manuring it is best to
+plough in the crop when it is in flower, as no additional benefit is
+gained by allowing it to ripen, seeing that no further absorption of
+fertilising ingredients takes place after the period of flowering.
+
+
+_Influence of excessive Manuring of Crops._
+
+The influence of large quantities of manures is seen in the case of
+certain root crops. It is found, in such a case, that while the roots
+are larger, they are more watery in composition and of less nutritive
+value. Again, it seems to be a fact pretty generally known to practical
+men, that nitrate of soda seems to have a bad effect on the quality of
+hay. It would seem, further, that the influence of nitrogenous
+fertilisers on cereals is to increase the percentage of nitrogen in the
+grain, but that they have no such influence in the case of leguminous
+crops. Phosphatic manures, on the other hand, in the case of leguminous
+crops, seem to have the effect of diminishing the amount of nitrogen in
+the seed.
+
+
+FOOTNOTES:
+
+[241] Though not necessarily at the same time or to each succeeding
+crop. There may be comparatively long intervals between the applications
+of farmyard manure in many cases.
+
+[242] Of course what is meant here is the direct influence of such
+manures. Their indirect value may be shown in the soil by the increased
+crop residues they give rise to.
+
+[243] This is very concisely and clearly put in Mr Warington's admirable
+'Chemistry of the Farm.'
+
+
+
+
+CHAPTER XXIII.
+
+MANURING OF THE COMMON FARM CROPS.
+
+
+In this chapter we shall attempt to summarise briefly the results of
+experiments on the manuring of some of the commoner crops, and we shall
+start with the manuring of cereals.
+
+
+CEREALS.
+
+As we have already pointed out, a certain similarity in the manurial
+requirements of the different members of this class exists. They are
+characterised, for one thing, by the comparatively small quantity of
+nitrogen they remove from the soil--less than either leguminous or root
+crops. Of this nitrogen the larger proportion--amounting to
+two-thirds--is contained in the grain, the straw only containing about a
+quarter of the total amount of nitrogen in the plant. The amount of
+phosphoric acid they remove from the soil is not much less than that
+removed by the other two classes of crops; but this, again, is also
+chiefly in the grain. It is on this account that the cereals may be
+regarded, in a sense, as exhaustive crops, seeing that the grain is
+almost invariably sold off the farm. But, on the other hand, owing to
+the comparatively small demands they make on fertilising ingredients,
+cereals will continue to grow on poor land for a longer period than most
+crops,--a fact of very great importance for mankind.
+
+
+_Especially benefited by Nitrogenous Manures._
+
+Despite the fact that cereals remove comparatively little nitrogen from
+the soil, it is somewhat striking to find that they are chiefly
+benefited by the application of nitrogenous manures. This fact may be
+explained by the shortness of the period of their growth, and the fact
+that they assimilate their nitrogen in spring and early summer, and are
+thus unable to utilise to the full the nitrates which accumulate in the
+soil during later summer and autumn. As they seem to absorb their
+nitrogen almost exclusively in the form of nitrates, they are especially
+benefited by the application of nitrate of soda.
+
+
+_Power of absorbing Silicates._
+
+A characteristic feature in the composition of cereals is the large
+amount of silica they contain. In common with the grasses, they seem to
+possess a power, not possessed by other crops, of feeding upon
+silicates.
+
+The special manure, therefore, required for cereals is a nitrogenous
+manure, and that, as a rule, of a speedily available character, such as
+nitrate of soda or sulphate of ammonia. Furthermore, certain members of
+the group are also specially benefited by phosphatic manures.
+
+We shall now consider individually a few of the more important cereal
+crops.
+
+
+BARLEY.
+
+Of cereal crops barley deserves to be considered first, owing to the
+fact that it is, of all grain crops, the most widely distributed. In
+England, in amount, it comes next to wheat among cereals. Its habits
+have also been studied in a very elaborate and careful manner, and have
+been made the subject of many experiments, both in this country and
+abroad.
+
+
+_Period of Growth._
+
+The first point to notice about barley is the fact that its period of
+growth is a short one. This has a most important bearing on its
+treatment with manure. It may be said to ripen, on an average, in
+thirteen or fourteen weeks in this country; although in Norway and
+Sweden its period of growth is much less--viz., from six to seven weeks.
+Indeed no fewer than three crops have been obtained in one year in
+certain districts in these countries, and two crops are common. With
+regard to the period of its growth, it differs from wheat, which in its
+general manurial requirements it resembles. Wheat, which is largely sown
+in autumn, has four or five months' start of barley. From the fact that
+it is a short-lived crop, and that its roots are shallower than wheat,
+and draw their nourishment chiefly from the surface-soil, it benefits to
+a greater extent from liberal manuring than wheat, which is more
+independent of artificial supplies of fertilisers.
+
+
+_Most suitable Soil._
+
+Again, while wheat does well on a heavy soil, and does not require a
+fine surface-tilth, barley does best on a light, rich, friable soil. It
+has, however, been very successfully grown on a heavy soil after wheat.
+Barley benefits more than wheat does from the application of
+superphosphate of lime, or some other readily available phosphatic
+manure. This may be accounted for by its shorter period of growth and
+shallower root system, which thus prevent it drawing much mineral
+sustenance from the subsoil. In fact, spring-sown crops, as a rule,
+benefit more from superphosphate than autumn-sown crops. The exhaustion
+of a soil under barley is essentially, as in the case of wheat, one of
+nitrogen, as Sir J. Henry Gilbert has pointed out.[244]
+
+
+_Farmyard Manure not suitable._
+
+It has been urged, with some show of reason, that farmyard manure is not
+suitable for barley, as its action is too slow to have much influence on
+so short-lived a plant, and that only quick-acting manures should be
+used. Where farmyard manure is applied, it should be to the preceding
+crop; and this is advisable for more reasons than one.
+
+
+_Importance of uniform Manuring of Barley._
+
+The use to which barley is put--viz., for malting purposes--renders the
+uniformity of its composition a point of great importance. Since its
+quality is very largely influenced by its treatment with manures,
+special care has to be exercised in their application. Grown as it
+generally is after roots, fed off with sheep, its quality, it is
+alleged, is apt to suffer from the unequal distribution of the manure
+applied in this way. It has consequently been recommended, in order to
+avoid this inequality, rather to grow a wheat crop immediately preceding
+the barley.
+
+
+_Norfolk Experiments on Barley._
+
+Mr Cooke, in summing up the results of the interesting Norfolk
+experiments on barley, points out that in these experiments barley
+always was benefited by nitrogenous manures, sometimes by superphosphate
+of lime, and more rarely by potash; that of nitrogenous manures those
+of quickest action exerted the best influence. On an average it was
+found that 1 cwt. nitrate of soda per acre gave an increase of 8 bushels
+of barley, and 2 cwt. gave 14 bushels; while 3/4 cwt. sulphate of
+ammonia (_i.e._, the amount containing the same quantity of nitrogen as
+1 cwt. nitrate of soda) gave only 5-1/2 bushels of an increase, and
+1-1/2 cwt. (= 2 cwt. nitrate of soda) gave 10 bushels.
+
+Mr Cooke recommends the following manures for the barley crop. From 1/4
+to 1 cwt. of nitrate of soda, according to previous treatment of soil;
+from 1 to 2 cwt. super; and where it is required, from 1/2 to 1 cwt.
+muriate of potash.
+
+
+_Proportion of Grain to Straw._
+
+Professor Hellriegel, the distinguished German investigator, has carried
+out most elaborate experiments on a small scale, with a view to
+investigating the habits of the barley plant. In the most perfectly
+developed of these plants, grown under the most favourable conditions,
+he found that the grain and straw were about equal in weight. Such a
+proportion of grain is, however, never realised in practice, the
+proportion of 2 of grain to 3 of straw being probably the common one.
+
+
+WHEAT.
+
+Wheat occupies the first position amongst cereals, in respect of extent
+of cultivation, in England. As a rule it is sown in autumn, although it
+is also sown in spring. It is generally taken after rotation grasses or
+a leguminous crop, such as peas or beans, or after potatoes or roots.
+
+Unlike barley, it does best on a clay soil, or at any rate on a firm
+soil, and requires a moist seed-bed. From the fact that wheat is often
+sown after such a crop as potatoes or a root crop to which a liberal
+application of manure has been given, it is not so necessary to manure
+it except with a top-dressing of nitrate of soda. In short, it is
+usually considered highly desirable to get land into "good heart" before
+wheat, so that the wheat may obtain its nourishment from the residue of
+the previous crop and the farmyard manure previously applied.
+
+Although, therefore, as a rule, the only manure it will be found
+necessary to add to wheat is a nitrogenous manure, such as nitrate of
+soda or sulphate of ammonia, still there are circumstances in which it
+will be well to supplement these by phosphatic or even potassic manures.
+On a light soil it may be advisable to add superphosphate of lime,
+guano, or bone-meal, in quantities of 2 to 3 cwt. per acre, in addition
+to a nitrogenous manure.
+
+
+_Rothamsted Experiments on Wheat._
+
+Of experiments carried out on the growth of wheat, those which have now
+been in progress for over half a century at Rothamsted are the most
+valuable and famous. In these experiments the comparative value of
+nitrogen and mineral manures on this crop was strikingly exemplified.
+The former gave a most marked increase in the crop, while with the
+latter little or no increase was obtained. A combination of nitrogenous
+and mineral manures, on the other hand, gave the most striking results.
+An explanation of these results may be afforded by the fact that in
+ordinary farming an excess of mineral matter, as compared with nitrates,
+is returned to the soil in the crop residues and in the straw of the
+farmyard manure.
+
+Of nitrogenous manures, nitrate of soda, on the whole, showed better
+results than sulphate of ammonia.
+
+
+_Continuous Growth of Wheat._
+
+The possibility of growing fair crops of wheat year after year for fifty
+years on the same land, and that without any manure whatever, is among
+the most striking of the results of these famous Rothamsted wheat
+experiments.
+
+
+_Flitcham Experiments._
+
+In conclusion, we may refer to Mr Cooke's Flitcham experiments. These
+were carried out for the purpose of ascertaining the most suitable
+manure for the wheat crop under different conditions.
+
+It will be sufficient here to give the recommendations made by Mr Cooke
+as the practical outcome of these experiments.
+
+He recommends the application of 10 tons of farmyard manure on light or
+mixed soils, after rotation seeds, ploughed in in the autumn, with from
+1/4 to 1 cwt. of nitrate of soda, sown in the spring. In certain cases
+farmyard manure will be sufficient without the nitrate of soda. When
+farmyard manure is not available, the most effective and economical
+substitute is 4 cwt. per acre of rape-cake, ploughed in in the autumn,
+or 1 cwt. of sulphate of ammonia, sown in the spring, with, in either
+case, 1 cwt. of nitrate of soda as a spring top-dressing. In addition to
+the above, on land in doubtful agricultural condition, or exceptionally
+deficient in one or other of these ingredients, Mr Cooke recommends the
+addition of 2 cwt. superphosphate, or 1 cwt. muriate of potash, or both
+of these manures, ploughed or harrowed in in autumn.
+
+
+OATS.
+
+Like barley, oats are generally sown in spring, and, like barley, may be
+described as a shallow-rooted crop. They require, therefore, manures
+which are readily available, and their demands on the different
+fertilising ingredients are very similar to barley. The manures which
+will pay best, consequently, for oats, are nitrate of soda, used as a
+top-dressing, and superphosphate of lime, applied along with the seed.
+Probably upon no other crop is nitrate of soda so safe and so effective
+as upon oats. In some respects, however, oats differ strikingly from
+barley.
+
+
+_A very hardy Crop._
+
+In the first place, oats are a much hardier crop than barley or wheat.
+They can grow on a wonderfully wide range of soil, and under
+comparatively adverse circumstances, both of climate and situation. They
+are better suited for a damp climate such as our own than a warm
+climate. They may be described as of all crops the least fastidious, and
+will flourish on sandy, peaty, or clayey soils. While this is so, they
+show a preference for soils rich in decayed vegetable matter. It is for
+this reason that they flourish so well on soils freshly broken up from
+pasture, and are often the first crop to be grown on such soils.
+
+
+_Require mixed Nitrogenous Manuring._
+
+Stoeckhardt has found, in experiments on the manuring of the oat crop,
+that they greedily absorb nitrogen during nearly the whole period of
+their growth, and that, consequently, it is desirable to manure them
+with a mixed nitrogenous manure which shall contain nitrogen, both in a
+readily available form to supply the plant during the early stages of
+its growth, and in a less available form for the later stages of
+growth. He was of the opinion that in this way a continuous and
+satisfactory growth of the crop would be promoted.
+
+
+_Arendt's Experiments._
+
+The oat-plant has been made the subject of many elaborate
+investigations. Of these, those carried out by Arendt are the most
+elaborate and best known. In these experiments the composition of the
+oat-plant at different stages of growth was investigated. It was found
+that the oat-plant increased during the whole period of its life, and
+that two-thirds of the nitrogen absorbed was absorbed during the later
+period of growth. It has since been shown, however, that the absorption
+of nitrogen is very much influenced by circumstances. Indeed its
+composition is peculiarly susceptible to the influence of manures, and
+especially the influence of weather. Thus Arendt found that the
+assimilation of nitrogen is checked by cold wet weather; while, on the
+other hand, it is promoted by warm dry weather. The grain of oats grown
+in warm seasons is better developed, and in composition more nutritious
+(_i.e._, contains more nitrogen), than that of oats grown in wet
+seasons, while the reverse is the case with the straw.
+
+
+"_Avenine._"
+
+A point of considerable interest in connection with the composition of
+oats is the fact that it contains a body which exerts a strikingly
+stimulating effect on the nervous system of the animal, and to which the
+name "avenine" has been given.
+
+
+_Quantities of Manures._
+
+The quantities of manures which may be applied to the oat crop are
+similar in amount to those which ought to be applied to barley--from 1/2
+to 1 cwt. of nitrate of soda, and from 2 to 3 cwt. superphosphate of
+lime. Very often, however, the oat crop receives directly little or no
+manure. In the Highland and Agricultural Society of Scotland's
+experiments, sulphate of ammonia was found to be of very much less value
+than nitrate of soda as a manure for oats. Potash manures, especially
+muriate of potash, had a very beneficial effect. The general conclusions
+drawn from these experiments were, that the treatment of the land should
+be such as to accumulate organic matter in it, to prevent too great a
+loss of moisture, and to provide the young plant with manures that come
+speedily into operation.
+
+
+GRASS.
+
+The manuring of grass is a question of very great interest and
+importance, but is, at the same time, beset with peculiar difficulties.
+Grass is grown under two conditions--first, that grown on soils
+exclusively set apart for its continuous growth (permanent pasture);
+and secondly, that grown for the purpose of being converted into hay and
+of providing pasture in the ordinary rotation of crops (rotation seeds).
+The manuring of the former is somewhat different from the manuring of
+the latter.
+
+
+_Effect of Manure on Herbage of Pastures._
+
+The nature of the herbage growing on pasture is very much influenced by
+the manure applied. This, indeed, is one of the most noteworthy features
+connected with the manuring of grass, and has been especially observed
+in the Rothamsted experiments, where the influence of the different
+manures on the various kinds of herbage has been investigated with great
+care. The herbage constituting pasture is, as every farmer knows, of a
+varied description. We have in pastures a mixture of plants belonging
+both to the gramineous and leguminous classes, as well as a variety of
+weeds. Now the result of the application of different manures tends
+respectively to foster the different kinds of grasses. Thus when one
+kind of manure is applied, grasses of one kind tend to predominate and
+crowd out grasses of another. It has been found that _the more highly
+pasture-land is manured the simpler is the nature of its herbage_ (that
+is, the fewer are the different kinds of herbage growing on it).
+_Unmanured pasture, on the other hand, is more complex in its herbage._
+The result is, that the application of manure to pasture-land is
+attended with certain dangers. To maintain good pasture it is desirable
+to effect a proper balance between the different kinds of grasses. For
+this reason permanent pasture may be said to be, of all crops, the least
+commonly manured. As a rule it is only manured by the droppings of the
+cattle and sheep feeding upon it.
+
+
+_Influence of Farmyard Manure._
+
+It is found that the influence of farmyard manure upon the composition
+of the pasture does not tend, to the same extent, to the undue
+development of one type of herbage over another; and in this respect it
+is probably to be preferred to artificial manures.
+
+The same reasons, however, do not hold with regard to rotation seeds,
+where an abundant growth is desired, and complexity of herbage is not so
+important. A further reason which exists for the manuring of meadow-land
+is the greater impoverishment of the soil taking place under such
+conditions. As illustrating the influence of different manures on
+different kinds of herbage, it may be mentioned that in New England
+wood-ashes, a manure commonly used there, have been observed, when
+applied to pasture, to bring in white clover, and that the application
+of gypsum had the same effect. An explanation of this fact may be found
+in the influence of potash on leguminous crops. The chief value of
+wood-ashes as a manure is due to the large percentage of potash they
+contain, while the value of gypsum is probably to be accounted for by
+the fact that it has an indirect action, and sets free potash from its
+inert compounds in the soil. In the Rothamsted experiments this point
+has been verified, and potash has been shown to increase the proportion
+of leguminous plants on a grass-field. Nitrogenous manures, on the other
+hand, more especially sulphate of ammonia, have been found to increase
+the proportion of grasses proper, and to diminish the proportion of
+leguminous plants. The effect of farmyard manure, while less marked in
+inducing simplicity of herbage, has a similar effect to sulphate of
+ammonia; while phosphates and other mineral manures exercise an
+influence similar to that of potash. Mixtures of mineral and nitrogenous
+manures gave the largest returns obtained, but their influence was to
+increase the proportion of grasses proper. Sewage irrigation also tends
+chiefly to develop grasses.
+
+
+_Influence of Soil and Season on Pastures._
+
+Manures are not the only factors influencing the quality of pastures.
+The nature of the soil, as well as the age of the pasture and the
+character of the season, exert a very considerable influence. Grass
+growing on damp or badly drained soil is invariably of poor quality, the
+coarser grasses predominating. Old pastures, again, are generally of
+better quality than new ones.
+
+
+MANURING OF MEADOW-LAND.
+
+Nitrate of soda is a common manure for grass grown for hay. It is often
+applied at the rate of 2 or 3 cwt. per acre. It is best, however, to
+apply it in smaller doses. On soils where lime is abundant,
+superphosphate may be applied, if necessary, at the rate of 2 or 3 cwt.
+per acre, or bones at a similar rate. Basic slag has been found to meet
+with good results as a manure for grass-land, especially where the soil
+is rich in organic matter.
+
+
+_Bangor Experiments._
+
+Mr Gilchrist of University College, Bangor, as a result of numerous
+experiments carried out in different parts of Wales, recommends for
+rye-grass and clover hay on land in good condition 1 cwt. of nitrate of
+soda or sulphate of ammonia per acre, the former being applied about the
+middle of April, the latter during March. For land in poor condition,
+the addition of 2 cwt. of superphosphate is recommended--this to be
+applied some time between December and March. Farmyard manure may be
+usefully applied to young grass and clover seeds in the autumn, more
+especially on light soils. For meadow-land which is growing hay every
+year, Mr Gilchrist further recommends the following 4-course rotation of
+manuring:--
+
+First year, 15 tons farmyard manure, applied in the autumn.
+
+Second year, 1 cwt. nitrate of soda.
+
+Third year, 4 cwt. basic slag or 3 cwt. superphosphate and 1 cwt.
+nitrate of soda.
+
+Fourth year, 1 cwt. nitrate of soda.
+
+
+_Norfolk Experiments._
+
+Mr Cooke, from his Norfolk experiments, recommends the following manures
+for rotation seeds:--
+
+One to 1-1/2 cwt. nitrate of soda as a top-dressing in early spring.
+Where the clover plant is a good one, and it is particularly desired to
+cultivate it, he recommends as a dressing 1 cwt. of muriate of potash
+per acre, to be applied immediately after the clover is sown. The
+practice of dressing growing seeds in their first winter has, so far as
+the experiments in Norfolk go, less to recommend it than the earlier
+dressing.
+
+
+MANURING OF PERMANENT PASTURES.
+
+In this case the manure should be applied so as not to impair the
+quality of the herbage. Slow-acting manures are consequently best, such
+as basic slag or bones, which have been found to be of special value. On
+wet or marshy land after draining, lime is perhaps one of the best
+manures to apply in the first instance. As we have already said,
+farmyard manure will do more to maintain the quality of pasture than any
+kind of artificial manure. Mr Cooke is of opinion that no system of
+manuring yet discovered will both thicken and improve the herbage at
+all equally in success to the careful and regular feeding upon the grass
+of cattle or sheep, the animals having a good allowance of decorticated
+cotton-cake, or even of linseed-cake.
+
+
+ROOTS.
+
+Of all crops roots may be said to require the most liberal application
+of manure, and to respond most freely to it. They contain large
+quantities of the fertilising ingredients--nitrogen, phosphates, and
+potash--and may be regarded as exceedingly exhaustive crops. This is
+especially the case with regard to mangels, which make particularly
+large demands on a soil's fertilising ingredients.
+
+Turnips are characterised by the large amount of sulphur they contain;
+and, according to some, this explains the beneficial effect which gypsum
+has when applied to them as a manure. This, however, is more probably to
+be explained by the indirect action of gypsum in setting free the potash
+of the soil. The fact that the successful cultivation of root crops
+depends on the application of large quantities of manure, is recognised
+in practice, as they receive the most manure of any crop of the
+rotation. Roots flourish best on a light soil which is neither too wet
+nor too dry; but with liberal manuring and careful tillage, they may be
+said to do well on any soil. Mangels are generally more benefited by
+the application of nitrogenous manures than are turnips or swedes,
+which, it would seem, have a greater power of absorbing nitrogen from
+the soil than the first-named crop; but it is a mistake to suppose that
+any of the root crops are not dependent on a ready supply of nitrogen;
+and the fact that large crops of turnips can often be grown by the
+application of superphosphate alone, may be taken as a proof that the
+soil contains plenty of nitrogen. Mangels are, from their deeper roots,
+more capable of drawing their supply of phosphoric acid from the soil
+than turnips. They respond, therefore, as a rule, less freely than
+turnips or swedes to an application of superphosphate. Generally
+speaking, we may say that the characteristic manure for turnips is
+superphosphate, and that for mangels is a nitrogenous manure such as
+nitrate of soda or sulphate of ammonia.
+
+A special reason for manuring root crops is the fact that they are more
+liable to disease than other crops; and this is especially the case in
+the early stages of their growth. One of the great benefits conferred on
+the turnip crop by an application of superphosphate, is the help it
+gives the crop to pass safely the critical period of its growth. The
+superphosphate is best drilled in with the seed, in quantities varying
+from 3 to 5 cwt. In Scotland, it may be well to point out, the manure
+applied to this crop is very much in excess of the amount customarily
+applied in England; for in the former country larger applications of
+manure may be profitably employed. Roots generally receive a large
+dressing of farmyard manure. Salt has been found in some districts to
+have a very good effect on the mangel crop, and potash is often found to
+amply repay application.
+
+
+_Influence of Manure on Composition._
+
+A most interesting point in connection with the manuring of roots is the
+effect of manure on their composition. This has been most elaborately
+investigated at Rothamsted and elsewhere. Thus it has been found that
+the effect of the application of excessive quantities of nitrogenous
+manures is to produce too great a development of leaves at the expense
+of the roots.
+
+
+_Nitrogenous Manures increase Sugar in Roots._
+
+Nitrogenous manures also tend to increase the proportion of sugar and
+diminish the proportion of nitrogenous matter in roots. This has an
+important bearing on the treatment of roots which are cultivated for
+their sugar, such as beets, in the growth of which nitrate of soda is
+the chief artificial manure applied.[245]
+
+The leaf, it may be pointed out, contains a larger percentage of dry
+matter, both in swedes and in turnips, than the root.
+
+
+_Amount of Nitrogen recovered in Increase of Crop._
+
+With regard to the amount of nitrogen recovered in the increased crop of
+mangel and roots when manured with different nitrogenous manures, it was
+found at Rothamsted, as an average of six years, that the following
+percentages of nitrogen were recovered: When nitrate of soda was
+applied, 60 per cent of the nitrogen it contained was recovered in the
+increased crop; when ammonia salts were applied, 52 per cent; when
+rape-cake was used, 50 per cent; and when a mixture of rape-cake and
+ammonia salts was used, 46 per cent.
+
+It may be pointed out that the influence of season and climate on the
+composition of root crops is very great--greater, indeed, than on any
+other crop. Like oats, turnips grow better in Scotland than in England,
+the moister climate of the former country being more suitable for their
+maximum development, and hence the economy of maximum dressings in
+Scotland.
+
+
+_Norfolk Experiments._
+
+In conclusion, a few words may be said on the Norfolk experiments,
+carried out under the direction of Mr Cooke for the purpose of
+ascertaining the best and most economical manure for mangels and swedes
+on different Norfolk soils. In most of these experiments it was found
+that superphosphate had not much effect in producing increase of crop in
+the case of mangels; that the best nitrogenous manure was nitrate of
+soda; and that on the whole it was not economical to apply farmyard
+manure at the rate of more than 10 tons per acre. It was further found
+that, although either potash or common salt gave a decided increase in
+weight of roots, it was not necessary to give both these manures at
+once, either of them being about as effective as the other.
+
+Mr Cooke recommends the following manures as best suited for
+mangels--viz., 2 cwt. nitrate, 3 cwt. common salt, and 2 cwt.
+superphosphate. Upon certain soils peculiarly adapted to mangels, and in
+warm localities where larger crops than 25 to 30 tons per acre are
+habitually grown, it would probably pay to increase or to double the
+above quantity of nitrate of soda. Ten tons of farmyard manure may, if
+preferred, be substituted for all or a part of the nitrate of soda, or
+may even be used in addition to it, according to the resources of the
+farmer in respect of it, and the return he desires to get from the dung
+in the first year of application or in future ones. It is best to apply
+the nitrate of soda in two instalments--half at the time of seeding, and
+half as a top-dressing immediately after the first hand-hoeing of the
+roots. A third dressing may often be given with advantage a month later.
+
+
+_Manure for Swedes._
+
+As a complete and economical dressing for swedes in Norfolk, Mr Cooke
+recommends 3 to 4 cwt. superphosphate, 1 cwt. sulphate of ammonia, and
+1/2 cwt. of muriate of potash. Occasionally it may be found advisable to
+reduce the quantity of sulphate of ammonia, or to leave it out
+altogether; and in other cases the potash may be judiciously omitted.
+The entire mixture should be sown at the time of drilling the turnips.
+If farmyard manure is used--and if used it should be applied in a
+well-decomposed state--no other manure than 3 cwt. of superphosphate
+will be required.
+
+
+_Highland Society's Experiments._
+
+Valuable experiments have been carried out on the subject of manuring of
+turnips by Dr A. P. Aitken, for the Highland and Agricultural Society of
+Scotland. The following are some of the results to be gathered from
+these experiments. The effect of a dissolved phosphate as compared with
+a ground phosphate is to produce a turnip of less feeding value.
+Superphosphate had a better effect when applied in April than when
+applied with the seed in June. It was further found that when the
+nitrogenous manure was given entirely in the form of nitrate of soda or
+sulphate of ammonia, the latter produced a denser and sounder turnip.
+Lastly, with regard to the application of potash, it was found that the
+best way was to apply it several months before sowing. The effect of
+potash manures is to increase the amount of turnips, but to retard the
+ripening of the bulbs. The effect of excessive potash manuring is to
+greatly injure the crop.
+
+
+_Manuring for rich Crops of Turnips._
+
+In Dr Aitken's own words: "In order to grow a large and at the same time
+a healthy and nutritious crop of turnips, such a system of manuring or
+treatment of the soil, by feeding or otherwise, should be practised as
+will result in the general enriching and raising of the condition of the
+land, so that the crop may grow naturally and gradually to maturity. For
+that purpose a larger application of slowly acting manures, of which
+bone-meal may be taken as the type, is much better suited than smaller
+applications of the more quickly acting kind. A certain amount of
+quickly acting manure is very beneficial to the crop, especially in its
+youth; but the great bulk of the nourishment which the crop requires
+should be of the slowly rotting or dissolving kind, as uniformly
+distributed through the soil as possible."
+
+
+_Experiments by the Author._
+
+Experiments by the author on turnip-manuring, carried out in different
+parts of the South and West of Scotland, showed that while farmyard
+manure is valuable in giving the crop a good start and bringing it well
+forward during the period of germination and early growth, by supplying
+a certain amount of easily assimilable plant-food, and in the case of
+dry weather attracting a quantity of moisture, its application in
+quantities of 20 or even 10 tons per acre can scarcely be regarded as
+profitable, giving to farmyard manure a nominal value of a few shillings
+a ton. In these experiments slag proved itself a most valuable manure,
+indeed one of the most economical of all the manures experimented with.
+They further showed that heavy dressings with superphosphate, amounting
+to as much as 8 cwt. per acre, are, from an economical point of view, as
+a rule justifiable in Scotland; and that nitrate of soda and sulphate of
+ammonia possess practically equal value as a manure for turnips. In
+almost every one of the experiments the benefit of supplementing
+superphosphate with nitrogenous manure was shown. Potash was also found
+in many cases to be a thoroughly paying manure for the turnip crop, when
+it was applied along with nitrogen and phosphates; but when applied
+alone, far from exercising any appreciable benefit, it seemed to exert
+an injurious action.
+
+
+POTATOES.
+
+Potatoes are often classed along with the root crops, and in their
+manurial requirements they offer many points of similarity. Next to root
+crops, they may be said to make the most exhaustive demands on the soil,
+and therefore require a liberal general manuring. A point of importance
+in the manuring of potatoes is a good tilth in the soil, so as to enable
+a free expansion of the tubers to take place. They may be said to grow
+best on deep warm soils; but, like roots, if liberally manured, they may
+be successfully grown on any kind of soil. Farmyard manure has long been
+regarded as specially valuable for the potato crop. In many parts of
+Scotland it is applied in enormous quantities, ranging from 20 to even
+40 tons per acre. There can be little doubt that the value of farmyard
+manure, as well as other bulky manures, for the potato crop, is partly
+due to their mechanical influence on the soil. Potatoes are
+surface-feeders, and require their food in a readily available
+condition. It is found desirable, therefore, to supplement farmyard
+manure by readily available artificial manures. Potatoes repay the
+application of a mixed manure containing all the fertilising
+ingredients--nitrogen, phosphoric acid, and potash--better than most
+crops.
+
+
+_Highland Society's Experiments on Potatoes._
+
+The nitrogen is, according to the Highland Society's experiments, best
+applied in the form of nitrate of soda. Sulphate of ammonia does not
+seem, when farmyard manure is also applied, to have an equally valuable
+effect, as it influences the size of the tuber, producing an undue
+proportion of small potatoes. When no farmyard manure is applied,
+however, sulphate of ammonia seems to have a good effect, especially in
+wet seasons.
+
+With regard to the nature of the phosphatic manure to be applied,
+superphosphate is to be preferred. Potatoes make large demands on
+potash, and consequently require potassic manures. In consequence of the
+fact that they receive large applications of farmyard manure, the
+necessity for adding potash in the form of artificial manures does not
+generally exist. Potash, if applied in too large quantities, has been
+found to exert a deleterious effect. We have already pointed out that
+muriate of potash tends to produce a waxy potato.
+
+
+_The Rothamsted Experiments with Potatoes._
+
+The Rothamsted experimenters have very fully investigated the conditions
+of the manurial requirements of potatoes. In these experiments potatoes
+were grown year after year in the same field. It was found that the
+effect of mineral manures alone was greater than the effect of
+nitrogenous manures alone, and that of mineral manures phosphates, as a
+rule, had a better effect than potash; that under the action of the
+growth of potatoes a greater exhaustion of phosphates than of potash
+takes place in the soil; and lastly, that it is essential to have an
+abundant supply of the different fertilising ingredients in order to
+grow successful crops. In the Rothamsted experiments, the slow action of
+farmyard manure in supplying fertilising ingredients to the potatoes is
+strikingly demonstrated. Thus, although farmyard manure was applied at
+such a rate that more than 200 lb. of nitrogen were added to the soil,
+the result was inferior to that obtained from the application of 86 lb.
+of nitrogen applied in the form of readily available artificial manure.
+
+
+_Effect of Farmyard Manure on Potatoes._
+
+It may be said, in this respect, that the potato is less able to utilise
+the fertilising ingredients of farmyard manure than any other of the
+farm crops. Yet, despite this fact, farmyard manure has been found to be
+one of the best manures to apply. The reconciliation of these seemingly
+contradictory statements depends on the influence exerted by the
+farmyard manure on the mechanical condition of the soil, rendering it
+more porous and easily permeable to the surface-roots, upon the
+development of which the success of the crop so much depends. The
+beneficial effect of farmyard manure is also doubtless due to the
+increased temperature which large applications of it produce in a soil.
+
+Sir J. Henry Gilbert, in his well-known Cirencester Lecture on the
+Growth of Potatoes, cites several examples of the manurial treatment of
+potatoes in different parts of the country. In Forfarshire, farmyard
+manure or stable manure is largely employed (at the rate of 12 to 14
+tons, and in some cases even 20 tons per acre), and it is also largely
+supplemented by artificial manures. These latter are applied to the
+extent of about 10 cwt., and consist of superphosphate, dissolved bones,
+and potash salts. Six tons of potatoes are considered a fair crop. In
+East Lothian the manuring is similar, with the exception that farmyard
+manure is applied in even larger quantities--30 to 40 tons being often
+used. Sometimes potatoes are grown with artificial manures alone. It
+would seem that the usual crop of potatoes ranges from 4 to 8 tons per
+acre.
+
+
+_Manuring of Potatoes in Jersey._
+
+The manuring of the potato crop, so largely grown in Jersey in the
+Channel Islands, is of interest. Potatoes are there grown two or three
+years, then corn, then grass for a few years, then potatoes again, no
+special rotation of crops being followed. Either farmyard manure or
+sea-weed is applied at the rate of 25 to 30 tons per acre, supplemented
+by 8 to 12 cwt. of artificial manures.
+
+These statements show how prevalent the practice of heavily manuring the
+potato crop is.
+
+
+_The Influence of Manure on the Composition of the Potato._
+
+The influence of manure on the composition of the potato crop is of much
+interest. Potatoes grown without manure, just as in the case of roots,
+are found to have a larger percentage of nitrogen than potatoes grown
+with manure. The effect of manuring, therefore, is to increase the
+proportion of starch, which is the most important constituent of the
+potato. Mineral manures have a greater effect in increasing the
+percentage of starch than purely nitrogenous manures; but when used
+together, a still greater increase is obtained than when used singly.
+The effect of nitrogenous manures on the composition of roots and
+potatoes is thus seen to be similar. In the case of both crops the
+effect is to increase the proportion of the characteristic carbohydrate
+constituent, which in roots is sugar, and in potatoes starch. Potatoes,
+like roots, are also much influenced by the season. The effect of season
+and manuring on the potato disease is worthy of notice. Wet seasons are
+favourable to the development of the disease. It has been found that in
+a highly nitrogenous manured crop the proportion of diseased tubers is
+greater than in a non-manured crop.
+
+
+LEGUMINOUS CROPS.
+
+We have already referred to the manuring of crops of the leguminous
+class in discussing the manuring of meadows and permanent pasture. It
+was there pointed out that the tendency of certain manures was to
+encourage the growth of the leguminous plants of the herbage, while
+other manures had the effect of encouraging those of the gramineous
+class. It was pointed out that a manure which had this effect was
+potash, or any manure which owed its characteristic action to the fact
+that it supplied potash to the soil or set it free in the soil.
+
+
+_Leguminous Plants benefit by Potash._
+
+This is one of the most important points to notice in manuring
+leguminous plants. Just as we can say that nitrogenous manures are
+specially beneficial to cereals, and phosphatic manures to roots, so
+potash is the special manure for leguminous crops.
+
+
+_Nitrogenous Manures may actually be hurtful._
+
+But we have, further, an even more striking characteristic of leguminous
+crops to notice. We have seen that, with regard to the crops already
+discussed, while there are cases in which a fertilising ingredient may
+be of no value, or may positively exert a hurtful action on the crops,
+such cases are only exceptional. With regard to leguminous crops,
+however, we find that almost invariably they derive little or no benefit
+from the use of artificial nitrogenous manures. And this is all the more
+striking since they contain large quantities of nitrogen in their
+composition--twice as much as the cereals. The fact, which has long been
+noticed with regard to certain members of this class of plants, such as
+clover, that not only do they contain a large amount of nitrogen, but
+that by growing them on a soil the soil is largely enriched in this
+valuable fertilising constituent, has long waited for a satisfactory
+explanation, which at last has been forthcoming. The discovery that
+leguminous crops can draw on the boundless store of nitrogen present in
+the air has done much to clear up the mystery. There are, however, other
+problems with regard to the growth of leguminous plants which still
+await solution.
+
+
+_Clover-sickness._
+
+One of these is the fact that land on which a leguminous crop like
+clover has been growing for a number of years becomes unfit to support
+its growth any longer. Such a soil is termed "clover-sick"; and many
+have been the theories put forward to explain the phenomenon, but none
+of them can be regarded as satisfactory.
+
+The knowledge that leguminous plants have the power of deriving their
+nitrogen from the air, furnishes us with an economical means of
+enriching our soils in nitrogen. By growing leguminous crops alternately
+with cereals, for example, the air should be made to furnish the
+necessary nitrogenous manure. As a matter of fact, modified forms of
+such a practice have long been in use--indeed the ordinary rotations of
+crops are, to a certain extent, adaptations of this practice.
+
+
+_Alternate Wheat and Beans Rotation._
+
+An interesting experiment carried out at Rothamsted may be here cited
+which illustrates in a striking manner the truth of the above statement.
+Wheat and the leguminous crop beans were grown alternately. It was
+found that almost as much wheat (containing nearly as much nitrogen) was
+yielded in eight crops of wheat so grown as was yielded by sixteen crops
+of wheat grown consecutively in an adjoining field.
+
+The most commonly cultivated leguminous crops are clover, beans, and
+peas. Clover having been already discussed, we need only say a word or
+two on the manuring of beans and peas.
+
+
+BEANS.
+
+Beans do best on strong land, and, unlike some of the crops considered,
+do not require a particularly fine tilth. They are generally grown after
+cereals, and as a rule are sown in spring. More rarely, however, they
+are sown in autumn. Spring-sown beans take about seven months to come to
+maturity. They are much affected, like other crops, but to a greater
+extent, by the nature of the season--a wet season inducing an undue
+development of straw.
+
+
+_Manure for Beans._
+
+In common practice the manure used for the bean crop is farmyard manure,
+applied to the soil in autumn after the harvest of the wheat, barley, or
+other cereal crop grown. So common is this practice, that the belief
+commonly exists that farmyard manure is necessary for a successful bean
+crop. But experiments conducted at the Highland Society's Experiment
+Station at Pumpherston show that full crops of beans may be grown with
+the aid of artificial manures on soils which have received no
+application of farmyard manure for ten years.
+
+
+_Relative Value of Manurial Ingredients._
+
+In the Appendix[246] will be found a table giving the results of
+manurial experiments with the nitrogenous, phosphatic, and potash
+manures on beans, carried out by Dr A. P. Aitken at the Highland
+Society's Experiment Station. From these experiments it will be seen
+that the application of phosphates and nitrogenous manures, either alone
+or together, exerted a comparatively small effect in increasing the
+yield of beans compared with that obtained with potash, either alone or
+combined with phosphates. As Dr Aitken says, "Without potash in the
+manure, the other two ingredients are of very little use, unless,
+indeed, the land be very rich in potash."
+
+
+_Gypsum._
+
+Gypsum has a good effect on the bean crop, both on account of the lime
+it contains, and of its indirect action in setting free potash.
+
+Superphosphate is a much better manure than insoluble phosphates, and
+similarly, in the few cases where nitrogenous manures are beneficial,
+the speediest acting are best. Hence nitrate of soda is to be preferred
+to other nitrogenous manures. When it is applied, it should be applied
+in small quantities. A slow-acting nitrogenous manure is positively
+injurious; so also, according to Dr Aitken, is nitrate of soda, applied
+as a top-dressing to the crop.
+
+Of potash manures, the muriate seems to be more effective than the
+sulphate.
+
+
+_Effect of Manure on Composition of Crop._
+
+Lastly, we may refer to the effect of manures on the composition of the
+crop. This is, on the whole, very slight, especially when compared with
+the effect manures exert on the composition of such crops as turnips or
+potatoes. It is the quantity and not the quality of the crop which the
+manure affects in the case of beans.
+
+
+PEAS.
+
+Peas are not grown to anything like the same extent as beans. As a rule,
+when they are cultivated it is along with beans, when they are
+necessarily manured in a similar manner. If grown alone, however, it may
+be well to point out that peas do best, unlike beans, on light, friable,
+chalky loam. When grown in clay they tend to develop an undue amount of
+straw. The effect of season on the crop is similar to that exerted on
+the bean crop. In conclusion, it may be pointed out that it is alleged
+that the effect of farmyard manure on peas is to force the straw.
+
+In concluding this chapter a word or two may be said on the manuring of
+two other crops which are cultivated to a considerable extent in this
+country--viz., hops and cabbages.
+
+
+HOPS.
+
+The requirements of the hop crop in the matter of manures are rather
+singular. It has been pointed out that in the case of most crops
+quick-acting manures are to be preferred to slow-acting manures. With
+hops, however, the case is very different; for they require, and cannot
+be successfully cultivated without, slow-acting manures. Hops are
+especially benefited by bulky nitrogenous manures--such as shoddy,
+horn-meal, hide-scraps, hoofs, rape-dust, &c.; and it is only when
+quick-acting manures are applied along with such slow-acting manures
+that they will exercise their full influence. It is best to manure hops
+twice a-year,--in spring with farmyard manure, supplemented by a
+slow-acting nitrogenous manure, such as shoddy; and again in summer with
+a more quickly acting manure. The dressings applied to hops are enormous
+relatively to those used on other farm crops.
+
+
+CABBAGES.
+
+Cabbages belong to that class of crops known as gross feeders, to which
+any sort of manure, applied in almost any quantities, does not come
+amiss. Cabbages grow best on good loams with a well-drained porous
+subsoil, although they also do well on clay soils. The quantity of
+fertilising ingredients, especially potash, which a large crop of
+cabbage removes from the soil is very great. They consequently require
+large quantities of manure, and are especially benefited by saline
+manures--such as kainit and common salt--and liberal doses of nitrate of
+soda, which may be regarded as the most effective of manures for all the
+cabbage tribe. Farmyard manure may be applied with benefit in larger
+quantities than it would be applied to any other crop.
+
+
+FOOTNOTES:
+
+[244] See his Lecture on the Growth of Barley.
+
+[245] Small roots are found to contain a larger proportion of sugar than
+large roots.
+
+[246] See Note I., p. 530.
+
+
+
+
+APPENDIX TO CHAPTER XXIII.
+
+
+NOTE I. (p. 526).
+
+EXPERIMENTS ON THE MANURING OF BEANS.
+
+Experiments with beans carried out at the Highland and Agricultural
+Society's Experiment Station at Pumpherston, showing the effect of
+potash:--
+
+No. of Bushels dressed
+plots. Kind of manure. grain, per acre.
+
+ 27. No manure 2-1/2
+ 12. Phosphate (bone-ash) 5-1/6
+ 18. Nitrate 6-1/4
+ 21. Phosphate and nitrate 5-1/3
+ 22. _Potash_ 26-1/2
+ 17. _Potash_ and phosphate 42-1/3
+ 10. _Potash_, phosphate, and nitrate 45-1/2
+ 38. _Potash_, phosphate, nitrate, and gypsum 51
+
+
+
+
+CHAPTER XXIV.
+
+ON THE METHOD OF APPLICATION AND ON THE MIXING OF MANURES.
+
+
+Having considered the manuring of the different crops, we may now pass
+on to the consideration of some points in the method of application and
+on the mixing of manures.
+
+
+_Equal Distribution of Manures._
+
+A most important object in applying manures is to effect equal
+distribution of the manure in the soil. This is often, however,
+unusually difficult to do, especially in the case of artificial manures,
+where the quantity to be spread over a large area of the soil is
+extremely small. The difficulty in the case of farmyard or other very
+bulky manure is not so great. In order to overcome this difficulty in
+the case of artificial manures, it is often advisable to mix them with
+some such substance as sand, ashes, loam, peat, or salt. The manure is
+thus diluted in strength, and a very much larger bulk of substance is
+obtained to work with. Circumstances must decide which of these
+substances to use. If the soil be a heavy clay, the addition of sand or
+ashes may have an important mechanical effect in improving its texture;
+while, on the other hand, if it be a light soil, the addition of peat
+may improve its mechanical condition. It must also be remembered that
+peat itself contains a large amount of nitrogen, and thus forms a manure
+of some value. In using loam or peat to mix with artificial manures,
+they should be first dried and then riddled; while if ashes be used,
+they should be previously reduced to a fine state. Wood-ashes, however,
+must be used with caution, and ought not to be mixed with ammoniacal
+manures, as they are apt to contain caustic alkali, which would tend to
+drive off the ammonia in a volatile state.
+
+It has been recommended, in order to save trouble and effect equal
+distribution, that the manure to be applied should always be made up to
+the same amount, so that the farmer by experience may ascertain the rate
+at which to apply it. And here it may be well to say a word or two on
+the subject of mixing manures--a subject with which the farmer is not
+always so conversant as it is desirable in the interests of his own
+pocket he should be.
+
+
+_Mixing Manures._
+
+It is to be feared that not unfrequently indiscriminate mixing may cause
+very serious loss in the most valuable constituent of a manure. It may
+be well, therefore, to point out one or two of the causes of the loss
+that is apt to ensue on the mixing of different kinds of manures
+together.
+
+As the subject depends for its clear comprehension on certain chemical
+elementary principles, it may be well for the benefit of non-chemical
+readers to state these pretty fully.
+
+
+_Risks of Loss in Mixtures._
+
+The risks of loss which may occur from the mixing of artificial manures
+together may be of different kinds. One is the risk of actual loss of a
+valuable ingredient through volatilisation; another is the risk of the
+deterioration of the value of a mixture through change of the chemical
+state of a valuable ingredient. Undoubtedly the most common and most
+serious source of loss is the former. Of the three valuable manurial
+ingredients--nitrogen, phosphoric acid, and potash--only the first is
+liable to loss by volatilisation, and this generally only when the
+nitrogen is either in the form of ammonia or nitric acid.
+
+
+_Loss of Ammonia._
+
+Ammonia, when uncombined, is a very volatile gas with a pungent smell, a
+property which enables its escape from a manure mixture to be very
+easily detected. It belongs to a class of substances which are known
+chemically as bases, and which have the power of combining with acids
+and forming salts. Sulphate of ammonia is a salt formed--as its name
+indicates--by the union of the base, ammonia, with the acid, sulphuric
+acid. Now when ammonia unites with sulphuric acid and forms sulphate of
+ammonia, it is no longer volatile and liable to escape as a gas, but
+becomes "fixed," as it is called.
+
+Although most salts are more or less stable bodies--not liable to
+change--if left alone, and not submitted to a high temperature or
+chemical action, they can be easily decomposed if they are heated or
+brought into contact with some other substance which will give rise to
+chemical action. Sulphate of ammonia is a salt that is very easily
+decomposed. This is due to the fact that its base, ammonia, is very
+volatile, and not capable of being held very firmly by an acid, even by
+sulphuric, which is among the least volatile of all the common acids.
+If, therefore, sulphate of ammonia be heated above the boiling-point of
+water, or brought in contact with any other substance which will give
+rise to chemical action, it is easily decomposed. Now a salt may be
+acted upon by a base or an acid or another salt. When it is brought in
+contact with a base, if the base with which it is brought in contact be
+a stronger base than the base of the salt, the salt is decomposed, and a
+new salt is formed. The acid, in short, exchanges its old base for the
+new one.
+
+
+_Effect of Lime on Ammonia Salt._
+
+This is exactly what takes place when the base lime comes in contact
+with an ammonium salt, such as sulphate of ammonia. The sulphuric acid
+exchanges its old base, ammonia, for the stronger base, lime, and
+sulphate of lime is formed, and ammonia is set free as a gas, and
+escapes and is lost. Sulphate of ammonia, or any substance in which
+there is an ammonia salt, must never be brought in contact with free
+lime, otherwise the ammonia will be lost, and should be harrowed in on
+chalky soils for this reason.
+
+It is different entirely with gypsum--which is sulphate of lime--or
+phosphate of lime, both of which may be safely mixed with sulphate of
+ammonia without any danger of escape of ammonia. It follows from the
+above that a mixture which must on no account be tried is slag phosphate
+and sulphate of ammonia. This is because the slag phosphate contains a
+large percentage of free lime, which would at once, on being brought in
+contact with the sulphate of ammonia, decompose it, and cause the
+ammonia to be lost. For this same reason guano must not be mixed with
+slag. It is perhaps unnecessary, however, to warn one against so doing,
+as it is not likely such a mixture would be made, as the ratio of
+phosphoric acid to nitrogen in guanos is generally greater than is
+required. If it be desired to mix the slag with a quickly available form
+of nitrogen, nitrate of soda is not liable to loss; although for other
+reasons it is not desirable to apply nitrate of soda along with the
+slag, as the former manure should be applied almost always as a
+top-dressing.
+
+
+_Loss of Nitric Acid._
+
+The risks of the loss of nitrogen in the form of nitric acid, although
+not so great as they are in the case of ammonia, are still considerable.
+As nitric acid is not a base but an acid, what is to be avoided in
+mixing nitrates is bringing them in contact with any other manure which
+contains another free and stronger acid--as, for example,
+superphosphate. The free acid present in superphosphate has the tendency
+to drive out the nitric acid from the nitrate and usurp its place. The
+risk of loss of expulsion in the above cases is always augmented by the
+rise of temperature which invariably accompanies chemical action of any
+kind; and although the loss of nitrogen, in the form of nitric acid,
+caused by mixing superphosphate and nitrate of soda, might, under
+ordinary circumstances, amount to very little, yet, if the mixture were
+to be allowed to stand any time, and the temperature of the mass to be
+heightened, the loss which would undoubtedly then ensue would be
+considerable.
+
+The nitrogen salt which it is safe to mix with superphosphate is
+sulphate of ammonia.
+
+
+_Reversion of Phosphates._
+
+But, as has already been mentioned, there is another loss which may
+result from the mixing of manures. This is the deterioration of the
+value of an ingredient by reason of change of chemical condition. This
+is a source of loss that was little suspected a number of years ago, but
+it is now well known that superphosphate of lime, under certain
+conditions, is changed from its soluble to an insoluble form. We have
+already referred to the reversion of phosphate in the chapter on the
+Manufacture of Superphosphates.[247] It was there pointed out that
+reversion is often caused by the presence of iron and alumina or
+undissolved phosphate, and that the risk of reversion is therefore very
+much less in a well-made article, made from pure raw material, than in
+one made from a raw phosphate containing much iron and alumina.
+Superphosphates containing a large percentage of insoluble phosphates
+ought not to be kept too long before being used as a manure, otherwise
+much of the labour and expense involved in their manufacture will be
+lost by the reversion of their soluble phosphate. Further, it is highly
+inadvisable to mix superphosphates with basic slag, which contains a
+large percentage of both iron and free lime. Lastly, if it is desired to
+mix superphosphate with insoluble phosphate, the mixture ought to be
+made just previous to application.
+
+
+_Manurial Ingredients should be applied separately._
+
+The question of applying manure in mixtures is one on which considerable
+difference of opinion may exist. For many reasons manures are often
+better applied in the unmixed condition. For example, a mixture of a
+quickly acting nitrogenous manure with a slowly acting phosphatic manure
+is not suitable. In such a case either the nitrogenous manure will be
+applied too long before it is required by the plant, and thus suffer
+from risk of loss, or the phosphatic manure will not be applied long
+enough before it is likely to be used. By applying manures in an unmixed
+condition the chances are that a more economical use of them is made
+than would otherwise be the case. On the other hand, while the
+application of the separate constituents may be desirable from the
+scientific point of view, it involves a considerable amount of extra
+trouble. Of course a further consideration is the desirability in many
+cases of having a complete manure. The above hints, therefore, on the
+risks of loss which exist in mixing manures, may be of service to the
+agricultural student.
+
+
+FOOTNOTES:
+
+[247] See p. 389.
+
+
+
+
+CHAPTER XXV.
+
+ON THE VALUATION AND ANALYSIS OF MANURES.
+
+
+_Value of Chemical Analysis._
+
+The value of a manure to the farmer depends on the proportion of
+_nitrogen_, _phosphoric acid_, and _potash_ it contains, as well as--and
+this is hardly less important--the condition in which the ingredients
+are present. Since these facts can alone be determined by a chemical
+analysis, it is obvious that manures should always be purchased with a
+chemical analysis. It is unfortunate, however, that very often a
+chemical analysis, even when procured, is unintelligible. It may be of
+advantage, therefore, to say a word or two on the correct interpretation
+of the significance of the data furnished in the ordinary chemical
+analysis of manures.
+
+
+_Interpretation of Chemical Analysis._
+
+The first thing that the farmer ought to look for in the analysis of a
+manure is the amount of nitrogen, phosphoric acid, and potash which the
+manure contains.
+
+
+_Nitrogen._
+
+The percentage of nitrogen in a manure is generally stated as equal to
+its equivalent percentage of ammonia. Very often, indeed, in the older
+analyses, its equivalent of ammonia was alone stated. Now this statement
+does not necessarily imply that the nitrogen in a manure is actually
+present in the form of ammonia. Thus, for example, when it is stated in
+an analysis of bone-meal that it contains 3.5 per cent of nitrogen,
+equal to 4.20 per cent of ammonia, it is not to be inferred that
+bone-meal actually contains nitrogen in the form of ammonia. In point of
+fact the nitrogen is present in an insoluble, slowly available, organic
+form, which possesses a manurial value very inferior to that possessed
+by ammonia. This custom is a most unfortunate one, and is much to be
+regretted, as it is often liable to give rise to serious
+misunderstanding. It must be remembered, therefore, that an ordinary
+chemical analysis does not always specify the exact form in which
+nitrogen is actually present. It is nevertheless of importance for the
+farmer to know this, of which the nature of the manure analysed is
+generally a good indication. Unfortunately this is not shown in the case
+of _mixed_ manures; and this constitutes one of the reasons why mixed
+manures are sometimes to be regarded with suspicion.
+
+
+_Phosphoric Acid._
+
+The amount of phosphates present in a manure is usually stated in its
+analysis as so much phosphoric acid, while in a footnote the quantity of
+tricalcic (or ordinary bone) phosphate this amount is equivalent to is
+also given, this being the unit of valuation. When the phosphates are in
+a soluble condition they are stated as such, and at the same time a
+statement is made as to the quantity of tricalcic phosphate which would
+be required to furnish this amount by treatment with sulphuric acid.
+Thus, for example, in an analysis of a superphosphate of lime, the
+statement, _monocalcic phosphate, 17.3 per cent, equal to tricalcic
+phosphate rendered "soluble," 27.2 per cent_, means that it would
+require 27.2 per cent of tricalcic phosphate to furnish 17.3 per cent of
+soluble phosphate. Paradoxically enough, the former amount is called
+_"soluble" phosphate_, and such a superphosphate as the above would be
+described as containing 27.2 per cent of "soluble" phosphate.
+
+Again, there are different forms of the so-called "insoluble"
+phosphates,[248] although they are often not distinguished in a chemical
+analysis. As we have already pointed out in the chapter on Basic Slag,
+phosphoric acid occurs in the slag in the form of tetrabasic phosphate
+of lime, although it is invariably stated in analysis as so much
+tricalcic phosphate. Then we have the so-called dibasic phosphate of
+lime, the form into which soluble phosphate in superphosphate is
+converted when "reversion" takes place. Hitherto it has not been
+customary in this country--although the custom is prevalent both on the
+Continent and in America--to distinguish in the analysis of a
+superphosphate the "reverted" phosphate from the undissolved phosphate;
+since the superior value of the former as a manure is not recognised in
+the manure-trade.[249]
+
+
+_Importance of Mechanical Condition of Phosphate._
+
+A further point to which it is desirable to draw attention is the
+_mechanical_ condition of the different insoluble phosphates, which has
+an important influence on their value. A very wide difference, for
+example, exists between the value of phosphate of lime in such a manure
+as Malden guano and in the crystalline mineral apatite; although,
+chemically considered, the form in which the phosphoric acid is present
+is the same in both substances.
+
+
+_Potash._
+
+Potash ought only to occur in a soluble form in manures. It is generally
+stated as so much potash, and in a footnote the equivalent amount of
+muriate or sulphate of potash is given, the former being the more
+concentrated form of potash.
+
+For purposes of reference a table will be found in the Appendix[250]
+giving some useful factors for converting different forms of nitrogen,
+phosphoric acid, and potash into one another.
+
+
+_Other Items in the Chemical Analysis of Manures._
+
+The other items in the analysis of a manure are of comparatively
+secondary importance compared with those already named. Among them may
+be mentioned the _moisture_, the _insoluble matter_, and the _organic
+matter_. The amount of moisture and the amount of sand are two items of
+importance, since, if these are excessive, they afford presumption that
+the manure has been adulterated.
+
+
+_Fertilisers and Feeding Stuffs Act._
+
+An Act was passed, and came into operation in January 1894, for the
+purpose of compelling every vendor of manure manufactured in this
+country or imported from abroad to give to the purchaser "an invoice
+stating the name of the article, and whether it is an artificially
+compounded article or not, and what is at least the percentage of the
+nitrogen, soluble and insoluble phosphates, and potash, if any,
+contained in the article, and this invoice shall have the same effect
+as a warranty by the seller of the statements contained therein."
+
+
+_Different Methods of Valuing Manures._
+
+The monetary value of a manure depends upon a number of more or less
+complicated commercial considerations, such as the questions of supply
+and demand, &c., which need not here be discussed, and which similarly
+regulate the monetary value of any other article of commerce.
+
+
+_"Unit" Value of Manurial Ingredients._
+
+For the purpose of affording data for ascertaining the approximate value
+of a manure, tables have been drawn up giving what is called the "unit"
+value of the different manurial ingredients in various manures. This is
+obtained by dividing the market value of a manure per ton by the
+percentage of nitrogen, phosphoric acid, and potash it contains. Thus,
+for example, sulphate of ammonia of 97 per cent purity contains 25 per
+cent of ammonia, and at present (Dec. 1893) is valued at £13, 15s. per
+ton. In order to obtain the unit value of ammonia in sulphate of
+ammonia, we have only to divide £13, 15s. by 25, which gives us 11s. The
+value of such tables depends on the competence of those drawing them up,
+and they require to be subjected to constant revision. In the Appendix
+will be found two of these tables, taken from the 'Transactions of the
+Highland and Agricultural Society of Scotland.'[251]
+
+
+_Intrinsic Value of Manures._
+
+But there is another way of valuing manures, and that is by attempting
+to ascertain what their intrinsic worth is in producing an increase in
+the returns of the crops. Of course it may be said that the intrinsic
+worth of manure affects directly its market value. This is doubtless
+true, but it is not the only factor in determining the market value of a
+manure.
+
+Again, the intrinsic worth of a manure may be said to vary according to
+the soil to which it is applied and the climatic conditions. This being
+so, it is important for every farmer to try and ascertain for himself
+what the intrinsic value of different manures is on the soil of his
+farm; and this can only be done by carrying out manuring experiments for
+himself. This leads us to say a word or two on the important subject of
+
+
+_Field Experiments._
+
+It is impossible that every farm should be able to support an experiment
+station for the purpose of carrying out elaborate experiments on the
+effect of different manures on different crops. Nevertheless it is
+possible and highly desirable for _every_ farmer who is engaged in
+arable farming on any scale to carry out simple experiments for the
+purpose of ascertaining the characteristic manurial requirements of his
+soil. This can be done at the expenditure of a little time and trouble,
+and should be carried out in the following way. The field on which it is
+desired to carry out the experiments should be divided into the
+requisite number of experiment plots. These, which may be the tenth,
+twentieth, or fortieth of an acre in extent, should be, if possible, on
+a level piece of ground--all of them equally free from the shelter of
+hedge or tree, and otherwise subjected to the same conditions. The
+nature of the soil of the different plots, as well as its past
+treatment, should be similar. It is desirable, in order to minimise
+experimental error as much as possible, to carry out the experiments in
+duplicate, or even triplicate. In the first place, there should be what
+is called a _nothing_ plot--_i.e._, a plot receiving no manure. The
+produce obtained from this plot, compared with the produce obtained from
+the other manured plots, will thus furnish data for estimating the
+respective amounts of increase obtained by different manures. One very
+simple kind of experiment is what is called the "seven-plot" test. It
+consists in testing the results obtained by using nitrogenous,
+phosphatic, and potash manures alone and in different combinations. Thus
+the plots would be manured respectively as follows:--
+
+No. No.
+ 1. Nothing plot. | 5. Nitrogen and phosphates.
+ 2. Nitrogen. | 6. Nitrogen and potash.
+ 3. Phosphates. | 7. Phosphates and potash.
+ 4. Potash.
+
+The subjects of other experiments might be such as the respective values
+of nitrogen in the different forms of sulphate of ammonia and nitrate of
+soda; phosphoric acid as superphosphate, and in an undissolved form as
+Thomas-slag; the relative importance of artificial and farmyard manure;
+the effect of manures applied at different times, as well as the effect
+of different quantities of the same manure; the most economical manures
+for different kinds of crops; and numerous other interesting problems
+connected with the practical application of manures.
+
+In carrying out these experiments, care should be taken not to have the
+experimental plots _immediately_ adjoining one another, as the manure
+applied to the one plot may, by soaking through the soil, affect the
+result on the adjoining plot. Especial note ought to be taken of the
+weather during the progress of the experiment. In order to make such
+experiments as valuable as possible, they ought to be continued year
+after year. At the conclusion of the experiment the produce obtained
+from each plot should be carefully weighed.
+
+
+_Educational Value of Field Experiments._
+
+The educative value of such experiments is very great, and in this
+connection the remarks made by Mr F. J. Cooke, in a recent lecture
+delivered to the London Farmers' Club, are worthy of most careful
+consideration.
+
+"Local experiments," he says, "teach the simple principles which should
+determine the selection of manures, as well as scientific accuracy and
+method in their use. The value of experiments is thus brought home to
+men who would not go far to discover it; and the practice of a few
+simple trials upon a correct system, each on his own farm, is
+encouraged. That such trials may be conducted with very little expense
+to the farmer, or other difficult qualifications, and yet to his great
+practical advantage, I will venture to assert on the ground of my own
+personal experience. For some twenty years I have annually conducted
+private experiments on a very humble scale, and am not aware of any
+other separate practice which has been so useful to me. It has been
+pursued upon two light-land farms in different parts of the same county.
+Yet, in respect of manurial requirements, the proper treatment for one
+of them has differed so essentially from the other that a common
+practice upon both would have been simply ruinous."
+
+
+_Value of Manures deduced from Experiments._
+
+Tables have been constructed for the purpose of showing the comparative
+value of different kinds of manures as deduced from such experiments,
+and may be fittingly compared with the tables giving the trade prices.
+We have already quoted some of these tables in the Appendix to the
+chapter on Mineral Phosphates. These tables show the relative intrinsic
+value of different forms of phosphatic manures. In the Appendix[252] to
+this chapter tables showing the relative value of different kinds of
+nitrogenous and potash manures will be found.
+
+
+_Value of Unexhausted Manures._
+
+A subject which has had much attention devoted to it of late years is
+the question of the value of unexhausted manures in the soil. In the
+Agricultural Holdings Act special provision is made for giving
+compensation to the out-going tenant of a farm for unexhausted manures
+in the soil. The Act has given rise to endless disputes between landlord
+and tenant, owing to the extreme difficulty of arriving at a
+satisfactory estimate of what the value of the unexhausted manures in
+reality is. The difficulty arises from the fact that we have not
+sufficient data available for guiding us in estimating this value, which
+further varies under different conditions. The fertilising ingredients
+of a soil are present in the soil for the most part in an inert
+condition, from which they are only slowly converted into an available
+form.
+
+
+_Potential Fertility of a Soil._
+
+As indicating the total amount of the more important mineral ingredients
+present in a soil, it may be mentioned that it has been calculated, in
+the case of a poor sandy soil, _that the amount of potash it contains_
+(_provided it were in an available condition_) would be sufficient to
+yield three or four average crops of potatoes; of phosphates, nineteen
+average crops; and of lime, seventy-three. But then only a very small
+amount of this fertilising matter is in a readily available form.
+
+It is for this reason that artificial manures, although added in such
+small amounts, exercise so striking an influence in increasing plants'
+growth. Their effect, however, is to a large extent only of a temporary
+nature; and in attempting to assess the unexhausted value of a manure a
+year or two after its application, we must remember this fact.
+
+Some manures are very speedily taken up by plants, and some are very
+easily washed out of the soil. Others, again, it would seem highly
+probable, have a tendency to become converted into a more or less inert
+condition after a while. This remark may be especially applied to the
+fertilising constituents (chiefly nitrogen) in farmyard manure.[253] The
+whole question, however, is little understood. One or two points may be
+drawn attention to. In the first place, it may be safely affirmed that
+little direct effect can be expected from such quickly available and
+easily soluble forms of nitrogenous manures as nitrate of soda and
+sulphate of ammonia a year after application. Potash and phosphates, on
+the other hand, may exercise an effect for a considerably longer period;
+and what the length of this period may be will depend on their amount
+and condition. Thus it is not likely that superphosphate will have much
+effect more than two years after application. On the other hand, such
+manures as bones, basic slag, and farmyard manure may exert an
+appreciable influence for a number of years. How long exactly, it is
+wellnigh impossible to say, the rate at which they are applied and the
+nature of the soil having an important influence.
+
+
+_Tables of Value of Unexhausted Manures._
+
+Numerous tables have been drawn up for the purpose of guiding farmers in
+estimating this unexhausted value at different periods after
+application, and in the case of different manures. Such tables, as a
+rule, furnish only very rough approximations, and are little better than
+mere guess-work. Still more complicated is the attempt to assess the
+manurial value of foods consumed by the stock of the farm. Lawes and
+Gilbert have devoted much attention to the elucidation of this difficult
+question, and have drawn up most elaborate and valuable tables,
+furnishing data for calculating unexhausted manure value in the case of
+commonly used foods. These tables are given in the Appendix.[254] In
+them will be found the manurial value of different cattle-foods,
+calculated on the basis of numerous experiments carried out at
+Rothamsted.
+
+Thus these experiments have demonstrated that, on an average, probably
+not more than _one-tenth_ of the nitrogen, phosphoric acid, and potash a
+food contains is removed from the food in its passage through the animal
+system. The exact amount will obviously depend on a variety of
+conditions, referred to already in a previous chapter.[255]
+
+In explanation of these tables, it may be pointed out that Table I.
+gives the total quantities of the three fertilising ingredients in
+various foods; while Table II. shows the proportion retained in the
+animal body and the proportion voided in the manure, as well as the
+manurial value of the food, assuming that it exercises its full
+theoretical effect. As this, however, is never fully realised, it is
+necessary to make some deduction. The deduction suggested by the
+Rothamsted experimenters, on the basis of their wide experience, is 50
+per cent for food consumed within the last year. That is to say, the
+manurial value of food consumed during the last year is _only one-half
+its theoretical value_. For food consumed within the last year but one,
+they suggest a deduction of one-third of the allowance for last year;
+while for food consumed three years back, a deduction of one-third from
+this latter sum should be made; and so on for whatever number of years,
+down to eight, may be taken.
+
+
+FOOTNOTES:
+
+[248] The term _insoluble phosphates_ is an unfortunate one, as the word
+insoluble is purely relative in its significance. _Undissolved_
+phosphates would be a better term.
+
+[249] The amount of "reverted" phosphate is estimated by _the ammonium
+citrate process_.
+
+[250] See Note I., p. 553.
+
+[251] See Note II., p. 554.
+
+[252] See Note III., p. 556.
+
+[253] See Chapter on Farmyard Manure, p. 271.
+
+[254] See Note IV., p. 557.
+
+[255] See Chapter on Farmyard Manure, pp. 224-236.
+
+
+
+
+APPENDIX TO CHAPTER XXV.
+
+
+NOTE I. (p. 543).
+
+USEFUL FACTORS FOR CALCULATING THE PERCENTAGE OF IMPORTANT MANURIAL
+INGREDIENTS IN A MANURE INTO THEIR DIFFERENT COMPOUNDS. (From the
+'Transactions of the Highland and Agricultural Society.')
+
+----------------------------+------------+----------------------
+ | Multiplied | Gives corresponding
+ Amount of | by | amount of
+----------------------------+------------+----------------------
+Nitrogen | 1.214 | Ammonia.
+ " | 6.3 | Albuminoid matter.
+Ammonia | .824 | Nitrogen.
+ " | 3.882 | Sulphate of ammonia.
+ " | 3.147 | Muriate of ammonia.
+ " | 3.706 | Nitric acid.
+ " | 5.0 | Nitrate of soda.
+Potash (anhydrous) | 1.85 | Sulphate of potash.
+ " | 1.585 | Muriate of potash.
+Phosphoric acid (anhydrous) | 2.183 | Phosphate of lime.
+ " " | 1.4 | Biphosphate.
+ " " | 1.648 | Soluble phosphate.
+Soluble phosphate | 1.325 | Phosphate of lime.
+Biphosphate | 1.566 | "
+Lime | 1.845 | "
+ " | 1.786 | Carbonate of lime.
+Chlorine | 1.648 | Chloride of sodium.
+----------------------------+------------+----------------------
+
+
+NOTES II. (p. 545).
+
+UNITS TO BE USED IN DETERMINING THE COMMERCIAL VALUE OF
+MANURES.
+
+_For Season 1893._
+
+A: Ichaboe.
+B: Peruvian (riddled).
+C: Fish guano.
+D: Frey Bentos guano.
+E: Steamed bone-flour.
+F: Dissolved or vitriolated bones.
+G: Superphosphates.
+H: Genuine.
+I: Genuine.
+J: Average.
+
+-----------------+-----------+-----------------+-----------+
+ | Guanos. | Scrap manures. | |
+ Items to be +-----+-----+-----+-----------+ Bone-meal.|
+ valued. | A | B | C | D | |
+-----------------+-----+-----+-----+-----+-----+-----+-----+
+ Classes | H | I | |_a._ |_b._ |_a._ |_b._ |
+-----------------+-----+-----+-----+-----+-----+-----+-----+
+Phosphates | | | | | | | |
+ Dissolved | - | - | - | - | - | - | - |
+ Undissolved-- | 2/-| 2/-| 1/5| 1/6| 1/4| 1/4| 1/3|
+ Ammonia | 16/-| 17/6| 10/-| 11/6| 10/-| 10/-| 9/6|
+ Potash | - | 3/6| - | - | - | - | - |
+ | | | | | | | |
+Prices per ton, | | | | | | | |
+ March 1893-- | | | | | | | |
+ From |250/-|230/-|130/-|150/-|120/-|105/-|100/-|
+ To |270/-|290/-|150/-|180/-|140/-|115/-|110/-|
+-----------------+-----+-----+-----+-----+-----+-----+-----+
+
+-----------------+-----+-----+-----+-----------------
+ | | | |
+ Items to be | E | F | G | Dissolved
+ valued. | | | | Compounds.
+-----------------+-----+-----+-----+-----+-----+-----
+ Classes |_a._ | | | From| To | J
+-----------------+-----+-----+-----+-----+-----+-----
+Phosphates | | | | | |
+ Dissolved | - | 2/6| - | 2/-| 2/6| 2/3
+ Undissolved-- | 1/5| 1/6| 1/11| 1/3| 1/9| 1/6
+ Ammonia | 10/-| 11/6| - | 10/-| 12/-| 11/-
+ Potash | - | - | - | 3/4| 3/8| 3/6
+ | | | | | |
+Prices per ton, | | | | | |
+ March 1893-- | | | | | |
+ From | 95/-| 95/-| 45/-| - | - | -
+ To |110/-|110/-| 60/-| - | - | -
+-----------------+-----+-----+-----+-----+-----+-----
+
+
+CASH PRICES OF DIFFERENT MANURES, MARCH 1893.
+
+---------------------------------+-----------+----------+--------------
+ | |Price per |
+ MANURES. | Guarantee.| ton. | Unit.
+---------------------------------+-----------+----------+--------------
+ | Per cent. |_£ s. d._|
+Sulphate of ammonia, 97 per cent | 24 Am. | 11 10 0 | Am. = 9/7
+Nitrate of soda, 95 per cent | 19 " | 10 5 0 | " = 10/9
+Castor-cake dust | 5.5 " | 3 10 0 | " = 12/9
+Horn-dust | 15 " | 8 10 0 | " = 11/4
+Dried blood | 15 " | 8 0 0 | " = 10/7
+Muriate of potash, 80 per cent | 50 Pot | 8 15 0 | Pot.= 3/6
+Sulphate of potash, 50 per cent | 27 " | 5 5 0 | " = 3/10
+Kainit, 23 per cent | 12 " | 2 0 0 | " = 3/4
+Nitrate of potash, 73 per cent | {14 Am.} | 14 10 0 | {Am. = 10/}
+ | {40 Pot.} | | {Pot.= 3/9}
+Ground Charleston phosphate | 57 Phos. | 3 0 0 | Phos.=1/
+Belgian phosphate | 50 " | 2 5 0 | " = 0/11
+Thomas-slag (fine) Scotch | 30 " | 1 16 0 | " = 1/2
+Thomas-slag (fine) English | 37 " | 2 3 0 | " = 1/2
+Phosphatic guano | {67 " } | 5 0 0 | {" = 1/4}
+ | {1 Am. } | | {Am. = 10/}
+---------------------------------+-----------+----------+--------------
+
+
+NOTE III. (p. 549).
+
+TABLES SHOWING RELATIVE MANURIAL VALUE OF NITROGEN AND POTASH IN
+DIFFERENT SUBSTANCES.
+
+ _Wolff, 1893._
+
+Nitrogen in form of ammonia and nitrates, and easily
+ decomposable organic compounds, as dried blood,
+ flesh-meal, meat-meal, Peruvian guano, and as urate 100
+ " in fine steamed bone-meal, fish-guano, oilcakes, and
+ better kinds of artificial guano 85
+ " in fine bone-meal and horn-meal 77
+ " in coarse bones and horn-shavings, woollen refuse,
+ farmyard manure, and poudrette 61
+
+ _American, 1892._
+
+ " in ammonia salts 100
+ " as nitrates 86
+ " in dry and fine-ground fish, meat, and blood 91
+ " in cotton-seed meal, and castor pomace 86
+ " in fine bone and tankage 86
+ " in medium bone and tankage 68
+ " in coarser bone and tankage 43
+ " in hair and horn-shavings, and coarse fish scrap 40
+Potash as high-grade sulphate, and in forms free from muriates
+ (or chlorides) 100
+ " as muriate 82
+
+Professor Wagner has drawn up, from numerous experiments, the relative
+manurial values of different nitrogenous manures, which he rates as
+follows:--
+
+Nitrate of soda 100
+Sulphate of ammonia 90
+Blood-meal, horn-meal, and green vegetable matter 70
+Finely ground steamed bone-meal, fish-meal, and meat-meal
+ guano 60
+Farmyard manure 45
+Shoddy 30
+Leather-meal 20
+
+
+NOTE IV. (p. 551).
+
+TABLE I.--AVERAGE COMPOSITION, PER CENT AND PER TON, OF
+CATTLE-FOODS.
+
+-----+-------------------+-----------------------------------------------+
+ | | PER CENT. |
+ NO. | FOODS. +---------+--------+---------+--------+---------+
+ | | Dry | Nitro- | Mineral | Phos- | Potash. |
+ | | Matter. | gen. | Matter | phoric | |
+ | | | | (Ash). | Acid | |
+-----+-------------------+---------+--------+---------+--------+---------+
+ | | per | per | per | per | per |
+ | | cent. | cent. | cent. | cent. | cent. |
+ 1 | Linseed | 90.00 | 3.60 | 4.00 | 1.54 | 1.37 |
+ 2 | Linseed-cake | 88.50 | 4.75 | 6.50 | 2.00 | 1.40 |
+ 3 | Decorticated | | | | | |
+ | cotton cake | 90.00 | 6.60 | 7.00 | 3.10 | 2.00 |
+ 4 | Palm-nut-cake | 91.00 | 2.50 | 3.60 | 1.20 | 0.50 |
+ 5 | Undecorticated | | | | | |
+ | cotton-cake | 87.00 | 3.75 | 6.00 | 2.00 | 2.00 |
+ 6 | Cocoa-nut-cake | 90.00 | 3.40 | 6.00 | 1.40 | 2.00 |
+ 7 | Rape-cake | 89.00 | 4.90 | 7.50 | 2.50 | 1.50 |
+-----+-------------------+---------+--------+---------+--------+---------+
+ 8 | Peas | 85.00 | 3.60 | 2.50 | 0.85 | 0.96 |
+ 9 | Beans | 85.00 | 4.00 | 3.00 | 1.10 | 1.30 |
+ 10 | Lentils | 88.00 | 4.20 | 4.00 | 0.75 | 0.70 |
+ 11 | Tares (seed) | 84.00 | 4.20 | 2.50 | 0.80 | 0.80 |
+-----+-------------------+---------+--------+---------+--------+---------+
+ 12 | Indian corn | 88.00 | 1.70 | 1.40 | 0.60 | 0.37 |
+ 13 | Wheat | 85.00 | 1.80 | 1.70 | 0.85 | 0.53 |
+ 14 | Malt | 94.00 | 1.70 | 2.50 | 0.80 | 0.50 |
+ 15 | Barley | 84.00 | 1.65 | 2.20 | 0.75 | 0.55 |
+ 16 | Oats | 86.00 | 2.00 | 2.80 | 0.60 | 0.50 |
+ 17 | Rice-meal* | 90.00 | 1.90 | 7.50 | (0.60) | (0.37) |
+ 18 | Locust-beans* | 85.00 | 1.20 | 2.50 | - | - |
+-----+-------------------+---------+--------+---------+--------+---------+
+ 19 | Malt-combs | 90.00 | 3.90 | 8.00 | 2.00 | 2.00 |
+ 20 | Fine pollard | 86.00 | 2.45 | 5.50 | 2.90 | 1.46 |
+ 21 | Coarse pollard | 86.00 | 2.50 | 6.40 | 3.50 | 1.50 |
+ 22 | Bran | 86.00 | 2.50 | 6.50 | 3.60 | 1.45 |
+-----+-------------------+---------+--------+---------+--------+---------+
+ 23 | Clover-hay | 83.00 | 2.40 | 7.00 | 0.57 | 1.50 |
+ 24 | Meadow-hay | 84.00 | 1.50 | 6.50 | 0.40 | 1.60 |
+-----+-------------------+---------+--------+---------+--------+---------+
+ 25 | Pea-straw | 82.50 | 1.00 | 5.50 | 0.35 | 1.00 |
+ 26 | Oat-straw | 83.00 | 0.50 | 5.50 | 0.24 | 1.00 |
+ 27 | Wheat-straw | 84.00 | 0.45 | 5.00 | 0.24 | 0.80 |
+ 28 | Barley-straw | 85.00 | 0.40 | 4.50 | 0.18 | 1.00 |
+ 29 | Bean-straw | 82.50 | 0.90 | 5.00 | 0.30 | 1.00 |
+-----+-------------------+---------+--------+---------+--------+---------+
+ 30 | Potatoes | 25.00 | 0.25 | 1.00 | 0.15 | 0.55 |
+ 31 | Carrots | 14.00 | 0.20 | 0.90 | 0.09 | 0.28 |
+ 32 | Parsnips | 16.00 | 0.22 | 1.00 | 0.19 | 0.36 |
+ 33 | Swedish turnips | 11.00 | 0.25 | 0.60 | 0.06 | 0.22 |
+ 34 | Mangel-wurzels | 12.50 | 0.22 | 1.00 | 0.07 | 0.40 |
+ 35 | Yellow turnips* | 9.00 | 0.20 | 0.65 | (0.06) | (0.22) |
+ 36 | White turnips | 8.00 | 0.18 | 0.68 | 0.05 | 0.30 |
+-----+-------------------+---------+--------+---------+--------+---------+
+
+
+-----+-------------------+-------------------------------
+ | | PER TON.
+ | +-----------+---------+---------
+ NO. | FOODS. | Nitrogen. | Phos- | Potash.
+ | | | phoric |
+ | | | Acid |
+-----+-------------------+-----------+---------+---------
+ | | lb. | lb. | lb.
+ 1 | Linseed | 80.64 | 34.50 | 30.69
+ 2 | Linseed-cake | 106.40 | 44.80 | 31.36
+ 3 | Decorticated | | |
+ | cotton cake | 147.84 | 69.44 | 44.80
+ 4 | Palm-nut-cake | 56.00 | 26.88 | 11.20
+ 5 | Undecorticated | | |
+ | cotton-cake | 84.00 | 44.80 | 44.80
+ 6 | Cocoa-nut-cake | 76.16 | 31.36 | 44.80
+ 7 | Rape-cake | 109.76 | 56.00 | 33.60
+-----+-------------------+-----------+---------+---------
+ 8 | Peas | 80.64 | 19.04 | 21.50
+ 9 | Beans | 89.60 | 24.64 | 29.12
+ 10 | Lentils | 94.08 | 16.80 | 15.68
+ 11 | Tares (seed) | 94.08 | 17.92 | 17.92
+-----+-------------------+-----------+---------+---------
+ 12 | Indian corn | 38.08 | 13.44 | 8.29
+ 13 | Wheat | 40.32 | 19.04 | 11.87
+ 14 | Malt | 38.08 | 17.92 | 11.20
+ 15 | Barley | 36.96 | 16.80 | 12.32
+ 16 | Oats | 44.80 | 13.44 | 11.20
+ 17 | Rice-meal* | 42.56 | (13.44) | (8.29)
+ 18 | Locust-beans* | 26.88 | - | -
+-----+-------------------+-----------+---------+---------
+ 19 | Malt-combs | 87.36 | 44.80 | 44.80
+ 20 | Fine pollard | 54.88 | 64.96 | 32.70
+ 21 | Coarse pollard | 56.00 | 78.40 | 33.60
+ 22 | Bran | 56.00 | 80.64 | 32.48
+-----+-------------------+-----------+---------+---------
+ 23 | Clover-hay | 53.76 | 12.77 | 33.60
+ 24 | Meadow-hay | 33.60 | 8.96 | 35.84
+-----+-------------------+-----------+---------+---------
+ 25 | Pea-straw | 22.40 | 7.84 | 22.40
+ 26 | Oat-straw | 11.20 | 5.38 | 22.40
+ 27 | Wheat-straw | 10.08 | 5.38 | 17.92
+ 28 | Barley-straw | 8.96 | 4.03 | 22.40
+ 29 | Bean-straw | 20.16 | 6.72 | 22.40
+-----+-------------------+-----------+---------+---------
+ 30 | Potatoes | 5.60 | 3.36 | 12.32
+ 31 | Carrots | 4.48 | 2.02 | 6.27
+ 32 | Parsnips | 4.93 | 4.26 | 8.06
+ 33 | Swedish turnips | 5.60 | 1.34 | 4.93
+ 34 | Mangel-wurzels | 4.93 | 1.57 | 8.96
+ 35 | Yellow turnips* | 4.48 | (1.34) | (4.93)
+ 36 | White turnips | 4.03 | 1.12 | 6.72
+-----+-------------------+-----------+---------+---------
+* In the case of neither rice-meal, locust-beans, nor yellow turnips have
+records of ash analyses been found. For rice-meal the same percentages of
+phosphoric acid and potash as in Indian corn, and for yellow turnips the
+same as in swedes, are provisionally adopted; but in all the Tables the
+assumed results are given in parentheses. For locust-beans no figure has
+been assumed, and the columns are left blank.
+
+
+NOTE IV.
+
+TABLE II.--LAWES' & GILBERT'S TABLES FOR CALCULATING UNEXHAUSTED
+VALUE OF MANURES.
+
+KEY:
+A - Fattening Increase in Live Weight (Oxen or Sheep).
+B - In Food.
+C - In Fattening Increase (at 1.27 per cent).
+D - In Manure.
+E - Food to 1 Increase.
+F - Increase per ton of Food.
+G - Per cent.
+H - Per ton.
+I - From 1 ton of Food.
+J - Per cent of total consumed.
+K - Total remaining for Manure.
+L - Nitrogen equal Ammonia.
+M - Value of Ammonia at 6d per lb.
+
+---+---------------+-----------+----------------------------------------------+
+ | | | NITROGEN. |
+ | | |------------+-----------+---------------------|
+ | | A | B | C | D |
+ | DESCRIPTION |-----+-----+-----+------+-----+-----+------+-----+--------|
+NO.| OF FOOD. | E | F | G | H | I | J | K | L | M |
+---+---------------+-----+-----+-----+------+-----+-----+------+-----+--------+
+ | | | lb. | % | lb. | lb. | % | lb. | lb. |£ s. d. |
+ 1 |Linseed | 5.0|448.0| 3.60| 80.64| 5.69| 7.06| 74.95| 91.0|2 5 6 |
+ 2 |Linseed-cake | 6.0|373.3| 4.75|106.40| 4.74| 4.45|101.66|123.4|3 1 8 |
+ 3 |Decorticated | | | | | | | | | |
+ | cotton-cake | 6.5|344.6| 6.60|147.84| 4.38| 2.96|143.46|174.2|4 7 1 |
+ 4 |Palm-nut-cake | 7.0|320.0| 2.50| 56.00| 4.06| 7.25| 51.94| 63.1|1 11 7 |
+ 5 |Undecorticated | | | | | | | | | |
+ | cotton-cake | 8.0|280.0| 3.75| 84.00| 3.56| 4.24| 80.44| 97.7|2 8 10 |
+ 6 |Cocoa-nut-cake | 8.0|280.0| 3.40| 76.16| 3.56| 4.67| 72.60| 88.2|2 4 1 |
+ 7 |Rape-cake |(10) |(224)| 4.90|109.76| 2.84| 2.59|106.92|129.8|3 4 11 |
+ | |-----+-----+-----+------+-----+-----+------+-----+--------+
+ 8 |Peas | 7.0|320.0| 3.60| 80.64| 4.06| 5.03| 76.58| 93.0|2 6 6 |
+ 9 |Beans | 7.0|320.0| 4.00| 89.60| 4.06| 4.53| 85.54|103.9|2 11 11 |
+10 |Lentils | 7.0|320.0| 4.20| 94.08| 4.06| 4.32| 90.02|109.3|2 14 8 |
+11 |Tares (seed) | 7.0|320.0| 4.20| 94.08| 4.06| 4.32| 90.02|109.3|2 14 8 |
+ | |-----+-----+-----+------+-----+-----+------+-----+--------+
+12 |Indian corn | 7.2|311.1| 1.70| 38.08| 3.95|10.37| 34.13| 41.4|1 0 9 |
+13 |Wheat | 7.2|311.1| 1.80| 40.32| 3.95| 9.80| 36.37| 44.2|1 2 1 |
+14 |Malt | 7.0|320.0| 1.70| 38.08| 4.06|10.66| 34.02| 41.3|1 0 8 |
+15 |Barley | 7.2|311.1| 1.65| 36.96| 3.95|10.69| 33.01| 40.1|1 0 1 |
+16 |Oats | 7.5|298.7| 2.00| 44.80| 3.79| 8.46| 41.01| 49.8|1 4 11 |
+17 |Rice-meal | 7.5|298.7| 1.90| 42.56| 3.79| 8.91| 38.77| 47.1|1 3 6 |
+18 |Locust-beans | 9.0|248.9| 1.20| 26.88| 3.16|11.76| 23.72| 28.8|0 14 5 |
+ | |-----+-----+-----+------+-----+-----+------+-----+--------+
+19 |Malt-combs | 8.0|280.0| 3.90| 87.36| 3.56| 4.08| 83.80|101.8|2 10 11 |
+20 |Fine pollard | 7.5|298.7| 2.45| 54.88| 3.79| 6.91| 51.09| 62.0|1 11 0 |
+21 |Coarse pollard | 8.0|280.0| 2.50| 56.00| 3.56| 6.35| 52.44| 63.7|1 11 10 |
+22 |Bran | 9.0|248.9| 2.50| 56.00| 3.16| 5.64| 52.84| 64.2|1 12 1 |
+ | |-----+-----+-----+------+-----+-----+------+-----+--------+
+23 |Clover-hay | 14.0|160.0| 2.40| 53.76| 2.03| 3.78| 51.73| 62.8|1 11 5 |
+24 |Meadow-hay | 15.0|149.3| 1.50| 33.60| 1.90| 5.65| 31.70| 38.5|0 19 3 |
+ | |-----+-----+-----+------+-----+-----+------+-----+--------+
+25 |Pea-straw | 16.0|140.0| 1.00| 22.40| 1.78| 7.95| 20.62| 25.0|0 12 6 |
+26 |Oat-straw | 18.0|124.4| 0.50| 11.20| 1.58|14.11| 9.62| 11.7|0 5 10 |
+27 |Wheat-straw | 21.0|106.7| 0.45| 10.08| 1.36|13.49| 8.72| 10.6|0 5 4 |
+28 |Barley-straw | 23.0| 97.4| 0.40| 8.96| 1.24|13.84| 7.72| 9.4|0 4 8 |
+29 |Bean-straw | 22.0|101.8| 0.90| 20.16| 1.29| 6.39| 18.87| 22.9|0 11 6 |
+ | |-----+-----+-----+------+-----+-----+------+-----+------- +
+30 |Potatoes | 60.0| 37.3| 0.25| 5.60| 0.47| 8.39| 5.13| 6.2|0 3 1 |
+31 |Carrots | 85.7| 26.1| 0.20| 4.48| 0.33| 7.37| 4.15| 5.0|0 2 6 |
+32 |Parsnips | 75.0| 29.9| 0.22| 4.93| 0.38| 7.71| 4.55| 5.5|0 2 9 |
+33 |Swedish turnips|109.1| 20.5| 0.25| 5.60| 0.26| 4.64| 5.34| 6.5|0 3 3 |
+34 |Mangel-wurzels | 96.0| 23.3| 0.22| 4.93| 0.30| 6.09| 4.63| 5.6|0 2 10 |
+35 |Yellow turnips |133.3| 16.8| 0.20| 4.48| 0.21| 4.69| 4.27| 5.2|0 2 7 |
+36 |White turnips |150.0| 14.9| 0.18| 4.03| 0.19| 4.71| 3.84| 4.7|0 2 4 |
+---+---------------+-----+-----+-----+------+-----+-----+------+-----+--------+
+
+
+
+KEY:
+ N - In Food.
+ O - In Fattening Increase at (0.86 per cent).
+ P - In Manure.
+ Q - In Food.
+ R - In Fattening Increase at (0.11 per cent).
+ S - In Manure.
+ T - Per cent.
+ U - Per ton.
+ V - From 1 ton of Food.
+ W - Per cent of total consumed.
+ X - Total remaining for Manure.
+ Y - Value at 3d per lb.
+ Z - Per cent.
+AA - Per ton.
+BB - From 1 ton of Food.
+CC - Per cent of total consumed.
+DD - Total remaining for Manure.
+EE - Value at 2-1/2d. per lb.
+FF - Total original Manure value per ton of Food consumed.
+
+---+---------------+------------------------------------------+
+ | | PHOSPHORIC ACID. |
+ |---------------+--------------+------------+--------------+
+ | | N | O | P |
+ | Description |------+-------+----+-------+-------+------+
+No.| of Food. | T | U | V | W | X | Y |
+---+---------------+------+-------+----+-------+-------+------+
+ | | % | lb. | lb.| % | lb. |s. d. |
+ 1 |Linseed | 1.54 | 34.50 |3.85| 11.16 | 30.65 | 7 8 |
+ 2 |Linseed-cake | 2.00 | 44.80 |3.21| 7.17 | 41.59 |10 5 |
+ 3 |Decorticated | | | | | | |
+ | cotton-cake | 3.10 | 69.44 |2.96| 4.26 | 66.48 |16 8 |
+ 4 |Palm-nut-cake | 1.20 | 26.88 |2.75| 10.23 | 24.13 | 6 0 |
+ 5 |Undecorticated | | | | | | |
+ | cotton-cake | 2.00 | 44.80 |2.41| 5.38 | 42.39 |10 7 |
+ 6 |Cocoa-nut-cake | 1.40 | 31.36 |2.41| 7.68 | 28.95 | 7 3 |
+ 7 |Rape-cake | 2.50 | 56.00 |1.93| 3.45 | 54.07 |13 6 |
+ | |------+-------+----+-------+-------+--- --+
+ 8 |Peas | 0.85 | 19.04 |2.75| 14.44 | 16.29 | 4 1 |
+ 9 |Beans | 1.10 | 24.64 |2.75| 11.10 | 21.89 | 5 6 |
+10 |Lentils | 0.75 | 16.80 |2.75| 16.37 | 14.05 | 3 6 |
+11 |Tares (seed) | 0.80 | 17.92 |2.75| 15.36 | 15.17 | 3 9 |
+ | |------+-------+----+-------+-------+--- --+
+12 |Indian corn | 0.60 | 13.44 |2.68| 19.94 | 10.76 | 2 8 |
+13 |Wheat | 9.85 | 19.04 |2.68| 14.08 | 16.36 | 4 1 |
+14 |Malt | 0.80 | 17.92 |2.75| 15.35 | 15.17 | 3 9 |
+15 |Barley | 0.75 | 16.80 |2.68| 15.95 | 14.12 | 3 6 |
+16 |Oats | 0.60 | 13.44 |2.57|(19.12)| 10.87 | 2 8 |
+17 |Rice-meal |(0.60)|(13.44)|2.57|(19.12)|(10.87)|(2 8)|
+18 |Locust-beans | - | - |2.14| - | - | - |
+ | |------+-------+----+-------+-------+------+
+19 |Malt-combs | 2.00 | 44.80 |2.41| 5.38 | 42.39 |10 7 |
+20 |Fine pollard | 2.90 | 64.96 |2.57| 3.96 | 62.39 |15 7 |
+21 |Coarse pollard | 3.50 | 78.40 |2.41| 3.07 | 75.99 |19 0 |
+22 |Bran | 3.60 | 80.64 |2.14| 2.65 | 78.50 |19 8 |
+ | |------+-------+----+-------+-------+------+
+23 |Clover-hay | 0.57 | 12.77 |1.38| 10.81 | 11.39 | 2 10 |
+24 |Meadow-hay | 0.40 | 8.96 |1.28| 14.28 | 7.68 | 1 11 |
+ | |------+-------+----+-------+-------+------+
+25 |Pea-straw | 0.35 | 7.84 |1.20| 15.31 | 6.64 | 1 8 |
+26 |Oat-straw | 0.24 | 5.38 |1.07| 19.89 | 4.31 | 1 1 |
+27 |Wheat-straw | 0.24 | 5.38 |0.92| 17.10 | 4.46 | 1 1 |
+28 |Barley-straw | 0.18 | 4.03 |0.84| 20.84 | 3.19 | 0 9 |
+29 |Bean-straw | 0.30 | 6.72 |0.88| 13.10 | 5.84 | 1 5 |
+ | |------+-------+----+-------+-------+------+
+30 |Potatoes | 0.15 | 3.36 |0.32| 9.52 | 3.04 | 0 9 |
+31 |Carrots | 0.09 | 2.02 |0.22| 10.89 | 1.80 | 0 5 |
+32 |Parsnips | 0.19 | 4.26 |0.26| 6.10 | 4.00 | 1 0 |
+33 |Swedish turnips| 0.06 | 1.34 |0.18| 13.43 | 1.16 | 0 4 |
+34 |Mangel-wurzels | 0.07 | 1.57 |0.20| 12.74 | 1.37 | 0 4 |
+35 |Yellow turnips |(0.06)| (1.34)|0.14|(10.78)| (1.20)|(0 4)|
+36 |White turnips | 0.05 | 1.12 |0.13| 11.61 | 0.99 | 0 3 |
+---+---------------+------+-------+----+-------+-------+------+
+
+---+---------------+---------------------------------------+---------
+ | | POTASH. |
+ |---------------+-------------------------+-------------+
+ | | Q | R | S |
+ | Description |------+------+----+------+------+------+
+No.| of Food. | Z | AA | BB | CC | DD | EE | FF
+---+---------------+------+------+----+------+------+------+---------
+ | | % | lb. | lb.| % | lb. |s. d. | £ s. d.
+ 1 |Linseed | 1.37 |30.69 |0.49| 1.60 |30.20 | 6 3 | 2 19 5
+ 2 |Linseed-cake | 1.40 |31.36 |0.41| 1.31 |30.95 | 6 5 | 3 18 6
+ 3 |Decorticated | | | | | | |
+ | cotton-cake | 2.00 |44.80 |0.38| 0.85 |44.42 | 9 3 | 5 13 0
+ 4 |Palm-nut-cake | 0.50 |11.20 |0.35| 3.13 |10.85 | 2 3 | 1 19 10
+ 5 |Undecorticated | | | | | | |
+ | cotton-cake | 2.00 |44.80 |0.31| 0.69 |44.49 | 5 11 | 3 5 4
+ 6 |Cocoa-nut-cake | 2.00 |44.80 |0.31| 0.69 |44.49 | 9 3 | 3 0 7
+ 7 |Rape-cake | 1.50 |33.60 |0.25| 0.74 |33.35 | 6 11 | 4 5 4
+ | |------+------+----+------+------+------+---------
+ 8 |Peas | 0.96 |21.50 |0.35| 1.63 |21.15 | 4 5 | 2 15 0
+ 9 |Beans | 1.30 |29.12 |0.35| 1.20 |28.77 | 6 0 | 3 3 5
+10 |Lentils | 0.70 |15.68 |0.35| 2.23 |15.33 | 3 2 | 3 1 4
+11 |Tares (seed) | 0.80 |17.92 |0.35| 1.95 |17.57 | 3 8 | 3 2 1
+ | |------+------+----+------+------+------+---------
+12 |Indian corn | 0.37 | 8.29 |0.34| 4.10 | 7.95 | 1 8 | 1 5 1
+13 |Wheat | 0.53 |11.87 |0.34| 2.86 |11.53 | 2 5 | 1 8 7
+14 |Malt | 0.50 |11.20 |0.35| 3.13 |10.85 | 2 3 | 1 6 8
+15 |Barley | 0.55 |12.32 |0.34| 2.76 |11.98 | 2 6 | 1 6 1
+16 |Oats | 0.50 |11.20 |0.33| 2.94 |10.87 | 2 3 | 1 9 10
+17 |Rice-meal |(0.37)|(8.29)|0.33|(4.00)|(7.96)|(1 8)|(1 7 10)
+18 |Locust-beans | - | - |0.27| - | - | - | -
+ | |------+------+----+------+------+------+---------
+19 |Malt-combs | 2.00 |44.80 |0.31| 0.69 |44.49 | 9 3 | 3 10 9
+20 |Fine pollard | 1.46 |32.70 |0.33| 1.01 |32.37 | 6 9 | 2 13 4
+21 |Coarse pollard | 1.50 |33.60 |0.31| 0.92 |33.29 | 6 11 | 2 17 9
+22 |Bran | 1.45 |32.48 |0.27| 0.83 |32.21 | 6 8 | 2 18 5
+ | |------+------+----+------+------+------+---------
+23 |Clover-hay | 1.50 |33.60 |0.18| 0.54 |33.42 | 7 0 | 2 1 3
+24 |Meadow-hay | 1.60 |35.84 |0.16| 0.45 |35.68 | 7 5 | 1 8 7
+ | |------+------+----+------+------+------+---------
+25 |Pea-straw | 1.00 |22.40 |0.15| 0.67 |22.25 | 4 8 | 0 18 10
+26 |Oat-straw | 1.00 |22.40 |0.14| 0.63 |22.26 | 4 8 | 0 11 7
+27 |Wheat-straw | 0.80 |17.92 |0.12| 0.67 |17.80 | 3 8 | 0 10 1
+28 |Barley-straw | 1.00 |22.40 |0.11| 0.49 |22.29 | 4 8 | 0 10 1
+29 |Bean-straw | 1.00 |22.40 |0.11| 0.49 |22.29 | 4 8 | 0 17 7
+ | |------+------+----+------+------+------+---------
+30 |Potatoes | 0.55 |12.32 |0.04| 0.32 |12.28 | 2 7 | 0 6 5
+31 |Carrots | 0.28 | 6.27 |0.03| 0.48 | 6.24 | 1 4 | 0 4 3
+32 |Parsnips | 0.36 | 8.06 |0.03| 0.37 | 8.03 | 1 8 | 0 5 5
+33 |Swedish turnips| 0.22 | 4.93 |0.02| 0.41 | 4.91 | 1 0 | 0 4 7
+34 |Mangel-wurzels | 0.40 | 8.90 |0.03| 0.34 | 8.93 | 1 10 | 0 5 0
+35 |Yellow turnips |(0.22)|(4.93)|0.02|(0.34)|(4.91)|(1 0)|(0 3 11)
+36 |White turnips | 0.30 | 6.72 |0.02| 0.30 | 6.70 | 1 5 | 0 4 0
+---+---------------+------+------+----+------+------+------+---------
+
+
+
+
+CHAPTER XXVI
+
+THE ROTHAMSTED EXPERIMENTS.
+
+
+Reference has been so repeatedly made in the preceding pages to the
+Rothamsted experiments on manures, that it may form a fitting conclusion
+to the present treatise to give a short account of these famous
+experiments.
+
+In describing these experiments, the author has remarked elsewhere[256]
+"that, in respect of their wide scope, dealing as they have done with
+almost every department of farming, the elaborate care and accuracy with
+which they have been carried out, the length of time they have been in
+progress, and, lastly, in respect of the important bearing their results
+have had on agricultural practice, these famous experiments may be
+justly described as unrivalled by any other similar ones."
+
+Started on a small scale in 1837 by Sir John (then Mr) Lawes, they were
+placed on a systematic basis in 1843, in which year Sir John Lawes
+associated with himself Sir (then Dr) J. Henry Gilbert. They have thus
+been in progress for a period of fifty years--a fact which was
+celebrated a few months ago by the presentation of numerous
+congratulatory addresses from various learned and agricultural societies
+to the distinguished investigators, and the erection of a memorial
+granite slab at Rothamsted. What increases the feeling of gratitude due
+to Sir John Lawes by the agricultural community, is the fact that the
+entire expense of conducting these experiments has been borne by
+himself, and he has further most generously handed over to the nation a
+large sum of money and a certain area of land for carrying them on in
+perpetuity.
+
+
+_Nature of Experiments on Crops and Manures._
+
+The earliest systematic experiments were on turnips, and since then
+almost every common crop has been experimented on. Table I. (p. 562) is
+a list of the different experiments, with their duration, area, and
+number of plots.
+
+
+_Soil of Rothamsted._
+
+Before describing the more striking results of these experiments, it may
+be advisable to say that the elevation of the land at Rothamsted is
+about 400 feet above sea-level; that the average rainfall is about 28
+inches per annum; and that the surface-soil is a heavy loam, and the
+subsoil a stiff clay, resting on chalk.
+
+
+TABLE I.--LIST OF ROTHAMSTED FIELD EXPERIMENTS.
+
+----------------------------------+------------+----------+------------
+ Crops. | Duration. | Area. | Plots.
+----------------------------------+------------+----------+------------
+ | Years. | Acres. |
+Wheat (various manures) | 50 | 11 | 34 (or 37)
+Wheat alternated with fallow | 42 | 1 | 2
+Wheat (varieties) | 15 | 4-8 | about 20
+Barley (various manures) | 42 | 4-1/4 | 29
+Oats (various manures) | 10[1] | 0-3/4 | 6
+Beans (various manures) | 32[2] | 1-1/4 | 10
+Beans (various manures) | 27[3] | 1 | 5
+Beans, alternated with wheat | 28[4] | 1 | 10
+Clover (various manures) | 29[5] | 3 | 18
+Various leguminous plants | 16 | 3 | 18
+ | | |
+Turnips (various manures) | 28[6] | 8 | 40
+Sugar-beet (various manures) | 5 | 8 | 41
+Mangel-wurzel (various manures) | 18 | 8 | 41
+ +------------+ |
+ Total root crops | 51 | |
+ +------------+ |
+ | | |
+Potatoes (various manures) | 18 | 2 | 10
+Rotation (various manures) | 46 | 3 | 12
+Permanent grass (various manures) | 38 | 7 | 22
+----------------------------------+------------+----------+------------
+1. Including one year fallow.
+
+2. Including one year wheat and five years fallow.
+
+3. Including four years fallow.
+
+4. Including two years fallow.
+
+5. Clover, twelve times sown (first in 1848), eight yielding crops, but
+ four of these very small, one year wheat, five years barley, twelve
+ years fallow.
+
+6. Including barley without manure three years (eleventh, twelfth, and
+ thirteenth seasons).
+
+
+WHEAT EXPERIMENTS.
+
+The first experiments we shall refer to are those on _wheat_, since they
+are among the oldest, and their results the most striking of any.
+
+
+_Unmanured Plots._
+
+Wheat has been continuously grown year after year on three plots for
+fifty years, without the application of any manure whatever.
+
+We shall first give the results of the first eight years as illustrating
+the effect of season, which accounts for the irregular results obtained.
+But for the difference in seasons, we should expect to find a steady
+decrease in the amount of produce; and this is shown in taking the
+average of groups of years, as we shall do in the next table.
+
+
+WHEAT GROWN CONTINUOUSLY ON SAME LAND (unmanured).
+
+TABLE II.--(a.) _Remits of first Eight Years (1844 to 1851)._
+
+Year. Bushels. | Year. Bushels.
+1844 15 | 1849. 19-1/4
+1845 23-1/4 | 1850. 15-7/8
+1846 18 | 1851. 15-7/8
+1847 16-7/8 | ------
+1848 14-3/4 | Average of 8 years 17-3/8
+ | ------
+
+TABLE III.--(b.) _Results of subsequent Forty Years (1852 to
+1891)._
+
+ Grain Weight per Straw
+ (bushels). bushel. (cwts.)
+20 years (1852-1871) 14-1/2 57-5/8 13
+20 " (1872-1891) 11-1/2 58-3/4 8-5/8
+40 " (1852-1891) 13 58-1/4 10-5/8
+49th season (1891) 9-3/8 59-1/2 7-1/2
+
+It is interesting to notice the comparatively slight decrease which has
+taken place in the yield of wheat during these fifty years. With such
+wide variations, due to season, it is extremely difficult, as Sir J.
+Henry Gilbert has pointed out, to estimate rate of decline due to
+exhaustion. Excluding the very bad seasons, this may be reckoned at from
+one-fourth to one-third of a bushel per acre per annum. _The return of
+the first year is 15 bushels, while the yield of the forty-ninth season
+is 9-3/8 bushels._ The average of the returns obtained during these
+fifty years is really in _excess of the average yield of the principal
+wheat-producing countries in the world_. This is truly a most astounding
+result.
+
+The next experiments we shall describe are those on the influence of
+farmyard manure on the wheat crop when grown continuously.
+
+
+TABLE IV.--WHEAT GROWN CONTINUOUSLY WITH FARMYARD MANURE (14
+tons per annum).
+
+ Weight per
+ Bushels. bushel Straw
+ (lb.) (cwts.)
+ 8 years (1844-1852) 28 - -
+20 " (1852-1871) 35-7/8 60 33-7/8
+20 " (1872-1891) 33-1/2 60-3/8 31-3/8
+40 " (1852-1891) 34-7/8 60-1/4 32-5/8
+
+It will be seen from the above results, which contain merely a selection
+from a very much greater number of experiments, that farmyard manure
+gives as good an average over the forty years as most of the artificial
+mixtures do. That this is due to the nitrogen it contains, is strikingly
+illustrated by the fact that mixed mineral manures alone give less than
+half the return, and also by the fact that ammonia salts alone give a
+return twice as great as mineral mixtures; while, lastly, the mixture of
+mineral manures and ammonia salts gives but a slight increase over that
+obtained with ammonia salts alone.
+
+The remaining results, selected from a much larger number, need no
+comment, and we shall give them in tabular form.
+
+
+Table V.--WHEAT GROWN CONTINUOUSLY WITH ARTIFICIAL MANURES, FARMYARD
+MANURE, AND UNMANURED.
+
+_Average of Forty Years (1852-91)._
+
+-------------------------------------+--------------------------------------+
+ | PRODUCE PER ACRE--AVERAGE PER ANNUM. |
+ +--------------------------------------+
+ | Dressed grain. |
+ MANURES PER ACRE PER ANNUM. +--------------------------------------+
+ | Quantity. |
+ +------------+------------+------------+
+ | 20 years, | 20 years, | 40 years, |
+ | 1852-71. | 1872-91. | 1852-91. |
+-------------------------------------+------------+------------+------------+
+ | bush. | bush. | bush. |
+Farmyard manure, 14 tons per annum | | | |
+ since 1843 | 35-7/8 | 33-1/2 | 34-7/8 |
+Unmanured continuously | 14-1/2 | 11-1/2 | 13 |
+Mixed mineral manures[1] and 3-1/2 | | | |
+ cwt. superphosphate | 17 | 12-7/8 | 15 |
+Mixed mineral manures, 3-1/2 cwt. | | | |
+ superphosphate, 200 lb. ammonium | | | |
+ salts | 26-1/2 | 21-3/4 | 24-1/8 |
+Mixed mineral manures and 3-1/2 cwt. | | | |
+ superphosphate, 600 lb. ammonium | | | |
+ salts | 38-1/4 | 34-3/4 | 36-1/2 |
+Mixed mineral manures, 3-1/2 cwt. | | | |
+ superphosphate, 275 lb. nitrate | | | |
+ of soda | 36-7/8 | 34 | 35-3/8 |
+275 lb. nitrate of soda | 26 | 19-3/8 | 22-3/4 |
+400 lb. ammonium salts every year | | | |
+ since 1845 | 22-1/2 | 19 | 22-1/2 |
+400 lb. ammonium salts, 3-1/2 cwt. | | | |
+ superphosphate | 28 | 22-1/4 | 25-1/8 |
+Mineral manure, 3-1/2 cwt. | | | |
+ superphosphate, 400 lb. ammonium | | | |
+ salts in autumn | 31-5/8 | 29-1/2 | 30-1/2 |
+-------------------------------------+------------+------------+------------+
+----------------------------------------------------------------------------+
+ | PRODUCE PER ACRE--AVERAGE PER ANNUM. |
+ +--------------------------------------+
+ | Dressed grain. |
+ MANURES PER ACRE PER ANNUM. +--------------------------------------+
+ | Quantity. |
+ +------------+------------+------------+
+ | 20 years, | 20 years, | 40 years |
+ | 1852-71. | 1872-91. | 1852-91. |
+-------------------------------------+------------+------------+------------+
+ | lb. | lb. | lb. |
+Farmyard manure, 14 tons per annum | | | |
+ since 1843 | 60 | 60-3/8 | 60-1/4 |
+Unmanured continuously | 57-5/8 | 58-3/4 | 58-1/4 |
+Mixed mineral manures and 3-1/2 | | | |
+ cwt. superphosphate | 58-7/8 | 59 | 58-7/8 |
+Mixed mineral manures, 3-1/2 cwt. | | | |
+ superphosphate, 200 lb. ammonium | | | |
+ salts | 59-3/8 | 60 | 59-5/8 |
+Mixed mineral manures and 3-1/2 cwt. | | | |
+superphosphate, 600 lb. ammonium | | | |
+ salts | 59 | 60 | 59-1/2 |
+Mixed mineral manures, 3-1/2 cwt. | | | |
+superphosphate, 275 lb. nitrate of | | | |
+ soda | 58-3/8 | 59-5/8 | 59 |
+275 lb. nitrate of soda | 56-5/8 | 56-5/8 | 56-5/8 |
+400 lb. ammonium salts every year | | | |
+ since 1845 | 58 | 57-3/8 | 57-5/8 |
+400 lb. ammonium salts, 3-1/2 cwt. | | | |
+ superphosphate | 57-3/8 | 58 | 57-5/8 |
+Mineral manure, 3-1/2 cwt. | | | |
+ superphosphate, 400 lb. ammonium | | | |
+ salts in autumn | 59-1/2 | 60 | 59-3/4 |
+-------------------------------------+------------+------------+------------+
+-------------------------------------+--------------------------------------
+ | PRODUCE PER ACRE--AVERAGE PER ANNUM.
+ +--------------------------------------
+ MANURES PER ACRE PER ANNUM. | Total straw.
+ +--------------------------------------
+ | 20 years, | 20 years, | 40 years
+ | 1852-71. | 1872-91. | 1852-91.
+-------------------------------------+------------+------------+------------
+ | cwt. | cwt. | cwt.
+Farmyard manure, 14 tons per annum | | |
+ since 1843 | 33-7/8 | 31-3/8 | 32-5/8
+Unmanured continuously | 13 | 8-5/8 | 10-5/8
+Mixed mineral manures and 3-1/2 | | |
+ cwt. superphosphate | 15 | 9-3/4 | 12-3/8
+Mixed mineral manures, 3-1/2 cwt. | | |
+ superphosphate, 200 lb. ammonium | | |
+ salts | 24-1/2 | 19-1/8 | 21-7/8
+Mixed mineral manures and 3-1/2 cwt. | | |
+superphosphate, 600 lb. ammonium | | |
+ salts | 41-3/8 | 39-5/8 | 40-1/2
+Mixed mineral manures, 3-1/2 cwt. | | |
+superphosphate, 275 lb. nitrate of | | |
+ soda | 41-1/2 | 37-3/4 | 39-5/8
+275 lb. nitrate of soda | 28-1/4 | 18-1/2 | 23-3/8
+400 lb. ammonium salts every year | | |
+ since 1845 | 24-3/4 | 16-1/4 | 20-1/2
+400 lb. ammonium salts, 3-1/2 cwt. | | |
+ superphosphate | 26-3/8 | 21 | 23-3/4
+Mineral manure, 3-1/2 cwt. | | |
+ superphosphate, 400 lb. ammonium | | |
+ salts in autumn | 31-1/4 | 28-3/8 | 29-3/4
+-------------------------------------+------------+------------+------------
+1. By the term mixed mineral manures is meant a mixture of mineral
+ fertilisers, not including phosphates.
+
+
+Table VI.--EXPERIMENTS ON THE GROWTH OF BARLEY FOR FORTY YEARS, 1852-91.
+
+-------------------------------------+--------------------------------------+
+ | PRODUCE PER ACRE--AVERAGE PER ANNUM. |
+ +--------------------------------------+
+ | Dressed grain. |
+ MANURES PER ACRE PER ANNUM. +--------------------------------------+
+ | Quantity. |
+ +------------+------------+------------+
+ | 20 years, | 20 years, | 40 years, |
+ | 1852-71. | 1872-91. | 1852-91. |
+-------------------------------------+------------+------------+------------+
+ | bush. | bush. | bush. |
+Unmanured continuously | 20 | 13-1/4 | 16-1/2 |
+3-1/2 cwt. superphosphate of lime | 25-1/2 | 17-3/4 | 21-3/4 |
+Mixed mineral manures | 22-1/2 | 13-1/2 | 18 |
+Mixed mineral manures, 3-1/2 cwt. | | | |
+ superphosphate | 27-1/2 | 17-1/4 | 22-3/8 |
+200 lb. ammonium salts | 32-1/2 | 25-5/8 | 29 |
+200 lb. ammonium salts, 3-1/2 cwt. | | | |
+ superphosphate | 47 | 38-1/2 | 42-3/4 |
+200 lb. ammonium salts, | | | |
+ mixed mineral manures | 35 | 27-3/4 | 31-3/8 |
+Manures, 3-1/2 cwt. | | | |
+ superphosphate of lime | 46-1/4 | 40-3/4 | 43-1/2 |
+275 lb. nitrate of soda | 37 | 28-3/8 | 32-3/4 |
+275 lb. nitrate of soda, 3-1/2 cwt. | | | |
+ superphosphate | 49-1/4 | 42-1/4 | 45-3/4 |
+275 lb. nitrate of soda, | | | |
+ mixed mineral manures. | 37-3/8 | 29-1/2 | 33-1/2 |
+275 lb. nitrate of soda, | | | |
+ mixed mineral manures, | | | |
+ 3-1/2 cwt. superphosphate | 49-3/4 | 41-1/4 | 45-1/2 |
+1000 lb. rape-cake | 45-1/4 | 37-1/8 | 41-1/4 |
+1000 lb. rape-cake, 3-1/2 cwt. | | | |
+ superphosphate | 46-3/4 | 40 | 43-3/8 |
+1000 lb. rape-cake, | | | |
+ mixed mineral manures | 43-5/8 | 35-5/8 | 39-1/2 |
+1000 lb. rape-cake, | | | |
+ mixed mineral manures, and | | | |
+ 3-1/2 cwt. superphosphate | 47-3/8 | 39 | 43-1/4 |
+Farmyard manure, 14 tons every year | 48-1/4 | 49 | 48-5/8 |
+-------------------------------------+------------+------------+------------+
+
+----------------------------------------------------------------------------+
+ | PRODUCE PER ACRE--AVERAGE PER ANNUM. |
+ +--------------------------------------+
+ | Dressed grain. |
+ MANURES PER ACRE PER ANNUM. +--------------------------------------+
+ | Quantity. |
+ +------------+------------+------------+
+ | 20 years, | 20 years, | 40 years |
+ | 1852-71. | 1872-91. | 1852-91. |
+-------------------------------------+------------+------------+------------+
+ | lb. | lb. | lb. |
+Unmanured continuously | 52-3/8 | 51-3/4 | 52 |
+3-1/2 cwt. superphosphate of lime | 53-1/4 | 53 | 53-1/8 |
+Mixed mineral manures | 53 | 51-7/8 | 52-1/2 |
+Mixed mineral manures, 3-1/2 cwt. | | | |
+ superphosphate | 53-3/8 | 52-3/8 | 53 |
+200 lb. ammonium salts | 52-1/8 | 52 | 52 |
+200 lb. ammonium salts, 3-1/2 cwt. | | | |
+ superphosphate | 53-3/8 | 52-1/4 | 52-7/8 |
+200 lb. ammonium salts, | | | |
+ mixed mineral manures | 52-3/4 | 52-1/2 | 52-5/8 |
+Manures, 3-1/2 cwt. | | | |
+ superphosphate of lime | 54 | 54-1/8 | 54 |
+275 lb. nitrate of soda | 52 | 52-1/8 | 52 |
+275 lb. nitrate of soda, 3-1/2 cwt. | | | |
+ superphosphate | 53-3/8 | 53-1/4 | 53-1/4 |
+275 lb. nitrate of soda, | | | |
+ mixed mineral manures. | 52-1/4 | 52-3/4 | 52-1/2 |
+275 lb. nitrate of soda, | | | |
+ mixed mineral manures, | | | |
+ 3-1/2 cwt. superphosphate | 53-3/8 | 54 | 53-5/8 |
+1000 lb. rape-cake | 53-3/4 | 53-7/8 | 53-7/8 |
+1000 lb. rape-cake, 3-1/2 cwt. | | | |
+ superphosphate | 53-7/8 | 54-3/8 | 54-1/8 |
+1000 lb. rape-cake, | | | |
+ mixed mineral manures | 53-3/4 | 54-1/8 | 54 |
+1000 lb. rape-cake, | | | |
+ mixed mineral manures, and | | | |
+ 3-1/2 cwt. superphosphate | 53-5/8 | 54-1/4 | 53-7/8 |
+Farmyard manure, 14 tons every year | 54-3/8 | 54-1/4 | 54-1/4 |
+-------------------------------------+------------+------------+------------+
+
+-------------------------------------+--------------------------------------
+ | PRODUCE PER ACRE--AVERAGE PER ANNUM.
+ +--------------------------------------
+ MANURES PER ACRE PER ANNUM. | Total straw.
+ +--------------------------------------
+ | 20 years, | 20 years, | 40 years
+ | 1852-71. | 1872-91. | 1852-91.
+-------------------------------------+------------+------------+------------
+ | cwt. | cwt. | cwt.
+Unmanured continuously | 11-3/4 | 6-7/8 | 9-3/8
+3-1/2 cwt. superphosphate of lime | 13-3/8 | 8-1/4 | 10-3/4
+Mixed mineral manures | 12-1/4 | 7 | 9-5/8
+Mixed mineral manures, 3-1/2 cwt. | | |
+ superphosphate | 14-3/8 | 8-3/8 | 11-3/8
+200 lb. ammonium salts | 18-1/2 | 13-1/2 | 16
+200 lb. ammonium salts, 3-1/2 cwt. | | |
+ superphosphate | 27-5/8 | 20-1/8 | 23-7/8
+200 lb. ammonium salts, | | |
+ mixed mineral manures | 20-1/4 | 15-1/8 | 18
+Manures, 3-1/2 cwt. | | |
+ superphosphate of lime | 28-1/2 | 23-3/8 | 25-7/8
+275 lb. nitrate of soda | 22-1/8 | 15-7/8 | 19
+275 lb. nitrate of soda, 3-1/2 cwt. | | |
+ superphosphate | 30-1/2 | 23-3/8 | 27
+275 lb. nitrate of soda, | | |
+ mixed mineral manures. | 23-7/8 | 17-1/2 | 20-3/4
+275 lb. nitrate of soda, | | |
+ mixed mineral manures, | | |
+ 3-1/2 cwt. superphosphate | 32-3/8 | 24-1/2 | 28-1/2
+1000 lb. rape-cake | 26-7/8 | 20 | 23-3/8
+1000 lb. rape-cake, 3-1/2 cwt. | | |
+ superphosphate | 28-3/8 | 21-1/2 | 24-7/8
+1000 lb. rape-cake, | | |
+ mixed mineral manures | 27-1/8 | 19-7/8 | 23-1/2
+1000 lb. rape-cake, | | |
+ mixed mineral manures, and | | |
+ 3-1/2 cwt. superphosphate | 29-3/4 | 21-7/8 | 25-5/8
+Farmyard manure, 14 tons every year | 28-1/4 | 29-3/4 | 29
+-------------------------------------+------------+------------+------------
+
+
+TABLE VII.
+
+EXPERIMENTS ON THE GROWTH OF OATS, 1869-78.
+
+-------------------------------------------+----------------------------
+ | AVERAGE PER ANNUM.
+ | 5 YEARS, 1869-73.
+ +----------------------------
+ MANURES PER ACRE PER ANNUM. | Dressed grain. |
+ +----------+--------+ Total
+ | Quantity.| Weight | straw.
+ | | per |
+ | | bushel.|
+-------------------------------------------+----------+--------+--------
+ | Bushels. | lb. | cwt.
+Unmanured | 19-7/8 | 33-3/4 | 10-3/8
+200 lb. sulphate potash, 100 lb. sulphate | | |
+ soda, 100 lb. sulphate magnesia, and | | |
+ 3-1/2 cwt. superphosphate of lime | 24-1/2 | 35 | 13-3/8
+400 lb. ammonium salts | 47 | 35-7/8 | 28-1/2
+400 lb. ammonium salts, 200 lb. sulphate | | |
+ potash, 100 lb. sulphate soda, 100 lb. | | |
+ sulphate magnesia, and 3-1/2 cwt. | | |
+ superphosphate | 59 | 37 | 41-1/8
+550 lb. nitrate of soda | 47-1/8 | 35-1/2 | 27-1/2
+550 lb. nitrate of soda, 200 lb. sulphate | | |
+ potash, 100 lb. sulphate soda, 100 lb. | | |
+ sulphate magnesia, and 3-1/2 cwt. | | |
+ superphosphate | 57-1/2 | 35-3/4 | 35
+-------------------------------------------+----------+--------+--------
+ | AVERAGE PER ANNUM.
+ | 4 YEARS, 1874-78.
+-------------------------------------------+----------------------------
+ | Bushels. | lb. | cwt.
+Unmanured | 13-3/4 | 31-1/4 | 6
+200 lb. sulphate potash, 100 lb. sulphate | | |
+ soda, 100 lb. sulphate magnesia, and | | |
+ 3-1/2 cwt. superphosphate of lime | 13-1/8 | 31-5/8 | 6-1/8
+200 lb. ammonium salts. | 28-7/8 | 33-1/4 | 14-1/8
+200 lb. ammonium salts, 200 lb. sulphate | | |
+ potash, 100 lb. sulphate soda, 100 lb. | | |
+ sulphate magnesia, and 3-1/2 cwt. | | |
+ superphosphate | 38 | 35-1/2 | 20
+275 lb. nitrate of soda | 26-3/8 | 31-5/8 | 11-1/8
+275 lb. nitrate of soda, 200 lb. sulphate | | |
+ potash, 100 lb. sulphate soda, 100 lb. | | |
+ sulphate magnesia, and 3-1/2 cwt. | | |
+ superphosphate | 28-1/2 | 34-1/8 | 14
+-------------------------------------------+----------+--------+--------
+
+ TABLE VIII.--EXPERIMENTS ON ROOT CROPS: SWEDISH TURNIPS.
+_Fifteen Seasons_, 1856-70.[1] Roots and Leaves carted off the Land.
+-----+--------------------------------------------+---------------------+
+ | | SERIES 1. |
+ | | |
+ | | Standard manures |
+ | | only. |
+ | | |
+ | | |
+ | | |
+ | | |
+ | | |
+ | | |
+PLOT.| STANDARD MANURES. | |
+-----+--------------------------------------------+---------------------+
+ | | Roots. | Leaves. |
+ | |----------+----------+
+ | |Tons. cwt.|Tons. cwt.|
+ 1 |Farmyard manure, 14 tons | 6 4 | 0 17 |
+ 2 |Farmyard manure, 14 tons, and superphosphate| 6 7 | 0 16 |
+ 3 |Without manure, 1846, and since | 0 11 | 0 3 |
+ 4 |Superphosphate, each year; sulphate potash, | | |
+ | soda, and magnesia, 1856-60 | 2 16 | 0 8 |
+ 5 |Superphosphate, each year | 2 12 | 0 9 |
+ 6 |Superphosphate, each year; sulphate potash, | | |
+ | 1856-60 | 2 7 | 0 7 |
+ 7 |Superphosphate, each year; sulphate, potash,| | |
+ | and 36-1/2 lb. ammonium salts, 1856-60 | 2 12 | 0 7 |
+ 8 |Unmanured 1853, and since; previously part | | |
+ | unmanured; part superphosphate | 1 3 | 0 4 |
+-----+--------------------------------------------+----------+----------+
+
+_Note._--Sulphate of ammonia is estimated to contain 23 per cent
+ammonia, and muriate of ammonia 27 per cent. Ammonium salts, in each
+case, equal parts sulphate and muriate of ammonia of commerce; and the
+mixture is estimated to contain 25 per cent ammonia. The 328 lb. nitric
+acid (sp. gr. 1.35) mixed with sawdust, and used as a cross-dressing on
+the plots of Series 2 from 1856-60, were estimated to contain nitrogen =
+50 lb. ammonia.
+
+1. The crops of 1859 and 1860 failed, and were ploughed in; but as the
+manures were applied, and there would be accumulation with the soil for
+the succeeding crops, the average produce is calculated as for fifteen
+years--that is, the produce of the thirteen years is, in each case,
+divided by 15.
+
+-----+-----------------------+-----------------------
+ | SERIES 2. | SERIES 3.
+ | |
+ | Standard manures, | Standard manures,
+ | and cross-dressed | and cross-dressed
+ | with-- | with--
+ | |
+ |5 years, 1856-60, |5 years, 1856-60,
+ |3000 lb. sawdust, and |200 lb. ammonium
+ |328 lb. nitric acid. |salts
+ | |
+ |10 years, 1861-70, |10 years, 1861-70,
+ |550 lb. nitrate soda. |400 lb. ammonium salts.
+PLOT.| |
+-----+-----------+-----------+-----------+-----------
+ | Roots. | Leaves. | Roots. | Leaves.
+ +-----------+-----------+-----------+-----------
+ |Tons. cwt.|Tons. cwt.|Tons. cwt.|Tons. cwt.
+ 1 | 7 9 | 1 2 |8 8 | 1 4
+ 2 | 7 13 | 1 3 |8 5 | 1 5
+ 3 | 0 19 | 0 4 |0 13 | 0 3
+ 4 | 5 2 | 0 16 |4 12 | 0 14
+ | | | |
+ 5 | 4 13 | 0 18 |3 16 | 0 15
+ 6 | 4 11 | 0 14 |4 5 | 0 13
+ | | | |
+ 7 | 4 13 | 0 14 |4 12 | 0 14
+ | | | |
+ 8 | 1 13 | 0 5 |1 2 | 0 5
+ | | | |
+-----+-----------+-----------+-----------+-----------
+
+-----+-----------------------+-----------------------
+ | SERIES 4. | SERIES 5.
+ | |
+ | Standard manures, | Standard manures,
+ | and cross-dressed | and cross-dressed
+ | with-- | with--
+ | |
+ |5 years, 1856-60, |5 years, 1856-60,
+ |200 lb. ammonium salts,|3000 lb. sawdust.
+ |and 3000 lb. sawdust. |
+ | |10 years, 1861-70,
+ |10 years, 1861-70, |2000 lb. rape-cake.
+ |400 lb. ammonium salts,|
+PLOT.|and 2000 lb. rape-cake.|
+-----+-----------+-----------+-----------+-----------
+ | Roots. | Leaves. | Roots. | Leaves.
+ +-----------+-----------+-----------+-----------
+ |Tons. cwt.|Tons. cwt.|Tons. cwt.|Tons. cwt.
+ 1 | 8 16 | 1 9 | 8 0 | 1 4
+ 2 | 8 14 | 1 9 | 7 16 | 1 2
+ 3 | 3 6 | 0 14 | 3 8 | 0 13
+ 4 | 6 12 | 1 5 | 5 8 | 0 17
+ | | | |
+ 5 | 5 16 | 1 7 | 5 0 | 0 19
+ 6 | 6 6 | 1 2 | 5 3 | 0 16
+ | | | |
+ 7 | 6 15 | 1 4 | 5 9 | 0 17
+ | | | |
+ 8 | 3 19 | 0 18 | 3 14 | 0 19
+ | | | |
+-----+-----------+-----------+-----------+-----------
+
+
+TABLE IX.--EXPERIMENTS ON MANGEL-WURZEL.
+
+_Average of Sixteen Seasons_, 1876-92. Manures per Acre per Annum.
+
+-----+--------------------------------------------+---------------------
+ | | SERIES 1.
+ | |
+ | | Standard manures
+ | | only.
+ | |
+ | |
+PLOT.| STANDARD MANURES. |
+-----+--------------------------------------------+----------+----------
+ | | Roots. | Leaves.
+ | |----------+----------
+ | |Tons. cwt.|Tons. cwt.
+ 1 |Farmyard manure, 14 tons | 16 6 | 2 17
+ 2 |Farmyard manure, 14 tons, and 3-1/2 cwt. | |
+ | superphosphate | 16 12 | 2 18
+ 3 |Without manure, 1846, and since | 4 9 | 1 8
+ 4 |3-1/2 cwt. superphosphate, 500 lb. sulphate | |
+ | of potash and 400 lb. mixed mineral manure| 5 8 | 1 1
+ 5 |3-1/2 cwt. superphosphate | 5 0 | 1 1
+ 6 |3-1/2 cwt. superphosphate, and 500 lb. | |
+ | sulphate of potash | 4 9 | 0 18
+ 7 |3-1/2 cwt. superphosphate, 500 lb. sulphate | |
+ | of potash, and 36-1/2 lb. ammonium salts | 5 17 | 1 8
+-----+--------------------------------------------+----------+----------
+
+-----+-----------------------+-----------------------+
+ | SERIES 2. | SERIES 3. |
+ | | |
+ |Standard manures, |Standard manures, |
+ |and cross-dressed |and cross-dressed |
+ |with 550 lb. |with 400 lb. |
+ |nitrate of soda. |ammonium salts. |
+PLOT.| | |
+-----+-----------+-----------+-----------+-----------+
+ | Roots. | Leaves. | Roots. | Leaves. |
+ +-----------+-----------+-----------+-----------+
+ |Tons. cwt.|Tons. cwt.|Tons. cwt.|Tons. cwt.|
+ 1 | 22 11 | 4 2 | 22 3 | 5 7 |
+ 2 | 23 12 | 4 14 | 21 8 | 5 6 |
+ | | | | |
+ 3 | 13 7 | 3 4 | 6 14 | 2 18 |
+ 4 | 12 17 | 3 15 | 16 2 | 3 0 |
+ | | | | |
+ 5 | 15 13 | 3 5 | 8 10 | 3 1 |
+ 6 | 15 15 | 2 18 | 14 6 | 2 16 |
+ | | | | |
+ 7 | 16 0 | 3 1 | 16 3 | 3 0 |
+ | | | | |
+-----+-----------+-----------+-----------+-----------+
+
+-----+-----------------------+-----------------------
+ | SERIES 4. | SERIES 5.
+ | |
+ |Standard manures, |Standard manures,
+ |and cross-dressed |and cross-dressed with
+ |with 2000 lb. rape |2000 lb. rape-cake.
+ |cake, and 400 lb. |
+PLOT.|ammonium salts. |
+-----+-----------+-----------+-----------+-----------
+ | Roots. | Leaves. | Roots. | Leaves.
+ +-----------+-----------+-----------+-----------
+ |Tons. cwt.|Tons. cwt.|Tons. cwt.|Tons. cwt.
+ 1 | 24 11 | 6 1 | 23 7 | 4 6
+ 2 | 23 12 | 6 1 | 23 1 | 4 6
+ | | | |
+ 3 | 10 11 | 3 17 | 11 2 | 3 0
+ 4 | 24 18 | 5 7 | 20 4 | 3 9
+ | | | |
+ 5 | 11 7 | 4 2 | 12 3 | 3 2
+ 6 | 21 6 | 5 7 | 16 14 | 2 15
+ | | | |
+ 7 | 21 6 | 5 9 | 17 10 | 3 3
+ | | | |
+-----+-----------+-----------+-----------+-----------
+
+TABLE X.--Experiments with different Manures on Permanent Meadow-land.
+
+_Thirty-six Years_, 1856-91.
+
+-------------------------------+--------------------------+--------------------
+ | Produce per Acre, weighed as Hay.
+ +--------------------------+--------------------
+ | Average per Annum, | Average per annum,
+ | 20 years, 1856-75 | 16 years, 1876-91
+ | (1st crops only). | (1st and 2d crops).
+ Manures per Acre per Annum. +--------+--------+--------+------+------+------
+ |10 years|10 years|20 years| 1st | 2d |
+ |1856-65.|1866-75.|1856-75.|crops.|crops.|Total.
+-------------------------------+--------+--------+--------+------+------+------
+ | cwt. | cwt. | cwt. | cwt. | cwt. | cwt.
+Unmanured continuously | 22-1/2 | 20 | 21-1/4 |18 | 8-1/2|26-1/2
+3-1/2 cwt. superphosphate of | | | | | |
+ lime | 23-1/4 | 21-1/4 | 22-1/4 |18 | 9 |27-1/2
+3-1/2 cwt. superphosphate of | | | | | |
+ lime, and 400 lb. ammonium | | | | | |
+ salts | 33-7/8 | 30-1/2 | 32-1/4 |30-3/4|10-1/2|41-1/4
+400 lb. ammonium salts | 30-1/2 | 22 | 26-1/4 |18-1/4|10-1/8|27-3/8
+275 lb. nitrate of soda, 3-1/2 | | | | | |
+ cwt. superphosphate, and | | | | | |
+ mixed mineral manure | 45-1/4 | 47-5/8 | 46-1/2 |41-1/8|12-1/8|53-1/4
+275 lb. nitrate of soda | 34-1/4 | 33-1/2 | 33-7/8 |30-1/8|10 |40-1/8
+-------------------------------+--------+--------+--------+------+------+------
+
+TABLE XI.--EXPERIMENTS ON THE GROWTH OF POTATOES.
+
+_Average of Five Seasons, 1876-80._[1]
+----+-------------------------------+-------------------------------------------
+ | | PRODUCE PER ACRE--TUBERS.
+Plot| MANURE PER ACRE PER ANNUM. |----------+----------+----------+----------
+ | | Good. | Small. | Diseased.| Total.
+----+-------------------------------|----------+----------+----------+----------
+Plot| |Tons cwt. |Tons cwt. |Tons cwt. |Tons cwt.
+ 1 |Unmanured | 1 18 | 0 6-1/4| 0 2-1/4| 2 6-1/2
+ 2 |Farmyard manure (14 tons) | 3 19-3/8| 0 7-5/8| 0 6-5/8| 4 13-5/8
+ 3 |Farmyard manure (14 tons), and | | | |
+ | 3-1/2 cwt. superphosphate | 4 9-1/2| 0 8 | 0 8-3/4| 5 6-1/4
+ 4 |Farmyard manure (14 tons), | | | |
+ | 3-1/2 cwt. superphosphate, | | | |
+ | and 550 lb. nitrate of soda | 5 8 | 0 7 | 0 19-1/2| 6 14-1/2
+ 5 |400 lb. ammonium salts | 1 19-1/2| 0 7-1/8| 0 3-1/2| 2 10-1/8
+ 6 |550 lb. nitrate of soda | 2 11-7/8| 0 6-7/8| 0 5-1/4| 3 4
+ 7 |400 lb. ammonium salts, 3-1/2 | | | |
+ | cwt. superphosphate, 300 lb. | | | |
+ | sulphate potash, 100 lb. | | | |
+ | sulphate soda, 100 lb. | | | |
+ | sulphate magnesia | 5 14-1/4| 0 8-1/4| 0 14-3/4| 6 17-1/4
+ 8 |550 lb. nitrate of soda, 3-1/2 | | | |
+ | cwt. superphosphate, 300 lb. | | | |
+ | sulphate potash, 100 lb. | | | |
+ | sulphate soda, 100 lb. | | | |
+ | sulphate magnesia | 5 19-7/8| 0 7-7/8| 0 19-1/8| 7 6-7/8
+ 9 |3-1/2 cwt. superphosphate | 3 0-3/4 | 0 8 | 0 4-5/8| 3 13-3/8
+ 10 |3-1/2 cwt. superphosphate, 300 | | | |
+ | lb. sulphate potash, 100 lb. | | | |
+ | sulphate soda, and 100 lb. | | | |
+ | sulphate magnesia | 3 4-1/2 | 0 6-1/2| 0 4-7/8| 3 15-7/8
+----+-------------------------------+----------+----------+----------+----------
+1. In each year the tops were spread on the respective plots.
+
+
+TABLE XII.--EXPERIMENTS ON THE GROWTH OF POTATOES--_Continued_.
+
+_Average of Twelve Seasons, 1881-92._
+
+----+------------------------------+-------------------------------------------
+ | | PRODUCE PER ACRE--TUBERS.
+Plot| MANURE PER ACRE PER ANNUM. |----------+----------+----------+----------
+ | | Good. | Small. | Diseased.| Total.
+----+------------------------------|----------+----------+----------+----------
+ | |Tons cwt. |Tons cwt. |Tons cwt. |Tons cwt.
+ 1 |Unmanured in 1876, and each | | | |
+ | year since | 1 3-3/4| 0 3-3/4| 0 0-1/4| 1 7-3/4
+ 2 |Unmanured in 1882, and since; | | | |
+ | previously farmyard manure | | | |
+ | (14 tons) | 2 14-1/4| 0 4-3/4| 0 2 | 3 1
+ 3 |Farmyard manure (14 tons) | | | |
+ | alone, 1883, and since; | | | |
+ | previously 3-1/2 cwt. | | | |
+ | superphosphate also | 4 3-1/4| 0 4-1/4| 0 4-1/2| 4 12
+ 4 |Farmyard manure (14 tons) | | | |
+ | alone, 1883, and since. In | | | |
+ | 1882 and previously 3-1/2 | | | |
+ | cwt. superphosphate, and in | | | |
+ | 1881 and previously 550 lb. | | | |
+ | nitrate of soda also | 4 6-1/4| 0 4-1/2| 0 4-3/4| 4 15-1/2
+ 5 |400 lb. ammonium salts | 1 2-3/4| 0 4-3/4| 0 0-1/2| 1 8
+ 6 |550 lb. nitrate of soda | 1 17-3/4| 0 3-3/4| 0 0-3/4| 2 2-1/4
+ 7 |400 lb. ammonium salts, 3-1/2 | | | |
+ | cwt. superphosphate, 300 lb.| | | |
+ | sulphate of potash, and 200 | | | |
+ | lb. mixed mineral manure | 5 6-3/4| 0 5 | 0 4-1/2| 5 16-1/4
+ 8 |550 lb. nitrate of soda, 3-1/2| | | |
+ | cwt. superphosphate, 300 lb.| | | |
+ | sulphate of potash, and 200 | | | |
+ | lb. mixed mineral manure | 5 7-1/2| 0 4-1/4| 0 3-3/4| 5 15-1/2
+ 9 |3-1/2 cwt. superphosphate | 2 17-3/4| 0 3-1/4| 0 1 | 3 2
+ 10 |3-1/2 cwt. superphosphate, 300| | | |
+ | lb. sulphate of potash, and | | | |
+ | 200 lb. mixed mineral manure| 3 2-1/4| 0 3-1/4| 0 1-1/4| 3 6-3/4
+----+------------------------------+----------+----------+----------+----------
+
+
+FOOTNOTES:
+
+[256] See Sir John Bennet Lawes, Bart., and the Rothamsted Experiments.
+By C. M. Aikman. ('Scottish Farmer' Office, Glasgow.)
+
+
+
+
+INDEX.
+
+
+ Abraum salts, 421.
+
+ Absorptive power of soils for water, 67, 98;
+ how to increase, 74.
+
+ Acidity in soils neutralised by lime, 458.
+
+ Acids fixed by soil, 58.
+
+ Adametz on organisms in soil, 92.
+
+ Adulteration of guano, 318-320.
+
+ Africa, guano from, 298, 328.
+
+ Agricultural chemistry, historical introduction to, 3-61;
+ Liebig's researches on, 23-32;
+ Liebig's services to, 31.
+
+ Agronomy, 56.
+
+ Air, ammonia in, 48, 118;
+ nitrates in, 118; nitrites in, 118;
+ nitrogen in, 116;
+ organic nitrogen in, 118.
+
+ Aitken, Dr, experiments with basic slag, 413
+ --with beans, 526, 530;
+ on germ-life in bones, 368;
+ on manuring of turnips, 515.
+
+ Albert, Heinrich, on solubility of basic slag, 409.
+
+ Albite, composition of, 103.
+
+ Albuminates, 460.
+
+ Albuminoids, in plants, 491;
+ of milk, nitrification in, 182;
+ phosphorus in, 205.
+
+ Algerian phosphate, 379.
+
+ Algoa Bay, guano deposits at, 328.
+
+ Alkalies, in cow-dung, 226, 227
+ --cow-urine, 230
+ --horse-dung, 226, 227
+ --horse-urine, 230
+ --pig-dung, 226, 227
+ --pig-urine, 230
+ --sheep-dung, 226, 227
+ --sheep-urine, 230.
+
+ Alkalinity necessary for nitrification, 172.
+
+ Alumina, in ash of plants, 55;
+ compounds, reversion caused by, 388, 400;
+ salts, in _salinas_, 335.
+
+ America, virgin soils of, 133.
+
+ American farming, 86.
+
+ Amides, 501.
+
+ Ammonia, absorbed by soil, 81;
+ amount dissolved in rain, 49;
+ amount in air, 48;
+ amount in soil, 127;
+ amount supplied to soil by rain, 155;
+ converted into nitrates in soil, 50;
+ converted into nitrous acid, 167;
+ fixed by soil, 58;
+ from decomposition of farmyard manure, 258;
+ from gas-works, 353;
+ lost in mixing manures, 533;
+ relation of, to plants, 48-50;
+ salts, most easily nitrifiable, 191;
+ salts of, in farmyard manure, 257;
+ sulphate of, 352-358;
+ value of, as a manure, 352.
+
+ Ammonium chloride in Chincha guano, 305.
+
+ Ammonium-magnesium phosphate in Chincha guano, 305.
+
+ Ammonium oxalate in concretionary nodules, 328.
+
+ Ammonium phosphate, in Chincha guano, 305;
+ in concretionary nodules, 328.
+
+ Ammonium sulphate, 352-358;
+ in Chincha guano, 305;
+ in concretionary nodules, 328.
+
+ Ammonium sulphocyanate, 355.
+
+ Ammonium urate in concretionary nodules, 328.
+
+ Amphibole, potash in, 220.
+
+ Analysis, of manures, 539-554;
+ of soils, value of, 90.
+
+ Anderson, Dr, analyses of minerals by, 103, 105-107;
+ on nitrogen in soil, 121, 124.
+
+ Angamos, guano from, 301, 329.
+
+ Animals, phosphoric acid in, 205;
+ potash in, 205;
+ solid excreta of, 224;
+ urine of, 228.
+
+ Apatite, Canadian, 201, 374;
+ composition of, 210;
+ most abundant form of phosphoric acid, 200;
+ varieties of, 200.
+
+ Application of manures, 474-492.
+
+ Arabian coast, guano deposits on, 328.
+
+ Arable soil, absorptive power of, 98.
+
+ Arbrohlos Island guano, 309.
+
+ Arendt, experiments on oats by, 503.
+
+ Aristotelian doctrine of chemical elements, 4.
+
+ Artificial soil, 54.
+
+ Aruba phosphate, 308, 328, 379.
+
+ Ash, constituents of plants, 53-55;
+ of rye, phosphoric acid in, 204;
+ of wheat, phosphoric acid in, 204;
+ of farmyard manure, composition of, 287, 288.
+
+ Ashes, an adulterant of guano, 319;
+ mixed with manures, 532.
+
+ Asia, guano from, 298.
+
+ Asparagin, nitrification in, 182.
+
+ Atacama, nitrate of soda deposits at, 342.
+
+ Atmosphere, ammonia in, 48, 81;
+ relation of, to plants, 39.
+
+ Atwater on nitrogen in plants, 44.
+
+ Augite, 105.
+
+ Australia, guano from, 298;
+ virgin soils of, 133.
+
+ Avenine in oats, 503.
+
+ Aves guano, 309, 328;
+ phosphoric acid in, 330.
+
+
+ Bacilli, 94.
+
+ Bacon, Lord, on salt as a manure, 469.
+
+ Bacteria, in soil, 92;
+ different classes of, 93-96.
+
+ Baker Island guano, 309, 328;
+ phosphoric acid in, 330.
+
+ Ballestas, guano from, 302, 327;
+ nitrogen in, 329;
+ phosphoric acid in, 329.
+
+ Barilla, potash in, 420.
+
+ Barley, farmyard manure not suited for, 497;
+ fertilising ingredients removed from soil by, 485;
+ manurial constituents in, 282;
+ manuring of, 495, 498;
+ nitrogen removed in crop of, 145;
+ Norfolk experiments on, 497;
+ period of growth of, 495;
+ period of ripening of, 495;
+ Rothamsted experiments on growth of, 566;
+ soils suited for, 496;
+ uniform manuring of, 497.
+
+ Barley soils, amount of nitrates and nitrogen in, 158.
+
+ Barley-straw, composition of, 238;
+ manurial constituents in, 282.
+
+ Basalt, phosphoric acid in, 202, 210.
+
+ Bases fixed by soil, 58.
+
+ Basic ammonium phosphate in concretionary nodules, 328.
+
+ Basic process of steel-smelting, 400.
+
+ Basic silicates, 103.
+
+ Basic slag, 401-417;
+ after-effects of, 412;
+ application of, method of, 416
+ --rate of, 414;
+ compared with other manures, 410-414;
+ composition of, 404, 417;
+ Darmstadt experiments with, 410;
+ discovery of value of, 403;
+ manufacture of, 401;
+ preparation of, processes for, 406;
+ relative activity of, 411;
+ soils best suited for, 414;
+ solubility of, 408;
+ Wagner's experiments with, 408-413.
+
+ Bat guano, 320, 325;
+ nitrogen in, 325;
+ phosphoric acid in, 325.
+
+ Beans, fertilising ingredients removed from soil by, 485;
+ good effect of gypsum on, 526;
+ manurial constituents in, 282;
+ manuring of, 525-527;
+ phosphorus in, 205;
+ relative value of manurial ingredients to, 526;
+ source of nitrogen, 153.
+
+ Bean-straw, manurial constituents in, 282.
+
+ Beatson, General, experiments of, with Peruvian guano, 301.
+
+ Beddington meadows, irrigation at, 432.
+
+ Bedfordshire, coprolites from, 374.
+
+ Belgian phosphate, 377.
+
+ Berthelot on sources of plant-nitrogen, 42.
+
+ Biological properties of soil, 92-96.
+
+ Blood corpuscles, potash in, 217.
+
+ Blood, dried, 424;
+ composition of, 424;
+ manure for sugar-cane, 425;
+ potash in, 217, 219;
+ rate of nitrification in, 192;
+ source of nitrogen, 152;
+ suited for horticulture, 425.
+
+ Bohemia, phosphoric acid removed from, 206.
+
+ Bolivia, guano deposits at, 327.
+
+ Bollaert on nitrate deposits, 333.
+
+ Bone-ash, 369;
+ composition of, 372.
+
+ Bone-black, 369;
+ composition of, 372.
+
+ Bone-char, 369;
+ composition of, 372.
+
+ Bone-dust, 360.
+
+ Bone-meal, 361, 364;
+ composition of, 371;
+ condition of nitrogen in, 540.
+
+ Bone-phosphate, 385.
+
+ Bones, 359-372;
+ action of, 365;
+ boiled, 361;
+ bruised, 361;
+ capable of nitrification, 182;
+ collected in Britain, 353, 362;
+ composition of, 362, 371;
+ compound, 372;
+ crops suited for, 368;
+ dissolved, 368, 371;
+ early use of, 359;
+ fermentation of, 361;
+ floated, 365;
+ forms of, 360;
+ grinding of, 365;
+ imports of, 151;
+ inorganic matter in, 363;
+ nitrogen in, 151;
+ organic matter in, 363;
+ putrefaction of, 365, 366;
+ raw, 361;
+ source of nitrogen, 151;
+ treatment of, 364.
+
+ Bonnet, Charles, discovery of source of plant's carbon by, 11.
+
+ Boracic acid in _salinas_, 335.
+
+ Bordeaux phosphate, 379.
+
+ Boussingault, on dry matter in horse-manure, 243;
+ early researches of,
+ in agricultural chemistry, 21;
+ experiments by, on nitrification, 185, 198;
+ on excrements of pig, 250;
+ on nitrates in guano, 304;
+ on nitrogen in plants, 41, 42;
+ on nitrogen in soil, 124;
+ on nitrogen in excreta, 234;
+ on nitrogen lost during fermentation, 245.
+
+ Bracken-fern, analyses of, 283;
+ as litter, 241.
+
+ Bran, manurial constituents in, 282.
+
+ Bretschneider on sources of plant-nitrogen, 42.
+
+ Brewers' grain, manurial constituents in, 282.
+
+ Bromine in ash of plants, 55.
+
+ Browse Island guano, 309, 328;
+ phosphoric acid in, 330.
+
+ Brüstlein and Peters on fixation of bases and acids by soil, 59.
+
+ Buckland, Dr, discovery of coprolites by, 373.
+
+ Buckwheat absorbs ammonia, 352.
+
+ Bull River, phosphates from, 376.
+
+
+ Cabbages, benefited by saline manures, 529;
+ manuring of, 528-529;
+ soils suited for, 529.
+
+ Caird, Sir James, experiments by, with Peruvian guano, 301.
+
+ Calcareous earth, absorptive power of, 98;
+ stones, phosphoric acid in, 211.
+
+ Calcium phosphate in Chincha guano, 305.
+
+ Calcium sulphate in concretionary nodules, 328.
+
+ _Caliche_, composition of, 342;
+ occurrence of, 341.
+
+ California, guano deposits at, 328.
+
+ Cambridgeshire, coprolites from, 373.
+
+ Cameron, Sir Charles, on assimilation of urea by plants, 46.
+
+ Canadian apatite, 201, 374.
+
+ Cape Vert guano, phosphoric acid in, 330.
+
+ Carbolic acid, action of, on nitrifying organisms, 177.
+
+ Carbon, fixation of, by plants, 37;
+ in plants, discovery of source of, 11.
+
+ Carbon bisulphide, effect of, on nitrification, 166, 176.
+
+ Carbonate of ammonia formed in fermentation of dung, 247, 258.
+
+ Carbonic acid, absorbed by plants, 12
+ --by soil, 81;
+ in ash of plants, 55;
+ oxidation of, by bacteria, 95;
+ produced in decomposition of farmyard manure, 258.
+
+ Carbonising-works, ammonia from, 353, 358.
+
+ Carburetted hydrogen, produced in decomposition of farmyard manure, 258.
+
+ Caribbean phosphates, 379.
+
+ Carnallite, 420.
+
+ Carolina phosphate, 376.
+
+ Carrots, manurial constituents in, 282.
+
+ Catacombs, bones from, 360.
+
+ Catch-cropping, 138, 489.
+
+ Cattle foods, average composition of, 557.
+
+ Caustic lime, 453.
+
+ Cereals, manuring of, 493-504;
+ nitrogenous manures benefit, 494;
+ potash in, 217;
+ silicates absorbed by, 494;
+ value of nitrate of soda as manure for, 346.
+
+ Chalk, an adulterant of guano, 319;
+ lias, phosphoric acid in, 211.
+
+ Charcoal, a filter for sewage, 437.
+
+ Charleston phosphate, 376.
+
+ Chemical analysis of manures, interpretation of, 539;
+ value of, 539.
+
+ Chemical composition of soil, 87-92.
+
+ Cheshire, bones used in, 360.
+
+ Chesterfield Island guano, 309.
+
+ Chili and Peru, chief source of nitrate of soda, 162.
+
+ Chincha Island guano, 302, 303, 327;
+ composition of, 305;
+ nitrogen in, 329;
+ phosphoric acid in, 329.
+
+ Chipana, guano deposits at, 327.
+
+ Chlorapatite, composition of, 210.
+
+ Chlorine in ash of plants, 55.
+
+ Chloroform prevents nitrification, 166, 176.
+
+ Chlorophyll, organisms destitute of, 169;
+ produced by nitrate of soda, 347;
+ relation of, to fixation of carbon by plants, 37.
+
+ Chuca, 341.
+
+ Citrate of ammonia, solubility of phosphates in, 408.
+
+ Clay, absorptive power of, 68;
+ analysis of, 107;
+ grey, evaporation of water from, 99;
+ loamy, evaporation of water from, 99;
+ sandy, absorptive power of, 98
+ --evaporation of water from, 99;
+ soils, benefited by basic slag, 414
+ --puddling in, 455;
+ stiffish, evaporation of water from, 99;
+ strong absorptive power of, 98.
+
+ Clover-hay, fertilising ingredients removed from soil by, 486;
+ manurial constituents in, 282;
+ manuring of, 522.
+
+ Clover-sickness, 522.
+
+ Coal, nitrogen in, 353.
+
+ Coke-works, ammonia from, 353, 358.
+
+ Colloids, 491.
+
+ Colour of soil, 80;
+ difference in temperature due to, 80.
+
+ Columbia, guano deposits at, 327.
+
+ Composts, 113, 445-448;
+ farmyard manure a typical, 446;
+ manufacture of, 445;
+ object of, 445;
+ purposes served by, 445;
+ substances used for, 447.
+
+ Compound bones, 372.
+
+ Concretionary nodules, composition of, 328.
+
+ Conglomerate, 341.
+
+ Connecticut, experimental station at, 33.
+
+ Cooke, F. J., on, farmyard manure, 272, 277;
+ field experiments. 547;
+ manuring of barley, 497
+ --of mangels, 514
+ --of meadow-land, 509
+ --of swedes, 514
+ --of wheat, 501.
+
+ Copper, oxide of, in plants, 55.
+
+ Copperas, as a fixer, 246, 247.
+
+ Coprolites, 373;
+ percentage of phosphates in, 201:
+ occurrence of, 201, 373.
+
+ Corcovado guano, nitrogen in, 329;
+ phosphoric acid in, 329.
+
+ Cordilleras, 340, 341.
+
+ Costra, 341.
+
+ Cotton-cake, decorticated, manurial constituents in, 282.
+
+ Cotton-cake, undecorticated, manurial constituents in, 282.
+
+ Cotton-seeds, imports of, 153.
+
+ Cova, 341.
+
+ Covered manure, potatoes grown with, 289;
+ wheat grown with, 289.
+
+ Cow-dung, alkalies in, 226;
+ composition of, in dry state, 227;
+ cool, 225;
+ nitrogen in, 226;
+ phosphoric acid in, 226;
+ water in, 226.
+
+ Cow-manure, 247;
+ amount voided per day, 248;
+ amount voided per year, 248;
+ analysis of, 286;
+ dry matter in, 248;
+ fermentation in, slow, 248;
+ mineral matter in, 248;
+ mucilaginous matter in, 248;
+ nitrogen in, 248;
+ resinous matter in, 248.
+
+ Cow-urine, alkalies in, 230;
+ composition of, in dry state, 231;
+ fertilising ingredients in, for food consumed, 232;
+ nitrogen in, 230;
+ phosphoric acid in, 230;
+ water in, 230.
+
+ Cows, percentage of food voided in excrements of, 281;
+ solid excrements of, 280;
+ urine voided by, 280.
+
+ Cress, experiments with, 41.
+
+ Crimea, bones from, 360.
+
+ Cropped soils, nitrates in, 157
+ --lost by drainage in, 141.
+
+ Crops, capacity of, for assimilating manures, 486;
+ difference in root-systems of, 488;
+ manuring of common farm, 493-530;
+ period of growth of, 489;
+ potash removed in, 218;
+ suited for sewage, 434;
+ variation in composition of, 490.
+
+ Crusius on phosphoric acid removed from the farm, 207.
+
+ Crust guanos, 308, 379.
+
+ Crystalloids, 491.
+
+ Curaçao phosphates, 308, 330, 379.
+
+
+
+ Darmstadt experiments with basic slag, 410-413.
+
+ Darwin on origin of nitrate-fields, 335.
+
+ Daubeny on mineral sources of phosphoric acid, 200.
+
+ Davy, Sir Humphry, lectures of, on agricultural chemistry, 17-19;
+ on heat and water absorbing and retaining properties of soils, 57;
+ on hygroscopic power of soils, 99.
+
+ Dehérain, on nitrification, 52;
+ on nitrification in sulphate of ammonia, 191;
+ on rate of nitrification, 186.
+
+ Denitrification, 177;
+ conditions favourable for, 178;
+ effected by bacteria, 178.
+
+ Derby, Lord, introduction of Peruvian guano by, 301.
+
+ Detmer on humus in soil, 47.
+
+ Dew, action of, on guano, 300;
+ explanation of, 77;
+ most abundant in summer, 78.
+
+ Dicalcic phosphate, 387;
+ formula of, 398;
+ molecular composition of, 398;
+ percentage composition of, 398.
+
+ Digby, Sir Kenelm, on value of nitrates to plants, 45;
+ theory of, on plant-food, 6-8.
+
+ Diorite, phosphoric acid in, 202, 211.
+
+ Direct manures, 113.
+
+ Dissolved-bone compound, 372.
+
+ Dissolved bones, 368; composition of, 371.
+
+ Dissolved guano, 310.
+
+ Dolerite, phosphoric acid in, 202, 211.
+
+ Dolomite, phosphoric acid in, 202, 211.
+
+ Downton experiments on sewage-sludge, 439.
+
+ Drainage, average of thirteen years, 160;
+ nitrates in, 160;
+ nitrates lost by, 140;
+ phosphoric acid lost by, 206;
+ potash lost by, 217.
+
+ Drainings of manure-heaps, analysis of, 290.
+
+ Dried blood, 424;
+ composition of, 424;
+ manure for sugar-cane, 425;
+ potash in, 219;
+ rate of nitrification in, 192;
+ source of nitrogen, 152;
+ suited for horticulture, 425.
+
+ Dried flesh, 425;
+ nitrogen in, 425.
+
+ Dried leaves, as litter, 242;
+ composition of, 242;
+ nitrogen in, 242;
+ phosphoric acid in, 242;
+ potash in, 242.
+
+ Ducks' dung, analysis of, 331.
+
+ Duhamel and Hales, theory of, on plant-growth, 8.
+
+ Dundonald, Earl, treatise by, on agricultural chemistry, 13.
+
+ Dung and urine, composition of, 234.
+
+ Dutrochet on absorption of plant-food, 55.
+
+ Dyer, Dr Bernard, analyses of stable manure by, 283;
+ experiments on peat as litter, 240;
+ on nitrate of soda as manure for mangolds, 349.
+
+
+ Earth, an adulterant of guano, 319;
+ composition of solid crust of, 102.
+
+ Ecuador, guano deposits at, 327.
+
+ Egyptian guano, nitrogen in, 329;
+ phosphoric acid in, 329.
+
+ Elbe, waters of, phosphoric acid in, 206;
+ potash in, 217.
+
+ Elm-tree, water transpired by, 71.
+
+ Enderbury Island guano, 309, 328;
+ phosphoric acid in, 328.
+
+ Endosmosis, 55.
+
+ English farming, 86.
+
+ Equalised guano, 311.
+
+ Essex, coprolites from, 374.
+
+ Estremadura phosphate, 375.
+
+ Ethylamine, nitrification in, 182.
+
+ Evaporation from soil, 71, 72, 98.
+
+ Excreta, amount of nitrogen in, 149, 292;
+ composition of, 226, 292;
+ difference in amount of, for food consumed, 279;
+ liquid, in farmyard manure, 224;
+ solid, in farmyard manure, 224;
+ solid, undigested food in, 224;
+ solid, voided by cows, 280, 292;
+ solid, voided by horse, 292;
+ solid, voided by oxen, 280;
+ solid, voided by sheep, 280, 292.
+
+
+ Factors for calculating manurial ingredients
+ into their different compounds, 553.
+
+ Falkland guano, 308;
+ nitrogen in, 330;
+ phosphoric acid in, 330.
+
+ Fallow-fields, nitrates formed in, 188.
+
+ Fanning Island guano, 328;
+ phosphoric acid in, 330.
+
+ Farmyard manure, 223-292;
+ action of, on soils, 273;
+ ammonia in, 258;
+ amount produced on farm per year, 252;
+ analyses of, 259, 286;
+ application of, 264;
+ ash of, 287, 288;
+ carbonic acid gas in, 258;
+ classes of constituents of, 224;
+ compared with artificials, 476;
+ composition of, 259;
+ denitrification in, 179;
+ depth to plough to, 267;
+ effect of, on potatoes, 520;
+ fertilising matter in, 270;
+ fire-fang in, 264;
+ fresh, composition of, 286, 288;
+ functions of, 268;
+ heat in fermentation of, 78, 253;
+ humates in, 259;
+ humic acid in, 258;
+ inadequate source of nitrogen to soil, 271;
+ indirect influence of, 273;
+ influence of, on soil, 475;
+ Lawes, Sir John, on composition of, 291;
+ Lord Kinnaird's experiments with, 289;
+ marsh-gas in, 258;
+ mineral matter in, 260;
+ moisture in, 260;
+ nitric acid in, 259;
+ nitrogen in, 260;
+ ratio of, to ash ingredients, 271;
+ organic matter in, 260;
+ phosphoretted hydrogen in, 258;
+ phosphoric acid in, 260;
+ potash in, 260;
+ products of decomposition of, 257;
+ rate of application of, 275;
+ retrogression of nitrogen in, 142;
+ rotten, composition of, 287, 288
+ --value of, 261;
+ rotting, effects of, on, 262;
+ solid excreta in, 224;
+ sulphuretted hydrogen in, 258;
+ supplemented with nitrogen, 271;
+ supplemented with phosphoric acid, 272;
+ temperature, effect of, on soil, 79, 274;
+ typical compost, 446;
+ ulmates in, 259;
+ ulmic acid in, 258;
+ unfavourable to certain crops, 477;
+ urine in, 228;
+ value of, 268;
+ variation in composition of, 223;
+ water in, 258.
+
+ Fatty acids in guano, 305.
+
+ Felspars, 103;
+ albite, 103;
+ composition of, 103;
+ labradorite, 220;
+ oligoclase, 103, 214, 220;
+ orthoclase, 103, 214, 220;
+ phosphoric acid in, 211;
+ potash manures, 213;
+ potash in, percentage of, 213, 220.
+
+ Ferment, aerobic, 173, 255;
+ anaerobic, 255.
+
+ Fermentation, ammonium carbonate formed during, 245;
+ in bones, 365;
+ heat of, 79;
+ of farmyard manure, 253;
+ of guano, 299;
+ temperature of, 256.
+
+ Fern, bracken, as litter, 241.
+
+ Ferric chloride, test for sulphocyanates, 355.
+
+ Fertilisers and Feeding Stuffs Act, 543.
+
+ Fertilising ingredients, amount of soluble, in soil, 90;
+ amounts removed by different crops, 484, 485;
+ chemical condition of, in soil, 89;
+ lodge in seed, 491;
+ in soil, 87.
+
+ Fertility, of the soil, 65-97;
+ potential, of soil, 214, 549;
+ properties necessary for, 66;
+ supply of oxygen necessary for, 81.
+
+ Field experiments, 545, 548;
+ educational value of, 547;
+ on rate of nitrification, 187.
+
+ Finger-and-toe prevented by lime, 461.
+
+ Fire-fang in farmyard manure, 264.
+
+ Fischer on absorption of plant-food, 55.
+
+ Fish-guano, 320-323;
+ application of, 323;
+ consumption of, 152;
+ manufacture of, 321;
+ nitrogen in, 321;
+ phosphoric acid in, 321;
+ production of, 322;
+ source of nitrogen, 152;
+ value of, 322.
+
+ Fixers, 246;
+ chemical reactions with, 284.
+
+ Fleece, potash in, 217.
+
+ Fleischer, Professor, on solubility of phosphates, 408.
+
+ Flesh-guano, 320.
+
+ Flint Island guano, 309.
+
+ Flitcham experiments on growth of wheat, 500.
+
+ Floated bones, 362, 365.
+
+ Florida phosphate, 378.
+
+ Fluorapatite, composition of, 210.
+
+ Food, consumed by pigs, 281;
+ dry matter of, voided in dung, 228;
+ percentage of, in excrements, 281.
+
+ Food-constituents, plant, necessary for nitrification, 170.
+
+ Forbes, David, on nitrate-fields of Chili, 334.
+
+ Forest-soils, absence of nitrification in, 193.
+
+ Fowl-dung, 320, 326;
+ analysis of, 331.
+
+ Fownes on phosphoric acid in rocks, 202.
+
+ Frankland, P. F., experiments on nitrification, 52, 167, 198.
+
+ Franklin, Benjamin, experiment of, with gypsum, 462.
+
+ Frey Bentos, meat-meal guano from, 324.
+
+
+ Galapagos Islands, guano deposits at, 327.
+
+ Garden earth, absorptive power of, 98;
+ ammonia in, 128.
+
+ Gas-liquor, ammonia in, 353.
+
+ Gas-works, ammonia from, 353, 358.
+
+ Gases, absorbed by soils, 81;
+ present in soil, 100.
+
+ Gazzeri on retention by soil of plant-food, 57.
+
+ Geese-dung, analysis of, 331.
+
+ Geic acid in humus, 47.
+
+ Gelatin, nitrification in, 182;
+ from bones, 364.
+
+ Germany, agricultural research in, 32;
+ bones imported from, 360;
+ manufacture of meat-meal guano in, 324.
+
+ Germination, influence of temperature on, 76;
+ oxygen necessary for, 81.
+
+ Gilbert, Sir J. Henry, on barley-manuring, 496;
+ on Liebig's mineral theory, 28;
+ on manuring of potatoes, 520;
+ Presidential address of, 61;
+ and see Lawes and Gilbert.
+
+ Glauber on artificial production of nitre, 164.
+
+ Glue, 364.
+
+ Glycin, assimilated by plants, 47.
+
+ Glycocoll, experiments with, 46.
+
+ Gneiss, 106;
+ phosphoric acid in, 207.
+
+ Grandeau, Professor, on forms of plant-food in soil, 107;
+ on loss of phosphoric acid, 207.
+
+ Granite, 105;
+ in guano, 303;
+ phosphoric acid in, 202, 211;
+ potash in, 214.
+
+ Grass, Bangor experiments on, 508;
+ effect of manure on, 505;
+ influence of farmyard manure on, 506;
+ manuring of, 504-510.
+
+ Gray, Asa, on transpiration by plants, 71.
+
+ Great Cayman guano, 379.
+
+ Green manures, 113.
+
+ Grouven on guano, 313.
+
+ Guanape Island guano, 302, 327;
+ nitrogen in, 329;
+ phosphoric acid in, 329.
+
+ Guanine, 304;
+ experiments with, 46.
+
+ Guano, 293-331;
+ action of, as a manure, 312;
+ adulteration of, 318;
+ application of, 315;
+ bat, 325;
+ composition of, 305, 329;
+ crust, 308;
+ deposits of the world, 327;
+ dissolved, 310;
+ equalised, 309;
+ fermentation of, 299;
+ fertilising constituents in, 314;
+ fish, 320-323;
+ importance of, in agriculture, 293;
+ inequality in composition of, 309;
+ influence of, on farming, 294;
+ meat-meal, 324;
+ mode of application of, 315;
+ nitrification in, rate of, 192;
+ nitrogenous, 300-308;
+ origin of, 297;
+ Peruvian, 300-306;
+ phosphatic, 308;
+ quantity to apply, 317;
+ rectified, 311;
+ so-called, 320;
+ source of phosphoric acid, 202;
+ source of potash, 219;
+ value of, as a manure, 296;
+ variation in composition of, 299.
+
+ Gulf of Mexico, guano deposits at, 328.
+
+ Gulls, guano from, 297.
+
+ Gunning on sources of plant-nitrogen, 42.
+
+ Gunpowder, exports of, 149;
+ nitrogen lost in, 149;
+ production, annual, of, 149;
+ saltpetre in, 149, 333.
+
+ Gypsum, 462-464;
+ absorptive power of, 98;
+ action of, mode of, 462--on nitrification, 173;
+ an adulterant of guano, 319;
+ as a fixer, 246, 247, 285;
+ decomposes double silicates, 463;
+ favourable to clover, 464;
+ as an oxidising agent, 464.
+
+
+ Hales, Stephen, theory of, on plant-growth, 8.
+
+ Hampe, Dr, on nitrogen in plants, 46.
+
+ Harting on sources of plant-nitrogen, 42.
+
+ Heat, of soils, 76-78;
+ of fermentation, 78.
+
+ Heiden, Dr, on application of farmyard manure, 265;
+ on fixation of bases and acids by soil, 59;
+ on loss of ammonia from dung, 249;
+ on percentage of food voided by animals, 253;
+ on straw as litter, 244, 249.
+
+ Hellriegel, on amount of water in soils, 75;
+ on barley, 498;
+ on nitrogen in plants, 44.
+
+ Helmont, Van, theory of, on source of plant-food, 4.
+
+ Henslow, Professor, on coprolites, 374.
+
+ Heraüs on organisms in soil, 95.
+
+ Herbage, effect of manure on, 505.
+
+ Herrings as manure, 321.
+
+ Hervé-Mangon, experiments on action of light on plants by, 38.
+
+ Hilgenstock on tetracalcic phosphate, 405.
+
+ Hippuric acid, experiments with, 46;
+ in farmyard manure, 257.
+
+ Hire, De la, on evolution of gases by plants, 11.
+
+ Hofmeister on horse excrements, 243.
+
+ Hoof-guano, source of nitrogen, 152.
+
+ Hoofs and horns, manure from, 425.
+
+ Hops, manuring of, 528;
+ potash removed by, 217;
+ slow-acting manures benefit, 528.
+
+ Horn, capable of nitrification, 182;
+ as manure, 425;
+ nitrogen in, 426;
+ phosphoric acid in, 426.
+
+ Hornblende, 105.
+
+ Horse-dung, alkalies in, 226;
+ composition of, in dry state, 227;
+ hot, 225;
+ nitrogen in, 225, 226;
+ phosphoric acid in, 226;
+ water in, 225, 226.
+
+ Horse-manure, 242;
+ amount produced per day, 243;
+ amount produced per year, 243;
+ analyses of, 283;
+ dry matter in, 243;
+ dry nature of, 245;
+ fermentation rapid in, 245;
+ mineral matter in, 243;
+ nitrogen in, 243, 244.
+
+ Horse-urine, alkalies in, 230;
+ composition of, in dry state, 231;
+ fertilising ingredients in, 232;
+ nitrogen in, 230;
+ phosphoric acid in, 230;
+ water in, 230.
+
+ Hosäus on assimilation of ammonia, 50.
+
+ Howland Island guano. 309, 328;
+ phosphoric acid in, 330.
+
+ Huanillos, guano from, 302, 327;
+ nitrogen in, 330;
+ phosphoric acid in, 330.
+
+ Huano, 297.
+
+ Hueppe on organisms in soil, 95.
+
+ Hughes, John, on bracken-fern as litter, 241;
+ on composition of bracken, 283.
+
+ Humates in farmyard manure, 259.
+
+ Humboldt, A., discovery of Peruvian guano by, 300.
+
+ Humic acid in farmyard manure, 258;
+ in humus, 47.
+
+ Humin in humus, 47.
+
+ Humus, absorptive power of, 68, 98;
+ evaporation from, 99;
+ nature of, in soil, 47;
+ soils improved by addition of, 273.
+
+ Huon Island guano, 309, 328;
+ phosphoric acid in, 330.
+
+ Huxtable and Thompson on retention of plant-food by soil, 57.
+
+ Hydrated silicates, 107, 459.
+
+ Hydrochloric acid as a fixer, 245.
+
+ Hydrogen, amount of, in plants, 40;
+ source of, in plants, 40.
+
+ Hygroscopic power of soils, 75.
+
+
+ Ichaboe guano, 307;
+ nitrogen in, 329;
+ phosphoric acid in, 329.
+
+ Independence Bay guano, 302, 327;
+ nitrogen in, 329;
+ phosphoric acid in, 329.
+
+ India, nitre soils of, 162.
+
+ Indirect manures, 113, 114, 449-473.
+
+ Ingenhousz, John, experiments by, on nitrogen in plants, 41;
+ on oxygen evolved by plants, 12.
+
+ Insoluble phosphate, 386;
+ value of, 396.
+
+ Iodine, in ash of plants, 55;
+ in nitrate of soda, 340, 342.
+
+ Iquique, nitrate of soda from, 333.
+
+ Iron in ash of plants, 54;
+ necessary for plant-growth, 55;
+ reversion in superphosphates caused by, 390, 399.
+
+ Iron-works, ammonia from, 353, 355, 358.
+
+ Irrigation, 431-433;
+ intermittent, 434;
+ subsoil, 432.
+
+
+ Jamieson, Professor, experiments with coprolites, 380.
+
+ Jarvis Island guano, 309, 328;
+ phosphoric acid in, 330.
+
+ Jersey, manuring of potatoes in, 521.
+
+ Johnson, Professor S. W., on application of superphosphate, 395;
+ on Earl Dundonald, 13;
+ on nitrogen in buffalo-horn shavings, 426;
+ on nitrogen in soils, 123;
+ on solubility of basic slag, 408;
+ value of organic nitrogen to plant, 46.
+
+ Jürgensen on nitrogen in excreta, 234.
+
+
+ Kainit, as a fixer, 247;
+ potash in, percentage of, 214, 220, 421;
+ rate of application of, 423.
+
+ Kaolin clay, analysis of, 104.
+
+ Karmrodt, analysis of Chincha Island guano, 305;
+ of concretionary nodules, 328.
+
+ Karnallite, potash in, 220.
+
+ Kellner, experiments on nitrification by, 52.
+
+ Kelp, potash in, 420.
+
+ Kieserite, 420.
+
+ Kinnaird, Lord, experiments by, with farmyard manure, 289.
+
+ Kitchen-garden soil, nitrogenous matter in, 122.
+
+ Knop on condition of nitrates in soil, 138.
+
+ Koosaw River, phosphates from, 376.
+
+ Kreatin assimilated by plants, 47.
+
+ Kuria Muria guano, 309, 328.
+
+
+ Labrador, guano deposits at, 328.
+
+ Labradorite, 214;
+ potash in, 220.
+
+ Lacepede Island guano, 309, 328;
+ phosphoric acid in, 330.
+
+ Lahn phosphate, 379.
+
+ Lava, phosphoric acid in, 202, 211.
+
+ Lawes, Sir J. B., and Gilbert, early researches of, at Rothamsted, 34;
+ experiments with farmyard manure, 271;
+ experiments with Peruvian guano, 301;
+ inauguration of Rothamsted experiments by, 33;
+ on composition of farmyard manure, 291;
+ on manuring of wheat, 483;
+ on motion of plant's sap, 56;
+ on percentage of food in excreta, 233;
+ on rate of nitrification, 186;
+ on sources of plant-nitrogen, 43;
+ on sulphate of ammonia, 356;
+ on unexhausted manures, 550, 557-559.
+
+ Lawes, Sir J. B., experiments with guano by, 301;
+ manufacture of superphosphate by, 382;
+ on application of superphosphate, 395;
+ on bones, 359;
+ on composition of farmyard manure, 291;
+ on farmyard manure, 477;
+ on loss of nitrates, 142;
+ on sources of nitrogen, 154.
+
+ Leather, as manure, 428;
+ nitrogen in, 428.
+
+ Leaves, dried, as litter, 242;
+ nitrogen in, 242;
+ phosphoric acid in, 242;
+ potash in, 242.
+
+ Legrange, Charles, on extent of nitrate-fields, 343.
+
+ Leguminous plants, benefited by basic slag, 414
+ --by potash, 523;
+ fixation of free nitrogen by, 42;
+ gain of nitrogen with, 135;
+ manuring of, 522-527, 530;
+ nitrogenous manures hurtful to, 523.
+
+ Lehmann on ammonia as plant-food, 50, 352.
+
+ Leipzig, bones from, 361.
+
+ Leones, guano deposits at, 327.
+
+ Leucite, potash in, 220.
+
+ Lias chalk, phosphoric acid in, 211.
+
+ Liebig, criticism of humus theory by, 25;
+ dissolved bones discovered by, 361;
+ first report to British Association, 24;
+ manufacture of superphosphate from bones by, 359;
+ mineral theory of, 26-29;
+ on ammonia as a manure, 352;
+ on importation of bones by Britain, 360;
+ researches of, in agricultural chemistry, 23-32;
+ services of, to agricultural chemistry, 31;
+ theory of manures by, 29;
+ theory of, on rotation of crops, 29.
+
+ Light, action of, on plant-growth, 38.
+
+ Lime, 449-461;
+ abundant occurrence of, 452;
+ action of, 461
+ --contradictory, 450
+ --not thoroughly understood, 449
+ --on nitrogenous organic matter, 460
+ --on soil's texture, 455;
+ antiquity of, as a manure, 449;
+ binding effect of, 457;
+ biological action of, 459;
+ caustic, 453;
+ chemical action of, 457;
+ decomposes minerals, 458;
+ different forms of, 453;
+ effect of, on soils, 112;
+ fixed by soils, 58;
+ in ash of plants, 54;
+ mechanical functions of, 455;
+ mild, 453;
+ necessary for nitrification, 171, 459
+ --for plant-growth, 55, 450;
+ neutralises acidity in soils, 458;
+ phosphates of, 385-388;
+ pig excrements contain, 281;
+ prevents clay puddling, 456;
+ returned to soil, 452;
+ soils contain, 450-452.
+
+ Limestone, analyses of, 106;
+ evaporation of water from, 99;
+ occurrence of, 452.
+
+ Linseed, imports of, 153;
+ manurial constituents of, 282.
+
+ Linseed-cake, manurial constituents of, 282.
+
+ Liquid manure, 442-444.
+
+ Lithia in ash of plants, 55.
+
+ Litter, loam as, 239;
+ peat as, 240;
+ straw as, 236;
+ uses of, 236.
+
+ Lloyd on fattening animals, 253.
+
+ Loam, as litter, 239;
+ evaporation of water from, 99;
+ poor in fertilising matter, 239.
+
+ Lobos, guano deposits at, 327.
+
+ Lobos de Afuera guano, 302, 327.
+
+
+ Macabi Island guano, 302, 327;
+ nitrogen in, 329;
+ phosphoric acid in, 329.
+
+ Maercker, Professor, on destruction of nitrifying organisms, 177.
+
+ Magnesia, fixed by soils, 58;
+ in ash of plants, 54;
+ in pig excrements, 281;
+ necessary for nitrification, 171;
+ necessary for plant-growth, 55;
+ sulphate of, as a fixer, 246, 285.
+
+ Maize, absorbs ammonia, 352;
+ fertilising ingredients removed from soil by, 485;
+ manurial constituents in, 282;
+ source of nitrogen, 153.
+
+ Malden Island guano, 309, 328;
+ phosphoric acid in, 330.
+
+ Malpighi on importance of atmospheric air for germination, 39.
+
+ Malt-dust, manurial constituents in, 282.
+
+ Manganese, oxide of, in ash of plants, 54.
+
+ Mangels, fertilising ingredients removed from soil by, 485;
+ guano a manure for, 318;
+ manurial constituents in, 282;
+ manuring of, 346, 511, 513, 514;
+ Rothamsted experiments on growth of, 568.
+
+ Manitoba soils, nitrogen in, at various depths, 156;
+ rate of nitrification in, 186.
+
+ Manure, cow, 247;
+ farmyard, 223-292;
+ horse, 243;
+ liquid, 442-444;
+ meaning of word, 109;
+ pig, 250;
+ sewage, 430-441;
+ sheep, 251;
+ stable, from peat-moss, 283
+ --wheat-straw, 283.
+
+ Manures, action of, 61;
+ analysis of, interpretation of, 539-544;
+ application of, 474-492;
+ method of, 531-538; cash prices of, 555;
+ equal distribution of, 531;
+ functions of, 109, increase soil-fertility, 474;
+ intrinsic value of, 545;
+ lasting effects of, 483;
+ methods of valuing, 544;
+ minor artificial, 424-429;
+ mixing of, 531-538;
+ nitrogenous, 293-359;
+ phosphatic, 359-417;
+ potassic, 418-423;
+ quantities of, applied to oats, 504;
+ unexhausted, 549-552, 558;
+ units for determining commercial value of, 554;
+ valuation of, 539-559;
+ value of, deduced from experiments, 548;
+ various classes of, 111-114.
+
+ Manurial constituents of various foods, 282.
+
+ Manurial ingredients, unit value of, 544.
+
+ Manuring of, barley, 495-498;
+ beans, 525-527, 530;
+ cabbages, 528;
+ cereals, 493-504;
+ clover, 524;
+ common farm crops, 493-530;
+ grass, 504-510;
+ hops, 528;
+ leguminous crops, 522-528;
+ mangels, 511, 513, 514;
+ oats, 493-504;
+ peas, 527;
+ potatoes, 517-522;
+ roots, 510-517;
+ turnips, 510, 511, 513-517;
+ wheat, 499-501.
+
+ Maracaïbo guano, nitrogen in, 330;
+ phosphoric acid in, 330.
+
+ Marl, phosphoric acid in, 211.
+
+ Marsh-gas from farmyard manure, 258.
+
+ Meadow-hay, fertilising ingredients removed from soil by, 485;
+ manurial constituents in, 282;
+ Rothamsted experiments on manuring of, 570.
+
+ Meadow-land, benefited by basic slag, 414, 508;
+ manuring of, 508;
+ Norfolk experiments on, 509.
+
+ Meat-meal guano, 320, 324;
+ composition of, 152;
+ imports of, 324;
+ manufacture of, 324;
+ nitrogen in, 324;
+ phosphoric acid in, 324;
+ rate of nitrification in, 192;
+ source of nitrogen, 152;
+ value of, 324.
+
+ Mechi on liquid manure, 442.
+
+ Mejillones guano, 309, 327;
+ phosphoric acid in, 330.
+
+ Mène, on sources of plant-nitrogen, 42.
+
+ Menhaddo, guano manufactured from, 322.
+
+ Mexico phosphate, 308, 328.
+
+ Mica, analysis of, 105;
+ potash in, 214, 220.
+
+ Micro-organisms, convert ammonia into nitrous acid, 167;
+ convert nitrous acid into nitric acid, 168;
+ effect fermentation, 80;
+ effect fixation of free nitrogen, 44;
+ effect nitrification, 161;
+ oxidising power of, 197.
+
+ Mild lime, 453.
+
+ Milk, nitrification in albuminoids of, 182;
+ nitrogen removed in, 147;
+ phosphoric acid removed in, 207;
+ potash removed in, 218.
+
+ Mineral phosphates, 373-381;
+ value of, as a manure, 380.
+
+ Mineral salts necessary for nitrification, 52.
+
+ Minor artificial manures, 424-429.
+
+ Mixing manures, 532-538;
+ ammonia lost in, 533;
+ nitric acid lost in, 536;
+ phosphates reverted in, 536.
+
+ Moisture, atmospheric, action on guano, 300;
+ in farmyard manure, 260;
+ in manures, 543;
+ necessary for nitrification, 52, 176.
+
+ Molds, 94.
+
+ Mona guano, 309.
+
+ Mond, Ludwig, on nitrogen in coal, 354.
+
+ Monks guano, 327;
+ phosphoric acid in, 330.
+
+ Monocalcic phosphate, 386;
+ formula of, 398;
+ molecular composition of, 398;
+ percentage composition of, 398;
+ reversion of, with iron and alumina compounds, 399
+ --with tricalcic phosphate, 399.
+
+ Mulder on humus in soil, 47, 126.
+
+ Müller, A., on nitrogen in soil, 121, 124.
+
+ Munro, Dr J. M. H., on nitrification, 52;
+ on sewage-sludge as manure, 439;
+ on urine voided, 292.
+
+ Müntz, on ammonia in air, 118;
+ on nitrifying organisms in soil, 180;
+ on oxidising power of micro-organisms, 197.
+
+ Muriate of potash, application of, 423;
+ forms calcium chloride, 422;
+ harmful effects of, 421;
+ more concentrated than sulphate, 422.
+
+ Mustard, 139.
+
+
+ Navassa phosphate, 308, 328, 379.
+
+ Nesbit on composition of guano, 301.
+
+ New Granada, guano deposits at, 327.
+
+ New Zealand, meat-meal guano from, 324.
+
+ Nile, nitrates in waters of, 159.
+
+ "Nitraries," 163.
+
+ Nitrate-fields, appearance of, 340;
+ origin of, 334.
+
+ Nitrate of soda, 332-351;
+ amount exported from Chili, 151, 332, 351;
+ amount imported into Britain, 151, 351;
+ appearance of fields of, 340;
+ application of, 347;
+ Chili and Peru chief source of, 161;
+ composition of, 343;
+ crops suited by, 346;
+ discovery of deposits of, 333;
+ extent of deposits of, 342;
+ encourages deep roots, 344;
+ formation of fields of, 334-340;
+ method of applying, 347;
+ method of mining, 341;
+ nitric acid in, source of, 337;
+ nitrogen in, percentage of, 343;
+ not an exhausting manure, 345;
+ origin of fields of, 334;
+ properties of, 343;
+ quantity to apply, 348;
+ shipments of, 351;
+ soils benefited by, 348;
+ source of
+ nitrogen, 150;
+ top-dressing with, 344.
+
+ Nitrates, amount lost by drainage, 140;
+ amount produced at different times, 189;
+ amount in soil, 129;
+ conditions diminishing loss of, 139;
+ constantly formed in soil, 138;
+ in barley-soils, 158;
+ in cropped soils, 130, 157;
+ in drainage-waters, 160, 188;
+ in fallow-soils, 129;
+ in manured wheat-soils, 131, 157;
+ in soil, 129, 162;
+ lost by drainage, 137;
+ most formed in summer, 139;
+ nitrogen as, in Rothamsted soils, 198;
+ position of, in soil, 188;
+ quantity formed in fallow-fields, 188.
+
+ Nitre, beds, 163;
+ occurrence of, 162;
+ soils of India, 162.
+
+ Nitric acid, amount of, supplied to soil by rain, 155;
+ derived from sea weed, 337;
+ formed from ammonia, 118;
+ formed from nitrous acid, 168;
+ in farmyard manure, 259;
+ in soil, 128;
+ lost in mixing manures, 536;
+ most important nitrogen compound for plants, 161;
+ relation of, to plants, 50;
+ source of, in nitrate of soda, 337.
+
+ Nitrification, 51, 52, 161-198;
+ action of gypsum on, 173;
+ alkalinity necessary for, 172;
+ in asparagin, 182;
+ bearing of, on agriculture, 193;
+ in bones, 182;
+ cause of, 165;
+ conditions favourable for, 170;
+ denitrification, 177-179;
+ effected by micro-organisms, 51, 167;
+ in ethylamine, 182;
+ in fallow-fields, 184;
+ food-constituents necessary for, 170;
+ field experiments on rate of, 187;
+ in gelatin, 182;
+ in horn, 182;
+ laboratory experiments on rate of, 185;
+ in manures, 190, 192;
+ in milk albuminoids, 182;
+ mineral salts necessary for, 52;
+ moisture necessary for, 52, 176;
+ old theories on, 196;
+ organic matter not necessary for, 169, 196;
+ oxygen necessary for, 52, 173;
+ plant-roots promote, 181;
+ in rape-cake, 182;
+ rate of, 183;
+ rotation of crops, bearing of, on, 195;
+ soil best suited for, 192;
+ in subsoils, conditions favourable for, 181;
+ substances capable of, 181;
+ in summer, 183;
+ sunlight, effect of, on, 176;
+ temperature necessary for, 52, 175;
+ in thiocyanates, 182;
+ in urea, 182;
+ in wool, 182.
+
+ Nitrifying organisms, depth found at in soil, 180;
+ distribution of, in soil, 179;
+ effect of poisons on, 176;
+ organic matter not required by, 169.
+
+ _Nitrobaeter_, 167.
+
+ Nitrogen, 115-160;
+ absorbed by soil, 81, 131;
+ accumulates in pastures, 134;
+ in air, 116;
+ as ammonia in soils, 127;
+ amount of, in plants, 40;
+ amount of, in soil, 123;
+ artificial supply of, 150;
+ in bat guano, 325;
+ in bones, 363, 364;
+ combined, in air, 118;
+ combined, in rain, 119, 155;
+ condition of, in manures, 540;
+ converted into nitrates in soil, 51;
+ in cow-dung, 226-228;
+ in cow excrements, 278;
+ in cow-urine, 230;
+ difference between surface and subsoil, 126;
+ different forms of, 45, 116;
+ dissolved in rain, 131;
+ in dried blood, 424;
+ in farmyard manure, 260;
+ in fish-guano, 321;
+ fixation of free, 136;
+ forms of, in plants, 491;
+ free, relation of, to plant, 117;
+ gain of, with leguminous crops, 135;
+ in guanos, 329;
+ in hoofs and horns, 426;
+ in horse-dung, 226-228;
+ in horse-manure, 243;
+ in horse-urine, 230;
+ importance of, in soil, 88;
+ in lean flesh, 424;
+ in leather, 428;
+ least abundant of manurial ingredients in soil, 271;
+ loss of, artificial sources of, 144;
+ loss of, by crops, 144;
+ loss of, on farm, 146;
+ loss of, sources of, 137-150;
+ loss of, total amount of, 142;
+ lost in the arts, 148;
+ lost in free condition, 141;
+ lost in treating farmyard manure, 146;
+ lost in milk, 147;
+ lost by retrogression, 142;
+ in Manitoba soils, 156;
+ in meat-guano, 324;
+ nature of, in soil, 124;
+ as nitrates in soil, 128;
+ as nitrates in cropped soils, 130, 157;
+ as nitrates in Rothamsted soils, 198;
+ as nitrates in wheat-soils, 157;
+ in nitrate of soda, 343;
+ nitric, in soil, 128;
+ organic, absorbed by plants, 47;
+ organic, in soil, 125;
+ original source of, in soil, 133;
+ in oxen excrements, 280;
+ in pasture-lands, 158;
+ peat-soils richest in, 123;
+ in Peruvian guano, 302, 306, 307, 329;
+ in pig-dung, 226-227;
+ position of, in agriculture, 115-160;
+ relative manurial value of, 556;
+ Rothamsted experiments on, 115;
+ in scutch, 427;
+ in sewage, 431;
+ in sewage-sludge, 439;
+ in sheep-dung, 226-228;
+ in sheep excrements, 280;
+ in sheep-urine, 230;
+ in soil, 120;
+ in soil, portion of, easily nitrifiable, 187;
+ in soils at various depths, 156;
+ in soot, 428;
+ source of, in plants, 15, 16, 40-52;
+ sources of soil, 131-137;
+ in straw, 237, 243;
+ in subsoil, 121;
+ in surface-soil, 121;
+ in swine-urine, 230;
+ in woollen rags, 427.
+
+ Nitrogenous guano, 300-308, 329.
+
+ Nitrogenous manures, application of, 478;
+ benefit cereals, 494;
+ hurtful to leguminous crops, 523.
+
+ Nitrogenous organic substances, in Chincha guano, 305;
+ in concretionary nodules, 328.
+
+ _Nitrosomonas_, 167.
+
+ Nitrous acid, converted into nitric acid, 168;
+ formed from ammonia, 167.
+
+ Nobbe, on fixation of free nitrogen, 136;
+ on potash in soil, 108.
+
+ Nöllner on origin of nitrate-fields, 339.
+
+ Norfolk, coprolites from, 374;
+ experiments on barley, 497
+ --on meadow-land, 509
+ --on turnips, 513.
+
+ North America, guano from, 298, 328.
+
+ Norwegian apatite, 375.
+
+
+ Oak-tree, water transpired by, 71.
+
+ Oat-straw, composition of, 238;
+ manurial constituents in, 282.
+
+ Oats, Arendt's experiments with, 503;
+ avenine in, 503;
+ fertilising ingredients removed from soil by, 485;
+ hardy crop, 502;
+ manurial constituents in, 282;
+ manuring of, 501-504;
+ nitrogen removed in crop of, 148;
+ require mixed nitrogenous manures, 502;
+ source of nitrogen, 153;
+ Rothamsted experiments on growth of, 567.
+
+ _Oficinas_, 342.
+
+ Ohlendorff, introduction of dissolved guano by, 311.
+
+ Oilcakes, imports of, 153;
+ source of nitrogen, 153.
+
+ Oil-seeds, source of nitrogen, 153.
+
+ Oligoclase felspars, 103, 214;
+ composition of, 103;
+ potash in, 220.
+
+ Organic matter, in bones, 363;
+ in dung, 228, 260;
+ in manures, 543;
+ not necessary for nitrifying organism, 169.
+
+ Orthoclase felspars, 103, 214;
+ composition of, 103;
+ potash in, 220.
+
+ Ox-dung, fertilising ingredients in, for food consumed, 228.
+
+ Ox-urine, fertilising ingredients in, 232.
+
+ Oxalic acid in guano, action of, 330.
+
+ Oxen, excrements of, 280;
+ food aided by, 280;
+ solid excreta voided by, 280;
+ urine voided by, 280.
+
+ Oxidation, 79;
+ products of, 79, 80.
+
+ Oxygen, absorbed by plant-roots, 81;
+ absorbed by soil, 81;
+ evolved by plants, 11;
+ necessary for fertility, 81;
+ necessary for nitrification, 52, 173;
+ percentage of, in plants, 39;
+ source of, in plants, 39.
+
+
+ Pabellon de Pica, guano from, 298, 302, 327;
+ nitrogen in, 330;
+ phosphoric acid in, 330.
+
+ Pacific Islands, guano from, 298.
+
+ Pacific Ocean, sea-weed in, 339.
+
+ Palagonite as potash manure, 213.
+
+ Palm-kernel meal, manurial constituents in, 282.
+
+ Pasteur, on fermentation in urine, 255;
+ on nitrification, 166.
+
+ Pastures, accumulation of nitrogen in, 134;
+ benefited by basic slag, 414;
+ deficient in lime, 451;
+ effect of manure on herbage of, 505;
+ nitrogen in, 158;
+ permanent, 138, 194
+ --manuring of, 509;
+ season influences, 507;
+ soil influences, 507.
+
+ Patagonian guano, 308, 327;
+ nitrogen in, 330;
+ phosphoric acid in, 330.
+
+ Patent phosphate meal, 405.
+
+ Patillos, guano deposits at, 327.
+
+ Patos Island, guano deposits at, 328;
+ phosphoric acid in, 330.
+
+ Patterson on superphosphate, 399.
+
+ Payen and Boussingault on composition of dried flesh, 425.
+
+ Peas, manurial constituents in, 282;
+ manuring of, 527;
+ phosphorus in, 205;
+ source of nitrogen, 153.
+
+ Peat, absorbing properties of, 239;
+ adulterant of guano, 317;
+ analysis of stable-manure from, 281;
+ litter, 239;
+ nitrogen in, 240;
+ retaining properties of, 240;
+ soils, 123.
+
+ Pelicans, guano from, 297.
+
+ Penguin Island guano, 330;
+ nitrogen in, 330;
+ phosphoric acid in, 330.
+
+ Penguins, guano from, 297.
+
+ Percival on carbonic acid in plants, 12.
+
+ Peru, guano deposits in, 327;
+ guano first used in, 297;
+ nitrate of soda from, 161, 162.
+
+ Peruvian guano, 300-306;
+ appearance of, 303;
+ composition of, 304-306;
+ deposits of, 301;
+ imports of, 151, 297;
+ source of nitrogen, 151.
+
+ Peters and Eichhorn on solvent power of salt, 471.
+
+ Petzholdt on sources of plant's nitrogen, 42.
+
+ Pfeffer on action of light on plant-growth, 38.
+
+ Phoenix Island guano, 309.
+
+ Phosphate of iron in Chincha guano, 305.
+
+ Phosphate of lime, in Algerian phosphate, 379;
+ in apatite, 374;
+ in Belgian phosphate, 377;
+ in bones, 364;
+ in Cambridge coprolites, 374;
+ in Carolina phosphates, 376;
+ in crust guanos, 379;
+ in Estremadura phosphate, 375;
+ in Florida phosphate, 378;
+ in French phosphates, 379;
+ in Lahn phosphates, 379;
+ in Somme phosphate, 378;
+ reverted in mixing manures, 537.
+
+ Phosphates of lime, 385-388, 398;
+ importance of mechanical condition of, 542.
+
+ Phosphates, mineral, 373-381;
+ imports of, 381;
+ value as a manure, 380.
+
+ Phosphatic guano, 308, 330.
+
+ Phosphatic manures, application of, 480.
+
+ Phosphoretted hydrogen in farmyard manure, 258.
+
+ Phosphoric acid, 199-211;
+ in ash of plants, 54;
+ in basic slag, 404;
+ in bat guano, 325;
+ in bones, 363;
+ condition of, in soil, 203;
+ in cow-dung, 226-228;
+ in cow excrements, 280;
+ in cow-urine, 230;
+ in farmyard manure, 260;
+ in fish-guano, 321;
+ fixed by soils, 58;
+ gain of, 208;
+ in guano, percentage of, 329, 330;
+ guano a source of, 202;
+ in hoofs and horns, 426;
+ in horse-dung, 226-228;
+ in horse-urine, 230;
+ importance of, 88;
+ loss of, artificial sources of, 206
+ --by drainage, 206
+ --in farmyard manure, 208
+ --in milk, 207
+ --in sewage, 208
+ --sources of, in agriculture, 205;
+ in meat-guano, 324;
+ mineral sources of, 200;
+ necessary for plant-growth, 55;
+ occurrence of, in animals, 205
+ --in nature, 199
+ --in plants, 204
+ --in soil, 203;
+ in oxen excrements, 280;
+ in pig-dung, 226, 227;
+ in pig excrements, 281;
+ in pig-urine, 230;
+ position of, in agriculture, 199-211;
+ relative trade values of, in manures, 400;
+ in rocks, 202, 211;
+ in sewage-sludge, 441;
+ in sheep-dung, 226-228;
+ in sheep excrements, 280;
+ in sheep-urine, 230;
+ statement of, in analyses of manures, 541.
+
+ Phosphorite, 201, 374.
+
+ Phosphorus, in albuminoids, 205;
+ in animals, 205;
+ in beans, 205;
+ in peas, 205;
+ in plants, 204;
+ in pig-iron, 401.
+
+ Physical properties of soils, 66-87.
+
+ Pichard on action of gypsum on nitrification, 173.
+
+ Pig-dung, composition of, 226;
+ in dry state, 227.
+
+ Pig excrements, 281;
+ composition of, 281.
+
+ Pig-manure, 250;
+ amount produced per day, 251;
+ mineral matter in, 251;
+ nitrogen in, 251;
+ poor in nitrogen, 251.
+
+ Pig-urine, composition of, 230
+ --in dry state, 231.
+
+ Pigeon-dung, 320, 325;
+ analysis of, 331.
+
+ Pigs, excrements of, 281;
+ food consumed by, 281.
+
+ Pisagua, nitrate-fields at, 340.
+
+ Plant, action of light on, 38;
+ amount of hydrogen in, 40
+ --nitrogen in, 40
+ --oxygen in, 40;
+ ash constituents of, 53-55;
+ carbon fixed by, 37, 38;
+ food, absorption of, by, 55;
+ phosphoric acid in, 204;
+ potash in, 216;
+ proximate composition of, 36;
+ relation of ammonia to, 48-50;
+ source of hydrogen in, 40
+ --nitrogen in, 40-52
+ --oxygen in, 39, 40.
+
+ Plant-food, absorption of, 490;
+ amount of soluble, in soil, 100;
+ early theories on source of, 4;
+ retained by soil, 57.
+
+ Plant-roots, grow downwards, 84;
+ nitrification promoted by, 181;
+ openness required by, 83;
+ room required by, 85;
+ soil in relation to, 84.
+
+ Pliny, on lime as a manure, 449;
+ on salt as a manure, 465.
+
+ Pockets a source of phosphoric acid, 202.
+
+ Poisons, effect of, on nitrifying organisms, 176.
+
+ Polstorff on ash constituents of plants, 53.
+
+ Polyhallite, potash in, 220, 420.
+
+ Porphyry, in guano, 303;
+ phosphoric acid in, 202, 211.
+
+ Potash, 212-220, 418-423;
+ in ash of plants, 54;
+ in barilla, 420;
+ chloride of, 218;
+ condition of, in soil, 216;
+ in cows' excrements, 280;
+ in drainage-waters, 217;
+ in farmyard manure, 260;
+ in felspars, 220;
+ in fleece, 217;
+ fixed by soils, 58;
+ importance of, in soil, 88;
+ in kelp, 420;
+ less important than phosphoric acid, 212;
+ manures, 218, 418-423;
+ muriate of, 218, 421;
+ necessary for nitrification, 171;
+ necessary for plant-growth, 55;
+ occurrence of, 213;
+ in ocean, 213;
+ in oxen excrements, 280;
+ in pig excrements, 280;
+ in plants, 216;
+ position of, in agriculture, 212-220;
+ relative manurial value of, 556;
+ Scottish soils supplied with, 419;
+ in sheep excrements, 280;
+ soda replaces, 466;
+ sources of loss of, 217;
+ in Stassfurt salts, 214;
+ statement of, in analyses of manures, 542;
+ in sugar-beet refuse, 219;
+ sulphate of, 218, 421;
+ in wood-ashes, 218, 220, 419.
+
+ Potash manures, 218, 418-423;
+ application of, 422, 480
+ --rate of, 423;
+ barilla as, 420;
+ crops suited for, 423;
+ relative importance of, 418;
+ soils suited for, 423;
+ sources of, 419;
+ Stassfurt salts as, 420;
+ wood-ashes a source of, 419.
+
+ Potassium phosphate in concretionary nodules, 328.
+
+ Potassium sulphate, in Chincha guano, 305;
+ in concretionary nodules, 328.
+
+ Potatoes, effect of farmyard manure on, 520;
+ fertilising ingredients removed from soil by, 485;
+ grown with covered manure, 289;
+ Highland Society's experiments on, 518;
+ manurial constituents in, 282;
+ manuring of, 517-522
+ --in Jersey, 529
+ --influences composition of, 521;
+ potash removed in, 217;
+ Rothamsted experiments on, 519, 571.
+
+ Precipitated ammonium phosphate in concretionary nodules, 328.
+
+ Precipitated phosphate, 330, 387.
+
+ Precipitation, treatment of sewage by, 436.
+
+ Priestley, discovery of evolution of oxygen by plants, 11;
+ on nitrogen in plants, 40.
+
+ Prussiate of potash, manufacture of, 353.
+
+ Pugh on sources of plant-nitrogen, 42.
+
+ Punta de Lobos guano, 302;
+ nitrogen in, 303;
+ phosphoric acid in, 303.
+
+ Punta de Patillos, guano deposits at, 327.
+
+ Pyroxene, potash in, 220.
+
+
+ Quartz, evaporation of water from, 99.
+
+ Queensland, meat-meal guano from, 324.
+
+ Quercitan, experiments of, with roses, 8.
+
+
+ Rape-cake, capable of nitrification, 182;
+ manurial constituents in, 282.
+
+ Rape-seeds, imports of, 153.
+
+ Raza Island guano, 328;
+ phosphoric acid, 330.
+
+ Rectified guano, 311.
+
+ Relative trade values of phosphoric acid, 400.
+
+ Resin in guano, 305.
+
+ Retentive power of soils for water, 70-73.
+
+ Retrogression, nitrogen lost by, 142.
+
+ Reverted phosphates, 389-391;
+ determination of amount of, 391;
+ formation of, 387;
+ value of, 391.
+
+ Rhine, nitrates in waters of, 158.
+
+ Rice-meal, an adulterant of guano, 319;
+ manurial constituents of, 282.
+
+ Rocks, phosphoric acid in, 202.
+
+ Roots, influence of manures on composition of, 512;
+ manuring of, 510-522;
+ Norfolk experiments on, 513;
+ potash removed in, 217.
+
+ Rotation of crops, bearing of, on nitrification, 195.
+
+ Rotations, phosphoric acid in, 290;
+ potash removed in, 290.
+
+ Rothamsted, alternate wheat and bean rotation at, 524;
+ ammonia in rain at, 49;
+ barley experiments at, 566;
+ Broadbalk Field, alteration in composition of, 159
+ --manuring of, 159
+ --produce of wheat on, 159;
+ early experiments at, 33-36;
+ experiments, 560-572;
+ experiments with nitrate of soda at, 347;
+ experiments on nitrogen question at, 115
+ --mangel-wurzel, 568
+ --oats, 567
+ --potatoes at, 519
+ --value of nitrogen in farmyard manure, 271;
+ increase of nitrogen with manures at, 137, 513;
+ nitrates in barley-soils of, 158;
+ nitrates in cropped soils of, 130, 157;
+ nitrates in drainage of, 189;
+ nitrates in wheat-soils of, 131, 157;
+ nitrogen as nitrates in soils of, 129, 198;
+ nitrogen, decrease of, in soils, 159;
+ nitrogen in pasture at, 126;
+ pasture, increase of nitrogen in, 158;
+ retrogression of nitrogen at, 142;
+ soil, nature of, 561
+ --nitrogen in, at various depths, 156;
+ total amount of nitrogen lost at, 142;
+ turnip experiments at, 568;
+ unmanured fallow-land loses nitrogen by drainage at, 141;
+ wheat experiments at, 500, 562-565.
+
+ Roy on sources of plant-nitrogen, 42.
+
+ Rubidia in ash of plants, 55.
+
+ Ruffle, John, on superphosphate, 388.
+
+ Rye, manurial constituents in, 282.
+
+ Rye-grass suited for sewage, 435.
+
+ Rye-straw, summer, composition of, 238;
+ winter, composition-of, 238.
+
+
+ St Helena, experiments at, with Peruvian guano, 301.
+
+ Saldanha Bay guano, 328;
+ nitrogen in, 329;
+ phosphoric acid in, 329.
+
+ _Salinas_, 335.
+
+ Salm-Horstmar, Prince, on water-culture, 54.
+
+ Salt, 465-473;
+ action of, on crops, 472;
+ adulterant of guano, 319;
+ amount applied, 473;
+ antiquity of use of, 465;
+ an antiseptic, 468;
+ application of, 472;
+ clarifies water, 470;
+ coagulates clay, 470;
+ decomposes minerals, 470;
+ a germicide, 468;
+ indirect action of, 468;
+ mechanical action of, 470;
+ nature of action of, 465;
+ not a necessary plant-food, 466;
+ occurrence of, 467;
+ prevents rapid fermentation, 471;
+ quantity to apply, 473;
+ solvent action of, 470;
+ sources of, 468.
+
+ Saltpetre, formation of, 164;
+ occurrence of, 215;
+ plantations, 163.
+
+ Sand, absorptive power of, 68;
+ an adulterant of guano, 319;
+ calcareous, absorptive power of, 98;
+ siliceous, absorptive power of, 98.
+
+ Sandy soils deficient in lime, 451.
+
+ Sandwich Islands, guano deposits at, 328.
+
+ Saragossa Sea, sea-weed in, 339.
+
+ Saussure, De, on absorption of gases by soil, 81;
+ on nitrogen in plants, 41;
+ researches on plant-food by, 15.
+
+ Sawdust an adulterant of guano, 319.
+
+ Scheibler, Professor, on basic slag, 404.
+
+ Schloesing and Müntz, on nitrification, 51, 166;
+ experiments on rate of nitrification by, 185;
+ on denitrification, 179;
+ on ferments effecting nitrification, 167;
+ on fixation of free nitrogen, 42;
+ on ammonia in air, 119, 132;
+ on nitrogen absorbed by soil from air, 132;
+ on temperature favourable for nitrification, 175.
+
+ Schoenite, potash in, 220.
+
+ Schübler, on absorptive power of soils, 98;
+ on retentive power of soils, 98.
+
+ Schulze on fixers, 246.
+
+ Scutch, 427;
+ manufacture of, 427;
+ nitrogen in, 427.
+
+ Sea-weed, nitric acid in, 339.
+
+ Seals, guano from, 297.
+
+ Seed, fertilising ingredients lodge in, 491.
+
+ Seine, nitrates in waters of, 158.
+
+ Sénébier, Jean, on carbon in plants, 12;
+ on nitrogen in plants, 41.
+
+ Sewage, 430-441;
+ charcoal a filter for, 437;
+ crops suited for, 434;
+ denitrification in, 179;
+ dry matter in, 431;
+ effects of continued applications of, 433;
+ filters for, 437;
+ irrigation with, 431-433;
+ nitrification in, 166;
+ nitrogen lost in, 149;
+ phosphoric acid lost in, 149;
+ purified by soils, 435;
+ treatment of, by precipitation, 436;
+ value of, as a manure, 430.
+
+ Sewage-sick land, 433.
+
+ Sewage-sludge, 438-441;
+ as a manure, experiments with, 438;
+ nitrogen in, 439;
+ phosphoric acid in, 439;
+ profitable treatment of, 441;
+ value of, 439;
+ water in, 438.
+
+ Shale-works, sulphate of ammonia, from, 358.
+
+ Shark's Bay guano, 309, 328.
+
+ Sheep, excrements of, 280, 281;
+ solid excreta voided by, 280;
+ urine voided by, 280.
+
+ Sheep-dung, alkalies in, 226;
+ composition of, in dry state, 227;
+ most valuable excrement, 227;
+ nitrogen in, 226;
+ phosphoric acid in, 226;
+ water in, 226.
+
+ Sheep-manure, 251;
+ amount produced per day, 251
+ --per year, 252;
+ dry matter in, 252;
+ mineral matter in, 252;
+ nitrogen in, 252.
+
+ Sheep-urine, alkalies in, 230;
+ composition of, in dry state, 231;
+ most valuable urine, 231;
+ nitrogen in, 230;
+ phosphoric acid in, 230;
+ water in, 230.
+
+ Shoddy, 427;
+ production of, 152, 425;
+ nitrogen in, 152, 427.
+
+ Sicily, bones from, 360.
+
+ Sidney Island guano, phosphoric acid in, 330.
+
+ Siemens, Dr, experiments by, with light on plants, 38.
+
+ Silica, in ash of plants, 55;
+ in Chincha guano, 305;
+ jelly, 169;
+ necessary for plant-growth, 55.
+
+ Silicates, 102;
+ absorbed by cereals, 494.
+
+ Silicic acid fixed by soils, 58.
+
+ Simon on humus in soil, 47.
+
+ Slaked lime, 454.
+
+ Slugs killed by lime, 461.
+
+ Smut prevented by lime, 461.
+
+ Soda, in ash of plants, 54;
+ fixed by soils, 58;
+ necessary for plant-growth, 55;
+ nitrate of, 332-351;
+ in _salinas_, 335;
+ replaces potash, 466.
+
+ Sodium chloride in Chincha Island guano, 305.
+
+ Sodium phosphate in concretionary nodules, 328.
+
+ Sodium sulphate in concretionary nodules, 328.
+
+ Soil, 65-108;
+ absorptive power of, for water, 67, 98;
+ acids fixed by, 58-60;
+ action of lime on, 453;
+ ammonia absorbed by, 81;
+ amount of soluble plant-food in, 100;
+ artificial, 54;
+ barley, nitrates in, 158;
+ bases fixed by, 58-60;
+ best suited for nitrification, 192;
+ biological properties of, 92-96;
+ capacity for heat, 76-78;
+ carbonic acid absorbed by, 81;
+ chemical composition of, 87-92, 101-107;
+ colour of, 80;
+ cropped, nitrates in, 157;
+ denitrification in, 177;
+ evaporation from, 71, 72;
+ farmyard manure, action of, on, 272;
+ fertilising ingredients in, 87;
+ fertility of, 65-108;
+ fineness of, 69-70;
+ gases in, 100;
+ hygroscopic power of, 75-76, 99;
+ improved by humus, 272;
+ influence of farmyard manure on, 475;
+ on nitrification, 180;
+ manures increase fertility of, 474;
+ nitrates in, amount of, 128-131;
+ nitrifying organisms in, 179;
+ distribution of, 179;
+ nitrogen absorbed by, 81, 82, 131;
+ nitrogen accumulates, 133;
+ nitrogen in, amount of, 120-128;
+ nitrogen least abundant of manurial ingredients in, 270;
+ nitrogen at various depths in, 156;
+ oxygen absorbed by, 81;
+ phosphoric acid in, 203
+ --condition of, in, 203
+ --occurrence of, in, 203;
+ peat, 123;
+ possesses power of fixing ammonia, 57;
+ potash in, 215
+ --condition of, in, 216;
+ potential fertility of, 549;
+ power of, for absorbing gases, 81;
+ relation of, to plant-roots, 84;
+ retention of plant-food by, 57;
+ retentive power of, for water, 70-73;
+ sewage purified by, 435;
+ shrinkage of, 74;
+ variation in absorbing powers of, 82;
+ varieties of, 67;
+ virgin, 133;
+ water in, most favourable amount of, 75;
+ water-logged, 179;
+ wheat, nitrates in, 157.
+
+ Soluble phosphate, 386.
+
+ Sombrero phosphate, 308, 328, 330, 379;
+ phosphoric acid in, 330.
+
+ Somme phosphate, 378.
+
+ Soot, 428;
+ application of, rate of, 429;
+ crops suited by, 429;
+ nitrogen in, 428.
+
+ South America, guano deposits in, 327;
+ meat-meal guano from, 324.
+
+ Starbuck Island guano, 309, 328;
+ phosphoric acid in, 330.
+
+ Stassfurt salts, 214;
+ potash in, 215, 420.
+
+ Stead and Ribsdale on formation of basic slag, 407.
+
+ Stoeckhardt, on composition of solid excreta, 226;
+ on composition of urine, 229.
+
+ Storer, Professor, on composition of birds' dung, 331;
+ on composition of leaves, 242;
+ on fish-guano, 323;
+ on nitrogen removed in milk, 147.
+
+ Straw, composition of, 238;
+ imports of, 153;
+ as litter, 236, 248;
+ mineral matter in, 238, 243;
+ nitrogen in, 237, 243;
+ variation in composition of, 237.
+
+ Subsoil, conditions favourable for nitrification in, 181.
+
+ Suffolk coprolites, 374.
+
+ Sugar-beet refuse, potash in, 219.
+
+ Sulphate of alumina, a precipitant of sewage, 437.
+
+ Sulphate of ammonia, 352-358;
+ ammonia in, 355;
+ application of, 356;
+ composition of, 355;
+ a concentrated nitrogenous manure, 356;
+ converted into nitrates, 356;
+ from gas-works, 353;
+ from iron-works, 355;
+ from shale-works, 354;
+ manure for cereals, 356;
+ most easily nitrifiable manure, 191;
+ production of, 151, 358;
+ properties of, 355;
+ source of nitrogen, 149;
+ sources of, 353, 354, 358;
+ sulphocyanate of ammonia in, 355.
+
+ Sulphate of lime a fixer, 246.
+
+ Sulphate of magnesia, an adulterant of guano, 319;
+ as a fixer, 246.
+
+ Sulphate of potash, application of, 422
+ --rate of, 423;
+ compared with muriate, 421;
+ sources of, 218, 420.
+
+ Sulphuretted hydrogen from farmyard manure, 258.
+
+ Sulphuric acid, action of, on bones, 382
+ --on guano, 311
+ --on tricalcic phosphate, 398;
+ in ash of plants, 54;
+ as a fixer, 245, 285;
+ necessary for plant-growth, 55;
+ superphosphate manufactured with, 384, 388.
+
+ Superphosphate, 382-400;
+ action of, 392-395
+ --sometimes unfavourable, 395;
+ application of, 395
+ --rate of, 397;
+ composition of, 391;
+ discovery of, 382;
+ hastens early growth, 394;
+ high-class, 392;
+ low-class, 392;
+ manufacture of, 383-385
+ --phosphates suitable for, 384;
+ medium-class, 391;
+ production of, 382;
+ reversion in, 389, 399, 400
+ --causes of, 389, 390;
+ reverted in soil, 392.
+
+ Surprise Island guano, 328.
+
+ Swan Island guano, 328.
+
+ Swedes, fertilising ingredients removed from soil by, 485;
+ manurial constituents in, 282;
+ manuring of, 514.
+
+ Swine-dung, alkalies in, 226;
+ composition of, 227;
+ nitrogen in, 226;
+ phosphoric acid in, 226;
+ water in, 226.
+
+ Swine-urine, alkalies in, 230;
+ composition of, 231;
+ nitrogen in, 230;
+ phosphoric acid in, 230;
+ water in, 230.
+
+ Sydney Island guano, 309.
+
+ Syenite, 106;
+ phosphoric acid in, 202, 211.
+
+ Sylvin, potash in, 220.
+
+ _Symbiosis_, 44.
+
+
+ Tamarugal, Pampa de, nitrate deposit in, 340.
+
+ Tarapaca, nitrate deposits in, 340.
+
+ Temperature necessary for nitrification, 52, 175.
+
+ Tetracalcic phosphate, 387;
+ occurrence of, 387, 405;
+ solubility of, 387.
+
+ Thaer on application of farmyard manure, 275.
+
+ Thiocyanates, nitrification in, 182.
+
+ Thomas-Gilchrist process of steel-smelting, 402.
+
+ Thomas-slag. See Basic slag.
+
+ Tillage increases number of plants, 86.
+
+ Timor Island guano, 309.
+
+ Tobacco, potash in, 217.
+
+ Torrefied horn, 426.
+
+ Torrefied leather, 428.
+
+ Tortola guano, 309.
+
+ Trachyte, phosphoric acid in, 202, 211.
+
+ Transpiration, by elm-tree, 71;
+ by oak-tree, 71.
+
+ Trees, as pumping-engines, 76;
+ water transpired by, 71.
+
+ Tricalcic phosphate, 386, 398.
+
+ Tubercles on roots of plants, 44.
+
+ Tull, Jethro, theory of, on plant-growth, 9-11, 69, 109.
+
+ Turkey, dung produced by, 331.
+
+ Turnips, fertilising ingredients removed from soil by, 485;
+ manurial constituents in, 282;
+ manuring of, 510, 511, 513-517;
+ Rothamsted experiments on growth of, 568.
+
+ Twigs, potash in, 217.
+
+ Tyrosin, assimilated by plants, 47.
+
+
+ Ulmates in farmyard manure, 259.
+
+ Ulmic acid, in farmyard manure, 258;
+ in humus, 47.
+
+ Ulmin in humus, 47.
+
+ Uncovered farmyard manure, 263, 289.
+
+ Unexhausted manures, valuation of, 549-552, 558.
+
+ Unit value of manurial ingredients, 544.
+
+ Units for determining commercial value of manures, 554.
+
+ Urate of ammonium in Chincha Island guano, 305.
+
+ Urea, assimilated by plants, 46;
+ in farmyard manure, 257;
+ nitrification in, 182.
+
+ Uric acid, experiments with, 46;
+ in Chincha Island guano, 305.
+
+ Urine, 228;
+ amount voided, 291;
+ composition of, varies, 228;
+ contains digested manurial ingredients, 228, 232;
+ devoid of phosphoric acid, 205;
+ and dung, composition of, 234;
+ influence of food on, 229;
+ nitrification in, 197;
+ nitrogen in, 292;
+ potash in, 292;
+ voided by cows, 280;
+ voided by oxen, 280;
+ voided by pigs, 281;
+ voided by sheep, 280.
+
+ Uruguay, meat-meal guano from, 324.
+
+
+ Valuation of manures, 539-559.
+
+ Vegetation, desirable to have soil covered with, 194.
+
+ Venezuela, guano deposits at, 327.
+
+ Ville, Georges, on assimilation of ammonia, 50;
+ theory of, on source of plant-nitrogen, 41.
+
+ Vine, potash removed by, 216.
+
+ Virgin soils, 133.
+
+ Voelcker, Dr, analysis of apatite, 210
+ --of farmyard manure, 259;
+ on action of superphosphate, 395;
+ on fresh and rotted dung, 261, 286;
+ on guano, 316;
+ on salt as a manure, 473.
+
+ Voss, Hermann, on manures used, 152.
+
+
+ Wagner, Professor, on, application of basic slag, 416;
+ assimilation of organic nitrogen, 46;
+ experiments with basic slag, 408-413;
+ fineness of basic slag, 409;
+ manures, 412;
+ relative manurial value of nitrogen compounds, 556;
+ solubility of basic slag, 408.
+
+ Wallace, Dr, on sewage purification, 436.
+
+ Walruses, guano from, 297.
+
+ Warington, R,., on ammonia in rain, 49;
+ on appearance of nitrous organisms, 168;
+ on conditions favourable for nitrification, 181;
+ experiments on rate of nitrification, 186;
+ on composition of farmyard manure, 260;
+ on manufacture of superphosphate, 383;
+ on manurial constituents of foods, 282;
+ on nitrification in alkaline solutions, 197;
+ on nitrogen in excrements, 233;
+ on nitrogen in soil, 122;
+ on potash in wool, 227;
+ researches of, on nitrification, 35, 52, 166-168, 180, 186.
+
+ Water, absorbed by plants, 73;
+ amount of, transpired by plant-leaves, 56;
+ an adulterant of guano, 319;
+ a carrier of plant-food, 55;
+ in cow-dung, 226
+ --cow-urine, 230;
+ from decomposition of farmyard manure, 257;
+ in horse-dung, 226
+ --horse-urine, 230;
+ necessary for plant, 67;
+ in pig-dung, 226
+ --pig-urine, 230
+ --sheep-dung, 226
+ --sheep-urine, 230;
+ transpired by elm-tree, 71
+ --oak-tree, 71.
+
+ Water-culture, 54.
+
+ Water-logged soils, 179.
+
+ Waterloo, bones from, 360.
+
+ Way, Thomas, on retention of plant-food by soil, 57, 59;
+ on sewage, 437.
+
+ West Indies, guano from, 298.
+
+ Whales, guano from, 322.
+
+ Wheat, fertilising ingredients removed from soil by, 485;
+ Flitcham experiments on, 500;
+ manurial constituents in, 282;
+ manuring of, 499-501
+ nitrogen removed in crop of, 145;
+ requires nitrogenous manures, 499;
+ Rothamsted experiments on, 500, 562-565;
+ a source of nitrogen, 153.
+
+ Wheat soils, nitrates in, 157.
+
+ Wheat-straw, analysis of stable manure made from, 283;
+ composition of, 238;
+ manurial constituents in, 282.
+
+ White clover, growth of, promoted by lime, 451.
+
+ Wiegmann on ash constituents of plants, 53.
+
+ Wilfarth on nitrogen in plants, 44.
+
+ Wilting, 73.
+
+ Winogradsky, on nitrification, 52, 167, 169, 197;
+ on organisms in soil, 94.
+
+ Wolff on, analysis of manure-heap drainings, 290;
+ composition of fresh and rotten dung, 288;
+ assimilation of organic nitrogen by plants, 47;
+ relative manurial value of manurial compounds, 556;
+ urine, 232.
+
+ Wood-ashes as potash manure, 218, 419.
+
+ Woodhouse, researches of, on nitrogen in plants, 41.
+
+ Wool, capable of nitrification, 182;
+ potash in, 217.
+
+ Wool-waste, 427;
+ nitrogen in, 427.
+
+ Woolney, on organisms in soils, 93, 95;
+ on water in soils, 75.
+
+ Wrightson, Professor, on application of basic slag, 414.
+
+
+ Yeast, 94.
+
+ Yorkshire, bones first used in, 359.
+
+
+ Zeolites, potash in, 220
+
+
+PRINTED BY WILLIAM BLACKWOOD AND SONS.
+
+
+
++---------------------------------------------------+
+| Transcriber's Note: |
+| |
+| Carats (^) signify superscript figures. |
+| Underscores (_) followed by a number in curly |
+| brackets signify subscript figures. |
+| |
+| Typographical errors corrected in the text: |
+| |
+| Page 58 Eichorn changed to Eichhorn |
+| Page 134 diferent changed to different |
+| Page 464 superposphate changed to superphosphate |
+| Page 553 biophosphate changed to biphosphate |
+| Page 579 Gallopagos changed to Galapagos |
++---------------------------------------------------+
+
+
+
+
+
+
+End of the Project Gutenberg EBook of Manures and the principles of manuring, by
+Charles Morton Aikman
+
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