i LIBRARY QF CONGRESS. : ^^^^- — i Shelf.: v\{_2L>'\ I LNUUifi^STATES OF AMERICA. TH£ Chemistry of the Farm, R. WARINGTON, F.C.S, NEW YORK: ORANGE JUDD COMPANY, 751 BKOADWAY. 1882. Entered, according to Act of Congress, in the year 1882, by the ORANGE JXJDD COMPANY, In the Office of the Librarian of Congress, at Washington. i^^^'b^ 5^0 "%.- ?:\ PUBLISHERS' PEEFACE. This work is offered in tlie belief that it will meet the wants of many intelligent farmers, and others interested in the cultivation of the soil, who, while they have neither the time nor the inclination to take up Chemistry as a study, would gladly learn the present relations of Chemistry to Agriculture. The author of this book occupies an important position at Rothamsted. The most casual reader of Agricultural journals is aware that this is the name of an old English estate to which the labors of Messrs. Lawes and Gilbert have given a world- wide reputation as a station where abundant means, ad- ded to the highest scientific ability, have been devoted to the elucidation of Agricultural problems, solely for the benefit of Agriculture. These labors are not for English agriculture especially, but have a world-wide applica- tion. The results which are freely given to the world, are those of experiments conducted in the field and stables, as well as in the laboratory, on a scale which gives them a practical value and commends them at once to the farmer as well as to the scientist. While the author modestly refrains from even a sug- gestion to that effect, we regard his work as in accordance III IV publishers' preface. with the latest results attained at the center of Agricul- tiiial investigation. The visitor at Eothamsted is struck with the thor- oughly practical character of everything about the place and the entire absence of anything like show. We were, during a visit last year, eppecially interested with the exhibition of the constituents of a piece of English pasture, in which the different grasses and other plants, including weeds, were given, not only in figures, but in parcels containing the plants themselves in their proper proportions. The author, in his Preface, ex- presses the hope that his work may be used for the teaching of Agriculture in schools. In this we must disagree with him. If any work will answer for the use of public schools, no doubt this one will take the first rank. The great obstacle to the use of this, or any similar work in schools, is the difficulty of finding teachers. Unless a teacher quite understands and is thoroughly imbued with his subject, he can not profitably instruct others. The author, in referring to the literature of the sub- ject, mentions such works as will be found useful to the student. Among these are Prof. Johnson's " How Crops Grow" and "How Crops Feed." These volumes are standard works of reference, abroad as well as at home. In place of the European works upon plant life and plant growth which the author recommends to English readers, we may mention Gray's * ' First Lessons " as superior to any other work in the language as an elementary work in the study of plant life. No farmer, be he American or publisher's preface. V otherwise, can read this volume without receiving very much valuable information and suggestions which will prove of real practical value. The language of the work is remarkably clear and con- cise, and avoids, so far as the subject will allow, the use of scientific technicalities. As in England the term cor7i is used, especially for wheat, and generally for the small grains, while in this country it especially applies to Indian corn or maize, it has been thought advisable in an American Edition to change the word to accord with general usage. Where Indian corn is referred to in the work it is mentioned as maize, the name by which it is generally known in Eng- land. The American reader should bear in mind the fact that the common or Field Bean of England is very differ- ent from the bean cultivated in this country. Garden forms of it, known as Windsor Bean, etc., are rarely tried by English gardeners in this country, but our hot sum- mers make it very uncertain, and it is not known here as a field crop. March, 1882. CONTENTS Chapter I. Plant Growth 9 Chapter II. Sources of Plant Food 20 Chapter III. Manures - - --- 29 Chapter IV. Crops 41 Chapter V. notation of Crops -- 53 Chapter VI. Animal Nutrition • 62 Chapter VII. Foods '72 Chapter VIII. Relation of Food to Animal Requirements. 94 Chapter IX. Relation of Food to Manure 107 Chapter X. The Dairy - - 113 VII THE CHEMISTRY OF THE FARM. CHAPTEK I PLANT GROWTH. The Comtituents of PZa^i^s.— Water— The combustible elements of vege- table matter — The proportion of ash constituents in various parts of plants — The essential and non-essential elements of the ash — Com- position of a crop of grass. Function of the Xe.t'es.— Assimilation of carbon from the air — Formation of vegetable substance — Plant res- piration—The transpiration of water. Function of the Roots.— Absorp- tion of ash constituents and nitrogenous matter from the soil— The excretion of useless matter by the plant— The part played by ash constituents. (?m/ima^ion.— General character of seeds— The con- ditions and processes of their germination. Pi,ant Development.— Annual plants— the order in which plant constituents are assimilated —Biennial and perennial plants— the storing up of food for a second season — spring sap rich in sugar. The first step towards a knowledge of plant chemistry must be an acquaintance with the materials of which plants are built up. The Constituents of Plants.— The most abundant in- gredient of a living plant is water. Many succulent vegetables, as turnips and lettuce, contain more than 90 per cent, of water. Timber felled in the driest time seldom contains less, than 40 per cent, of water. If a branch of a tree is burned the greater part is con- sumed and passes away in the form of gas, but there is left behind a small quantity of white ash. The same happens if any other part of a plant is burned. The con- stituents which form the dry matter of plants maybe thus 9 10 THE CHEMISTRY OF THE FARM. conveniently divided into two classes — the combustible and tlie incombustible. The combustible part of plants is made up of five chemical elements — carbon, oxygen, hydrogen, nitrogen, and sulphur ; without these no i^lant is ever produced. Carbon generally forms about one-half of the dry com- bustible matter of plants. Nitrogen seldom exceeds 4 per cent, of the dry matter, and is generally present in much smaller amount. Sulphur is still smaller in quantity. The remainder is oxygen and hydrogen. The carbon, hydrogen, and oxygen form the cellulose, lignose, pectin, starch, sugar, fat, and vegetable acids which plants contain. The same elements united with nitrogen form the amides and alkaloids; and further united w^ith sulphur the still more important albumi- noids, which are essential constituents of all plants. The incombustible or ash constituents form generally but a small part of the plant. The timber of freely- growing trees sontains but 0.2 — 0.4 of ash constituents m 100 of dry matter. In seeds free from husk the ash is generally 2 — 5 per cent. In the straw of cereals 4—7 per cent. In farm roots ^/^ — 8 per cent. In hay 5 — 9 per cent. It is in leaves, and especially did leaves, that the greatest proportion of ash is found ; in the leaves of root crops the ash will amount to 10 — 25 per cent, of the dry matter. The incombustible ash always contains five chemical elements — potassium, magnesium, calcium, iron, and phosphorus, besides sulphur already mentioned. Iron is present in only very small quantity. These five elements, though forming a very small portion of the plant, are indispensable to its life. Besides the elements just named, an ash will generally contain sodium, silicon, and chlorine, with frequently manganese, and perhaps minute quantities of other elements. The supplementary ele- ments just named are not apparently essential to plant PLAINT GROWTH. 11 life, though some of them discharge useful functions in the plant. The metals above-named occur in the plant as salts, being combined with phosphoric, nitric, sulphuric, and various vegetable acids, of which oxalic, malic, tartaric and citric acid are the most common. The metals are also sometimes present as chlorides. Phosphorus occurs in the form of phosphates ; silicon is present as silica. Sulphur occurs partly as sulphates, and partly as a constituent of albuminoids. In the ash of plants the nitrates, and the salts of the vegetable acids are found m the form of carbonates. It is common to speak of the combustible ingredients of a plant as ^^ organic," and the incombustible ingre- dients as "inorganic." This distinction is scarcely accu- rate, as those ash constituents which are indispensable parts of plants have, during the plant's life, as much right to be called '^ organic " as albumin or cellulose. In the following table will be found the average com- position of a crop of meadow grass weighing five tons when cut, and producing one and one-half ton of hay ; this will illustrate wJiat has just been said as to the con- stituents of plants. Further information as to the com- position of crops will be found on page 42. COMPOSITION OF A CROP OF MEADOW GRASS. Water 8,378 lbs. Carbon 1,3151 Hydrogen 144 Nitrogen 49 Oxygen and Sulphur 1,105 Pota^sh 56.3 Soda 11.9 Lime 28.1 Magnesia 10 . 1 Oxide of Iron 9 i ^ Pliospboric Acid 12.7 f^ Sulpliuric Acid 10.8 Chlorine 16.2 Silica 57.5 Sand, etc 4.5 - Combustible matter 2,613 Ibg. Ash 209 lbs. Total crop 11,200 12 THE CHEMISTRY OF THE FARM. Plants obtain the elements of which they are built up partly from the soil, and partly from the atmosphere. From the soil they obtain, by means of their roots, all their ash constituents, all their sulphur, and nearly the whole of their nitrogen and water. From the atmosphere they obtain, through the instrumentality of their leaves, the whole, or nearly the whole of their carbon, with prob- ably small quantities of nitrogen and water. Function of the Leaves.— The source of vegetable carbon is the carbonic acid gas present in the atmosphere. Carbonic acid gas passes more readily through the cuticle of a plant than do the nitrogen and oxygen which make up the bulk of the atmosphere. The carbonic acid thus absorbed is decomposed within the chlorophyl cells of the plant under the influence of light, oxygen being evolved, and the carbon retained by the plant. All green parts of a plant probably share in this action, but it is preeminently the function of the leaves. The decompo- sition of carbonic acid does not proceed in darkness, or at a very low temperature. The rays of light most active in effecting the decomposition are the yellow and orange rays ; the blue, violet, and dark red rays of the spectrum have scarcely any influence. The oxygen gas given off by a green plant exposed to light is equal in volume to the carbonic acid decomposed, so that apparently the whole of the oxygen contained in the carbonic acid is returned to the atmosphere ; the re- action is, however, really more complicated, as water is probably decomposed at the same time as the carbonic acid. The exact nature of the reaction which takes place when carbonic acid is decomposed in the chlorophyl cells is still unknown. Starch, composed of carbon and the elements of water (C,,H,„0,), is undoubtedly among the earliest products. Starch being an insoluble substance is plajn't growth. 13 converted into sugar (glucose) for the nourishment of distant parts of the plant, to which it is conveyed by the movement of the saj). In parts where growth is taking place, and new cells are being formed, the sugar of the sap is converted into cellulose, the substance which forms the cell walls, and of which the whole structure of the plant primarily consists. The conversion of starch into sugar and cellulose presents no chemical difficulties, as all these substances are carbo-hydrates, that is they are composed of carbon and the elements of water. The formation of albuminoids in the plant is not at present understood ; we can only say that they are con- stituted out of the carbo-hydrates and some of the simple n'trogenous substances, most probably amides, present in the sap. The vegetable acids in a plant are probably formed by oxidation ; most likely by the oxidation of some of the carbo-hydrates. ' The fatty matter of a plant may be formed from carbo- hydrates ; or possibly from the splitting up of albumi- noids. We have just referred to oxidation as taking place in the plant. This is always going on in the interior during life, and as a result the plant is continually consuming a small quantity of oxygen, and giving out a small quantity of carbonic acid, an operation precisely similar to animal respiration. This action is not readily perceived during the day-time, being hidden by the opposite action of the chlorophyl cells, which absorb carbonic acid and evolve oxygen. If a plant is placed in darkness the respiratory action becomes manifest. The oxidation of matters already formed is an iniportant means for the production of new bodies. The decomposition of carbonic acid by green plants during daylight is of the utmost importance in maintain- ing an atmosphere suitable for the respiration of animals. 14 THE CHEMISTEY OF THE FARM. An animal in breatliing inspires atmospheric air ; it expires air in which a part of the oxygen has been re- placed by carbonic acid ; the result of animal life is thus to accumulate carbonic acid in the atmosphere. Such accumulation would be injurious to health, but is pre- vented by the growth of plants. It has been calculated that an acre of forest, producing annually 5,755 lbs. of dry matter, will consume the carbonic acid produced by the respiration of 15.4 men. Besides carbonic acid, plants are apparently capable of absorbing a small quantity of ammonia through their leaves. The uncombined nitrogen of the atmosphere is not appropriated by plants. When rain occurs after severe drouth water may be taken up to some extent through the leaf. Plants which have no chlorophyl cells, and possess, consequently, no green color, do not decompose carbonic acid. We have familiar examples of such plants in the broomrape and dodder of our clover fields, and in the common fungi. The broomrape and dodder are fed by the juices of the plant on which they live as parasites. The fungi derive their carbon from the decayed vegetable matter in the soil. Another important function of leaves consists in the transpiration of water. This transpiration takes place through small openings in the under side of the leaves, known as stomata, which have the property of closing in dry air and opening in moist. Transpiration takes phice only in hght ; it will occur abundantly, even in an atmos- phere saturated with water, if the plant be only exposed to sunshine. A small amount of general evaporation, distinct from transpiration proper, may occur in dark- ness. The amount of water evaporated from the surface of a growing plant is very large ; land that has borne a crop is always much drier than a bare fallow. The results of transpiration to the plant are most im- PLA]SrT GROWTH. 15 portant, the evaporation of water from the leaves being a principal cause of the rise of the sap, and the consequent drawing up of 'Water from the soil containing plant food in solution. Function of the Roots. —The roots of a plant are the organs by which it absorbs water from the soil, and with this water a variety of food elements are introduced. The roots take up apparently all the diffusible sub- stances (those capable of passing through a membrane) which are present in the water which they draw from the soil. The plant may thus receive a number of substances not actually required for its nutrition. The feeding power of roots is not, however, confined to the taking up of ready-formed solutions, they are also capable of attacking some of the solid ingredients of the soil, which they render soluble and then appropriate. This important action of roots exists in different degrees with different plants. The action only takes place at the points of contact between the rootlets and the particles of the soil, and is brought about by the acid sap which the roots contain. This action of roots probably plays an important part in the supply of phosphoric acid and potash to the plant, as these substances, especially the former of them, exist in the soil in difficultly soluble forms, and are rarely found in solution in the water present in soils. Besides furnishing the plant with its ash constituents, the root has the important function of supplying nitrogen; this is nearly always taken up in the form of nitrates. A plant is capable of making use of nitrogen in the form of nitric acid or ammonia ; it also, according to several ex- perimenters, is able to assimilate nitrogen when in the form of urea, uric and hippuric acids, and several other amide bodies. The facility, however, with which ammonia and other nitrogenous substances, are converted into nitric acid in the soil is so great that nitrates become by far the 16 THE CHEMISTRY OF THE FARM. most important source of nitrogen at a plant's disposal. Most plants are unable to assimilate the nitrogenous humus contained m soil. The very weak solutions taken up by the roots are concentrated in the upper parts of the plant, the water being rapidly evaporated by the leaves, as already men- tioned. The essential ash constituents are employed in the formation of new tissues. The non-essential ash constitaents which have been taken up by the roots are partly disposed of in a solid form, as a permanent incrus- tation of the older tissues. The soluble salts which are not thus disposed of, at first accumulate in the sap, and are probably more or less removed from the surface of the leaves and stem by the washing e^ect of rain. The deposition of silica upon the external tissues of wheat, barley, and other graminaceous plants is a familiar example of the excretion of a non-essential ash con- stituent. Silica is also abundant in the old leaves, and in the outer bark of many trees, and is commonly found as an incrusting constituent of old tissues. Insoluble calcium salts, frequently the oxalate, are also deposited as incrusting matters in old tissues. These incrustations are indirectly of service to the plant, as they tend to harden the tissues and thus protect them from injury. Soluble non-essential ash constituents, as chloride of sodium, are found abundantly in the succulent parts of plants when such ash constituents have been present in the soil. They generally diminish in quantity as the plant matures, and are never stored up in the seed. The amount and composition of the ash of succulent plants, as meadow grass, clover, and mangel, is greatly influenced by the character of the soil, and the manure applied. The ash of a seed, on the other hand, is very constant in composition, resulting from the selective powers of the plant. Of the particular action of the ash constituents within PLANT GROWTH. 1";* the plant little is known. Phosphoric acid and potash are undoubtedly the most important of the ash constituents ; they are always found concentrated in those parts of the plant where cell growth is most active, as, for instance, in the layer (cambium) between the wood and bark of a tree, and are abundantly stored up in the seed. Silica was long supposed to be an essential constituent of wheat, barley, and other similar plants, and to be the ingredient on which the stiffness of their straw chiefly depended. It has been shown, however, that maize may be successfully grown without any supply of silica, and with no perceptible difference as to the stiffness of the stem. The grass growing on peat bogs contains scarcely any silica, though silica is abundant in ordinary hay. Germination. — The seed is a storehouse of concentrated plant food, intended to nourish the germ until the root an^leaf are developed. In the seeds of the cereals, and of many other plants, the chief ingredient is starch. Another class of seeds, of which linseed and mustard- seed are examples, contain no starch, but in its place a large quantity of fat. A seed generally contains a con- siderable amount of albuminoids ; its ash is rich in phos- phoric acid and potash. For germination to take place, moisture, oxygen, and a suitable temperature are necessary. Under these con- ditions the seed swells, oxygen is absorbed, a part of the carbonaceous ingredients is oxidized, heat is developed, and carbonic acid evolved. During these changes the solid ingredients of the seed gradually become soluble ; the starch and fat are converted into sugar ; the albu- minoids are converted into amides — as for instance aspara- gine, probably also into peptones. With this supply of soluble food the radicle and plumule are nourished ; they rapidly increase in size, emerge through the coats of the seed, and, if the external conditions are suitable, soon 13 THE CHEMISTRY OF THE FARM. commence their separate functions as root and leaf. The process of germination may be easily studied in the ordinary operation of malting barley. Seeds buried too deeply in the soil may not germinate for lack of oxygen. Or if germination takes place the plumule may fail to reach the surface, the store of food in the seed being exhausted before the layer of soil is pene- trated, and daylight reached. The smaller the seed, the less, as a rule, should be the depth of earth with which it is covered. Plant Development, — The development of the plant after germination follows a regular course. With au annual, which produces seed and dies during the first season, we have first a great development of root and leaf, which collect and prepare materials for growth ; next comes the formation of a flower stem ; and lastly, the production of flower and seed ; after which the plant dies. The materials furnished by the root preponderate in the young plant ; but as the plant matures, the proportion of carbon compounds derived from the action of the leaves steadily increases. A cereal crop contains at the time of full bloom all the nitrogen and potash which is found in the mature crop , the assimilation of phos- phoric acid continues somewhat later ; the increase of carbon and silica proceeds as long as the plant is in a green state. When seed formation begins an exhaustion of the other parts of the plant sets in, starch, albuminoids, phosjDhoric acid and potash being transferred from the root, leaf, and stem, and stored up in the seed. If the season is a good one, and the development of the seed fully accomj^lished, the straw of the crop is left very thoroughly exhausted ; while in a bad season it will retain far more of the mate- rials acquired during growth. For the same reason straw PLANT GROWTH. 19 cut while the crop is still green is far more nutritlTe than when perfect ripeness has been attained. With a biennial or perennial crop the case is somewhat different. The first development of root and leaf is the same as in an annual ; but towards the end of summer there is a storing up of concentrated plant food in the root or stem to serve for the commencement of growth in the following spring. In a biennial root crop, the turnip for instance, the root attains a great size in autumn, the leaves dying after transferring to the root their most important constituents. The next season the root throws up a flower stem, and the store of matter accumulated during the preceding autumn is consumed in the production of seed. With the production of seed the root is exhausted and the plant dies. In trees plant food is stored up at the end of summer in the pith, the pith rays, and in the layer between the wood and bark. The leaves which fall in autumn have lost nearly all their starch, albuminoids, phosphoric acid and potash, these having been transferred to the stem. By the action of the sun in spring-time the new buds swell, the sap rises, the starch and other matters deposited in the wood during the previous autumn are re-dissolved, and employed at once for the production of new growths. The sugar found in maple sap during spring results from the transformation of starch stored up in the preceding autumn. CHAPTER II. THE SOURCES OF PLANT FOOD. The Atmosphere. — The carbonic acid, ammonia, and nitric acid which it supplies — The quantity of combined nitrogen and chlorides contained in rain. The soil. — Its origin — Properties of sand, clay, calcareous matter, and humus ; their relation to water and heat — The plant food contained in soil, its quantity, and condition — Losses by drainage — The absorptive power of soils — Influence of tillage, drainage, and burning. The Atmosphere. — We have already stated that the whole of the carbon of plants is obtained from the car- bonic acid present in the atmosphere ; 10,000 volumes of of air contain about Sy^ volumes of carbonic acid, or about 1 lb. of carbon in 3,500 cubic yards of air. This small amount is made sufficient by the action of winds, which bring an enormous quantity of air in contact with both soil and plant. The atmosphere also contains a very small and variable quantity of ammonia. Schloesing found from 1 lb. in 6,000,000 cubic yards, to 1 lb. in 119,000,000 cubic yards. The quantity is greatest, according to the same experi- menter, in warm southerly winds. The ammonia of the air is directly absorbed by plants to a very small extent, it is rendered available chiefly through absorption by the soil, and by means of rain, which brings it in solution to the earth. The atmosphere also furnishes a small amount of nitric acid. The nitrogen and oxygen of the atmosphere com- bine under the influence of electric discharges, nitrous acid being formed ; this is converted into nitric acid by the action of ozone, or peroxide of hydrogen. This formation of nitric acid in the atmosphere is the only original source of combined nitrogen, on our globe, the 20 THE SOURCES OF PLANT FOOD. 21 existence of which has been placed beyond dispute. Nitric acid may also be formed in the atmosphere by the oxidation of ammonia by ozone and peroxide of hydrogen. The total amount of nitrogen, in the form of ammonia and nitric acid, annually carried to the soil by rain, varies in different years and places. The average of many ex- periments on the continent gives 10.23 lbs. of nitrogen per acre. The average of two years' experiments at Rothamsted gave 7.29 lbs. The continental average is probably rather above the truth for the open country, many of the determinations having been made near towns. Rain also furnishes small quantities of alkaline chlo- rides, especially in the neighborhood of the sea ; sulphates are also present. At Cirencester the chlorides in the rain are on an average equal to about 53 lbs. of common salt per acre per annum ; at Rothamsted in Hertfordshire the quantity is about 22 lbs. The Soil. — All soils have been produced by the dism- tagration of rocks, generally through the prolonged action of water, air, and frost. The character of a soil largely depends on the character of the rock from which it has been derived. Primitive and igneous rocks yield soils rich in potash ; fossiliferous rocks produce soils rich in phocphoric acid. The principal ingredients of soils are sand, clay, carbonate of calcium and humus ; as each of these preponderate the soil is said to be sandy, clayey, calcareous, or peaty. Sand is either composed of pure quartz (silica), or con- sists of fragments of more complex minerals — mica, for example. When the former is the case, the sand will supply no plant food ; but in the latter case the gradual decomposition of the mineral will slowly increase the ash constituents available for the plant. Clay is a silicate of aluminium, produced by the decom- position of felspar and other silicates ; if absolutely pure 22 THE CHEMISTRY OF THE FARM. it would furnisli nothing to the plant ; it always, however,. contains some potash, and frequently a considerable quan- tity. Clay has the important property of absorbmg and retaining phosphoric acid, ammonia, potash, lime, and other substances necessary for plant nutrition. The calcareous matter of soils supplies lime to the plant ; limestone also generally contains phosphoric acid. Carbonate of calcium is beneficial to the soil in many ways. It preserves the particles of clay in a separate coagulated condition, thus making heavy soils friable and pervious to water. It enables clay to exercise its absorbent power on various salts, which would otherwise escape its action. It also jDromotes the decomposition of vegetable matter, and the formation of nitrates in the soil. The presence of some salifiable base is essential for the ^er- formance of the chemical operations belonging to a fertile soil ; the salifiable bases usually present are either carbonate of calcium, or the alkalies derived from the decomposition of silicates. The humus, or decayed vegetable matter of soils, has its origin in the dead roots, leaves, etc., of a previous vegetation. It is the principal nitrogeiious ingredient of soils. A black soil, rich in humus, is sure to be also rich in nitrogen ; a soil destitute of humus will contain scarcely any nitrogen. The fertility of virgin soils is largely due to the nitrogenous humus which they contain. Of all soil ingredients sand has the least, and humus the greatest capacity for retaining w^ater. Light sandy soils thus suffer most from drouth, while applications of farm-yard manure, or the plowing in of green crops, increase the water-holding power of the soil by increasing the proportion of humus. The capillary power of soil, by which water is raised from the subsoil to the surface m dry weather, is least in open sandy soils composed of coarse particles, and greatest in the case of loam or clay. Dark-colored soils absorb the greatest amount of heat THE SOURCES OF PLAKT FOOD. 23 from the sun's rays, and liglit-colored soils least. The presence of humus is thus favorable to soil warmth. Quartz sand is an excellent conductor of heat ; chalk is a bad conductor. A soil rich in sand will thus be warmed or cooled more rapidly, and to a greater depth than a soil containing but little sand. Water has a very sonsiderable effect in cooling a soil, partly from its high specific heat, and partly from the immense consumjDtion of heat during its evaporation. A wet soil is always colder than a dry one. The drainage of wet land will thus result in a greater warmth of the surface soil, and consequently an earlier growth in spring. The 23roportion of plant food present in soils is very small, even when the soil is extremely fertile. The sur- face soil (first 9 inches) of a pasture may contain when dry 0.25 of nitrogen per cent., while soil of the same depth from a good arable field may yield 0.15 per cent., and a clay sub-soil 0.05 per cent. A good surface soil may contain 0.20 per cent, of phosphoric acid, or not un- frequently a smaller quantity. Potash varies much, rising to 1.0 ])ev cent, or more in some clay soils, but being generally much smaller. The weight of soil on an acre of land is, however, so enormous, that small proportions of plant food may amount to very considerable quantities. Nine inches' depth of arable soil (clay or loam) will weigh, when per- fectly dry, about 3,000,000 or 3,500,000 lbs. A pasture soil will be lighter, the first 9 inches weighing when dried and the roots removed about 2,250,000 lbs. Supposing, therefore, a dry soil to contain 0.10 percent, of nitrogen, phosphoric acid, or 'potash, the quantity in 9 inches of soil will be from 2,250 lbs. to 3,500 lbs. per acre. A large part of the elements of plant food contained in soils is present in such a condition that plants are unable to make use of it. A soil may contain many thousand pounds of phosphoric acid or of nitrogen, and yet be in 24 THE CHEMISTRY OF THE FARM. a poor condition ; while a small dressing of readily avail- able food, as superphosphate or nitrate of sodium, may greatly increase the fertility. The nitrogen contained in humus is not in a condition to serve as a general plant food; cereal crops are appa-' rently unable to appropriate it ; leguminous crops, how- ever, possibly assimilate some humic matters. By the action of a minute Bacterium present in all soils, humus and ammonia are oxidized, and their nitrogen converted into nitric acid. Nitritication only takes place in moist soil, sufi&ciently porous to admit air. It is also necessary that some base should be present with which the nitric acid may combine : this condition is usually fulfilled by the presence of carbonate of calcium. Mtrification is most active at summer temperatures ; it ceases apparently near the freezing point. The fragments of rock present in soil, as stones, gravel, and sand, are as a rule of little value to a plant, the elements of plant food which they contain being in too insoluble a condition to be attacked by the roots. These fragments of rock may however be slowly decomposed by the mechanical action of frost, and by the chemical action of water, and their contents thus gradually made availa- ble to the plant. The solvent power of the water in a soil is greatly increased by the carbonic acid, and perhaps also by the humic acid it holds in solution. Water con- taining carbonate of calcium in solution is especially capable of attacking silicates. If water is allowed to drain through a soil it carries with it a part of the readily soluble matter which a soil contains. The substances chiefly removed by the water will be the nitrates, chlorides, and sulphates of calcium and sodium. When heavy rain falls these substances are washed into the subsoil, and partly escape by the nearest outfall into the springs, brooks, and rivers. The loss of nitrates from highly manured land during a wet season is THE SOURCES OF PLANT FOOD. 25 very considerable. "When dry weather sets ii^ evaporation takes place at the surface of the soil, the water of the subsoil is slowly brought again to the surface by capillary attraction, and the salts it contains are concentrated once more in the upper soil, forming in some rare instances a white crust of salt upon the surface. Capillary attraction has little influence in the case of sandy soils. Of these readily soluble salts the nitrates are of the greatest importance to plant food. The quantity of nitrates in a surface soil will vary greatly, depending on the richness of the soil in nitrogen, the previous condi- tions as to temperature and moisture, the extent of recent washing by ram, and on whether the soil is or is not under crop. Where a crop is growing the nitrates will be kept nearer the surface, the evaporation of water from a growing crop being far greater than from a bare soil. The nitrates will also be constantly taken up by the roots, and employed as plant food. The loss of nitrates by drainage is thus far less when the land is under crop than in the case of a bare fallow. * Phosphoric acid, potash, and ammonia are very rarely found in drainage water. If a solution containmg phos- phoric acid, potash, or ammonia is poured on a sufficiently large quantity of fertile soil, the water which filters through will be found destitute of these substances. This retentive power of soil for phosphoric acid, potash, etc., is of the utmost importance in agriculture. The action is a complex one. All salts are doubtless retained to some extent by soil through mere mechanical adhesion ; salts, thus feebly retained, as nitrates and chlorides, can be easily removed by washing with water. Other sub- stances are, on the contrary, retained by chemical affin- ity ; these are not removed by washing, or but to a small extent. The ingredients of the soil which exercise a chem- ical retentive power are the hydrates of ferric oxide and alumina, the hydrous silicates of aluminium, and humus. 2 26 THE CHEMISTRY OF THE FAEM. Ferric oxide is a common ingredient of soils ; to it the red color of many soils is owing. To the presence of fer- ric oxide the retention of phosphoric acid is chieily due, an insoluble basic phosphate of iron being produced. Alumina acts in the same manner. Ferric oxide and alumina have also a retentive power for ammonia and potash, but the compounds formed are more or less de- composed by water. To the hydrous silicates the perma- nent retention of potash and other bases is probably chiefly due. Humus has a great absorbent power for ammonia. Other bases, as magnesia and lime, are also retained by soil, but in a less powerful manner than are potash and ammonia. Soils destitute of carbonate of calcium take up very little potash or ammonia when these are applied as salts of powerful acids, as for instance, the chlorides, nitrates, and sulphates. When carbonate of calcium is present the potassium or ammonium salt is decomposed, the base is retained by the soil, while the acid escapes into the drainage-water united with calcium. The addition of carbonate of calcium may thus greatly increase the reten- tive power of a soil for bases. The fertility of a soil is nearly connected with its power of retaining plant food. Sandy soils, from their small chemical retentive jDowei;, and free drainage, are of small natural fertility, and dependent on immediate sup- plies of manure. There can be little doubt that the plant food contained in soil which is capable of being taken up by roots, exists either in solution, or in the states of combination just referred to — that is in union with ferric oxide, hydrous silicates, and humus. Different crops have very differ- ent powers of attacking these various forms of plant food. The operations of tillage and drainage serve m se\'eral ways to increase the amount of plant food which is at the disposal of a crop. THE SOURCES OF PLANT FOOD. 27 By tillage tlie surface soil is kept in an open porons condition, favorable for the distribution of roots. By this means also capillary attraction is diminished, and the land consequently suffers less from drouth ; the water- holding power of the surface soil is also increased. A more important result of tillage is that the soil is thoroughly exposed to the influence of the air. Soils containing humus or clay will absorb ammonia from the atmosphere, and thus increase their store of nitrogen. The organic remains of former crops and manuring are also oxidized, the nitrogen being converted into nitric acid. The rocky fragments which a solid contains, as fragments of silicates or limestone, will at the same time be more or less disintegrated by the combined action of water and air, assisted by the carbonic and humic acids arising from the oxidation of vegetable matter, and a portion of the insol- uble plant food be thus brought into a state suited for assimilation by the roots of crops. In winter time the disintegration of the various ingredients of the soil is greatly assisted by frost. Water in freezing expands, arUl thus rends asunder the substance frozen. Of the various results brought about by tillage, the increased production of nitrates mast be ranked among the most important. By drainage the various chemical actions we have just mentioned are carried down to a greater or less extent into the subsoil, for as the water level is lowered the air enters from above to fill the cavities in the soil. By drainage also the depth to which roots will penetrate is increased, for roots will not grow in the absence of oxy- gen, and rot as soon as they reach a permanent water level. In a water-logged soil deoxidation is active, the nitrates present are destroyed, a part of the nitrogen being envolved as gas ; the soil may thus suffer a consid- erable loss of plant food. Burning is occasionally resorted to as a means of in- creasing the available plant food, and improving the 28 THE CHEMISTRY OF THE FARM. texture of a heavy soil. The soil is burned in heaps, which are then spread over the land. If the soil contains limestone it is easy to see that the phosphates of the lime- stone may become more available by the complete disin- tegration which attends the conversion into lime. The lime will also attack the silicates of the soil at a high temperature, and liberate a part of the potash from its insoluble combinations. To produce the best results it is essential that the burning should take place at a low temperature. This treatment by burning is a very ex- treme one, and can be recommended only in a few cases ; it must always be attended with an entire loss of the nitrogen in the soil burned. The plowing in of burned clay is of use in improving the texture of heavy land. CHAPTER III. MANURES. Difference between natural vegetation and agriculture — ^necessity for manuring. Farm-%jard J/a/iwre.— Cireumstances which influence its character ; its average composition ; slowness of its effect— Seaweed similar to farm-yard manure — Ghmno — Sulphate of Ammonium— Ni- trate of Sodium— Soot, Dried Blood, and Woollen Sef use— Bones- Ground Phosphates— Superphosphate— Gypsum — Lime, Chalk, and Marl — Ihtassium Salt.' — Common Salt— Application of Manure — Import- ance of thorough distribution— Best time for application— The re- turn made by the crop. In the natural vegetation of a forest or prairie the soil suffers no diminution of plant food. The elements taken from the soil are returned to it on the decay of the plants which the soil has nourished, or on the death of the animals which have fed on these plants. Under these circumstances the surface soil becomes rich in carbon and nitrogen, the quantity contributed by the atmosphere exceeding all losses. The surface soil also becomes rich in the ash constituents of plants, these being collected from the subsoil by the roots, and left at the surface on the decay of the plant. A virgin soil thus generally con- tains an abundance of plant food, and will produce large crops without manure. In human agriculture, on the other hand, both vege- table and animal produce are consumed off the land that has reared them. Provision must therefore be made, sooner or later, to return to the land a part at least of the plant food removed from it, if permanent fertility is to be maintained. Hence the necessity for manuring. The most complete return to the land would be ac- complished by manuring it with excrements of the men and animals consuming the crops. This is partially done 29 30 THE CHEMISTRY OF THE FARM. by the application of barn-yard manure ; but the congre- gation of men in cities, and the difficulty of employing sewage with profit, prevent this plan being thoroughly carried out. The farmer is thus generally obliged to pur- chase manures for the land in exchange for the crops and stock sold off it. On very poor soils it is necessary to make a very com- plete return of all the elements of plant food removed by the crops, but in most soils there is an abundance of some one or more of these elements, and a partial manuring will consequently suffice. With high farming the con- tributions to the soil may be in excess of the exports, and the land consequently increase in fertility. The nature of the exhaustion resulting from the growth of particular crops, and the economic application of manure to meet their special requirements, will be considered in Chapter IV. The losses which a farm sustains by the sale of animal products will be treated of in the section on *^ The Constituents of Animals." Farm-yard Manure consists of the liquid and solid ex- crements of the 'farm stock, plus the straw employed as litter. Its composition will vary according to the char- acter of the animals contributing to it, the quality of their food, and the nature and proportion of the litter. The composition of the manure will also depend a good deal upon the method in which it has been prepared. In the case of an adult animal, neither gaining nor losing weight — a working horse for instance — the excre- ments will contain the same quantity of nitrogen and ash constituents as was present in the food consumed. If however the animal is increasing in size, is producing young, or furnishing milk or wool, the nitrogen and ash constituents in the excrements will be less than those contained in the food, the difference appearing as animal increase. The manure from animals of this class will MANURES. 31 therefore be poorer than that obtained from the former class, supposing the same food given to each. We must not expect valuable manure from a cow in full milk, or from a rapidly growing pig. The character of the food will affect the quality of the manure even more than the character of the animal. A diet of -maize and straw chaff can yield only a poor ma- nure, because these foods contain a very little nitrogen or phosphates. A diet including a liberal amount of oil- cake or beans will, on the other hand, yield a valuable manure, these foods being rich in nitrogen and ash con- stituents. A common mode of increasing the supply of manure on a farm is by the consumption of purchased food by the stock. This part of the subject will be more fully discussed in Chapter IX. The treatment of the manure is also most important. A large proportion of the nitrogen is voided in the form of urine, and generally the richer the diet the higher will this proportion be. If, therefore, the manure is washed by rain, and the washings are allowed to drain away, serious loss will occur. Hence the superiority of box ma- nure to that made in an open yard. It must also be recollected that the urea, which forms the chief nitrogenous ingredient of urine, is speedily changed by fermentation into corbonate of ammonium ; as this is a volatile substance, a loss of a part of the nitro- gen may easily occur, especially if an insufficient amount of litter is employed. Farm-yard manure rapidly undergoes fermentation. If placed in a heap the mass gets sensibly hot, and a large quantity of carbonic acid is given off. When the fer- mentation occurs in a place protected from rain, carbona- ceous matter is destroyed, but little loss of nitrogen takes place. Kotten manure, when well made, is more concen- trated than the fresh, having diminished in weight dur- ing fermentation, with but little loss of valuable con- 32 THE CHEMISTRY OF THE FARM. stituents. Some of the constituents have also become more sohible. Farm-yard manure will contain from G5 to 80 per cent, of water. The nitrogen may be 0.40 to 0.65 per cent., or higher, if produced by highly fed animals. The ash con- stituents will be 2.5 to 3.0 per cent., exclusive of the sand and earth always present. Of these ash constituents 0.4 to 0.7 will be potash ; and 0.2 to 0.4 phosphoric acid. One ton of farm-yard manure will thus supply 9 — 15 lbs. of nitrogen, a similar amount of potash, and 4 — 9 lbs. of phosphoric acid. Farm-yard manure is a '^general" manure ; that is it supplies all the essential elements of plant food. The immediate return from an application of farm-yard ma- nure is much less than from the same amount of plant food applied in artificial manures. The effect of farm- yard manure is spread over a considerable number of years, its nitrogen being chiefly present not as ammonia but in the form of carbonaceous compounds, which de- compose but slowly in the soil. Seaweed when fresh is, on the whole, similar in value to farm-yard manure. It becomes more valuable as it loses water. Guano. — This manure consists chiefly of the dried ex- crements of sea fowl. When guano has been deposited in the absence of rain it contains a large amount both of nitrogenous matter and phosphates. If exposed to rain the original nitrogenous matter is decomposed, and the nitrogen volatilized in the form of carbonate of ammo- nium ; the guano remaining is then almost purely jdIios- phatic. Ichaboe guano, for example, is a recent deiiosit, containing about 12 per cent, of nitrogen, and 12 per cent, of phosphoric acid ; while Mejillones guano is a phosphatic guano, containing 0. 9 per cent, of nitrogen, and 32.5 per cent, of phosphoric acid. From its great MAJEURES. 33 yariation in composition guano should always be pur- chased on analysis. In a nitrogenous guano the nitrogen is chiefly present as uric acid, and as ammonium salts. The strong smell of a damp guano is due to carbonate of ammonium. Tlie phosphoric acid exists principally in the form of phos- phate of calcium, but in nitrogenous guanos a small part exists as phosphate of ammonium, a salt readily soluble in water. Guano which has not suffered by washing may contain 3 to 4 per cent, of potash. Nitrogenous guano is a highly concentrated manure, and may be employed with excellent effect for grain crops, potatoes, and roots. Phosphatic guanos may be employed for turnips, but such guanos are more usually converted into superphosphate before they are applied to the land. Sulphate of Ammonium.— This substance is prepared from the ammoniacal products of gas works ; in its crys- tallized form it is the most highly nitrogenous of all the manures at a farmer's disposal, containing about 20 per cent, of nitrogen. It should be ascertained in every case that the manure is free from sulphocyanate of ammonium, as this substance is very injurious to plants. If sulphocyanates are pres- ent a solution of the salt will become blood-red on the addition of ferric chloride. Sulphate of ammonium is a '' special " manure, valua- ble solely for its nitrogen. It is a powerful manure for grain crops, for which it is best employed in conjunction with superphosphate. Nitrate of Sodium.— An enorm6us deposit of the crude salt, containing much chloride of sodium* is found in Peru. The nitrate sent to this country has been puri- fied by crystallization ; it will contain about 15. 6 per cent. of nitrogen. The most usual impurity is common salt. This manure, like the preceding, is valuable solely for 34 THE CHEMISTRY OF THE FARM. its nitrogen. It is an excellent manure for all crops re- quiring artificial supplies of nitrogen, especially grain crops and mangels. For grain crops it is best employed together with superphosphate. Nitrate of sodium should not be mixed with a damp superphosphate, else nitric acid may be lost. It is best to mix the two immediately before use ; or the superphosphate may be sown with the grain, and the nitrate applied afterwards as a top-dressing. Nitrate of sodium is especially suited for clay land. It is quicker in its action than any other nitrogenous ma- nure, and is therefore the best manure to employ when a late dressing has to be given. Soot, Dried Blood, and Woollen Refuse are all purely nitrogenous manures. Soot owes its value to the pres- ence of a small and variable quantity of ammoDium salts. Dried blood is an excellent manure, containing 10 to 13 per cent, of nitrogen. Shoddy, and other forms of wool and hair are very variable in composition, owing to the ad- mixture of dirt, grease, and other foreign matter ; the ni- trogen they contain will range from about 5 to 10 per cent. The nitrogen of blood, wool, and hair, is not in a form suitable as plant food. Blood readily decomposes in the soil, yielding ammonia and nitric acid. Wool and hair decompose much more slowly, and their effect is spread over many years. Soot is generally employed as a top-dressing for spring grain. Dried blood is an excellent manure for wheat. Wool and hair are chiefly used for hops. Bones. — These are largely employed as manure ; the fat is usually first extracted by steaming. Commercial bones contain about 3.6 per cent, of nitrogen, and 23 per cent, of phosphoric acid, existing as phosphate of calcium. Bones that have been boiled to extract the gelatine contain much less nitrogen, but a larger propor- tion of phosphates. MANURES. 35 Bones decompose but slowly in tlie soil, especially on heavy land ; their effect is thus spread over several years. The finer the bones have been ground the more imme- diate IS their effect. Bones are usually employed for pas- ture, and for turnips. Ground Phosphates. — Some phosphates when finely ground may on certain soils be successfully employed as manure without previous conversion into superphosphate. The phosphates most suitable for this purpose are phos- phatic guanos, bone-ash, and South Carolina phosphate. The soils most suitable for such manures are those rich in humus, and poor in carbonate of calcium ; these being the conditions (presence of humic and free carbonic acid) most favorable to the solution of phosphate of calcium. Pasture soils are especially suitable for such treatment. The solution of the ground phosphate may be facilitated by forming it into a compost with farm-yard manure be- fore its application, or by employing with it sulphate of ammonium. The phosphate should be employed in very fine powder. ' Superphosphate. — An abundance of mineral phosphates (phosphates of calcium) occur in nature ; many of these are so little soluble that their effect as manure is but small ; by treating them with sulphuric acid the sparingly soluble tricalcic phosphate is converted into the readily soluble monocalcic phosphate, sulphate of calcium being at the same time produced. Superphosj)hate is thus a mixture of monocalcic phosphate, and generally some free jDhosphoric acid, with gypsum, and various impuri- ties (as sand and compounds of iron and aluminium), derived from the original mineral. A superphosphate will always contain more or less of undissolved phos- phate ; this amount will be more considerable if the ma- nure is badly made, or if the original mineral contained much ferric oxide or alumina. 36 THE CHEMISTRY OF THE FAEM. The yalue of a superphosphate chiefly depends on the percentage of " soluble phosphate " present. By this term analysts do not mean monocalcic phosphate, but the quantity of tricalcic phosphate rendered soluble. In England there is an excellent deposit m the Cam- bridge coprolite. This is largely used for making super- phosphate. Other coprolites are also employed, but they are less suitable. Immense quantities of mineral phos- phates are imported principally from South Carolina, Spain, Bordeaux, and Canada, besides considerable quan- tities of phosphatic guano. The superphosphates richest in soluble phosphate (40 to 45 per cent.) are prepared from phosphatic guauos. Bone, ash, and some phosphorites, also yield high quality manures. The great bulk of our superphosphates is at present prepared from Carolina phosphate or coprolite ; such manure will contain 23 to 27 per cent, of soluble phosphate. Superphosphates form the basis of almost all manu- factured manures. By using bones, or by adding shoddy or crude ammonium salts, turnip manures are produced containing a small amount of nitrogen. By mixing with the superphosphate a larger amount of ammonium salts, or nitrate of sodium, the articles sold as gram, grass, mangel, and potato manures are prepared. Superphos- phate made largely from bones is known as dissolved bones. When superphosphate is applied to a soil containing carbonate of calcium, the soluble phosphate is speedily precipitated, but in a form easily taken up by the roots of plants. In most cases the phosphoric acid is finally conyerted into basic phosphate of iron, a substance at- tacked with difficulty by plants. Superphosphates are naturally more speedy in their effect than manures consisting of undissolved phosphate. A small quantity of phosphoric acid applied as super- MANURES. 37 phosphate will have as great an effect as a considerable quantity applied as bones or ground phosphate. Superphosphate is chiefly employed for turnips^ for which it IS invaluable ; it is also of considerable use for grain crops, especially barley. Its use tends to early ma- turity m the crop. Gypsum.— This manure is one of limited value. It is composed of calcium and sulphuric acid, and is most suitable for crops, such as clover and turnips, which re- quire a considerable amount of sulphur. As superphos- phate always contains much gypsum, special applications of gypsum will be unnecessary where superphosphate is employed. Lime, Chalk, and Marl, are frequently manures of the greatest importance. On soils naturally destitute of lime, as is the case with many clays and sandstones, these ma- nures will supply an indispensable element of plant food. Some marls will also supply a notable quantity of phos- phoric acid. In most cases, however, the beneficial influ- ence of these manures is due to the chemical actions which lime performs m the soil ; the chief of these have been already glanced at under the head of '^ Soil." Burned lime is much more powerful in its action on vege- table matter than chalk or marl ; it should be used with discrimination, lest the humus of the soil be unduly di- minished. Heavy clays, or soils rich in humus, are those most benefited by burned lime. In reclaiming peat bogs lime is of the highest value. The acid humic matter of the peat is neutralized by the hme, and the nitrogen held m combination is converted into ammonia and nitric acid, and thus made available to a crop. The general effect of lime is to render available the plant food already m the soil, without itself supplying any significant amount ; limmg cannot, therefore, be suc- cessfully repeated except at considerable intervals. 38 THE CHEAIISTKY OF THE FARM. Potassium Salts. — These salts are now obtained from Stassf urt and Leopoldshall in large quantities ; they form a thick deposit overlying an enormous mass of rock salt. The commonest potassium salt employed as manure is kainit ; it consists of chloride of potassium, sulphate of magnesium, and water, with frequently chloride of mag- nesium and common salt in addition. Kainit will contain 13 to 14 per cent, of potash. Calcined kainit contains less water, and some magnesia in place of the chloride of magnesium ; it will contain 15 to 17 percent, of potash. Wood ashes may also be employed as a potash manure ; they will contain between 5 and 15 per cent, of potash. The ash of young boughs is richer than that from full- sized timber. Potash manures produce their greatest effect on pas- ture ; clover and turnips may also be benefited by their use. Many soils are naturally well furnished with pot- ash, on these soils potash manures are almost without effect. fomDioii Salt* — Chloride of sodium supplies no essen- tial ingredient of plant food. The little value which salt possesses as a manure is probably due to its action in the soil, where it may help to set free more important constituents. Application of Manures. — A manure can be efficacious only v^hen its constituents are brought into contact with the roots of the crop. To obtain this contact to the full- ' est extent the manure must be thoroughly and evenly distributed throughout the depth of soil mainly occupied by the roots. Soluble manures — as nitrate of sodium, chloride of sodium, ammonium salts, potassium salts, and superphosphate — have the great advantage that they dis- tribute themselves within the soil after the first heavy shower far more perfectly than can be done by any mode of sowing. When manure is especially required by the MAi;rURES. 39 plant in its earliest stages — as superphosphate for turnips — it may be drilled with the seed ; but, as a rule, manure should be sown broadcast, and plowed in or harrowed. Top-dressing, that is sowing manure on the surface of land already under crop, should generally be confined to manures that are soluble, or the principal constituents of which easily become soluble in the soil. Nitrate of sodium is sown with advantage in this manner if showery weather can be depended on to distribute the manure in the soil. On pasture all manures are necessarily applied as top- dressings. Whenever possible, manure should be reduced to a fine powder before application. Artificial manures, if distri- buted by hand, should first be made up to a considerable bulk by mixing with fine dry soil or ashes. Manures con- taining ammonia must not be mixed with alkaline ashes, else some of the ammonia will be lost. Manures of little solubility, or those of which the soil has a great retentive power, may be applied to the land some time before the growing period of the crop. Dif- fusible manures, on the other hand, should be applied only when the crop is ready to make use of them, else serious loss may occur from drainage. Farm-yard manure, rape cake, and bones, and to some extent superphosphate and potassium salts, belong to the former class ; while nitrates, and all manures containing ammonia, belong to the latter class. It was formerly supposed that the great retentive power of fertile soils for ammonia would eifectu- ally prevent any loss by drainage ; we now know that ammonia is speedily converted into nitrates after mixing with the soil, and that these nitrates are readily washed out by heavy rain. Following these principles, an autumn manuring for what may consist of farm-yard manure, blood, or shoddy, with or without superphosphate ; but dressings of guano, ammonium salts, or nitrate of sodium should be deferred 40 THE CHEMISTRY OF THE FARM. until the spring. The question is, howeyer, clearly one of climate, and with a dry winter climate ammonium salts or guano may be applied with advantage in the autumn. On soils of open texture, and little retentive power, preference must often be given to manures of little solu- bility, in order to diminish the loss occasioned by heavy rain. Bulky organic manures, as farm-yard manure or seaweed, are in such cases very suitable. No dressing of manure is completely taken up by the crop to which it is applied, dressingij larger than the actual requirements of the crop must therefore be applied to obtain a given result. Soluble and active manures produce their principal effect at once, and are of little benefit to subsequent crops. Sparingly soluble manures, and those which must suffer decomposition in the soil before they are of service to the plant, as farm-yard manure and bones, will on the contrary continue to pro- duce an effect over many years. Farmers have a preju- dice in favor of the latter class of manures, but it is clear that the quickest return for capital invested is afforded by the former class. Nitrogen applied as ammonium salts or nitrates will give all its effect during the first year ; 45 to 50 percent, of the nitrogen apjolied in this form to wheat and barley is, according to Lawes and Gilbert, recovered on an aver- age in the increase. In the case of farm-yard manure, applied on the heavy land at Eothamsted to wheat and barley, only about 10 to 15 per cent, of the nitrogen was recovered in the increase, but the effect on the barley continued many years after the application of the manure ceased. It is evident that a small quantity of an active manure will accomplish the same work as a large quantity of one less active. The residues of phosphatic and potassic manures are available for subsequent crops, but are distinctly less active than fresh applications of the same manures. CHAPTER IV. CROPS. The dry matter, nitrogen, and ash constituents, in average crops. Cereal (7y(^5. —Characteristic composition— Mode of feeding— Most suitable manuring. Meadow ifa?/.— Characteristic composition— Demand for ash constituents— Influence of manures on quantity and quality- Pasture especially suited for obtaining nitrogen from the atmosphere. Leguminous Crops.— Characteristic composition— Source of nitrogen obscure— Clover-sickness. Root Crops.— Characteristic composition —Differences in the nutrition of turnips, mangels, and potatoes. Fwest Growth— LsiVge production of dry matter for small consump- tion of ash constituents and nitrogen. Adaptation of Manures to Crops.— The feeding power of each crop must be taken into account- Economic distribution of manure in a rotation— The practical value of manures only known by experiments on each farm. Influence of Climate and Season. To understand the chemistry of crops we must first in- quire as to their composition. The following table gives the average composition of ordinary farm crops and of the annua! produce of three kinds of forest. The quan- tities of carbon, hydrogen, and oxygen present are omit- ted, also some of the smaller ash constituents. By " pure ash" is understood the ash minus sand, charcoal, and car- bonic acid. The composition of grain, and of all seeds, is tolerably constant ; but the composition of straw, leaves, roots, and tubers, will vary very considerably according to the character of the soil, manure, and season. 41 42 THE CHEMISTRY OF THE FARM. 02 Ph O ^ ^ I O •§ c ! 81 H a o I— ( .IC'^ tH OlT 00 CO T-H 00 00 a: t- "f>ms ^dc tH 0>T^ S ^s 05 S «© 0^ t> 'dUlMlUQ w^^t^ Oi rt^cq «5 .0 10 C5 •TtH 10 T—l £0-H r-t 00: CO •0 iO s 05 r-l 00 s ■PPY mCO-^ S> 0?rh 00 r- 05 J> 1— 1 COOJ »o ouoiidsoi/j; ^'^ Xi (?:! <:>} 1:0 Tf § 00 0: gi^- CO •pisdu6vji[ mt-O i> 00 10 OiCO 01 00 CO ^ rOco-* I- ^(M COiC COO TtH CO •9mn mOC-> oi COO 00 000 GO ^ T-l c^e:! _^ ;2^'ci iHOO OS aoi T-< 00 ^^ CO T—l 00 .C5JO '^ oc:f ^. 00 OSOi r-l CJOO ^c= CO ;^CJO t- CI CO COTji 00 05 ■*-* Oi 'U3Do.i}is;[ 1^^ « ^s ^s 1 ^ ^^ s l-g 1 1 :^| 1 CO i i ^i 00 P oco CO i> mcc 00 CQ CO CO ^ 00 1-1 ^ 05 00 ^^ ^ 6 " Th" r-((M CO 1-tC^ CO (M co-^ CO OX X) OJ> {> oir »o S TtT 00 1 ^ i to* ^^1 1!-^ Tin" ccTo^ 8?^ ^^ 05o5 T-Tof T-l ,;3 a, 3 CU D, £3 3 Cu ^ p 3 2 ? E3 He. ^ -^r: ^ facto rt d^ 5 ^ ^ W ^ i^ 2 I ^ H 5 t> fac-S ^ - rt H <) » H^:: s 1 g r K t^- M -5] :: <1 3' S M oq CROPS. 43 <£>^ J> rHCO r> -<*C5 CO 05^ o C5 05 rH OS CO (M »O00 CO Oiin J> COCO o CO 55" ^ 05 (M o «o= Jg ^^ ^ OiO CO Oi(M r-t QOCO ^ CO 00 T*^ lOOi Thi Oi-i C<{ OCO iO 2S o COrH o • • • • • TtlTjH 05 rtnt- ^ OS 00 I> Ol-H 1-H ,-H> 00 coco OS COJ- O ©CO CO ^S S§ O^ 55 ^ja ^ ^^ ^ rHCO Ttl I* GO lO CO-* OJ 1>Tt< ^ '^CS CO 00 C3 o ICCO 00 uiso Oi tool Oi 05I> ^ OCM on coo TtH rHCO on rH-* lO iHN rH rH r-^ tOiO O 3>l> Tj< C5i-( CO OiJ> CO OirH o ClTti CO ooo 00 ^^ ^ S?i ^ ^§^ s§ <^^ ^ Sf2 s ^^ g OS CO ^ OiC iO 00 iHTtl iO T*H,-I »o WOO o COCO cs COCO CO ^,^ ^ §^ g^ Sri CO JC.H 5S Tt^OO CO COtH J> (M"tJ< CO T-l T-^ <-'* f on> a ^(?5 t> 05r-t o J>tH 00 . , . . . inio o '^CO TH05 ^ C^'CM* Ttl • • • r-l .V. tH F^^ o rJHQO 1^ COiH Tt< ■^l-i CO rH . • . GQ . . © , .