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Etymological meaning of word manure 109 Definition of manures 110 Different classes of manures 111 Action of different classes of manures 113

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

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

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

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

Total shipments from South America, 1830-1893 351 Total imports into Europe and United Kingdom, 1873-1892 351

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

Production of sulphate of ammonia in United Kingdom, 1870-1892 358

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

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

Imports of phosphates 381

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

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

Analysis of basic slag 417

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

Scutch 427 Shoddy and wool-waste 427 Soot 428

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

Farmyard manure a typical compost 446 Other composts 447

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

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

Experiments on bean-manuring 530

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

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

INDEX 573

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.

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.

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."

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.' , 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.

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 S?n?bier.

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: "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.'"

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 , 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.

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, affords us an opportunity of gauging, pretty accurately, the state of knowledge on the subject at the time.

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."

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.

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

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