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 The food of crops and how to apply it.( A 
 
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THE 
 
 FOOD OF CHOPS 
 
 AND 
 
 HOW TO APPLY IT. 
 
 (An Elementary Handbook on the Science and Practice of Manuring.') 
 
 sr / 
 
 C. M. AIKMAN, M.A., D.Sc, P.R.S.E., F.I.C., 
 
 Author of "Manures and Manuring,* "Farmyard Manure" " Milk: Its Nature and 
 Composition " ; Editor of New Editions of Johnston's " Elements of Agricultural 
 Chemistry " and " Catechism of Agricultural Chemistry," and of 
 Fkischmann's "Science and Practice of Dairying" <fcc, <tc. 
 
 LONDON : 
 
 VINTON & CO., Ltd., 9, NEW BRIDGE STREET, E.O. 
 
 1895 iy 
 
PEE FACE, 
 
 This little work is intended as a guide to the 
 elementary principles involved in the application 
 of fertilisers. It does not in any sense claim to 
 be a treatise on the subject of manures ; and may 
 be regarded as forming an introductory text" 
 book to the author's manual on " Manures and 
 Manuring" (Blackwood). It is hoped that the 
 elementary facts of agricultural chemistry, neces- 
 sary for an intelligent comprehension of the 
 subject, are stated in such a way that readers 
 unacquainted with natural science will have no 
 difficulty in mastering them. 
 
 In the hope that the book may prove itself to 
 be suitable for use in rural schools, where agricul- 
 tural science is taught, a number of questions 
 have been added as an Appendix. 
 
 It is surely unnecessary at the present time to 
 say a single word on the enormous economic 
 importance of the subject treated. The use 
 of fertilisers has become a necessity of modern 
 husbandry, and the amount of money yearly spent 
 on them in this country alone amounts to millions 
 sterling. Any book, therefore, which helps, in 
 however humble a way, to diffuse a knowledge of 
 the correct principles underlying this practice 
 may claim to have a raison d'etre. 
 
 C. M..Aikman. 
 
 Analytical Labobatory, 
 
 128, "Wellington Steeet, Glasoow, 
 October,. 1895. 
 
CONTENTS. 
 
 CHAPTER ;I. 
 
 SOURCES OF PLANT FOOD. 
 
 Composition of plant tissue — Consists of water — Organic 
 matter — Mineral matter — -Variation in the relative proportions 
 of organic and inorganic matter — Elementary composition of 
 organic matter — Carbon, oxygen, hydrogen, and nitrogen — 
 Carbohydrates — Cellulose, starch, sugar, and fat — Albuminoids — 
 Gluten — -Elementary composition of ash — Sources of plant 
 food — The soil and the air 1 — 7 
 
 CHAPTER II. 
 
 HOW PLANTS PEED. 
 
 Germination of the seed — Conditions necessary for germina- 
 tion—Carbon assimilation — Sources of carbonic acid present in 
 the air — Sources of oxygen and hydrogen in plant tissue — 
 Absorption of nitrogen— Forms in which nitrogen is present in 
 the soil— rThe processes which change nitrogen from one form 
 to another in the soil — Nitrification — Favourable conditions for 
 its development — Fixation of the "free" nitrogen by leguminous 
 plants — Amount of combined nitrogen in the air — Importance 
 of nitrogen, phosphates, and potash as fertilising constituents — 
 Chemical forms in which phosphoric acid and potash are present 
 in the soil 8—17 
 
 CHAPTER III. 
 
 THE NATURE AND FUNCTIONS OF FERTILISERS. 
 
 Formation of virgin soils — Diminution of fertility in agri- 
 cultural practice — Amount of plant food removed by common 
 
VI CmTEM'S. 
 
 crops — Farmyard manure — Loss of its value through careless 
 management in Britain and France — Loss of fertilising- con- 
 stituents of the soil through drainag-e — Processes which make 
 good this loss— Classification of manures — Indirect and direct 
 manures — Natural,, artificial, mineral, and vegetable manures — 
 General and special manures 18 — 23 
 
 CHAPTER IV. 
 
 FARMYARD MANURE AND SEWAGE. 
 
 Variation in composition — Value of straw as litter — Amount 
 of fertilising constituents in farmyard manure — Liquid manure 
 — Composts — Sewage as a manure ......... 21 — 29 
 
 CHAPTER V. 
 
 GUANO. 
 
 Guano deposits- of the world — Peruvian guano — Its appearance,, 
 colour, &c. — Conditions in which its fertilising ingredients are 
 present — Nitrogen, phosphates, and potash in Peruvian guano — 
 Spurious guanos — Fish guano — Amounts of fertilising con- 
 stituents in fish guano — Its value as a manure — Meat guano — 
 Composition — Dung- of bats, pigeons, and fowls . . . 30—34 
 
 CHAPTER VI. 
 
 NITEATE OF SODA, SULPHATE OP AMMONIA, AND OTHER 
 NITROGENOUS FERTILISERS. 
 
 Occurrence of nitrate of soda — Caliche — Nitrate of soda — Its 
 composition — Its action in the soil — Benefits of its application 
 — Sulphate of ammonia — Its properties — Its composition — Its 
 sources — Its application — Dried blood — Percentage of nitrogen 
 in dried blood — Its application and action in the soil — Horns 
 and hoofs — Their action as manures — Shoddy — Scutch — Rape 
 dust — Soot 35—39 
 
CONTENTS. vii 
 
 CHAPTER VII. 
 
 BONES. 
 
 Old use of bones as a manure — Forms in which they are 
 applied — Bone meal — Bone dust — Composition — Dissolved bones 
 — Application of bones — Fermentation of bones — Bone ash — Bone 
 black — Spent char 40 — 42 
 
 CHAPTEE VIII. 
 
 SUPERPHOSPHATE AND MINERAL PHOSPHATES. 
 
 Apatite — Its sources and composition — Carolina phosphate — 
 Belgium phosphate — French phosphate — Florida phosphate — 
 English and French coprolites — Crust guanos — Manurial value 
 of undissolved mineral phosphate — Superphosphate — Compo- 
 sition — Its action when applied to the soil — Basic slag — Its 
 composition and application . . 43—47 
 
 CHAPTER IX. 
 
 POTASH FERTILISERS. 
 
 Limited use of potash fertilisers — Soils usually well supplied 
 with potash — Soils benefited by the application of potash — 
 Wood ashes first form of potash fertiliser — Kainit — Muriate and 
 sulphate of potash — Seaweed 48 — 49 
 
 CHAPTER X. 
 
 INDIRECT MANURES. 
 
 Lime — Soils benefited by its application — Its action when 
 applied to the soil — Forms in which.it is used in agriculture — 
 Caustic and mild lime — Their action on soils — Mechanical action 
 — Chemical action — Biological action — Care to be exercised in 
 the application of lime — Gypsum — Its action in the soil — Salt 
 — Application of — Crops benefited by ...... . 50 — 55 
 
▼"I CONTENTS. 
 
 CHAPTER XL 
 
 THE COMPOSITION AND APPLICATION 03? FERTILISERS. 
 
 Value of fertilisers determined by chemical analysis— Fer- 
 tilisers and Feeding Stuffs Act— Different forms of nitrogen in 
 fertilisers— Value of different forms of nitrogen— Value of 
 different forms of phosphate — Unit value of fertilisers— Import- 
 ance of equal distribution of fertilisers in the soil— Methods for 
 effecting uniform distributions — Mixing of fertilisers— Risks of 
 loss in — Chemical decomposition — Volatilisation of ammonia — 
 Mixing of nitrogenous with phosphatic fertilisers — Reversion of 
 phosphates — Manures best applied in unmixed condition. 
 
 56—64 
 
 CHAPTER XII. 
 
 THE MANURING OP THE COMMON FARM CROPS. 
 
 Permanent fertility of soils - Influence of manuring — Farm- 
 yard manure — Some crops not suited for farmyard manure — 
 Rotation of crops— Quick-acting and slow-acting fertilisers — 
 Fertilisers suited for application in autumn — Those suited for 
 spring use— Nature of the soil to be kept in view when 
 applying fertilisers — Agricultural Holdings Act— Manuring of 
 common farm crops— Cereals — Alternation of leguminous crops 
 with — Cereals an exhausting crop — Benefited by nitrogenous 
 fertilisers — Barley — Wheat — Oats — Grass— Permanent pastures 
 — Rotation seeds — Turnips — Mangolds — Potatoes — Clover — 
 Beans — Peas — Vetches — Lucerne — Cabbages— Hops . . 65 — 80 
 
THE FOOD OF CROPS 
 
 AND 
 
 HOW TO APPLY IT. 
 
 CHAPTER I. 
 
 SOURCES OF PLANT FOOD. 
 
 The phenomenon of plant growth is one of the most 
 interesting of the many striking phenomena which 
 nature presents for our observation. What further 
 serves to invest it with interest is the fact that it is one 
 of enormous economic importance, for on it the great 
 industry of agriculture rests. 
 
 The questions — What is the food of plants ? and 
 Whence do they derive this food ? were doubtless asked 
 by many searchers after truth in the past ; but were 
 destined long to remain unanswered. 
 
 If we take any piece of vegetable tissue, whether it 
 belong to the root, stem, or leaf of a plant, and submit 
 it to chemical analysis, we shall, by this means, discover 
 its composition. 
 
 In the first place, if we take and heat it for some time 
 at the temperature of boiling water, we drive off what is 
 its largest constituent — viz., water. This amounts, in 
 many plants, to over 90 per cent, of their total weight, 
 
z THE FOOD OF CROPS. 
 
 and is rarely less than 40 per cent. The plants which 
 contain most water are succulent vegetables — such as 
 lettuce, gourds, melons, &c. These, indeed, are almost 
 entirely made up of water — some of them containing as 
 much as 97 per cent. Such plants as turnips contain over 
 90 per cent., mangolds slightly less, while potatoes con- 
 tain about 75 per cent. On the other hand, timber, when 
 felled, contains only about 40 per cent. In the grains 
 and seeds of plants we find the percentage of water very 
 much less, being only about 14 per cent. The amount 
 of water in plant tissue depends on the period of growth. 
 It is greatest in young plants, and as the plant grows 
 older it decreases. 
 
 By proceeding a step further, and submitting the 
 dried plant tissue to a higher temperature, we find that 
 it speedily blackens, while smoke is given off. This 
 blackening indicates to the eye of the chemist the 
 presence of the element carbon. If we steadily raise the 
 temperature to a red heat,., the carbon gradually 
 disappears, until all that remains, after a time, of the 
 plant substance is a small amount of ash. 
 
 The dry matter of plants can thus be divided into two 
 portions — one which we can burn aivay, and which is by 
 far the larger portion; and one which iviihstands the 
 actinn of heat. This combustible portion is generally 
 called the organic matter, while to the incombustible 
 portion the terms inorganic or mineral matter have been 
 applied. 
 
 The relative proportion of the organic and inorganic 
 parts of pianos varies, and the different parts of even 
 the same plant show a variation in composition. . Thus, 
 as a rule, the leaves will be found to contain more ash 
 than the stem or roots. So great, indeed, is thiB varia- 
 
SOTJKCES OF PLANT FOOD. o 
 
 tion that it would be misleading to give any amount as 
 furnishing an average. Almost never, however, does the 
 ash in a plant, or in any part of a plant, exceed 20 per 
 cent, of its dry matter ; while in certain cases it may 
 not exceed the mere fraction of a per cent. In the 
 commou agricultural plants, the grain, or seed, may be 
 said to contain 2 to 3 per cent, of asb, and the straw 
 about 5 per cent. The organic matter in these parts 
 of the plaut will thus vary between 95 and 98 per 
 cent. 
 
 If we examine more minutely these two portions of 
 the plant tissue — the organic and inorganic matter — 
 with a view to discovering their chemical composition, 
 we shall find that the organic matter is made up chiefly 
 of carbon. That this is so we can prove by collecting 
 the gaseous products of combustion, when it will be 
 found that the largest percentage consists of carbonic 
 acid gas, a substance formed out of carbou and oxygen, 
 and produced whenever carbon is burned in the air. 
 Broadly speaking, this may be said to amount to close 
 on 50 per cent., or one-half of the entire amount of the 
 dry substance Of the plant. Next in amount to carbon 
 comes oxygen, which is present in quantities only a little 
 less than the carbon, viz., about 40 per cent. The 
 remaining portion is chiefly made up of hydrogen and 
 nitrogen, the latter substance being present to the extent 
 of only 1 or 2 per cent., while the former amounts to 
 about 6 per cent. The presence of hydrogen in the 
 organic matter of plants is shown by the fact that when 
 dry plant tissue is burned in air a certain quantity of 
 water is formed. 
 
 These four elements, which, along with small quantities 
 of sulphur, constitute the organic matter of the plant, are 
 
4 THE FOOD OF CROPS. 
 
 combined together in different proportions to form a 
 large variety of bodies. Most of them are made up of 
 only the three elements — carbon, hydrogen, and oxygen. 
 To one large class of such bodies the name carbohydrates 
 is given. Cellulose, or woody fibre (the most abundant 
 substance in plant tissue), starch, and sugar may be 
 cited as examples of this class of substances. Other 
 bodies, made up of the same three elements, are fats. 
 
 But a certain proportion of plant tissue consists of 
 bodies which, in addition to carbon, hydrogen, and 
 oxygen, also contain nitrogen. These are known as 
 proteids or albuminous bod es. Gluten, that glue-like 
 substance familiar to most as an important constituent 
 of wheat, may be taken as a type of this class of body. 
 
 Turning, in the second place, to the ash, we find that 
 the elements constituting this portion of the plant 
 tissue are more numerous than those forming the 
 organic part. Among them may be mentioned potassium, 
 calcium, magnesium, sodium, silicon, iron, and phosphorus. 
 These elements are combined with oxygen, and are 
 present in the form of a number of different kinds of 
 
 We see, therefore, that plant tissue is made up of 
 water, organic matter (consisting of compounds of carbon, 
 hydrogen, oxygen, and nitrogen), and of certain mineral or 
 ash ingredients. 
 
 The next question which we have to consider is — 
 Whence does the plant derive these substances ? Now, 
 there can be only two sources, viz. : the air and the soil. 
 An examination of the composition of the air will reveal 
 that it is chiefly made up of two gases, nitrogen and 
 oxygen, but that it also contains comparatively small 
 quantities of carbonic acid gas, as well as waPr (in a state 
 
SOURCES OP PLAST FOOD. 5 
 
 of vapour), and certain other gases in, however, very 
 minute quantities ; while an examination of the soil will 
 show that it contains, in addition to varying quantities of 
 organic matter, all the mineral constituents which we find 
 • to be present in the plant. We see, then, that the source 
 of certain constituents of the plant must be the soil, since 
 these ingredients are not present in the air. This is the 
 case with regard to the ash or mineral portion. With 
 regard to the others, however, the matter is not so quickly 
 decided. Thus, with regard to carbon, for example, we 
 find that this substance is present in a combined form 
 — i.e., in chemical combination with some other substance 
 — both in the soil and in the air. Again, oxygen is 
 abundantly present in a combined form in the soil as well 
 as in the free state in the air. Hydrogen, further, is present 
 in a combined form, both in the air and in the soil. While, 
 lastly, nitrogen is present in both the air and the soil — 
 in the former, both in the free state and, in very minute 
 quantities, in the combined form ; and in the latter, only 
 in the combined form. The question, therefore, arises, 
 From which of these sources, respectively, does the plant 
 derive these elements ? 
 
 With regard to carbon, hydrogen, and oxjgeD, we 
 know that while the first named is obtained by the plant 
 from the small quantity of carbonic acid gas present in 
 the air, the source of the hydrogen and oxygen is water. 
 With regard to nitrogen, however, we find that the 
 plant draws on both the soil and the atmosphere for 
 its supply of this important element, although, to most 
 plants, the soil furnishes the only source. The dis- 
 covery that so-called leguminous plants — a large and 
 important class, including the pea, bean, and clover 
 crops — are capable of- deriving their nitrogen from the 
 
THE FOOD OF CROPS. 
 
 free nitrogen in the air, has only been made within 
 recent years, and may be rightly regarded as one of the 
 most important discoveries made in agricultural science 
 for a long time. 
 
 . We thus see that the plant derives by far the larger 
 portion of its substance from the air and water, and 
 that only a small portion is derived from the soil. 
 And here an iuteresting question presents itself, viz., 
 Are all the ingredients commonly found in plants 
 absolutely necessary for the plant's proper development ? 
 To this an answer in the negative must be made. 
 Most of the substances we have mentioned, which go 
 to form plant tissue, are absolutely necessary, and 
 among these are all the elements which go to form its 
 organic matter. But among the ingredients forming 
 the inorganic or ash portion there are one or two which, 
 although they commonly occur in most plants, are yet 
 not absolutely necessary for plant-growth, and without 
 which the plant can make shift to grow perfectly well. 
 
 It would seem at first sight, therefore, that the 
 influence which the farmer can exert on the growth of 
 his crops must necessarily be very small, since by far 
 the largest portion of the substance of these crops is 
 derived from a source not under his control. When, 
 however, we come to examine the problem of plant 
 growth more nearly, this will be seen to be a mistaken 
 conclusion. For, while such ingredients as phosphoric 
 acid and potash are only required by a plant to a 
 comparatively small extent, yet both these substances 
 are as necessary for its growth as carbonic acid gas or 
 water — food ingredients out of which plant tissue is so 
 largely built up. 
 
 All the necessary plant foods, therefore, may be re- 
 
SOUJtCES OF PLANT FOOD. 7 
 
 garded, as far as the growth of a plant is concerned, 
 as of equal importance. It thus happens that although 
 the farmer is ODly able to control the source of supply 
 of a very small portion of the plant's food, he is yet 
 able to regulate, to a large extent, its growth. 
 
 And here it may be well to point out that plant 
 growth is not alone determined, by the amount of plant 
 food available, but that such conditions as climate, alti- 
 tude, physical texture of the soil, &c, are also quite as 
 potent factors. As, however, we are not here concerned 
 with anything but the food of plants, it will be un- 
 necessary to consider the extent or nature of these other 
 influencing conditions of plant growth. 
 
CHAPTER II. 
 
 HOW PLANTS FEED. 
 
 When the seed is put into the ground, provided the 
 conditions of warmth and moisture are favourable, it 
 soon begins to sprout. A shoot is pushed upwards, and 
 a root downwards. Now, during this period of germi- 
 nation, as it is called, the external sources of the plant's 
 food, the soil and the air, are not drawn upon, except 
 in so far as one ingredient is concerned, viz., water. 
 The seed itself supplies, for some little time, all the 
 food necessary, there being in it a sufficient amount of 
 concentrated nourishment to permit of the plant's 
 growth, until it is able, by means of its leaves and roots, 
 to draw its nourishment from external sources. With 
 the exact nature of the changes which go on in the seed 
 during this important stage of the plant's life we need 
 not here concern ourselves. It may be sufficient to 
 mention that the seed contains a certain proportion of 
 carbohydrates in the form of starch, nitrogenous 
 bodies of the nature of gluten, and mineral matter. 
 In some seeds, it is true, we have no starch — its place 
 being taken by oil. 
 
 When germination takes place the starch is converted, 
 by means of a fermeut called diastase, into soluble 
 bodies which are able to travel in the sap to the 
 shoot or root, and thus to permit of the development 
 
KOW PLANTS FEED. 9 
 
 of these organs. If this initial stage of growth is to 
 take place satisfactorily, a proper amount of moisture, 
 a certain temperature, and a free supply of air are all 
 required. It is for this reason that seeds, if buried 
 too deep, where the air does not penetrate, refuse to 
 germinate. As soon, then, as the plant's roots and 
 stem have developed so far as to permit of it draw- 
 ing upon the soil and the air for its food, it does 
 so. 
 
 As we have pointed out, the carbon, which forms 
 the largest portion of plant tissue, is derived from the 
 carbonic acid in the air. Under the influence of sun- 
 light this gas is decomposed in the green portion of the 
 leaves of the plant into carbon and oxygen, the carbon 
 being retained, and the oxygen given out. This process 
 of carbon assimilation, as it is called, only takes place 
 in the day time, since sunlight is necessary for its 
 action, and the rapidity with which it goes on depends 
 on the intensity of the sun's rays. This accounts for 
 the fact that during periods of the year when the sun's 
 rays are most powerful, and daylight is longest, plant 
 growth is greatest. 
 
 But an interesting question may occur to the reader, 
 viz., how can such a minute quantity of carbonic acid as 
 that present in the air (amounting to only some three to 
 four parts per 10,000) supply plants with the large 
 amount of carbon they require, for it has been calculated 
 that an acre of a good wheat crop will assimilate in four 
 months as much as one ton of this element ; and this is 
 as much as would be contained in a column of air 
 covering an acre of ground, and stretching to a height of 
 three miles. We must remember, however, that alihough 
 the quantity of carbonic acid gas in the air is very small, 
 
 2 
 
10 THE POOD OF CROPS. 
 
 and the surface that the plant leaves offer to the atmos- 
 phere is also comparatively small, the air surrounding a 
 plant is constantly undergoing change. This constant 
 shifting of the atmosphere around the plant is, of course, 
 effected by the wind, and, as an example of the rapidity 
 with which it takes place, it may be mentioned that 
 even on the least windy day, when the wind is only 
 moving at the rate of two mile3 an hour — and this is so 
 slow as scarcely to be noticeable— the air in a space of 
 twenty feet is changed more than 500 times in an 
 hour. 
 
 And here we may explain how the carbonic acid gas, 
 which is such an important plant food, and which is thus 
 constantly being removed from the air, is supplied. In 
 the first place, we have large quantities formed from the 
 decay of vegetable matter. This process of putrefaction 
 of organic matter is constantly going on in all soils, and 
 in illustration of its extent it may be mentioned that it 
 has been calculated that one acre of good garden land in 
 summer evolves more than six tons of carbonic acid. 
 Another large source is the combustion of organic 
 matter, which is especially great in the neighbourhood 
 of large towns. To the respiration of man and animals 
 the air also owes a not inconsiderable proportion of its 
 supply of this valuable plant-food. While, lastly, in 
 the gases from volcanoes, from mineral springs, and 
 from various other subterranean sources, the air is 
 constantly receiving carbonic acid gas. 
 
 Since the carbonic acid is a product of the respiration 
 of animals, the influence of plant life on our atmosphere 
 is towards purifying it of this noxious (to animal life) 
 ingredient ; and the counteracting influence of animal 
 and vegetable life is illustrated by the calculation that 
 
HOW PLiKTS FEID. 11 
 
 an acre of forest will decompose the carbonic acid 
 produced by the respiration of fifteen men.* 
 
 la view of the importance of carbonic acid as a plant 
 food, it may naturally be asked whether plants flourish 
 better in an atmosphere containing a larger proportion of 
 carbonic acid than that present in the air. It has been 
 found by experiment that plants flourish better when the 
 proportion of carbonic acid in the air surrounding them 
 is increased. This takes place, however, only up to a 
 certain point, viz., 8 to 10 per cent, of carbonic acid ; 
 and when air contains more than that amount it is no 
 longer suitable for supporting plant life. 
 
 The decomposition of carbonic acid by the leaves of 
 plants is intimately connected with the green colouring 
 matter called chlorophyl. "What exact functions chloro- 
 phyl performs is not fully known ; but examination by 
 the microscope has shown that caibonic acid is only 
 decomposed in those portions of the plant which contain 
 chlorophyl. To this there must be an exception made, 
 since it has been recently ascertained that in the case 
 of very minute low forms of plant life (certain soil 
 organisms) neither light nor the presence of chlorophyl 
 are necessary conditions for the assimilation of carbon 
 and the evolution of oxygen. 
 
 With regard to the absorption of oxygen and hydrogen, 
 we know very little beyond the fact that these two 
 substances are probably almost entirely obtained from 
 water. Oxygen, it would seem, is not derived from the 
 free oxygen in the atmosphere, although that doubtless 
 
 * The sources of supply seem pretty nearly to equal the 
 demands made on them by the plant world, and the amount in 
 the air thus remains approximately constant. 
 
 2* 
 
12 THE FOOD OF CROPS. 
 
 plays an important part in the growth of plants, and a 
 free supply of it is necessiry for their development. 
 
 With regard to the assimilation of nitrogen, the ques- 
 tion is nob so shortly or so simply disposed of. The 
 amount of this element in plants is not less than 2 per 
 cent. Now, as four-fifths of the rolume of the air consists 
 of this element, one would naturally suppose that from 
 this source plants would derive all their nitrogen ; and 
 it isttrue, for a certain class of plants, that they do draw 
 upon this source. But most plants derive their nitrogen 
 from the compounds of that body in the soil. This sub- 
 stance occurs ill the soil in the form of what is termed 
 organic nitrogen,, that is, as albuminoids and other 
 analogous forms, as well as in the form of nitrates, 
 n'trites, and ammonia. The first-mentioned form (organic 
 nitrogen) is the most abundant, and nitrogen is only 
 gradually converted from this form by various processes, 
 in which minute organisms play a very important part, 
 into the other forms we have just mentioned. This is 
 an important fact, since, in the form of nitrates, nitrogen 
 is apt to be washed out of the soil. In the form of 
 ammonia it is more tenaciously held, but it does not long 
 remain in this state, being speedily converted into 
 nitrates. 
 
 Of these different forms of nitrogen, that in the form 
 of nitrates is the most valuable for the plant, since it is 
 in this form that plants absorb nearly the whole of the 
 nitrogen they require. For the reasons above mentioned, 
 nitrogen in the form of ammonia may be described as 
 ui almost equal value. With regard to the value of 
 nitrogen in the organic form, it is impossible to speak 
 generally, since this depends very much on the nature of 
 the special organic compound. We have organic forms 
 
HOW PIAHTS FEED. 13 
 
 of nitrogen, such as urea, the fo m in which it is present 
 in fresh urine, which, from the fact that when they are 
 applied to the soil they are rapidly converted into 
 nitrates, are almost as valuable as nitrates themselves. 
 On the other hand, nitrogen in the form in which it 
 occurs in hones is of very inferior value, since such 
 nitrogen is only very slowly converted into nitrates. 
 
 As the processes by which the various forms of 
 nitrogen are converted into nitrates in the soil have a 
 very important bearing on their value as plant food, 
 it may be well here to shortly describe them, as well as 
 to say a word or two on the method in which certain, 
 plants are enabled to draw their nitrogen from the free 
 nitrogen in the air. 
 
 The conversion of nitrogen in the organic form, and 
 in the form of ammonia salts, into nitrates is effected 
 by different minute organisms which inhabit the soil, 
 and which have only of recent years been discovered 
 and investigated. In the conversion of ammonia into 
 nitrates two classes of organisms are active. The 
 ammonia is first converted into nitrites by one class of 
 organisms, and the nitrites are converted i^to nitrates by 
 another class of organisms. Where the nitrogen is in an 
 ■organic form, the process is more complicated, as it has 
 ■first to be converted into ammonia by a third class of 
 organisms. Now, the conditions whieh favour the 
 development of these processes, which are known under 
 the term ammonification and nitrification, are, from an 
 agricultural point of view, of the very- highebt import- 
 ance, since, in the cultivation of his land, the farmer 
 should aim at developing them to the greatest possible 
 extent. 
 
 In the first place, the nitrification organisms require, 
 
14 THE FOOD OF CROPS. 
 
 just like the higher plants, a certain amount of fool 
 constituents, a free supply of air, and a certain amount 
 of moisture. Another important influencing condition 
 is the temperature. Experiments have shown that they 
 will only develop between 40° Fa.hr., and 131° Fahr. ; 
 and that a temperature slightly less than 140° Fahr. 
 is the most favourable. Soils where any of tlese 
 conditions are wanting are, therefore, not likely to 
 prove themselves fertile. 
 
 While it has long been suspected that the free nitrogen 
 in the air is available as a source of plant food, it is 
 only within the last few years that this fact has been 
 demonstrated beyond doubt. So far as is at present 
 known, the power of utilising the free nitrogen of the air 
 is limited to a certain class of plants, viz., those known 
 as leguminous plants, and examples of which are clover, 
 beans, peas, &c. The method in which these plants can 
 utilise this free nitrogen is still a point requiring much 
 research. The fixation of the nitrogen, as it is called, is 
 effected by means of micro-organisms present in certain 
 minute root-excrescences found on the roots of these 
 plants. 
 
 In addition to the nitrogen which is absorbed by 
 leguminous plants, the air supplies minute quantities 
 of it to the soil in a combined form. This combined 
 nitrogen is in the form of ammonia and nitrates, 
 which exist in minute traces in the air, and are washed 
 down by the rain. The amount obtained in this way, 
 however, is very trifling. Thus, at Bothamsted, in 
 England, that falling on an acre of land, in the rain, was 
 only some 3'37 lbs. during a year. It is possible that, in 
 addition to this, minute quantities of ammonia may be 
 absorbed by the soil from the air. The large bulk of the 
 
HOW PLANTS FEED. 15 
 
 nitrogen which the plant requires is obtained from the 
 soil. Hence the amount of nitrogen in the soil is one of 
 the regulating factors of plant growth. With regard to 
 the ash constituents of plants, we have seen that all those 
 commonly occurring in plants are not of equal import- 
 ance, and that only some of them are absolutely necessary 
 for plant growth. Those that are necessary are as 
 follows : potash, lime, magnesia, ox de of iron, phosphoric 
 acid, and sulphuric acid. Some of these are only 
 required in very minute quantities, this being the 
 case with regard to oxide of iron. Of them, two 
 possess for us especial importance, viz., potash and 
 phosphoric acid. This is due to the fact that they are 
 generally present in the soil, in an available condition at 
 any rate, in very small amount; whereas the other 
 necessary ingredients are contained by most soils in 
 abundant quantity. As we have already had occasion to 
 point out, the rate of growth of a plant is determined by 
 the amount of the least abundant necessary available plant 
 constituent in the soil. Thus, for example, crops will not 
 properly grow in the absence of any one neeessary plant 
 constituent, no matter how abundant the other necessary 
 plant constituents are. It is, therefore, the con&tituent 
 which is relatively least abundant that regulates the rate 
 of growth. As these two constituents, among mineral 
 constituents, are potash and phosphoric acid, they 
 possess, for the farmer, the greatest interest, and are the 
 only two which, as a rule, it is found necessary to apply 
 as manures. Under ordinary agricultural conditions, 
 therefore, the question of manuring may be said to be 
 limited to the addition to the soil of nitrogen, phosphoric 
 acid, and potash. "We have already seen the forms in 
 which nitrogen is present in the soil and is absorbed by 
 
16 THE TOOD OF CROPS. 
 
 plants. Before concluding this chapter, let ns see in 
 what forms these two mineral ingredients are present in 
 the soil, and are absorbed by plants. 
 
 The number of different chemical compounds of 
 phosphoric acid in. the soil are not so numerous as those 
 of nitrogen. Unlike this latter ingredient, it is probably 
 never present in a soluble form,* and when added to the 
 soil in this state it is speedily converted into an insoluble 
 cjndition. This is a fortunate circumstance, since it is 
 not liable to be lost by being washed out of the soil by 
 raia. But the readiness with which the different 
 compounds of phosphoric acid are acted upon by the 
 plant's roots, and by soil water, varies very considerably. 
 Many compounds of phosphoric acid, although insoluble 
 in pare water, are yet acted upon more or less easily by 
 soil water charged with carbonic acid. 
 
 Perhaps the most insoluble form of phosphoric acid 
 in the soil is apatite — a crystalline mineral which consists 
 almost entirely of phosphate of lime. This mineral is 
 only very slowly decomposed, and yields its phosphoric 
 acid to the plant only after a long period of decom- 
 position. The other compounds of phosphoric acid in 
 the soil are phosphates of iron and aluminium, and, 
 possibly, also phosphates of magnesium and ammonium. 
 But amoDg the phosphates of lime great difference 
 exists in their assimilability by the plant's roots. Thus 
 phosphates derived from animal or vegetable matter 
 become more speedily available in the soil for the plant's 
 needs than mineral phosphates such as apatite. The 
 fertility of a soil may be said to depend more on the 
 amount of speedily available plant food than on the 
 
 * By soluble and insoluble is meant soluble and insoluble in water. 
 
HOW PLANTS FEED. 17 
 
 total amount of this plant food. Very many methods 
 have consequently been suggested for the purpose of 
 attempting to gauge this amount of available mineral 
 plant food. That recommended by Dyer consists in the 
 treatment of the soil with a 1 per ceut. solution of 
 citric acid. The amount of phosphoric acid dissolved 
 by such a solution from most soils would probably be 
 very little. 
 
 Potash is a more abundant ingredient in most soils 
 than phosphoric acid ; yet the amount present, in a form 
 available for the plant's needs, is also comparatively 
 small. The form in which it most commonly occurs 
 is as the mineral felspar. This mineral, which may 
 contain it to the extent of 14 per cent., is extremely 
 hard, and is only very slowly decomposed. The potash 
 in it is in combination with silica — that is, in a totally 
 insoluble form. Through the process of "weathering" 
 the potash in this mineral is slowly set free, and rendered 
 available for the plant's uses. .Another common potash 
 mineral is mica — so large a constituent of granite. 
 
 The form in which potash is probably absorbed by 
 plants' roots is in combination with chlorine, sulphuric 
 acid, or phosphoric acid, all three forms being soluble. 
 Jt is more liable to be washed from the soil by rain than 
 phosphoric acid, although loss of it from this source does 
 not occur to anything like the extent which one would 
 be inclined to suppose, since the soil has the power of 
 retaining it and certain other plant foods, although in a 
 soluble condition, against the action of rain — an 
 extremely economjcal provision of nature. 
 
CHAPTER III. 
 
 THE NATURE AND FUNCTIONS OF FEETILISEKS. 
 
 In a state of nature, where plants decay where they grow, 
 the mineral and nitrogenous food which they extract 
 from the soil is returned to it, and the soil, instead of 
 becoming impoverished in food constituents, is found, on 
 the contrary, to slowly become enriched. When this pro- 
 cess continues for centuries, the result is the formation of 
 soils of wonderful fertility, of the type of the old " virgin 
 soils " — now becoming so rapidly extinct — in America. 
 This enrichment is due to the fact that the soil has had 
 concentrated on its surface layers large quantities of 
 readily available food ingredients, gathered by the plants' 
 roots from its lower portions, as well as accumulated from 
 the air by the fixation of free nitrogen. 
 
 In agricultural practice, however, where such a process 
 of accumulation is not allowed to take place, the case is 
 very different. As is well known, the tendency in such a 
 case is towards a diminution iu the fertility of the soil, 
 due to a steady loss of plant food. This takes place in a 
 variety of ways. In the first place, large quantities of 
 pl-mt food are removed from the soil by the crops which 
 are not consumed on the farm. The extent to which the 
 different important plant foods are removed by the 
 common agricultural crops is as follows : Average crops 
 of cereals (oats, wheat, and barley) remove about 50lbs. of 
 nitrogen, 20 lbs. of phosphoric acid, and about 40 lbs. of 
 
THE NATURE AND FUNCTIONS OF FERTILISERS. 19 
 
 potish psr acre. A certain proportion of this, however, 
 is almost invariably returned in the straw, which contains 
 about 15 lbs. of nitrogen, 5 lbs. of phosphoric acid, and 
 about 301b3. of potash. An average crop of turnips 
 removes even larger quantities of these constituents, viz., 
 about 119 lbs. of nitrogen, 33 lbs. of phosphoric acid, 
 and 139 lbs of potash per acre ; while an average crop 
 of mangolds removes 138 lbs. of nitrogen, 53 lbs. 
 of phosphoric acid, and 300 lbs. of potash per 
 acre. 
 
 A more striking way of indicating the amount of 
 fertilising constituents removed from the soil in this 
 way is to calculate what the total produce of a year's 
 growth represents iu these ingredients. The present 
 writer had oscasion some years ago to calculate the 
 amount of nitrogen removed by the three cereal crops, 
 wheat, barley, and oats, from the soil of Great Britain 
 in a single year. This was found to amount to over 
 120,000 tons, to replace which it would require over 
 half a million tons of sulphate of ammonia, or more 
 than three-quarters of a million tons of nitrate of soda 
 — the two most abundant and valuable of our artificial 
 nitrogenous manures. . 
 
 Of course, it must be remembered that all this is not 
 removed from the farm. Much of it finds its way 
 back again to the soil in an indirect manner. And 
 this leads us to say a word or two on the chief method 
 in which this is effected, viz., by the application of 
 farmyard manure. 
 
 Farmyard manure is made up of straw and the 
 excreta of farm animals. Its chief value is due to 
 the nitrogen which it contains in a soluble form, 
 derived from the urine. It also contains a certain 
 
20 THE FOOD OF CROPS. 
 
 quantity of phosphoric acid and potash in a soluble 
 form. Now, ia keeping for some time, farmyard 
 manure is apt to lose much of these soluble plant foods, 
 which are apt to be washed out of it by the rain. 
 Much of this loss can be easily prevented when the 
 manure is properly kept. Unfortunately, however, 
 there has been in the past, and there still is, an enormous 
 loss annually taking place in different farms throughout 
 the country in this way. Taking only into account the 
 nitrogen, this loss has been reckoned at about 40,000 
 to 50,000 tons, equal to as much nitrogen as is contained 
 in from 240,000 to 300,000 tons of nitrate of soda. 
 If we take the value of this substance at £10 a ton, 
 some conception of the loss is afforded. Grandeau, 
 an eminent French authority, calculates that the value of 
 the farmyard manure produced in France is initially 
 worth £66,000,000 a year, and that about a sixih of its 
 value is lost by careless management. 
 
 Again, the system of thorough drainage — which is so 
 characteristic of modern agriculture — has much increased 
 the loss of fertilising constituents. It is impossible, of 
 course, to estimate what this loss amounts to, because so 
 much depends on a variety of conditions. It has been 
 found at Kothamsted that, under circumstances most 
 favourable to extreme loss — that is, on unmanured fallow 
 land — as much as 54 lbs. of nitrogen per acre was lost 
 by drainage in the course of a year ; that is to say, as 
 much nitrogen as is containtd in 2 cwts. of nitrate of 
 soda. This, of course, is under the most unfavourable 
 circumstances. The average loss per acre is probably far 
 below this, and has been estimated by a well-known 
 authority at not more than 8 lbs. per annum per acre 
 for this country. 
 
THE NATURE AND FUNCTIONS OF FERTILISERS. 21 
 
 The loss of phosphoric acid and potash, although very 
 much less, is still considerable, as is evidenced by the 
 statement that the river Elbe has been found to carry 
 out to sea, yearly, more than 1,200 tons of phosphoric 
 acid ; and more than 43,000 tons of potash, which have 
 been derived from the drainage water of the fields of 
 Bohemia. 
 
 It is true that in nature we have certain processes 
 going on which help, to a certain extent, to neutralise 
 this loss. Such processes are the fixation of free nitrogen 
 from the air by certain plants — already referred to — as 
 well as the slight quantity of combined nitrogen washed 
 down in the rain. It is found, however, in actual 
 practice that such sources of gain are generally 
 entirely inadequate to make good the loss constantly 
 going on. The above considerations show, therefore, 
 the necessity for the app'ication of artificial fertilisers. 
 
 But while it is comparatively easy to see the strong 
 reasons there exist for applying artificial manures, the 
 art of their economical application is far from easy ; in 
 fact, it may be fairly regarded as one of the most difficult 
 problems which the farmer has to face. Their expensive 
 nature, and the great risk they run of being lost through 
 injudicious application, are two points which contribute 
 to this difficulty. The fact that plants differ very 
 considerably in the capacity they possess for utilising 
 the different food materials in the soil is a further 
 consideration which has to be taken into account in the 
 application of fertilisers. Altogether the subject is 
 fraught with great difficulty. Before dealing with the 
 manuring of the different common farm crops, it will 
 be advisable to give a short description of the chief 
 fertilisers in use. 
 
22 THE FOOD OF CROPS. 
 
 In the first place, it may be advisable to say a word 
 or two on the classification of the different fertilisers. 
 We have already mentioned that the only plant food 
 ingredients which are, as a rule, applied as fertilisers 
 are nitrogen, phosphoric acid, and potash. The commer- 
 cial value of a manure is, therefore, dependent on the 
 amount, as well as the chemical form, in which 
 any of these substances is present in it ; and when 
 manures are analysed under the Fertilisers and Feeding 
 Stuffs Act only the percentage of these three substances 
 is stated. It is well that all who have to deal with 
 fertilisers should clearly understand this. 
 
 If we define a fertiliser, however, to be a substance 
 which when added to the soil increases its fertility, and 
 thus enables plants to grow in it more luxuriantly, we 
 must include under the definition of fertiliser certain 
 substances which, although they do not contain any of 
 the above-mentioned plant foods, yet when applied to 
 soil exercise an influence on its fertility. This they 
 effect in an indirect manner ; some by improving the 
 soil texture, and thus influencing certain physical or 
 mechanical properties which have a bearing on its 
 fertility, and others by acting upon the dormant or 
 reserve plant-food in the soil and converting it into a 
 condition in which it is available for the immediate 
 needs of plants. Such substances are generally known 
 as indirect fertilisers. Of these the chief are com- 
 pounds of lime such as iurnt lime, mild lime, gypsum, 
 common salt, &c. 
 
 Fertilisers may thus be divided into two great classes : 
 first, those containing nitrogen, phosphoiic acid, and 
 potash, and which contribute directly to the fertility of 
 the soil — such substances being known as direct manures 
 
THE NATURE AND FUNCTIONS OF FERTILISERS. 23 
 
 (more commonly known simply as manures) ; and, 
 secondly, substances which influence soil fertility in an 
 indirect manuer, and which are consequently known as 
 indirect manures. 
 
 It sometimes happens that a direct manure, when 
 applied to the soil, exerts also an indirect influence. An 
 example of this is furnished by farmyard manure, of 
 which it may be said that its indirect value on many 
 soils is quite as great as its direct one. Again, there are 
 soils so poor ia lime that they have actually not sufficient 
 for the requirements of plant growth, and, in such a 
 Cise, lime may act in a doable capacity. Such soils are 
 very rare. 
 
 Manures are further classified according to their 
 source, such as natural and artificial, mineral and 
 vegetable, or according to the number of fertilising 
 ingredients they contain — general or special. We shall, 
 in the first place, proceed to deal with manures which 
 balong to the direct class, and which are valuable from 
 the fact that they contain nitrogen, phosphoric acid, and 
 potash in varying quantities. 
 
CflAPTEB IV. 
 
 ' FARMYARD MANURE AND SEWAGE. 
 
 In dealing with manures, farmyard manure merits 
 consideration first of all, since it is not only the most 
 widely used of all fertilisers, but is also the oldest. Its 
 composition is by no means uniform, and probably no 
 two samples would be found to yield, on analysis, the 
 same result. This is due to a variety of causes. For 
 one thing, the manurial value of the animal excrements, 
 which form an important constituent of the manure, 
 varies according to the food supplied to the animal — a 
 rich food naturally producing a manure of greater value 
 than a poor food. 
 
 Farmyard manure is made up of three ingredients, the 
 solid and liquid excreta of animals, and the litter which is 
 used to absorb them, and which, almost invariably, 
 consists of straw, but sometimes may consist of peat- 
 moss or other substance. The most valuable pjrt of the 
 manure is its liquid portion, which chiefly consists of 
 urine, a substance lich in soluble nitrogenous coinpouuds. 
 And here it may be well to point out that the diffeient 
 foods in their postage through the animal system tuffer 
 comparatively little loss in respect of their fertilising 
 constituents. Numerous experiments have shown that 
 from three-fourths to nine-tenths of the nitrogen 
 
FARMYARD MANURE AND SEWAGE. 25 
 
 phosphoric acid, and potash which different foods 
 contain may be recovered in the manure if it is proper'y 
 treated. The proportion varies with ihe kind and con- 
 dition of the animals fed. While foods, therefore, in 
 their passage through the animal system suffer compara- 
 tively little diminution in the amount of fertilising 
 constituents they contain, the condition of these 
 fertilising constituents is considerably increased in value 
 by the changes which they undergo ; changes which 
 render the manurial ingredients, especially the nitro- 
 gen, more speedily available for the plant's 
 needs. 
 
 Straw, the common substance used as litter, possesfes 
 but small manurial value. On an average, it contains 
 but little more than half a per cent, of nitrogen, and in 
 the 5 per cent, of ash it contains only a fourth, or 1J 
 per cent., consists of phosphoric ac'd and potash. It is 
 a good absorbent, but where it can profitably be used for 
 feeding purposes it seems a pity to use it as litter, 
 especially where substances such as peat-moss or dried 
 bracken may be easily obtained. 
 
 As farmyard manure is constantly undergoing rapid 
 fermentative and putrefactive changes, and as the 
 conditions under which it is generally kept render it 
 liable to serious loss, great care should be taken in its 
 treatment. The rate at which it decays depends on a 
 number of conditions which do not admit of discussion in 
 a small elementary treatise like the present. A most im- 
 portant influence is that of temperature, which requires to 
 be carefully regulated to prevent serious loss. The most 
 important loss, however, is apt to take place through the 
 draining away of the black liquor, which becomes more 
 abundant the longer the manure is kept. The com- 
 
 3 
 
2& THE FOOD OF CEOPS. 
 
 position of farmyard manure, as we have just -said, varies 
 considerably. The largest ingredient is water, which 
 .may be taken at from 55 to 80 per cent., rotted manure 
 containing a larger amount than fresh manure. The 
 n mount of nitrogen present may be stated at about half 
 a per cent. ; the amount of potash being about the same, 
 and the phosphoric acid somewhat less. A ton of 
 farmyard manure will contain about 9 to 15 lbs. of 
 nitrogen, about the same quantity of potash, and from 
 4 to 9 lbs. of phosphoric acid. What, then, it may be 
 asked, are the characteristic qualities of farmyard 
 manure as a fertiliser ? As a direct manure — that is, 
 as a supplier of plant food — it can scarcely be regarded 
 as a concentrated fertiliser, seeing that it only contains 
 about a twentieth of its total weight of such ingredients 
 as are necessary for plant growth. Furthermore, with 
 regard to the proportion in which it contains its 
 fertilising ingredients, it may be said that this is not in 
 the proportion in which most crops require these con- 
 stituents. It may be said to be richer in mineral foods 
 than in nitrogen. Again, the condition in which it 
 contains much of that nitrogen is not one in which it is 
 readily available to the plant. Much of it seems to become 
 only very slowly available in the soil, and some of it 
 may even take years before it is converted into nitrates. 
 Yet, despite these facts, its properties as a manure are 
 in many respects quite unique. As we have stated, 
 its value must be largely held to be due to its 
 mechanical and indirect properties. It may be con- 
 sidered to be better suited to restore to poor soils a 
 state of fertility than any of the more concentrated 
 and costly artificial fertilisers. The rate and period of 
 year at which it may be applied, as well as the crops 
 
FAEIIYABD MANURE AND SEWAGE. 27 
 
 which benefit most from its treatment, are important 
 points, which, however, we shall reserve to a future 
 chapter. 
 
 It has been the custom, in the past, to apply the 
 liquid oozings from manure heaps, the drainings of 
 farmyard byres, stables, piggeries, &c, directly to the soil. 
 Indeed, so strongly has the belief in the superiority of 
 liquid manure over the other manure been held by certain 
 farmers that they have washed the solid excreta with 
 water in order to extract from it its soluble fertilising 
 constituents. Superphosphate itself, it may be added, 
 was applied to the soil in a liquid form in the early years 
 of its use. With regard to the merits of liquid manure, 
 there can be no doubt that it is the most valuable form 
 in which to apply manure, as it secures for the manurial 
 ingredient it contains a speedy and uniform diffusion 
 in the soil. On the other hand, many objections exist 
 against its use. For one thing, the expense of dis- 
 tributing such a bulky manure is great. For another 
 thiDg, it is not desirable to impoverish farmyard manure 
 by removing from it that which promotes its fermenta- 
 tion, viz., the urine ; and, lastly, it is apt to be a 
 one-sided manure. 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 use it for composts. 
 
 The use of composts is an old one. Before artificial 
 manures were so plentiful, much attention was paid by 
 farmers to their preparation. A compost is generally 
 made by mixing some substance of animal origin, rich 
 in manurial ingredients, along with peat or loam, and 
 often along with lime, alkali salts, common salt, or, 
 indeed, any refuse which may be regarded as possessing 
 
 3* 
 
28 THE FOOD OF CROI J S. 
 
 manurial value. It is a useful method of turning 
 to profit refuse, of various kinds, accumulating on 
 the farm. In composting, the object aimed at is to 
 promote fermentation of the materials out of which the 
 compost is formed, and thereby to convert their manurial 
 ingredients into a condition available for plant needs. 
 In short, farmyard manure may be described as a typical 
 compost, and its manufacture serves to illustrate the 
 principles of composting. 
 
 A manure regarding the value of which much dis- 
 cussion has taken place is sewage. Many attempts 
 have been made in the past towards utilising the 
 undoubtedly great quantitiis of fertilising constituents 
 contained by it, with the result that its manurial value, 
 from being formerly enormously overrated, has probably 
 now come to be underrated. So many considerations 
 have to be taken into account, sanitary as well as 
 economic, that the question does not permit of easy 
 discussion. Many schemes have been proposed for 
 utilising it as a manure. The difficulty in the successful 
 application of the sewage of a large town consists 
 in the fact that the amount to be disposed of. is 
 so enormous. This is the difficulty in irrigating land 
 with sewage. To properly utilise the sewage of a 
 large town, enormous tracts of land would be" required. 
 The sludge resulting from the treatment of sewage 
 with various chemicals possesses manurially little value. 
 The most profitable method of treating sewage must be 
 determined by various local considerations. It must 
 clearly be understood that the question of sewage dis- 
 pjsal is primarily a sanitary one, and that any method 
 which does not comply with sanitary requirements 
 shjuld not be practised. For utilising its manurial 
 
FARMTARD MANURE AND SEWAGE. 29 
 
 value a combination of chemical precipitation and 
 land irrigation is, in most cases, doubtless the most 
 profitable. Up till now it has been chiefly employed 
 in this country by market gardeners for irrigating 
 meadows. 
 
CHAPTER V. 
 
 GUAKO. 
 
 Guano is- a fertiliser which at one time was used in this 
 country to an enormous extent, bat which of late years, 
 owing to its chief sources of supply being well-nigh 
 exhausted, is now only available in comparatively small 
 amounts. It was tbe first artificial manure to be used 
 in large quantities in this country, and its influence on 
 agricultural practice has been very great, as it has led tbe 
 way to what is known as intensive farming. 
 
 Guano is the excrements of sea-birds. Under the 
 influence of a tropical sun, and in countries where rain is 
 hardly known, these excrements soon become dried, and 
 remain little changed in composition through centuries. 
 
 Guano deposits have been found in various parts of the 
 world, the largest and most valuable being those in Peru, 
 in South America. This is due to the fact that, owing 
 to the dry climate of that part of the world, the guano 
 has retained most of its original nitrogen. Guano is 
 found in other parts of the world, where, owing to the 
 dampness of the climate, it has lost all or the greater part 
 of this its most valuable manurial consiituent. Certain of 
 its other manurial constituents are generally found to be 
 wanting in such guano, which depreciates its fertilising 
 value. The result is that very considerable difference has 
 existed in the composition of the different kinds of guano 
 
GUANO. 31 
 
 which have been used in the past. These have varied in 
 composition from the rich Peruvian deposits, containing 
 a high percentage of nitrogen, down to the purely 
 phosphatic guanos, which have lost all their nitrogen. 
 
 Guano deposits have been chiefly found on the south- 
 east coast of South America, or on small adjacent 
 islands, the most valuable deposits ever found being 
 those on the Chincha Islands, three small islands off the 
 coast of Peru, which alone furnished, during a period of 
 thirty years, over ten million tons of this valuable 
 fertiliser. The deposits vary in depth from a few feet to 
 several hundreds. In appearance guano varies somewhat. 
 Its colour is from a light to a dark brown, and it 
 possesses a characteristic pungent odour. The value of 
 most guanos is due chiefly to the nitrogen and phosphoric 
 acid they contain, and also to a small percentage of 
 potash. As has been pointed out, many guanos only 
 contain phosphates. Such guanos are not generally 
 used directly as fertilisers, but are converted into 
 dissolved manures. 
 
 What is especially characteristic of this valuable 
 manure is the fact that it contains its fertilising 
 ingredients in a variety of conditions. This is especially 
 the case with its nitrogen, which is present in a large 
 variety of more or less easily soluble forms. Some of it 
 is in a condition in which plants can immediately absorb 
 it ; while the rest is in a series of less and less available 
 forms, which, however, are gradually converted into 
 available forms as the plant requires them. With its 
 phosphoric acid the same is the case, though to a less 
 " extent. 
 
 The great inequality in the composition of guano has, 
 of late years, led to the introduction of " dissolved " and 
 
32 THE FOOD OF Ci.OPS. 
 
 " rectified " guanos. Such guano consists of that which 
 baa been treated with sulphuric acid for the purpose of 
 increasing the manurial action of its fertilising in- 
 gredients, especially its phosphoric acid ; or that to 
 which sulphate of ammonia has been added to bring up 
 its percentage of nitrogen. A guano of a uniform com- 
 position may thus be produced, and the composition of 
 which resembles that of the older rich deposits, now 
 exhausted. It need scarcely be pointed out, however, 
 that such a guano differs considerably in its action from 
 the genuine article. 
 
 Peruvian guano, as now commonly sold, is of two 
 kinds, the first clisj being guaranteed to contain from 
 6£ to 7j- per cent, of nitrogen (equal to from 8 to 9 per 
 cent, of ammonia), 30 to 35 per cent, phosphates, and 2 
 to 3 per cent, of potash ; while the second class contains 
 only about half as roach nitrogen (between 3 to 4 per 
 cent.), but the phosphates are somewhat higher, 35 to 
 40 per cent. 
 
 The great popularity of guano has led to the applica- 
 t'on of the name to a number of manures. Of these 
 fish guano and meat-meal guano are the best known 
 examples. 
 
 Fish guano is a manure which is either made of fish, 
 which, from various causes, cannot be used as food, or 
 from fish-offal, obtained as a bye-product at fish-curing 
 stations. The use of this manure is largely increasing, 
 and there can be no doubt that it forms a valuable 
 fertiliser. Its quality depends on how it is manufactured, 
 and whether it is made from whole fish or from fish 
 scrap. The general method of manufacture consists in 
 extracting the oil from the fish, which are then dried and 
 reduced to powder. In America it is largely manu- 
 
GUANO. 33 
 
 factured from the menhaddo, a coarse sort of herring, 
 which is caught for the sake of its oil ; while in Norway, 
 where fish guano has hitherto been chiefly manufactured, 
 it is sometimes made from the carcass of the whale. 
 
 The best quality of fish guano may be said to contain 
 from 8 to 10 per cent, of nitrogen, while the phosphates 
 may vary from 4 to 15 per cent. Its composition, 
 however, is very variable — the richer it is in nitrogen, as a 
 rule, the poorer it is in phosphates. It also contains small 
 quantities of potash. Fish guano, it must at once be 
 said, is by no means so valuable a manure as genuine 
 guano. Its fertilising constituents, especially its 
 nitrogen, are not nearly so easily dissolved as those of 
 genuine guano. When applied to the soil it is apt to 
 decompose very slowly. This is due to the oil, which, 
 despite the process of manufacture, is never wholly 
 removed from the manure. It may be said that the less 
 oil it contains the more rapidly will it become available. 
 When used, the fact that it is slowly available should be 
 borne in mind, and sufficient time should be given it to 
 become properly fermented in the soil. 
 
 " Meat " or " meat-meal " guano is made .from the 
 refuse of the carcasses of cattle, after they have been 
 treated for the meat-extract according to Liebig's 
 process. It comes chiefly from South America, Australia, 
 Queensland, and New Zealand, and, as commonly 
 imported, contains from 4 to 8 per cent, of nitrogen — 
 some of it occasionally containing as much as 11 to 13 
 per cent. The amount of phosphates in it varies, and 
 is greatest in such samples as contain least nitrogen. 
 Its percentage of phosphoric acid may be stated approxi- 
 mately at from 13 to 20 per cent. 
 
 In some parts of the world the carcasses of horses, 
 
.34 THE FOOD OF CROPS. 
 
 cattle, dogs, pigs, &c, which have died of disease 
 are converted into guano. Such guano is similar in 
 composition to that just mentioned. 
 
 Among other fertilisers similar in nature to guano 
 which have been, and still are, used may be mentioned 
 the dung of bats, pigeons, and fowls. All these aie 
 considerably inferior in value to either genuine guano 
 or the so-called fish and meat guanos. 
 
CHAPTER VI. 
 
 NITRATE OF SODA, SULPHATE OF AMMONIA, AND OTHER 
 NITROGENOUS FERTILISERS. 
 
 The most important of nitrogenous fertilisers is nitrate 
 of soda — the substance -which, along with sulphate of 
 ammonia, occupies the position formerly occupied by 
 Peruvian guano. This substance, which is imported 
 in enormous quantities from the west coast of South 
 America, where it is found in large deposits in Chili, 
 is valuable only for the nitrogen it contains, which is 
 in the most speedily available form for plant life. It 
 is a white, crystalline substance, very easily soluble in 
 water. The raw form, in which it occurs in South 
 America, and which is known as caliche, contains only 
 from 30 to 50 per cent, of the pure article, which 
 has, therefore, to be obtained from it by refining 
 processes. The ordinary commercial nitrate of soda 
 contains about 95 per cent, of pure nitrate of soda — 
 that is, about 15 j per cent, of nitrogen. Next to 
 sulphate of ammonia, it is the most concentrated 
 nitrogenous fertiliser. From the speed with which it 
 becomes diffused in the soil, and from the fact that 
 its nitrogen is in a form immediately available for 
 absorption by the plant's roots, it should only be used 
 as a fertiliser when the plant is ready to make use 
 of it, and not beforehand, as is the case with most 
 
86 THE FOOD OF CROPS. 
 
 fertilisers. It is, consequently, only applied in the 
 form of a top dressing — that is, after the crop has 
 developed to some extent. Among some of its benefits 
 may be mentioned the tendency it has to encourage 
 deep roots. It is best suited, perhaps, to exercise its 
 full value in dry seasons, since the risks it runs of 
 being washed away by rain is, under such circumstances, 
 minimised ; and, by inducing the roots of the plant to 
 seek their nourishment at greater depths in the soil 
 than would otherwise be the case, it enables them to 
 withstand more successfully the action of drought. The 
 old charge brought against it — that it is an exhausting 
 manure — is, in the light of a wider knowledge of the 
 subject, being largely abandoned. In order to exercise 
 its full value, it must always be remembered that a 
 plentiful supply of the other fertilising constituents is 
 necessary. It can only be regarded as exercising an 
 influence during the first year of application. 
 
 Sulphite of ammonia, the other great nitrogenous 
 manure, is only second in importance to nitrate of 
 soda, and has long been in use. While its nitrogen 
 is not in such an available form for plant uses as the 
 nitrogen in nitrate of soda, in several respects sulphate of 
 ammonia may be regarded as possessing superior 
 properties to nitrate of soda. For one thing, it is not so 
 liable to be lost through drainage as is the case with 
 nitrate of soda. For another thing, it is a more con- 
 centrated manure, being, indeed, the most concentrated of 
 all nitrogenous manures. It is, like nitrate of soda, a 
 whitish, more often greyish or brownish, crystalline salt, 
 extremely soluble in water. The commercial article 
 contains about 20i per cent, of nitrogen, that is to say, 
 about 5 per cent, more than nitrate of soda. Three tons 
 
NITRATE OF SODA, ETC. 37 
 
 of sulphate of ammonia, therefore, would contain the 
 same quantity of nitrogen as 4 tons of nitrate of soda. 
 The oldest and what is still one of the chief sources of 
 this valuable salt is the gas works, where it is obtained 
 as a bye-product in the manufacture of coal gas. It 
 is also obtained, although to a less extent, from coke 
 and carbonising works. The dry distillation of bones, 
 horn, leather, and other substances rich in nitrogen in 
 certain manufactures also yields sulphate of ammonia as 
 a bye-product. 
 
 Although not liable to be immediately washed out of 
 the soil by rain after application, it is yet under most 
 circumstances so speedily converted into nitrates that 
 hardly less care should be taken in its application than in 
 that of nitrate of soda. The mode in which this con- 
 version takes place, known as nitrification, has been already 
 described, so that there is no need to further refer to it 
 here. The relative merits of these two great nitrogenous 
 fertilises have been made the subject of many carefully 
 conducted trials. The results of these seem to point to 
 the fact, that nitrate of soda is more likely to prove 
 itself the more economical manure of the two in dry 
 seasons ; while the reverse is the case with sulphate of 
 ammonia. It may be applied at least a month earlier 
 than nitrate of Boda. 
 
 While the manures we have just been discussing, viz., 
 sulphate of ammonia and nitrate of soda, constitute the 
 largest sources of nitrogenous fertilisers, there are a 
 number of nitrogenous manures which, although used 
 to a smaller extent, are of considerable value. Among 
 these may be mentioned dried blood, horns, hoofs, shoddy, 
 scutch, rape dust, die. 
 
 The first mentioned of these, dried blood, is a 
 
38 - THE POOD OP CROPS. 
 
 very concentrated and valuable fertiliser, arnd has 
 long been used as such in France. The commercial 
 article contains on an average about 12 per cent, of 
 nitrogen, and about 1 per cent, of phosphoric acid. It 
 is a quickly acting manure, since when added to the 
 soil it rapidly ferments. The nitrogen it contains, 
 although less rapidly available than that in nitrate of 
 Soda or sulphate of ammonia, may be described as equal 
 to that in Peruvian guano. It is imported in large 
 quantities from America, as well as manufactured at 
 home. While peculiarly suited for horticulture — it is 
 chiefly used in this country as a manure for hops — it 
 has been applied with much benefit to wheat, grass, and 
 turnips. On sandy or loamy soils it will be found to 
 exert its maximum effect. Considerable quantities are 
 exported to the sugar-growing colonies as a manure for 
 sugar cane. 
 
 Horns and hoofs form a regular source of nitrogenous 
 fertilisers. The quantity of nitrogen they contain varies 
 very considerably, and may be approximately stated at 
 from 7 to 14 per cent. Unlike dried blood, they are 
 very slow-acting manures, and hence very inferior in value 
 to that article. The^ have also been used with benefit 
 for the hop crop. The same may be said of shoddy, the 
 name applied to a manure made from waste wool 
 products, and largely manufactured in this country. 
 Its composition varies within considerable limits, low 
 qualities containing only a small percentage of nitrogen, 
 while the higher qualities contain from 8 to 12 per cent. 
 
 Scutch is the name given to the manure made from 
 the waste products incidental to the manufacture of glue 
 in the dressing of skins, and may be described as con- 
 taining 7 per cent, of nitrogen. All these manures, with 
 
NITRATE OF SODA, ETC. 30 
 
 the exception of dried blood, are better suited, on the 
 whole, for application to such a crop as hops, or in the 
 case of market gardening, where it is desired to have a 
 bulky manure and to accumulate large quantities of 
 decomposing organic substances in the soil. Among other 
 minor nitrogenous manures may be mentioned rape dust, 
 containing about 5 per cent, of nitrogen, a valuable 
 manure ; soot, a manure which has long been used, and 
 which contains about 3 per cent, of nitrogen, but which 
 varies very much in composition. 
 
CHAPTER VII. 
 
 BONES. 
 
 The value of bones, in the form of bone-meal, bone-dust, 
 dissolved bones, &o., as a fertiliser, has long been recog- 
 nised. Indeed, bones were used in England as early as 
 the end of last century, at a time when no other artificial 
 fertiliser was used, and they are still regarded as one 
 of the most valuable of manures. They were at first 
 applied in a comparatively coarse condition ; but we now 
 know that their action, when applied in such a form, is 
 very slow, as pieces of bone may lie in the soil in an 
 undecomposed condition for years. The common forms 
 in which they are at present applied are as bone-meal or 
 bone-dust. Bones, before conversion into bone-dust, 
 should be boiled to remove the fat, which is apt to retard 
 their decomposition when applied to the soil. Bone-meal 
 or dust, of a first-class quality, contains from 45 to 50 
 per cent, of phosphates, and about 3£ per cent, of 
 nitrogen. It may be added that the finer their state of 
 division the more speedy their action. Even in a very 
 fine state of division, they are a slow-acting fertiliser. It 
 has, therefore, long been the custom to treat them with 
 sulphuric acid, to dissolve the insoluble phosphate. Such 
 bones are known as "dissolved bones," and generally 
 contain about 20 per cent, of soluble phosphates. 
 "Dissolved bones" are not to be confused with 
 
BONES. 41 
 
 " dissolved bone compounds," which contain other 
 constituents in addition to bones, and which are largely 
 in use. 
 
 The great popularity of bones as manure among 
 farmers is doubtless due to the fact that their action in 
 the soil continues for a loDger time than most manures. 
 When in an undissolved condition, they should always be 
 applied to the soil a considerable time before they are 
 likely to be needed by the growing plant, so that their 
 fermentation may be well started, and the plant food 
 they contain be partly in an assimilable condition before 
 plant-growth Btarts. Indeed, it was formerly the custom, 
 before they were ground to such a fine state of division, 
 to ferment them before application, by allowing them to 
 lie in heaps for a week or two in a damp condition. 
 Sometimes the fermentation was further promoted by 
 sprinkling the heap with urine or other refuse matter. 
 Of all crops, permanent pasture is best suited to benefit 
 by bones, and they are consequently most largely used for 
 this purpose. " Dissolved bones," however, may be 
 described as a quick-acting manure. " Dissolved bone 
 compounds " may be made from a variety of materials, 
 such as shoddy, wool waste, dried blood, fish guano, &c, 
 along with bones. The composition of such manures 
 varies considerably, and their value depends on this, and 
 on the nature of the material used. 
 
 It is an open question whether bones have not been in 
 the past, as a rule, over valued by farmers. They give, no 
 doubt, what has been termed " backbone " to a soil, but the 
 tendency of modern agricultural practice is to use quick- 
 acting manures rather than slow. The economy of putting 
 much capital into the soil in the form of such slow-acting 
 manures as undissolved bones may well be doubted. 
 
 4 
 
42 THE FOOD OF CROPS. 
 
 The manures which give the speediest returns according 
 to our modern notions ought to be regarded as the 
 most valuable. On the other hand, it seems a pity 
 to utilise for the manufacture of superphosphate the 
 dearer bones as raw material when the cheaper mineral 
 phosphate may be had. As we have pointed out, bones 
 are commonly regarded as being specially beneficial to 
 pasture land, to which they are applied as a top dressing. 
 In America they have been extensively used, mixed with 
 wood ashes, as a substitute for farmyard manure. 
 
 Other substitutes derived from bones which are used 
 as fertilisers or for manufacturing fertilisers are bone 
 ashes, obtained from burning bones. That substance is 
 extremely rich in phosphates, containing as much as 
 from 70 to 80 per cent, of phosphate of lime ; but is, 
 of course, devoid of nitrogen. It is well suited for 
 the manufacture of high-class superphosphates. Bone 
 char or bone black is another article derived from bones. 
 This substance is obtained when bones are heated in 
 closed retorts, and is used largely as a filter in the 
 filtration of sugar. After a time, however, it becomes 
 unsuited for this purpose, owing to having undergone 
 repeated heating. When this takes place it is techni- 
 cally known as spent char, and is used for the manu- 
 facture of superphosphate. Spent char may contain 
 about 70 per cent, of phosphate of lime. 
 
CHAPTER VIII. 
 
 SUPERPHOSPHATES AND MINERAL PHOSPHATES. 
 
 The chief sources of phosphatic fertilisers, in addition 
 to guano and boneB, which have already been mentioned, 
 are the abundantly occurring mineral phosphates. The 
 most abundant of these is apatite, which consists of 
 calcium phosphate and small quantities of calcium 
 fluoride and chloride. It is also known under the 
 name phosphorite. While present in small quantities 
 in most rocks, it is found in certain parts of the world 
 in large masses, being particularly abundant in Canada. 
 It occurs chiefly in a crystalline form, but is also found 
 in an amorphous form. In colour it may be white, 
 red, brown, green, grey, or blue, and it may contain from 
 70 per cent, to 90 per cent, of phosphate of lime. It may 
 be described as a very hard, insoluble form of phosphate, 
 atidT is only valuable as a manure when dissolved in 
 sulphuric acid. In addition to the Canadian mines, 
 the chief deposits are at Estremadura, in Spain, and 
 in Norway. Enormous quantities of superphosphate 
 of lime have been manufactured from apatite 
 during recent years, but, in view of the discovery 
 of other abundant mineral phosphate deposits of a 
 less insoluble nature, apatite has largely ceased to be 
 used as a raw material in the manufacture of super- 
 phosphate. Very large quantities of mineral phosphates 
 
 4* 
 
44 THE FOOD OF CROPS. 
 
 have come from South Carolina, and for years have 
 formed the largest source of phosphate of lime used 
 in the manufacture of superphosphate. These phos- 
 phates are of two kinds, the so-called land and river 
 phosphates, the latter being dredged from different 
 rivers. Such phosphate contains from 50 per cent, to 
 60 per cent, phosphate of lime. Among the other 
 phosphate deposits may be mentioned the Belgian, 
 containing from 35 to 40 per cen h . phosphates, French 
 phosphate, which contains about 80 per cent., and 
 F.orida phosphate. The last-named deposits have only 
 been discovered a few ye irs ago, and have been found 
 to be of enormous extent, and for the most part of 
 high quality. Like the South Carolina phosphates, 
 they are of two classes, land and river phosphates, the 
 former containing from 70 to 80 per cent., and the 
 latter about 50 per cent. 
 
 Among other phosphatic deposits reference may be 
 made to the so-called coprolites, or phosphatic nodules, 
 found in large quantities in the green-sand formation, in 
 the crag of the eastern counties, and in the chalk of the 
 southern counties. They are composed of the fossil 
 excrements and remains of ancient animals, and are in 
 the form of rounded nodules. They have also been 
 found in France. English coprolites contain from 50 to 
 60 per cent, of phosphate of lime ; while the French are 
 somewhat poorer, containing only about 45 per cent. 
 The above-mentioned mineral phosphate deposits, along 
 with the so-called " crust " guanos — that is, guanos con- 
 taining only phosphate of lime, and which, are found in 
 the West Indian Islands and elsewhere — furnish 
 materials for the manufacture of the largest used of all 
 artificial fertilisers, viz., superphosphates. 
 
SUPERPHOSPHATES AND MINERAL PHOSPHATES. 45 
 
 While certain mineral phosphates, if ground fine enough, 
 applied in certain circumstances and to certain soils, iu 
 an undissolved state, have been proved by numerous ex- 
 periments to possess considerable value, yet it has long 
 been recognised that for general use the only economical 
 method of using mineral phosphates is in a soluble 
 condition — that is, after treatment with sulphuric acid. 
 Liebig was the first to discover that the effect of adding 
 oil of vitriol to bones was to render the phosphate soluble, 
 and this discovery may be said to mark an epoch in the 
 history of fertilisers. The treatment of mineral phos- 
 phates with sulphuric acid soon followed, and now 
 probably more than a million tons of superphosphate are 
 annually made in this country ; while the amount in the 
 United States is considerably more. 
 
 Superphosphate of lime, as ordinarily manufactured, 
 may be divided into three classes — low class, medium 
 class, and high class ; the quality of the phosphate 
 depending on the quality of the raw material used, and 
 on the care and efficiency with which the manufacture 
 is carried out. The medium quality contains from 25 to 
 27 per cent, of "-soluble " phosphate, the low class less 
 than 25 per cent., while the high clas3 contains from 30 
 to 45 per cent. The value of superphosphate as a manure 
 may be ascribed not merely to the readily assimilable 
 condition which its phosphate assumes when applied to 
 the soil, but also to the intimate nature of its mixture 
 with the soil particles which is thus effected. When it 
 is added to the soil, being soluble in water, it is soon 
 dissolved and carried down by the rain into the pores of 
 the soil. At the same time, it is speedily converted from 
 a soluble to an insoluble condition — that is, a precipita- 
 tion of the phosphate takes place, due to the lime, iron, 
 
46 THE FOOD OF CROPS. 
 
 and alumina salts which the soil contains. The question 
 may naturally be asked — If this is so, why is it worth while 
 to be at the trouble and expense of dissolving the phos- 
 phate ? To this the answer is twofold. In the first 
 place, it has to be pointed out that the insoluble 
 condition into which superphosphate is converted when 
 applied to the soil is a form of phosphate which, while 
 insoluble in water, is yet much more readily assimilable 
 by plant roots than the ordinary insoluble phosphates, 
 out of which the superphosphate has originally been 
 manufactured. It is, indeed, an intermediate stage 
 between the ordinary bone phosphate and the super- 
 nhosphate. Secondly, the result of adding it in a 
 soluble form is to efi\ ct its admixture with the soil in a 
 state of division iufinitely more minute and iDtimate 
 than could iu any other way be obtained. Hence 
 precipitated phosphate — that is, phosphate obtained 
 under conditions similar to those obtaining in the soil — 
 although in an equally fine state of division, cannot 
 possibly be so intimately mixed with the soil particles. 
 Tor these reasons it will be easily seen that the rate of 
 action of superphosphate must always be quicker than 
 that of any other form of phosphatic manure. The 
 phosphate is uniformly distributed in the soil, and the 
 plant roots are thus furnished with a continuous supply 
 throughout their growth, regularity in which is thus 
 secured, a point of great importance. Moreover, micro- 
 organisms, which require for their development a supply 
 of this necessary plant food, are propagated. 
 
 A phosphatic fertiliser which has recently come 
 into the market is basic slag or Thomas phosphate. 
 This substance is a bye-product obtained in the manu- 
 facture of steel by the so-called basic process. It 
 
SUPERPHOSPHATES AMD MINERAL PHOSPHATES. 47 
 
 consists mainly of phosphate of lime, silicate of lime, 
 free lime, and free magnesia, with oxides of iron 
 and manganese. The amount of phosphoric acid it con- 
 tains may be said to vary from 10 to 20 per cent., 
 equal to from 22 to 44 per cent, tricalcic phosphate. 
 Its phosphoric aeid is combined with the lime, not, how- 
 ever, in the form of tricalcic phosphate, but in a new 
 form unknown except in this compound — viz., tetracalcic 
 phosphate. Various processes Lave been tried for pre- 
 paring the slag as a fertiliser. These, however, have 
 been found to be for the most part unsuccessful ; the best 
 and most economical method being to apply it in a state 
 of very fine division. Indeed, unless ground to a very 
 fine powder, it may be said to possess little fertilising 
 value. When ground, however, to such a state of fineness, 
 that 80 per cent., or thereabouts, passes through a fine 
 gauze sieve containing 250 wires to the linear inch, it is 
 found in many soils to be a manure of considerable value. 
 Its efficacy has been calculated to be about half that of 
 superphosphate. Its action as a manure is much more 
 favourable on some soils than on others. Those best 
 suited to benefit from it are peaty soils, poor in lime. It 
 should be applied in considerable quantities, and some 
 time before it is likely to be required by the crop. 
 
CHAPTER IX. 
 
 POTASH FERTILISEES. 
 
 The use of potash fertilisers is very much more limited 
 in extent than either nitrogenous or phosphatic. As a 
 rale, potash does not require to be applied to the soil in 
 the form of a fertiliser to the same extent as nitrogen or 
 phosphates. Indeed, in many cases, the addition of 
 potash has little or no effect on the fertility of the soil. 
 The reason of this is that many soils, more especially 
 clayey soils (but not necessarily always), are well supplied 
 with potash. On the other hand, there are soils which 
 are greatly benefited by the addition of this fertiliser. 
 Among those may be mentioned sandy, chalky, or peaty 
 soils. We must also remember that under the ordinary 
 conditions of farming the tendency is towards an 
 accumulation of potash in the soil. Where large 
 dressings of farmyard manure are applied, the soil 
 receives much potash. On the other hand, whenever 
 forage crops or straw are sold off the farm in large 
 quantities, or where beets, cabbages, carrots, potatoes, 
 onions, etc., are grown in large quantities, the necessity 
 for potash manuring arises. This is specially the case 
 with potatoes, which benefit more by potash than any 
 other crop. 
 
 The value of potash as a fertiliser first came to be 
 realised by the favourable action of wood ashes, in which 
 
POTASH FERTILISERS. 49 
 
 it is the dominant fertilising constituent. As, however, 
 the supply of substances suitable for use as potassic 
 fertilisers is in excess of the demand, only the more 
 concentrated substances are used. These are chiefly 
 obtained from the Stassfurt deposits, and consist of 
 hainit, sulphate, and muriate of potash. Kainit, which 
 may be described as an impure form of sulphate of 
 potash, contains, on an average, about 12 per cent, of 
 P'-tash ; whereas the muriate or the sulphate, as com- 
 mercially sold, contains about four times that amount. 
 In all three forms the potash may be said to be in a 
 readily available form for plant uses ; but, inasmuch as 
 this substance is retained by the soil particles, it ought 
 to be applied to the soil some time before it is likely to 
 be required by the crop. Speaking generally, it may be 
 said that potash benefits crops of. the leguminous order 
 most. 
 
 Under the heading of potash manures we may consider 
 one which is largely used in maritime agricultural 
 districts— viz., seaweed. In a fresh condition, this 
 manure may be described as containing about 8 per 
 cent, of potash, and about half of that amount of 
 nitrogen, with a fraction of a per cent, of phosphates. 
 Its manurial value and action are generally reckoned 
 as similar to that of farmyard manure ; but this is 
 perhaps hardly correct. It no doubt, however, forms a 
 valuable manure. 
 
CHAPTER X. 
 
 INDIRECT MANURES— LIME, GYPSUM, SALT, ETC. 
 
 The indirect manures are those the value of which is 
 due not to their direct action as suppliers of plant food, 
 like those previously discussed, but to their indirect 
 action. Of these, lime is the oldest, and one of the 
 most important. -Indeed, the use of lime is of great 
 antiquity, and its action is at once complicated and 
 many-sided. There are soils — though by no means of 
 common occurrence — which lack a sufficient supply of 
 lime for promoting plant growth, and to which its 
 addition directly aids the growth of the crop. Poor 
 sandy soils are of this nature ; so, also, are peaty 
 soils. 
 
 The action of lime is, as we have said, many-sided. 
 The benefit derived by permanent pasture soils from an 
 application of this manure is often of a striking nature. 
 The surface of sueh soils, in the first place, is apt to 
 lack a sufficiency of lime from the fact that this 
 ingredient h:is a tendency to sink down to the lower 
 layers of the soil. In ordinary arable soils this tendency 
 is largely counteracted by tillage operations, in which 
 the lime is again brought to the surface. In pasture 
 soils, however, no such counteracting influence is at 
 work ; hence the impoverishment in lime of the surface 
 
INDIRECT MANURES — LIME, GYPSUM, SALT, ETC. 51. 
 
 soil results. Lime also seems to have a striking effect 
 in improving the quality of pasture by inducing the 
 finer grasses to predominate. Especially does it promote 
 the growth of white clover. 
 
 It is used in agriculture in different forms — viz., as 
 carbonate, or mild lime as it is commonly called ; 
 burnt, caustic, or quick lime ; and as gypsum. 
 G-ypsum will be treated immediately by itself, so that 
 we shall only deal here with caustic lime and mild 
 lime. 
 
 The method in which these two forms of lime act 
 is to some extent similar, the only difference being 
 that in the burnt or caustic form its action is some- 
 what more intense. When lime is applied in a caustic 
 state to the soil, it slowly absorbs carbonic acid gas, 
 and becomes converted into the mild form, and to 
 this change some of its effect is due. It may be said 
 to act upon a soil both mechanically and chemically, by 
 altering its texture and affecting its physical properties, 
 such as its absorptive, retentive, and capillary powers 
 with regard to water, and by acting upon its dormant 
 fertilising ingredients, and decomposing its mineral 
 constituents as well as its organic matter, and, finally, by 
 exerting an influence upon the ^development of micro- 
 organic life, and in this way playing an important 
 part in the preparation and elaboration of plant 
 food. 
 
 It is rather a striking fact that its action on different 
 soils seems to vary in its nature. Thus, when applied 
 to a stiff clay, it effects a change in its texture by 
 lessening its adhesive properties, that is its objection- 
 able tendency to puddle when mixed with water, and 
 by rendering it much more friable when in the dry 
 
52 THE FOOD OF CHOI'S. 
 
 state. This it effects by causing a flocculation or 
 aggregation of the fine particles, and by rendering 
 the clay less liable to shrinkage in dry weather. 
 This latter effect of lime is seen in the case of even 
 very small additions, and is what is meant when it is 
 stated that lime has a lightening effect on soils. On 
 the other hand, however paradoxical it may seem, it 
 would appear that its influence on a light soil is of 
 very much an opposite nature, since it seems to increase 
 the cohesive power of such a soil. Indeed, this 
 binding influence of lime ta-es place in some soils, 
 rich in it, to such an extent, that a hard cake is formed, 
 known as a lime-pan. 
 
 But more important than even its mechanical effect 
 is the chemical action of lime, for 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. In this action, caustic 
 lime is much more potent than mild lime. On vegetable 
 matter it exercises a similar decomposing effect, and 
 renders the inert nitrogen it contains available for the 
 plant's use. This may be described as one of the 
 most important effects of lime, and accounts for its 
 beneficial action when applied to soils (such as peaty.ones) 
 rich in organic matter. Its use as a corrective for sour 
 lands has long been recognised. Acidity in a soil is 
 hurtful to vegetable life ; and lime, by neutralising this 
 acidity and removing the sourness of land, does much to 
 restore it to a condition suitable for the growth of 
 cultivated crops. In such soils compounds poisonous to 
 plant life are apt to be formed ; by the addition of lime 
 the conditions favourable to the formation of those 
 compounds are removed. Its application to badly 
 
INDIRECT MANURES — LIME, GfPSUM, SALT, ETC. 53 
 
 drained meadow land not merely ameliorates the general 
 condition, but also checks the growth of the coarser and 
 lower forms of grasses, and promotes the growth of the 
 more nutritive and valuable grasses. Lime also gives rise 
 to the formation of a class of compounds of great import- 
 ance in the soil — viz , hydrated silicates, compounds 
 which retain or fix the available mineral fertilising 
 matter and prevent it from being washed, into the 
 drains. 
 
 What has been called the biological action of lime is 
 also highly important, although its value in this respect 
 has only been comparatively recently recognised. The 
 presence of carbonate of lime in the soil is, as has 
 already been pointed out, a necessary condition for the 
 important process of nitrification. It furnishes a base 
 with which nitric acid can, when formed, combine. A 
 certain amount of alkalinity is necessary for fermentative 
 action of the organic matter ; and lime, by furnishing 
 this alkaline reaction, directly promotes its decomposition 
 in the soil. 
 
 In applying lime, care must be had not to do so too 
 often, or in too large quantities, and to have due regard 
 to the nature of the soil ; indeed, it is a manure which 
 can only be applied wiih great care and discrimination. 
 It should never be applied along with, or even shortly 
 before, certain nitrogenous manures, such as sulphate of 
 ammonia, or any manure containing ammonia, since the 
 result would be to dissipate this most valuable form of 
 nitrogen. 
 
 Gypsum has been so long in use as a manure that it 
 merits description by itself. In some respects its action 
 is similar to that of other lime compounds ; in other 
 respects it is quite different. Its valuable and character- 
 
54 THE FOOD OP CROPS. 
 
 istic action is probably due more to its sulphuric acid than 
 to its lime. It acts as a fixer or absorber of ammonia ; 
 it decomposes the double silicates in the soil and sets free 
 the potash. Indeed, an application of gypsum practically 
 amounts to an application of potash in many soils, and 
 the valuable and striking effect it has in promoting the 
 growth of clover may be accounted for in this way. 
 Experiments have shown that it exerts a very favourable 
 effect on the process of nitrification. It is highly 
 probable, also, that its effect as an oxidising agent 
 in the soil may explain the favourable nature of its 
 action. 
 
 The only other indirect manure which we may here 
 mention is salt. Its fertilising effect, when applied to the 
 soil, has been noted from the very earliest times, although 
 its merits have been variously estimated. Its action may 
 be well described as a most complicated one, and often 
 may be far from beneficial. It is, as a rule, only applied 
 along with other manures. Its mechanical action is 
 probably similar to that exerted by lime, inasmuch as it 
 causes a similar flocculation or coagulation of the fine 
 particles when applied to a clayey soil. Likewise, it 
 exercises a solvent action on the inert plant food, and 
 liberates the necessary mineral constituents from their 
 compounds. Nor must its antiseptic properties be lost 
 sight of, and this no doubt accounts for the beneficial 
 action it has when applied aloDg with Peruvian guano. 
 It is often applied along with nitrate of soda. 
 Plants of the cabbage tribe seem to benefit much 
 by it, so also do mangolds. Both on the beetroot 
 crop and on the potato crop its action, however, is 
 deleterious, since it has been proved to affect the 
 percentage of sugar in the former, and the percentage 
 
INDIRECT MANURES — LIME, GYPSUM, SALT, ETC. 55 
 
 of starch in the latter. Light, sandy soils are more 
 likely to benefit by it than heavy soils. It may be said 
 that its action as a manure is as yet ill understood, 
 but that on certain crops, such as cabbages, it is 
 undoubtedly beneficial. 
 
CHAPTER XL 
 
 THE COMPOSITION AND APPLICATION OF FERTILISERS. 
 
 It cannot be too clearly emphasised for the guidance 
 of the agriculturist that the value of a fertiliser as a 
 commercial article depends on the percentage of nitrogen, 
 phosphates, and potash it contains, as well as the 
 chemical condition of these different fertilising con- 
 stituents. Since these facts can alone be determined- 
 by a chemical analysis, it is obvious that manures 
 should always be purchased on this basis. It is an 
 unfortunate fact that a chemical analysis, even when 
 procured, is not always very intelligible to one ignorant 
 of chemistry. By means of the Fertilisers and Feeding 
 Stuffs Act recently introduced, any farmer can have his 
 fertilisers tested by agricultural analysts specially 
 appointed by the County Councils for, in most cases, a 
 trifling fee. In such a case the only constituents of the 
 fertiliser tested' for are nitrogen, phosphates (soluble and 
 insoluble), and potash, and every manure vendor is 
 compelled to give a guarantee on selling the fertiliser of 
 the percentage of these ingredients it contains. Should 
 the result of the district agricultural analyst's analysis 
 show the fertiliser to be under guarantee, the matter 
 is reported to the Board of Agriculture, which institutes 
 a prosecution under the Act. No difficulty exists, there- 
 fore, in such a case, for the farmer in interpreting the 
 
COMPOSITION AND APPLICATION OF FERTILISERS. 57 
 
 results of an analysis. But in many cases where a full 
 analysis is given, and where the results are not stated so 
 simply, a farmer is apt to be bewildered at the different 
 figures given, and not clearly to understand the meaning 
 of the analysis. One or two words, therefore, may be 
 said in explanation of the method in which the results 
 of an- analysis are stated. 
 
 Discarding all other constituents except the nitrogen, 
 phosphates, and potash as not affecting the commercial 
 value of a fertiliser, a word or two may be said on the 
 different forms in which nitrogen may be present. As 
 was pointed out in speaking of the nitrogen of the soil, 
 nitrogen may exist, broadly speaking, in three different 
 forms — viz., as organic nitrogen, as ammonia, and as 
 nitrates. Now, obviously the fact of first importance is to 
 ascertain what the percentage of nitrogen in a fertiliser is. 
 "This should always be stated, whatever chemical form 
 it is in — whether as nitrates, ammonia, &c. — and no 
 doubt in the future this will be the case. Unfortunately, 
 however, in the past, it has been common to state the 
 nitrogen as ammonia, irrespective of the fact of whether 
 it is present in the manure in that form or not. In 
 a statement of analysis a manure was often said to 
 contain so much ammonia, when in point of fact it 
 contained no ammonia whatever.* With regard 
 to phosphates there is not the same risk of misappre- 
 hension, seeing that the phosphoric acid is always 
 
 * In order to calculate how much nitrogen a certain percentage 
 of ammonia represents, all that has to be done is to multiply it by 
 . 14 and divide by 17, since 17 per cent, of ammonia is equal to 14 
 per cent, of nitrogen. If, on the other hand, it be desired to 
 convert the percentage of nitrogen into the percentage of ammonia, 
 multiply by 17 and divide by 14. 
 
 5 
 
58 * THE FOOD OF CROPS. 
 
 stated in its equivalent of tribasic phospbate of 
 lime. 
 
 Hiving thus discovered, by inspection of the analysis, 
 the amounts of thes<i const tuents, the question which 
 ttie farmer should mxt seek enlightenment on is as 
 to the condition in which they are present in the 
 manure. Now, with regard to nitrogen, this is often 
 not very clearly indicated by the analysis, but generally, 
 even where the analysis does not specify its exact 
 nature, this may often be inferred from the nature of 
 the manure itself. In the case of such manures as 
 sulphate of ammonia and nitrate of soda, no ambiguity 
 exists. It is, however, iu the cise of mixed manures, 
 somewhat different, and tbh, it may be remarked, is 
 one of the objections agiin^t the use of mixed manures. 
 
 With regard to the value of different forms of nitrogen, 
 we may say generally th it that in the form of nitrates 
 and ammonia, and in certain of the more easily decom- 
 posable organic compounds, such as dried blood, meat 
 meal, and of Peruvian guano, is from a fertilising point 
 of view of practically similar value. That their com- 
 mercial value is not always the same is due to a variety 
 of causes with which we are not here concerned. Of 
 considerably les3 value is the nitrogen in steamed bone 
 meal, fish guano, oil cakes, and the better kinds of 
 artificial guanos ; while of least value is that in bone 
 meal, horn meal, woollen refuse, &c. 
 
 With regard to phosphates, commercially only two 
 forms are recognised — viz., soluble and insoluble; but 
 among the so-caled insoluble phosphates considerable 
 difference in value exists, the term " insoluble " being a 
 comparative one. Thus, for example, very wide difference 
 in their respective fertilising values exists between a 
 
COMPOSITION AND APPLICATION OF FERTILISERS. 59 
 
 mineral phosphate, such as apatite, and precipitated 
 phosphate. There is reason, also, to believe that the 
 phosphates in basic si ig, when that article is in a fine 
 enough state of division, is more valuable than that in 
 such a mineral phosphate as apatite. While, lastly, 
 phosphate in such organic compounds as bones and 
 guanos of various kinds, both natural and artificial, are, 
 from the fact of their mechanical condition, and their 
 being associated with large quintities of fermentable 
 organic matter, more valuable as fertilisers than the 
 mineral phosphates.* 
 
 For the purpose of affording data for ascertaining 
 the approximate value of a fertiliser, tables have been 
 drawn up giving what is called the " unit " value of 
 the different fertilising ingredients in various fertilisers. 
 This is obtained by dividing the market value of a 
 fertiliser per ton by the percentaje of nitrogen, 
 phosphates, and potash it contains. Thus, for example, 
 sulphate of ammonia of 97 per cent, purity contains 
 25 per cent, of ammonia, and 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 give* us lis. The value of such 
 tab'es, however, depends on the competence of those 
 drawing them up ; and they require to be subjected to 
 constant revision. 
 
 A most important object in applying fertilisers is to effect 
 equal distribution of the fertiliser in the soil. This 
 
 * It may be well to explain that the term " soluble " phosphate 
 in the statement of an analysis really means the amount of 
 trioalcic phosphate (i.e., insoluble phosphate) which would be 
 originally required to furnish the soluble phosphate present. 
 
60 THE FOOD OP CEOPS. 
 
 is often, however, difficult to do, especially in the 
 case of artificial fertilisers, 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 fertiliser is not so great. In order to overcome 
 this difficulty in the case of artificial fertilisers, it is often 
 advisable to mix them with some such substance as sand, 
 ashes, loam, peat, or salt. The fertiliser 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 
 remembdred that peat itself contains a large amount of 
 nitrogen, and thus forms a manure of some value. In 
 using loam or peat tj mix with artificial fertilisers, 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 fertilisers, as 
 they are apt to contain caustic alkali, which would tend 
 to drive off the ammonia. 
 
 It is to be feared that not unfrequently indiscriminate 
 mixing of fertilisers may cause very serious loss in the 
 most valuable constituent of a fertiliser. It may be well, 
 therefore, to point out one or two causes of the loss that 
 is apt to ensue on the mixing of different kinds of 
 fertilisers together. 
 
 The risks of loss which may occur from the mixing of 
 artificial fertilisers together may be of different kinds. 
 One is the risk of actual loss of a valuable ingredient 
 
COMPOSITION AND APPLICATION OF FERTILISERS. 61 
 
 thro lgh volatilisation ; another is the risk of the 
 deterioration of the value of a mixture through chanjre 
 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 fertilising 
 ingredients — nitrogen, phosphates, 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. 
 
 Ammonia, when uncombined, is a very volatile gas 
 with a pungent smell, a property which enables its 
 escape from a fertiliser 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 com- 
 bining with acids and forming salts. Sulphate of 
 ammonia, as its name indicates, is a salt formed 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 le?s stable 
 bodies — not liable to change — if lefc alone and not sub- 
 mitted to a high temperature or chemical action, they 
 can be easily decomposed if they are heated or brought 
 in 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 
 
G2 THE POOD OF CROPS. 
 
 action, it is easily decomposed. Now a salt may be acted 
 upon by a base, or an acid, or another salt. Wht-n it is 
 brought in contact with a base, if the base with which it 
 is brought into contact be a stronger base than the base 
 of the sj.lt, the salt is decomposed and a new salt is 
 formed. The acid, in short, exchanges its old base for 
 the new one. 
 
 This is exactly what takes place when the base lime 
 comes in contact with an ammonia salt such as 
 sulphate of ammonia. The sulphuric acid exchanges its 
 old base, ainmonia, for the stronger base, lime, and 
 sulp'iate of lime is formed, the ammonia being set free 
 as a gas, which escapes and is lost. Sulphate of 
 amuonw, or any substance in which there is an ammonia 
 silt, mast never be brought in contact wiLh free lime, 
 otherwise the ammonia will be lost. It is entirely 
 different with gypsum — which is sulphate of lime — or 
 phosphate of lime, both of which may be safely mixed 
 with sulphite 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 
 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. 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 fertiliser should be applied almost always 
 as a top-dressing. 
 
 The risks of the loss of nitrogen in the fqrm of nitric 
 
COMPOSITION AND APPLICATION OF FERTILISERS. 63 
 
 acid, a 1 though not so great as they are in the case of 
 ammo:iia, are still considerable. As nitric aciJ is not a 
 base bat an acid, what is to be avoided in mixing 
 nitrates is bringing them in contact with any other 
 fertiliser, as for example superphosphate, which con- 
 tains another free and stronger acid. The free acid in 
 th« 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 los3 of nitrogen, in the form of Dime acid, caused 
 by mixing superphosphate and nitrate of soda, might, 
 under ordinary circumstances, amount to very little, yet 
 if the mixture were allowed to stand any time, and the 
 temperature of the mass to be raised, the I033 which 
 would undoubtedly then ensue would be considerable. 
 The nitrogen salt which it is safe to mix with super- 
 phosphates is sulp'ute of ammotiia. 
 
 But, as has been already mentioned, there is another 
 loss which may result from the mixing of fertilisers. 
 This is the deterioration of the value of an ingredient by 
 reason of change of chemical condition. This is a source 
 of I033 that was little suspected a number of years 
 ago, but it is now well known that superphosphate of 
 lime, under certain coalitions, is changed from its 
 soluble to an insoluble form. Reversion, as this form of 
 change is called, is ofteu caused by the presence of iron 
 and alumina, or undissolved phosphate, and 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 CDntaining a large percentage 
 
64 THE FOOD OF CROPS. 
 
 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 superphosphate 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. 
 
 The question of applying fertilisers in mixtures is one 
 on which considerable difference of opinion may exist. 
 For many reasons fertilisers are often better applied in 
 the unmixed condition. For example, a mixture of a 
 quickly acting nitrogenous fertiliser with a slowly acting 
 phosphatic fertiliser is not suitable. In such a case, 
 either the nitrogenous fertiliser will be applied too long 
 before it is required by the plant, or the phosphatic 
 fertiliser will not be applied long enough before it is 
 likely to be used. By applying fertilisers 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 fertiliser. 
 
CHAPTER XII. 
 
 THE MANURING OF THE COMMON FARM CHOPS. 
 
 Some crops are removed from the farm, such as the 
 cereals ; while others are consumed on the farm, and the 
 manurial ingredients they contain find their way back 
 into the soil. Of the latter class of crops are roots, 
 leguminous crops, and grass. The rotation of crops 
 is thus a question which has an intimate relationship 
 with the question of the application of fertilisers. 
 
 The influence of manuring, it must be at once stated, 
 on what we may call the permanent fertility of the soil 
 is very slight. It cannot be too strongly insisted upon 
 that the fertile condition of a soil, once it has been 
 exhausted by injudicious treatment, is extremely difficult 
 to be restored, and can only be done by very gradual 
 degrees. After all, when we reflect on the compara- 
 tively small quantity of fertilising constituents we 
 add in the ordinary ferli'isers, it is not astonishing 
 that they should have but an insignificant effect in 
 restoring an exhausted soil to a good condition. In 
 fact, the very nature of the highly concentrated and 
 quickly available artificial fertilisers now in use renders it 
 impossible that they should directly affect the condition 
 of the soil. The slow-acting fertilisers, whose influence 
 tells through' several years, are no longer regarded with 
 such favour as they once were — and rightly so. 
 
66 THE FOOD OP CHOPS. 
 
 Of all fertilisers, farmyard manure may be said to 
 have the best effect in influencing what we call the 
 permanent fertility of a soil. This is owing to the fact 
 that it is app'ied in such large quantities, as well as 
 to the fact of its composition. Systematically carried 
 out, liberal manuring will, in time, do much to build 
 up a soil's fertility. But even with artificials the same 
 end may be effected in an indirect way ; for under a 
 system of liberal manuring the quantities of produce of 
 such crops as are consumed on the farm, as well as the 
 residues of such crops as are removed, will be much 
 greater. 
 
 It is not likely that farmyard manure will ever 
 be superseded by artificial fertilisers. The proper and 
 economical use for these latter consists in judiciously 
 supplementing the former. Farmyard manure, we must 
 remember, only returns, as a rule, to the soil what has 
 come off it ; and that minus a certain varying quantity 
 which is los-t in the transition. No doubt, under certain 
 circumstances, where purchased foods, such as linseed 
 cake, &c, are largely used, this loss may be largely 
 made good ; but it is rarely entirely made good. It 
 is, therefore, to supplement farmyard manure that 
 artificial fertilisers should be used. The nature of their 
 action is in many respects so dissimilar that they may 
 be regarded as comp'ementary to one another. 
 
 In applying m inures, consideration must not only be 
 had to the crop to which the manure is applied, but 
 to the whole rotati m pra tised. Some crops are best" 
 q. l.ipbe 1, for a variety of reasons, to benefit more by 
 farmyard manure than others ; while the app icatioii 
 of farmyard manure to other crops is, under certain 
 conditions, highly injudicious,. Thus, it is inadvisable, 
 
THE MANURING OF THE COMMON FAEM CHOPS. C7 
 
 on strong, rich soils, to apply it to grain crops such as 
 barley or wheat, Bince it is apt to encourage rankness 
 of growth. Where the soil is a light one, the risk is 
 not so great. Again, many are of the opinion that 
 potatoes are similarly not benefited by the applica- 
 tion of farmyard manure. In the most generally 
 practised rotation of crops, the one, indeed, on which 
 all others are based — or, rather, of which all others 
 are mere variations — viz., the Norfolk, the farmyard 
 manure is applied to the turnips, and not directly 
 to the grain. 
 
 Furthermore, in the application of artificial fertilisers 
 the nature of the fertiliser should be taken into account — • 
 that is to say, whether it is quick-acting or slow- 
 acting. Nitrate of soda, for example, should only be 
 applied as a top-dressing. Such a fertiliser as bones, 
 on the other hand, should be applied some consider- 
 able time before the plaut is ready to make use of 
 them. Ammonia salts, while le4s speedily available for 
 the plant's uses than nitrate of soda, is much more so 
 than the nitrogen in such a manure as dried blood. So 
 also with the different forms of phosphates, soluble 
 phosphates being much more speedily available than 
 insoluble. With regard to potash, it is a common 
 experience that this, although applied invariably in a 
 soluble form, is best applied a considerable time before it 
 is likely to be used by the crop. Hence we find that 
 fertilisers may be divided broadly into two classes — those 
 which should be applied in autumn, and those which 
 should be applied in spring. To the former class belong 
 manures containing undissolved phosphate, basic slag, 
 nitrogen in an organic form, shoddy, and potash 
 manures ; while to the latter class belong soluble 
 
68 THE FOOD OF CROPS. 
 
 nitrogenous fertilisers, nitrates, ammonia, salts, guano, 
 and soluble phosphates. 
 
 The nature of the soil must also be kept in view, as 
 well as its previous treatment. Generally speaking, soils 
 poor in organic matter are those which are most likely 
 to be benefited by the application of nitrogenous 
 fertilisers. Soils of a dry, light character require less 
 phosphates than they do of nitrogen and potash. A soil 
 rich in organic matter generally requires phosphates or 
 potash. With regard to the application of phosphatic 
 manures, a point of considerable importance in their 
 choice is the nature of the soil to which they are to be 
 applied. Where the soil is poor in lime there is a 
 certain risk in applying acid phosphate. In such a 
 soil it is preferable to use a phosphatic manure of 
 the nature of bones or slag or guano. If, however, 
 there is a sufficiency of lime in the soil, the dissolved 
 phosphate is to be preferred. The nature of the season 
 is also a matter of importance. For instance, in a very 
 wet season it has been found that such a manure as 
 sulphate of ammonia has a better effect than nitrate of 
 soda. To a light and non-retentive soil the risk of loss in 
 applying certain kinds of soluble manure is considerably 
 increased. The previous treatment of the soil with 
 manure has also to be taken into account. A soil 
 liberally treated with farmyard manure is especially 
 benefited by the application of artificial nitrogenous 
 fertilisers. As has been already indicated, the effect of 
 most fertilisers is chiefly seen on the crop to which they 
 are directly applied. Some, however, exert a more 
 lasting influence. As manures which have no influence 
 beyond the first year of application may be mentioned 
 nitrate of soda and sulphate of ammonia. On the other 
 
THE MAMIRING OF THE COMMON FARM CROPS. GO 
 
 hand, bones, slag, &c, may exercise an influence for 
 several years following their application. For the 
 purpose of compensating a quitting tenant of a farm 
 for the value of unexhausted manures, the Agricultural 
 Holdings Act has been framed. The working of the 
 Act, however, has been found to be surrounded by 
 extreme difficulties, as is only natural. 
 
 In conclusion we may say a word or two on the 
 manuring of the more common farm crops. 
 
 We may start with cereals. To this class belong 
 harley, wheat, and oats. A certain similarity in the 
 manurial requirements of the different members of 
 this class exists. For one thing, they are characterised 
 by the comparatively small quantity of nitrogen they 
 remove from the soil, which is considerably less 
 than either of the other classes of crops — leguminous 
 and root crops. Of this nitrogen the larger portion, 
 amounting to two-thirds, is contained in the grain. 
 The amount of phosphates they remove, however, is 
 not much less than that removed by the other two classes 
 of crops. This, again, is also chiefly in the grain. It 
 is on this account that the cereals may be regarded as 
 exhaustive crops, seeing that the grain is sold off the 
 farm. As cereals constitute a very important element of 
 human food, arable farming in the past has been carried 
 out with a view to growiDg such crops in a manner least 
 exhaustive to the soil. Before the rotation of crops was 
 introduced it was customary to grow cereals for a number 
 of years in succession, and then to have recourse to bare 
 fallow, or in some ca?es to abaudon the land to the 
 growth of rough herbage. An advance in this practice 
 is marked by the introduction of alternating leguminous 
 crops wioh cereals. The introduction of such a crop has 
 
?0 THE FOOD OF CROPS. 
 
 very much, the simj effect in resting the land as fallow 
 hai, b^iles being much more economical. Toe intro- 
 duction of roots into the rotation marks a still later 
 improvement. lo is a curious fact, however, that 
 albhoagh cereils may be regarded as distinctly an 
 exhaustive crop they will yet continue to grow on poor 
 land for a longer period than most orops 
 
 It has been already pointed out that in judging of the 
 manorial requirements of a crop attention must be had 
 not merely to the absolute amount of fertilising ingre- 
 dients such a crop removes from the soil, but also to the 
 ability of the crop to absorb from the soil these 
 fertilising constituents. Now, although cjreals remove 
 comp iratively little nitrogen from the soil, they are most 
 benefited by the application of nitrogenous fertilisers. 
 This fact may be explained by the shortness of their 
 period of growth, and also by the fact that they assimilate 
 their nitrogen in spriDg anl early summer, and are thus 
 enabled to utilise to the full the nitrates which accumu- 
 late ia the soil, du^ to the process of nitrification, in later 
 summer and autumn. The speeial fertiliser, therefore,- 
 required for cereals is a nitrogenous manure, and that of 
 a spesdily available character. But while the different 
 members of this class resemble each other in several 
 points, they have their special characteristics, which we 
 will now notice". 
 
 Barley, like oats, has a very short period of growth. 
 In this country barley may be said, on an average to 
 ripen in thirteen or fourteen weeks. It is a spring 
 crop, and from the fact that its roots, which are 
 shallower than wheat, draw their nourishment chiefly 
 fiom the surface soil, benefits much from liberal 
 manuring. It does best on a light, rich, friable soil ; 
 
THE MAXCRFNG OF TH8 COMMON FARM CROPS. 71 
 
 and while, like the other members of the cereal group, 
 it especially benefits by a nitrogenous manure, Mich as 
 nitrate of soda, applied as a top dressing, it al.-o responds 
 to the application of superphosphate of lime. Indeed, 
 it may be said that spring-sown crops, as a rule, benefit 
 more from superphosphate than autumn crops. The 
 exhaustion of a soil under barley is one of nitrogen. 
 Barley is not suited to benefit by the direct application 
 of farmyard manure. The use to which barley is 
 put — viz., malting purposes — renders uniformity in its 
 composition of importance. S nee its quality is very 
 'largely influenced by its treitment with manure, special 
 attention has to be exercised in their application. Care, 
 therefore, must be taken not to manure too richly barley 
 which is destined for malting purposes. Barley is often 
 grown immediately after wheat crops, and occasionally 
 without manure, where the land is rich. It is claimed 
 that bxrley, grown under such cireum-stancas, will be best 
 for milting purposes. The amount of the manure to 
 bs applied to any crop will necessarily depend on the 
 treatment of the land throughout the rotation. In 
 experiments cirried out in Norfolk it was found that 
 from -} to 1 cwt. of nitrate of soda, according to the 
 previous treatment of the soil ; from 1 to 2 cwt. of 
 superpho -ph ite ; and, where required, from J cwt. to 
 1 cwt. of mud ite of potash, were suitable quantities of 
 fertilisers to apply to the b irley crop. 
 
 Wheat, unlike birley, is generally sown in autumn 
 although it is aho sown in the spring. Unlike barley, 
 it does best on a clayey soil, and requires a moist seed- 
 bed. As it often follows a crop which has been heavily 
 manured, it is not so necessary to manure it. Indeed, 
 the only manure generally applied is a top dressing of 
 
72 THE FOOD OF CROPS. 
 
 nitrate of soda. It is usually considered highly desirable 
 to get land into good "heart" before wheat. On a 
 light soil, however, it may often be desirable to add 
 superphosphate of lime or guano or some other phosphate 
 manure at the rate of from 2 to 3 cwt. per acre. The 
 quantity of nitrate of soda applied as a top dressing 
 varies from | cwt. to 1 cwt. per acre. 
 
 It may be mentioned in passing that the possibility of 
 growing fair crops of wheat continuously on the same 
 land for a period of fifty years has been demonstrated 
 by the famous Kothamsted experiments. 
 
 Wheat is generally grown after clover or other 
 leguminous crop to which farmyard manure has been 
 applied. Such a crop, by its ability to fix the atmospheric 
 nitrogen, and to draw nitrogen from the subsoil, serves 
 to greatly enrich the surface soil in that fertilising 
 constituent. A large clover crop is thus an admirable 
 preparation for a wheat crop. Where the previous crop 
 has not been liberally treated with manure, it may be well 
 to manure the soil with phosphates in autumn, before the 
 wheat is sown. As a rule, it is advisable to top-dress 
 wheat with nitrate of soda in spring — about 1 cwt. of 
 nitrate per acre being sufficient. 
 
 Oats, like barley, are a shallow-rooted crop, and require 
 manures which are readily available. They may be 
 treated very similarly to barley. Perhaps on no crop is 
 nitrate of soda so safe and so effective a manure. 
 Superphosphate of lime may also be applied with 
 advantage along with the seed. In some respects oats 
 are different from barley. For one thing, they are a 
 much hardier crop than barley, and they can grow on a 
 wonderfully large variety of soil, and under comparatively 
 adverse circumstances both of climate and situation. 
 
THE MANURING OF THE COMMON FARM CROPS. 73 
 
 They are well suited for a damp climate, and flourish on 
 sandy, peaty, or clayey soils. They show a preference, 
 however, for soils rich in decayed vegetable matter. It 
 is for this reason that they flourish so well in soils freshly 
 broken up from pasture, and are often the first crop to be 
 grown on such soils. 
 
 Oats absorb nitrogen during nearly the whole period of 
 their growth. By some it has, for several reasons, been 
 considered advisable to manure them with a mixed 
 nitrogen manure, containing nitrogen in different 
 conditions of availability. 
 
 The quantity of manure which should be applied to 
 the oat crop is similar in amount to that applied to the 
 other cereal crops. Often, indeed, the oat crop is not 
 manured at all. 
 
 We may next consider the manuring of grass. Grass 
 is grown under two conditions — viz., on soils set apart 
 for its continuous growth (permanent pasture) ; or it is 
 grown for the purpose of being converted into hay, and 
 providing pasture in the ordinary rotation of crops 
 (rotation seeds). The manuring of the former differs 
 from that of the latter. Eotation grasses may be liberally 
 manured. Permanent pasture, on the other hand, 
 requires very careful and judicious treatment. It is a 
 curious but well ascertained fact that the nature of the 
 herbage growing on pasture is very much influenced by 
 the fertiliser used. 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 
 
 6 
 
74 THE FOOD OP CHOPS. 
 
 grasse3 of one kind tend to predominate and crowd out 
 grasses of another kind. 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 maintain 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. 
 
 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 kind of 
 grass over another ; and in this respect it is probably to 
 be preferred to artificial fertilisers. Sometimes, however, 
 it is desirable to supplement farmyard manure with 
 phosphates, in which case one of the best and justly 
 esteemed phosphatic manures is bone dust, which may 
 with great advantage be applied in autumn at the rate 
 of from 4 to 5 cwt. per acre. Basic cinder is also a 
 good manure. 
 
 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 under 
 such conditions. Nitrogenous fertilisers, more especially 
 sulphate of ammonia, increase the proportion of the 
 grasses proper, and diminish the proportion of the 
 leguminous plants. The effect of farmyard manure, 
 
THE MANURING OF THE COMMON FARM CROPS. 75 
 
 while less marked in inducing simplicity of herbage, is 
 similar to sulphate of ammonia. Potash manures, on 
 the other hand, tend to develop leguminous plants in a 
 herbage, so also do phosphates. Potash fertilisers, as a 
 rule, are unnecessary, but in light or peaty soils they 
 may be of service. Grass grown for hay may be 
 manured with nitrate of soda in comparatively large 
 quantities — viz., 2 to 3 cwt. per acre. 
 
 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 three 
 fertilising ingredients — nitrogen, phosphates, and potash 
 — and may be regarded as exceedingly exhaustive 
 crops. This is especially the case with mangolds, 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 auy soil. Mangolds are generally more 
 benefited by the application of nitrogenous fertilisers 
 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 
 
76 THE FOOD OF CEOPS. 
 
 that any of the root crops are not dependent on a ready 
 supply of nitrogen, and the fact that large crops of 
 turnips c.in often be grown by the application of super- 
 phosphate alone may be taken as a proof that the soil 
 contains plenty of nitrogen. Mangolds are, from their 
 deeper roots, more capable of drawing their supply of 
 phosphoric acid from the soil thai turnips. They 
 respond, therefore, as a rule, less free'y than turnips or 
 swedes to an application of superphosphate. General ly 
 speaking, we imy say that the characteristic manure for 
 turnips is superphosphate ; and that for mangolds 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 ate more liable -to disease than any other crops, 
 and this is especially the ca-e 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 stages 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 large applications of manure may be profitably 
 employed. Roots generally receive a large dressing of 
 farmyard manure. Salt has been found in some dis- 
 tricts to have a very good effect on the mangold crop, 
 and potash is found to amply repay application. 
 
 Roots most commonly receive the bulk of the farmyard 
 manure applied throughout the rotation. They may be 
 regarded as the starting crop, and on them the most 
 manure is expended, not mi rely on their own account, 
 
THE MANURING OF THE COMMON FARM CROP 1 '. 77 
 
 but also on account of the crops that are to follow. In 
 many respects they are well suited to be the recipients of 
 this plant food. They are gross feeders, and distribute a 
 very large amount of fibrous feeding rootlets in the soil. 
 They are enabled, on this account, as well as on account 
 of the long period of their growth — which extends for 
 months — to avail themselves of the fertilising constituents 
 supplied by the manure to a much greater extent than 
 the cereals could do, and as they are generally fed off 
 the land with sheep their manurial ingredients are thus 
 returned to the soil. 
 
 Potatoes are often classed 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 dem»nds 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. Indeed, the mechanical condition of the soil 
 is a consideration of first-rate importance in the growing 
 of potatoes. They may be said to grow best on deep, 
 warm soils ; but, like roots, if liberally manured, they 
 may be successfully grown on any 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 40 tons per 
 acre. There can be little doubt that the value of farm- 
 yard 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. 
 
78 THE FOOD OF CHOPS. 
 
 Potatoes repay the application of mixed manure 
 containing all the fertilising ingredients better than most 
 crops. The nitrogen is btst applied in the form of nitrate 
 of so'la. 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 amount 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. 
 
 The influence of the 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. 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. 
 
THE MANURING OF THE COMMON FARM CROPS. 79 
 
 It has been found that in a highly nitrogenous manured 
 crop the proportion of diseased tubers is greater than in 
 an unmanured crop. 
 
 In leguminous crops, which include clover, beans, peas, 
 vetches, lucerne, etc., we have examples of crops not 
 benefited by direct application of nitrogenous manures. 
 They have the power of accumulating nitrogen in the 
 surface soil in very large quantities, and are thus admir- 
 ably suited for preceding in the rotation such crops as 
 cereals, which benefit largely by nitrogenous manures, 
 and which, from the fact of their being sold off the farm, 
 are essentially exhausting. The value of alternating 
 cereals with leguminous crops was, as we have already 
 pointed out, recognised by the Romans. The best 
 manure for them is farmyard manure. Phosphatic 
 manures may often with advantage be applied, potash 
 still more rarely. 
 
 In several respects the manurial requirements 
 of cabbages are similar to those of turnips, though in 
 other respects they differ. Cabbages are gross feeders, 
 to whi'ih any kind of manure, applied in any quantity, 
 does not come amiss. They must be liberally treated 
 both with phosphates and with nitrogenous manures, 
 since they remove from the soil a very large quantity 
 of fertilising ingredients. Nitrate of soda in large 
 quantities — as much as 4 cwt. per acre — may be applied 
 with profit to them. The addition of salt to the nitrate 
 of soda is highly to be recommended. This may be 
 applied at the rate of 5 to 6 cwt. per acre. Potash 
 is also a most effective manure ; indeed, the amount 
 of potash cabbages remove from the soil is very great. 
 Farmyard manure may be applied in larger quantitiis 
 to them with benefit than to any other crop. 
 
80 THE FOOD OF CROPS. 
 
 The requirements of the hop crop in the matter 
 of manures ar<; rather lingular, inasmuch as they 
 require a slow-acting fertiliser. They 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 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 quick-acting manure. 
 The dressings applied to hops are very large. As we 
 have pointed out, the nature and amount of farmyard 
 manure or artificial fertiliser applied to the different 
 crops must be largely determined by the treatment of 
 the crop preceding it in the rotation, and must not 
 simply be determined by the crop itself. 
 
QUESTIONS. 
 
 OHAPTER I. 
 
 1. What does chemical analysis teach us regarding' the 
 composition of plants ? 
 
 2. What is the percentage of water in plants 1 
 
 3. Does the amount of the mineral matter of plants vary ? 
 
 4. Out of what elements is the organic matter composed, and 
 in what percentage are they respectively present 1 
 
 5. What are the chief chemical compound substances out of 
 which plants are formed, and into what groups can you divide 
 them? 
 
 6. What are some of the elements present in the ash ? 
 
 7. What are the sources of plant food ? 
 
 8. What elements do plants derive from the soil, and what 
 from the air 1 
 
 CHAPTER n. 
 
 9. What is meant by germination ? 
 
 10. What are the conditions of germination ? 
 
 11. What is meant by carbon assimilation, and under what 
 conditions does it take place ? 
 
 12. What are the sources of the carbonic acid gas present in 
 the air ? 
 
 13. Whence do plants derive the oxygen and hydrogen out of 
 which a large portion of their tissue is formed ? 
 
 14. In what forms do plants absorb their nitrogen 1 
 
 15. How are these various forms of nitrogen converted into 
 one another in the soil 1 
 
 16. What is meant by ammonification and nitrification ? 
 
 17. How do leguminous plants " fix " free nitrogen ? 
 
82 THE FOOD OF CROPS. 
 
 18. Why are nitrogen, phosphoric acid, and potash of special 
 importance as fertilising constituents ? 
 
 19. What are the chemical forms in which phosphoric acid 
 and potash are present in the soil ? 
 
 20. On what may the fertility of a soil be said to depend ? 
 
 CHAPTER III. 
 
 21. How are virgin soils formed ? 
 
 22. In what way, under agricultural practice, are the fertilising 
 -constituents of a soil removed-? 
 
 23. Which crops are the most exhausting ? 
 
 24. In what way do the fertilising constituents removed in 
 crops from the soil find their way back again ? 
 
 25. In what way does farmyard manure lose in value through 
 careless management ? 
 
 26. What is the nature of the losses which take place from a 
 soil by drainage ? 
 
 27. To what extent is nitrogen probably lost in this way ? 
 
 28. Are there any natural processes whereby the soil gains in 
 fertilising constituents ? 
 
 29. How may fertilisers be classified ? 
 
 30. What is the difference between direct and indirect 
 manures ? Give examples. 
 
 CHAPTER IV. 
 
 31. Why should the composition of farmyard manure be 
 variable ? 
 
 32. Into what three classes may the constituents of farmyard 
 manure be divided ? 
 
 33. What substances, in addition to straw, are suitable for use 
 as litter ? 
 
 34-. Why should the black liquor of farmyard manure be its 
 most valuable constituent 1 
 
 35. State approximately the amounts of nitrogen, phosphoric 
 acid, and potash which farmyard manure, of average composition, 
 may contain. 
 
 36. How are composts generally made ? 
 
 37. How is sewage usually applied to land ? 
 
QUESTIONS. 83 
 
 CHAPTER V. 
 
 38. What influence has guano had on the development of agri- 
 cultural practice ? 
 
 39. What is guano ? 
 
 40. Where have the chief guano deposits been found ? 
 
 41. Describe the properties of guano. 
 
 42. In what chemical conditions are its fertilising constituents 
 present ? 
 
 43. What is " rectified " guano ? 
 
 44. State the percentages of nitrogen, phosphates, and potash 
 in ordinary Peruvian guano. 
 
 45. What is fish guano ? State the percentages of nitrogen 
 and phosphates it usually contains. 
 
 46. What percentages of nitrogen and phosphates does meat 
 guano contain ? 
 
 CHAPTER VI. 
 
 47. Where is nitrate of soda obtained ? To what does it owe its 
 value as a fertiliser ? 
 
 48. What is the composition of ordinary commercial nitrate of 
 soda? 
 
 49. Why is nitrate of soda almost invariably applied as a top 
 dressing ? 
 
 50. Mention some of the benefits obtained from an application 
 of nitrate of soda. 
 
 51. What is peculiarly characteristic of sulphate of ammonia 
 as a nitrogenous manure ? 
 
 52. Is the nitrogen in sulphate of ammonia as readily available 
 as that in nitrate of soda ? 
 
 53. What percentage of nitrogen does commercial sulphate of 
 ammonia contain ? 
 
 54. Mention the chief sources of sulphate of ammonia ? 
 
 55. Under what conditions is nitrate of soda found to be a 
 more economical nitrogenous manure than sulphate of 
 ammonia ? 
 
 56. State the percentage of nitrogen contained by dried 
 blood. 
 
 57. Describe the action of dried blood when applied to the 
 soil, and state what crops are benefited by its application. 
 
84 THE FOOD OF CROPS. 
 
 58. On what soils does dried blood exert its maximum effect ? 
 
 59. What is trie percentage of nitrogen in horns and hoofs ? 
 Describe their action. 
 
 60. What is shoddy? What percentage of nitrogen does it 
 contain ? 
 
 61. To what constituent does soot owe its manurial value? 
 
 CHAPTER VII. 
 
 62. When were bones first used as manure in this country ? 
 
 63. In what forms are bones usually applied 1 
 
 64. State the percentages of phosphates and nitrogen bone 
 meal and flour contain. 
 
 65. What are " dissolved bones," and in what respects do they 
 differ from ordinary bones ? 
 
 66. Describe the action of bones when applied to the soil. 
 
 67. What crop benefits most from the application of bones ? 
 
 68. From what materials are " dissolved bone compounds " 
 usually made ? 
 
 69. What is bone-ash, and what percentage of phosphate of 
 lime does it contain ? 
 
 70. How is bone black obtained ? 
 
 71. What is spent char 1 
 
 CHAPTER VIH. 
 
 72. Describe the properties and composition of apatite. 
 
 73. What phosphates are most largely used in the manu- 
 facture of super-phosphates 1 
 
 74. What are coprolites 1 What is their composition ? 
 
 75. Have undissolved mineral phosphates any manurial value .' 
 
 76. How is superphosphate obtained from mineral phos- 
 phates 1 
 
 77. What is the composition of superphosphate of lime ? 
 
 78. Explain the action of superphosphate when applied to 
 the soil. 
 
 79. What is basic slag ? What percentage of phosphate of 
 lime does it contain ? 
 
 80. What is peculiar about the chemical condition of phosphate 
 in basic slag ? 
 
QUESTIONS. 85 
 
 CHAPTER IX. 
 
 81. Why is there less necessity for potash manuring than for 
 either nitrogenous or phosphatio manuring 1 
 
 82. What soils are benefited by the application of potash ? 
 
 83. Mention the chiaf potash fertilisers, with their percentages 
 of potash. 
 
 84. What crops are most benefited by potash 1 
 
 85. State the amount of fertilising constituents in seaweed. 
 
 CHAPTER X. 
 
 86. Explain the meaning of the term " indirect manure." 
 
 87. What soils are usually deficient in lime ? 
 
 83. Why is the surface of pasture soils apt to be deficient in 
 lime? 
 
 89. In what forms is lime used in agriculture ? 
 
 90. Give an account of the mechanical action of lime in a 
 soil. 
 
 91. What is the chemical action of lime when applied to the 
 soil .' 
 
 92. What effect has lime on the micro-organic life of the 
 soil? 
 
 93. Explain the action of gypsum as a fertiliser. 
 
 94. What crops are benefited by the application of salt ? 
 
 CHAPTER XI. 
 
 95.' What value has chemical analysis in determining the value 
 of a fertiliser ? 
 
 96. What constituents of a fertiliser are tested for under the 
 Fertilisers and Feeding Stuffs Act ? 
 
 97. In what forms doss nitres an occur in different fertilisers .' 
 State these in their order of value. 
 
 98. What are the different forms of phosphates of lime in 
 fertilisers ? 
 
 99. Is the phosphate in a mineral phosphate, such as apatite, 
 as valuable as that in bones ? 
 
 109. What is meant by the unit value cf a fertiliser, and how 
 is it determined ? 
 
86 THE FOOD OF CROPS. 
 
 101. What means are adopted to effect the equal distribution 
 of a fertiliser in the soil ? 
 
 102. Mention the risks of loss which are apt to ensue on 
 mixing manures. 
 
 103. How is sulphate of ammonia formed ? 
 
 104. What is the result of mixing' lime with an ammonia 
 salt? 
 
 105. Is it safe to mix basic slag with sulphate of ammonia ? 
 
 106. Why should nitrate of soda not be mixed with super- 
 phosphate ? 
 
 107. What is meant by the reversion of soluble phosphate, 
 and how is it caused ? 
 
 108. Why should a quick-acting nitrogenous fertiliser not be 
 mixed with a slow-acting phosphatic fertiliser ? 
 
 CHAPTER XII. 
 
 109. Have fertilisers much influence on the permanent fertility 
 of a soil 1 
 
 110. What manure has the best influence on the permanent 
 fertility of a soil, and why 1 
 
 111. Name the fertilisers best applied in spring, and those best 
 applied in autumn. 
 
 112. What fertilising ingredients are best applied to dry, light 
 soils ? What does a soil rich in organic matter usually require ? 
 
 113. In a wet season whether is nitrate of soda or sulphate of 
 ammonia the more economical manure ? 
 
 114. Have bones any influence on the fertility of a soil after 
 the first year of application ? 
 
 115. What is the characteristic difference between the 
 manurial requirements of cereals compared with other crops ? 
 
 116. What class of manures have the best influence on 
 cereals .' 
 
 117. What kind of soil is most suitable for the growth of 
 barley ? 
 
 118. Mention the fertilisers, and the amounts usually applied 
 to barley. 
 
 119. What fertiliser is usually applied to wheat ? 
 
QUESTIONS. 87 
 
 120. Do roots respond to the application of slow-acting 
 fertilisers 1 
 
 121. What fertilising ingredient is usually required by oats ? 
 
 122. Why is permanent pasture very seldom manured ? 
 
 123. What is the safest manure to apply to permanent 
 pasture ? 
 
 124. Why are roots exhausting crops ? 
 
 125. On what soils do roots grow best ? 
 
 126. What is the characteristic manure for turnips and 
 mangolds ? 
 
 127. Why can roots avail themselves of the fertilising con- 
 stituents applied much better than cereals ? 
 
 128. The farmyard manure applied throughout the rotation is 
 usually applied to the root crop. Why is this ? 
 
 129. On what soils do potatoes grow best, and why are they 
 usually classed with the roots ? 
 
 130. What are the best nitrogenous and phosphatic fertilisers 
 to apply to potatoes 1 
 
 131. Describe the influence of fertilisers on the composition of 
 potatoes. 
 
 132. What is the best manure to apply to leguminous crops ? 
 
 133. Why should cabbages be liberally manured ? 
 
 134. What fertilisers have the best effect on cabbages ? 
 
 13.j. What is the best kind of manure for hops, and how often 
 are they generally manured 1 
 
INDEX. 
 
 Air, source of plant-food, 4. 
 Albuminoids in plants, 4. 
 Ainmonification, 13. 
 Apatite, 43. 
 Ash of plants, 3, IS. 
 
 Barley, manuring of, 70. 
 Blood dried, 37. 
 Bones, 40-42. 
 
 Cabbages, manuring of, 79. 
 
 Carbon, in plant- tissue, 2-3. 
 
 Carbonic acid gas, assimilation of, 
 by plant, 9 ; source of plant- 
 food, 5; sources of, 11. 
 
 Carbohydrates in plants, 3. 
 
 Cellulose in plants, 4. 
 
 Cereals, fertilising matter removfd 
 by, 18; manuring of, 69. 
 
 Cbar, spent, 42. 
 
 Chlorophyl in plants, 11. 
 
 Composts, 27. 
 
 Coprolites, 44. 
 
 Farmyart> manure, 19, 24; 
 
 application of, 66 ; composition 
 
 of, 26. 
 Fertilisers Act, 22. 
 Fertilisers, application of , 65 -80 ; 
 
 composition of, 56-58 ; mixing 
 
 of, 60-61 ; valuation of, 59. 
 Fish guano, 34. 
 
 Germination, 8. 
 Grass, manuring of, 73. 
 Gluten in plants, 4. 
 Guano, 30-34. 
 Gypsum, 53-55. 
 
 Hoofs, 37. 
 Hops manuring of, 80. 
 Horns, 37. 
 Hydrogen in plants, 3. 
 
 Kainit, 49. 
 
 Leguminous crops, 79. 
 Lime, 50-53. 
 
 Mangolds, manuring of, 75 ; 
 w ater in, 2. 
 
 Meat-meal guano, 33. 
 
 Mineral matter in plants, 3, 15. 
 
 Nitkate op soda, 35-36. 
 
 Nitrification, 13. 
 
 Nitovgen, assimilation of, by 
 plants, 12; different forms of, 
 12 ; in rain, 14 ; in plants, 3 ; 
 removed from the soil, 20. 
 
 Oats, manuring of, 72. 
 Organic matter in pUnts, 3. 
 Oxygen in plants, 3. 
 
 Phosphates, mineral, 44. 
 
 Phosphoric acid, necess ry for 
 plant-growth, 6, 16; removed 
 from soils, 21. 
 
 Plants, composition of, 1-4. 
 
 Potash; fertilisers. 48-49 ; manur- 
 ing of soil, 21 ; muriate of, 
 49 ; necessary for plant • growth, 
 6, 16; removed from (.oil, 
 21 
 
 Potatoes, manuring of, 77 water 
 in, 2. 
 
 Proteids in plants, 4. 
 
 Rape-dust, 37. 
 
 Soutoh, 37. 
 
 Seaweed, 49. 
 
 Sewage, 28. 
 
 Sboddy, 37. 
 
 Slug, basic, 46. 
 
 Soil, source of plant food, 4. 
 
 Starch in plants, 4. 
 
 Sugar in plants, 4. 
 
 Sulphate of ammonia, 36-37. 
 
 Superphosphates, 43-45. 
 
 Timber, amount of water in, 2. 
 Turnips, manuring of, 75; 
 amount of water in, 2. 
 
 Virgin soils, 18. 
 
 Water, amount of, in plants, 
 
 1-2. 
 Wheat, manuring of, 71. 
 
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 SOME PRESS OPINIONS. 
 "Professor Wrightson has done his work exceedingly well." — Meld. 
 " The several breeds are well described and illustrated." — Standard. 
 " Deserves to be widely read."— Morning Post. 
 
 " The book is one of the best of its kind." — North British Agriculturist. 
 " Will take a place altogether its own. We heartily commend it."— Scottish Farmer. 
 
 No. 2. LIGHT HORSES. 
 
 Breeds and Management. [end Edition. 
 
 By W. C. A. BLEW, M.A. ; WILLIAM SCARTH DIXON; Dr. 
 GEORGE FLEMING, C.B., F.R.C.V.S. ; VERO SHAW., B.A., 
 &c. 226 pages, demy 8vo, cloth, gilt lettered. Illustrated with two 
 Steel Engravings (St. Simon and Real Yorkshire), and 28 full-page 
 Wood Engravings of the various Breeds. 3s. 6d. ; post free, 3s. iod. 
 SOME PRESS OPINIONS. 
 "The trustworthy character of the work is guaranteed by the well-known names of 
 the writers."— Times, 
 
 "A history and description of the different kinds of light horses, together with 
 succinct directions for their management-."- .Fiefrf. 
 " Most useful addition to the Hcrse Breeder's Library." — Land and Water. 
 " The work of men who thoroughly understand the subjects upon which they write, 
 and should be of general service," — Yorkshire Post 
 " Full of instruction. A moat useful volume."'— Sporting Life. 
 " A valuable addition to any sportsman's library." — Sportsman. 
 " Nothing more interesting, complete, aud concise has ever appeared.'* 
 
 Veterinary Journal, 
 
 No. 3. HEAVY HORSES. 
 
 Breeds and Management. 
 
 By HERMAN BIDDELL; C. I. DOUGLAS; THOMAS DYKES; 
 
 Dr GEORGE FLEMING, C.B., F.R.C.V.S. ; ARCHIBALD 
 
 MACNEILAGE; GILBERT MURRAY; and W. R. TROTTER. 
 
 224 pages, demy 8vo, cloth, gilt lettered, with 29 full-page Illustrations. 
 
 SOME PRESS OPINIONS. 
 
 "This admirable work, exhaustive and ably written, will certainly command the interest 
 
 of all who are interested in the breeding of draught horses." — North British Agriculturist. 
 
 " Cheap, readable, and instructive, and we heartily commend it to lovers of the hoi se." 
 
 The Scottish Farmer. 
 "Quite equal in tieatment to either of its predecessors, and will supply a long-felt 
 want among the breeders of heavy horses."— Yorkshire rost. 
 " May in every respect be conscientiously recommended." — Morning Advertiser. 
 " The time was ripe for the appearance of a volume devoted exclusively to this subject, 
 and we are glad to find the task has been so ably du charged."— Times. 
 
 Price 3s. 6d. each, or post-free 3s. iod. ; or if Nos. 1, 2, and 3 be 
 ordered together direct from the office, 10s. 6d., carriage free. 
 
 Other volumes on British Breeds of Live Stock in preparation. 
 
 VINTON & CO., Limited, 9, New Bridge Street, London, E.C.