Takes place chiefly during the Summer Months.

Although in this climate, as has already been pointed out, nitrification probably goes on during most of the winter months, owing to the fact that the temperature of our soils is only occasionally below the minimum temperature at which the process takes place, yet there can be little doubt that the great bulk of the soil-nitrates are produced during a few months in summer. A fair conception of this amount is afforded by the interesting experiments on the composition of drainage-waters made at Rothamsted, which we shall have occasion to refer to immediately. It may be pointed out, however, that it is not always safe to take the amount of nitrates found in drainage-waters as an infallible indication of this rate, for this amount will depend to a certain extent on the amount of rainfall, and would be misleading in the case of a long period of drought. On the whole, however, it furnishes us with extremely useful data for the elucidation of this important problem.

Process goes on most quickly in Fallow Fields.

It has been shown in the Rothamsted experiments that the process goes on best in fields lying in bare fallow; and in this fact lies the explanation of one of the many reasons why the practice of leaving fields in bare fallow, so common in past times, and still practised in the case of clay soils in some parts of the country, was so beneficial to the land thus treated. But despite this fact, the practice of leaving soils in bare fallow can scarcely be justified from this point of view, as the loss of nitrates through the action of rain is very great in our moist climate.

Laboratory Experiments on Rate of Nitrification.

Several interesting experiments have been carried out with the object of affording data for estimating the rate at which the process may go on in our soils under certain conditions. An old experiment, carried out by Boussingault, illustrates, in a general way, how rapid the process is under favourable circumstances. A small portion of rich soil was placed on a slab protected by a glass roof, and was moistened from time to time with water. The amount of nitrate of potash formed under these circumstances was estimated from time to time during a period of two months. During the first month (August) the percentage was increased from .01 to .18 (equal to about 5 cwt. of nitrate of potash per acre). The increase during the second month (September) was very much less,—indeed only about a seventh of the amount.[120] The soil experimented with was an extremely rich garden soil, and all the conditions for nitrification were most favourable.

Of recent experiments on the rate of nitrification, the most striking, perhaps, are those by Schloesing. He mixed sulphate of ammonia with a quantity of soil fairly rich in organic matter, and containing 19 per cent of water. During the twelve days of active nitrification no less than 56 parts of nitrogen per million of soil were nitrified per day. Taking the soil to a depth of 9 inches, this would be equal to more than 1 cwt. per acre—an amount of nitrogen equal to that contained in 6 cwt. of commercial nitrate of soda. These experiments are interesting as showing what is probably the maximum rate of nitrification under the most favourable circumstances, and where there is an abundant supply of easily nitrifiable nitrogen. That nitrification ever takes place in our soils to this extent is not to be for a moment supposed.

Warington, in his Rothamsted experiments, has found that the greatest rate, working with ordinary arable soil (first 9 inches) from the Rothamsted farm, was .588 parts per million of air-dried soil per day—i.e., 1.3 lb. per acre (equal to about 8 lb. of nitrate of soda). Similar soil, when supplied with ammonia salts, showed nearly double this quantity. Higher results were obtained by Lawes and Gilbert with rich Manitoba soils, the average rate being .7 parts per million per day.

The last of these interesting laboratory experiments on the rate of nitrification we shall refer to, are those by Deherain. He experimented with soils containing different amounts of nitrogen and moisture. With a soil containing .16 per cent of nitrogen he obtained, during a period of 90 days, rates of nitrification varying from .71 to 1.09 per million parts of soil. The maximum quantity was formed when the soil contained 25 per cent of moisture. On a soil considerably richer—viz.,.261 per cent of nitrogen—a higher rate of nitrification took place—1.48 parts per million. The highest rate obtained in these experiments showed, when calculated to pounds per acre, about 5-1/2, taking the soil to a depth of 9 inches. When the soil was alternately dried and moistened the process was most rapid.

Portion of Soil-nitrogen more easily Nitrifiable than the rest.

Lastly, it may be noticed that in the above-cited experiments, and others of a similar kind, the process goes on most rapidly at first, and steadily diminishes thereafter. This is due to the fact, that there is generally a certain quantity of nitrogen in most soils in a more easily nitrifiable condition than the rest, so that when this becomes oxidised nitrification proceeds more slowly. It would further seem that the nitrogen of the subsoil is less easily nitrified than that of the surface-soil.

Rate of Nitrification deduced from Field Experiments.

While the above experiments throw much light on the question of the rate at which nitrification may go on under different circumstances, the results furnished by actual analyses of soils and their drainage-waters are of still more practical value; and the Rothamsted experiments fortunately furnish us with a number of these valuable results.

Quantity of Nitrates formed in the soils of Fallow Fields.

These researches had to be carried out on soil taken from fields lying in bare fallow; for no true estimate of the amount of nitrates formed could have been obtained from cropped fields. In the first 27 inches of soil of six separate fields, nitrate-nitrogen was found to vary from 36.3 lb. to 59.9 lb. per acre. In four of these fields the largest proportion was found in the first 9 inches of soil; in the remaining two, in the second 9 inches; while the third 9 inches in two fields showed almost as large a proportion as the first 9 inches.[121]

Position of Nitrates depends on Season.

The position of nitrates in the soil depends largely on the season; for, as has been already pointed out, their production is almost entirely limited to the surface-soil, and it is only by being washed down in rain that they find their way to the lower layers. A wet season, therefore, has the effect of increasing their percentage in the lower soil-layers.

Nitrates in Drainage-waters.

As there is a certain proportion of nitrates that finds its way even below the first 27 inches of soil, the above results do not show their total production. To accurately estimate this amount we must ascertain the quantity escaping in drainage-water. Here, again, the Rothamsted experiments furnish us with valuable data. The amount found in drainage-waters of course naturally varies very much, and depends largely on the rainfall; but taking an average of twelve years, this has been found to amount to between 30 and 40 lb. per acre—an amount not so very far short of that found in the first 27 inches of the soil itself. This was from comparatively poor soil, it must be remembered, and a much larger quantity would undoubtedly be produced in the case of richer soils. Adding then the results together, we find that in soils like those at Rothamsted, when in bare fallow, between 80 and 90 lb. of nitrogen are converted into nitrates in some fourteen months' time—an amount equal to about 5 cwt. of nitrate of soda. It is a fact of no little practical significance that nearly one-half of this large quantity is found in the drainage-water.

Amount produced at Different Times of the Year.

Some indication of the rate at which nitrification takes place during the different months of the year is obtained from a study of the results of the analyses of drainage-waters which we have just referred to. This, however, it must be remembered, only furnishes us with a very approximate indication. The month showing the greatest amount of nitrates in the drainage-water must not necessarily be regarded as that during which nitrification has been most active, for the amount chiefly depends on the rainfall. In illustration of this it will be found that the drainage-water during the autumn and early winter months contains most nitrates, not because nitrification is most active then, but because the rainfall is greatest, and a large proportion of the nitrates formed during the drier summer months is being only then washed from the soil. The amount of nitrates in drainage-waters steadily diminishes from autumn through the winter months, and is least in spring. The total amount of nitrates found in the drainage-water is, therefore, not a safe guide. What, however, does furnish us with a more reliable indication is the percentage of nitrates in the drainage-water. Regarding the results of the analyses of drainage-water (see Appendix) from this point of view, it will be seen that this is greatest during the month of September, and least during April.[122]

Nitrification of Manures.

A subject which has not yet been specially referred to, but which is of great practical importance, is the nitrification of manurial substances. It is unfortunate that the amount of research hitherto devoted to this important question has been slight, and that the knowledge we possess is therefore very limited.

Ammonia Salts most easily Nitrifiable.

One fact, however, about which there can be little doubt, is that nitrogen in the form of ammonia salts is, of all compounds of nitrogen, the most easily nitrifiable. Indeed, as we have already indicated, it is highly probable that the conversion of the different forms of organic nitrogen into ammonia is an intermediate stage in the nitrification of these bodies. At any rate it seems to be invariably the case that when a mixture of nitrogen compounds, including ammonia salts, are allowed to nitrify, the nitrogen in the form of ammonia is the first to become nitrified.

Sulphate of Ammonia most easily Nitrifiable Manure.

It follows from this that sulphate of ammonia, the most common of ammoniacal manures, is one of the most speedily nitrified when applied to the soil. The rate at which the nitrification of this manure takes place naturally varies according to the quantity applied, and other circumstances, such as the nature of the soil and the weather, &c. That, under favourable circumstances, the conversion of ammonia into nitrates is very rapid, has been shown by a number of experiments. Deherain has found that when sulphate of ammonia was mixed with soil at the rate of 2 cwt. per acre, nitrification took place at the rate of 1/100th of its nitrogen per day.

Rate of Nitrification of other Manures.

Of other nitrogenous manures, guano, it would seem, comes next to sulphate of ammonia in the rate at which it becomes nitrified in the soil; while next to guano stand green manures, dried blood, meat-meal, &c. As we should expect, such a manure as shoddy is very slowly nitrified. The rate at which the nitrogen compounds in farmyard manure become nitrified, when incorporated with the soil, vary very much according to circumstances. It goes on probably at a greater rate than the ordinary nitrification of soil-nitrogen. It is a somewhat striking fact that the effect of adding nitrate of soda to the soil may be at first to check nitrification. That the addition of common salt, even in small quantities, has this result, is at any rate certain. The presence of salt to the extent of one-thousandth of the weight of the soil, has a prejudicial effect.

Soils best suited for Nitrification.

To recapitulate, then, nitrification is effected through the agency of micro-organisms, which are present to a greater or less extent in all soils. It requires for its favourable development air, warmth, moisture, absence of strong light, presence of a salifiable base—viz., carbonate of lime—the presence of certain mineral food-constituents, such as phosphates, and a certain amount of alkalinity. It consequently takes place to the least extent in barren sandy soils. Soils rich, light, well ventilated, uniformly moist, warm, and chalky, are best suited for its development. Other things being equal, it develops better in a fine-grained soil than in a coarse-grained soil, because, in the case of the former, aeration and uniform moistening of the soil are best secured.

Absence of Nitrification in Forest-soils.

A point of considerable interest is the practical absence of the process in forest-soils. The absence, or occurrence in the most minute traces, of nitrates in forest-soils has been accounted for by the lowness of the normal temperature of such soils and their extreme dryness. This latter condition is accounted for by the enormous transpiration of water which takes place through the trees, especially in summer-time, which is such as to render the soil almost air-dry. Lastly, it may be accounted for by the want of mineral food ingredients.

Important Bearing of Nitrification on Agricultural Practice.

Before concluding this chapter, it may be well to draw attention to the important bearing which nitrification has on agricultural practice. The light which our present knowledge—imperfect as it is—of this most interesting process throws on the theory of the rotation of crops is very striking, for it shows how the adoption of a skilful rotation may be made to prevent the loss of enormous quantities of the most valuable of all our soil-constituents,—the one on the presence of which fertility may be said most to depend—viz., nitrogen.

Desirable to have Soil covered with Vegetation.

The constant production of nitrates going on in the soil, the inability of the soil to retain them, and the consequent risk of their being removed in drainage, furnish a strong argument in favour of keeping our soils as constantly covered with vegetation as possible.

Permanent Pasture most Economical Condition of Soil.

From the point of view of conservation of soil-nitrates, permanent pasture may be said to be the most economical condition for the soil to be in. In such a case the nitrates are assimilated as they are formed, and, by being converted in the plant into organic nitrogen, they are at once removed from all risk of loss. A consideration, therefore, of the process of nitrification furnishes many arguments in favour of laying down land in permanent pasture—a practice which of late years has been increasingly followed in many parts of the country. As, however, it is not possible or desirable to carry out this practice beyond certain limits, the rotation which most nearly conforms to the condition of keeping the soil covered with vegetation, and most approximates in this respect to permanent pasture, is most to be recommended.

Nitrification and Rotation of Crops.

The chief risk of loss of nitrates is in connection with a cereal crop such as wheat. Where turnips follow wheat, there is a period during which the soil is left uncovered, and during which most serious loss of nitrates is apt to ensue. The risk of loss is enhanced by the fact that the assimilation of nitrates by cereals ceases before the season of their maximum production in the soil. The soil is then left bare of vegetation during the autumn, which is the most critical period of all, and the result must be serious loss. In order to minimise this loss, the practice of growing catch-crops has been had recourse to. As, however, this practice will be dealt with elsewhere, nothing further need here be said.

FOOTNOTES:

[97] As the formation of nitrites is a stage in the process, the term nitrification includes the formation of nitrites as well as nitrates.

[98] Nitre seems to have been known as early as the thirteenth century.

[99] Lawes and Gilbert, for example, have shown that in the Rothamsted soils it only amounts to a few parts per million of soil.

[100] See Appendix, Note I., p. 196.

[101] The artificial production of nitre seems to have been first effected by Glauber in the seventeenth century.

[102] The lime-rubbish from old buildings, especially those parts which have come in contact with the earth, or plastering from the walls of damp cellars, barns, stables, &c., have been found to be rich in nitrate of lime, and, as has been long well known, constitute by themselves a valuable manure. The formation of the nitrate of lime can be accounted for by the contact of the lime with nitrogenous matter of different kinds.

[103] As much of the nitric acid in this solution was present as nitrate of lime, it was usually treated with a solution of potassium carbonate, the result being the precipitation of the lime as carbonate, pure saltpetre being left in solution, according to the following equation—

K{2}CO{3} + Ca(NO{3}){2} = 2 KNO{3} + CaCO{3}.

Under the French mode of manufacture, the process was considered to have developed satisfactorily when 1000 lb. of earth, at the expiration of two years, yielded 5 lb. of nitre.

[104] Pasteur had already in 1862 expressed the opinion that nitrification might probably be in some way connected with ferments. A. Mueller (see 'Journal of Chemical Society,' 1879, p. 249) was the first to advance the opinion that nitrification was due to the action of a ferment. This conclusion he was led to by the observation that while the ammonia in sewage was converted into nitric acid, no change took place in solutions of ammonia or urine prepared in the laboratory.

[105] Bisulphide of carbon and phenol (carbolic acid) have also been experimented with in connection with their antiseptic action on nitrification. In these experiments the former had a similar effect to chloroform; the phenol, however, while hindering it did not entirely suspend it, due probably to the difficulty of bringing the phenol vapour into thorough contact with the soil-particles.

[106] Winogradsky has named the nitrous organism nitrosomonas, and the nitric organism nitrobaeter.

[107] From a series of Lectures delivered by him in connection with Lawes Agricultural Trust, in the United States.

[108] This silica-jelly consists of dialysed silicic acid, ammonium sulphate, potassium phosphate, magnesium sulphate, calcium chloride, and magnesium carbonate.

[109] This fact is all the more striking when we remember that this decomposition of carbonic acid is best effected in the dark, since light is prejudicial to nitrification.

[110] See Appendix, Note II., p. 196, and Note III., p. 197.

[111] See Appendix, Note V., p. 198.

[112] This is shown by the fact that nitrification will only continue in a solution of carbonate of ammonia till one-half the ammonia is nitrified. It then stops. The base, with which the nitrous acid combines as it is formed, being at that stage entirely used up, nitrification is no longer possible. With regard to urine solutions the same is the case. Nitrification thus will only take place where there is a sufficiency of base.

[113] See Appendix, Note IV., p. 197.

[114] It would seem that an alkalinity much exceeding four parts of nitrogen per million is prejudicial to the process.

[115] According to Warington, solutions containing 50 per cent of urine become nitrifiable when sufficient gypsum is added. The gypsum neutralises the alkalinity of nitrifying solutions by converting the alkaline ammonium carbonate into neutral ammonium sulphate, the calcium carbonate being precipitated.

[116] See Chapter on Farmyard Manure.

[117] As practically illustrating this fact, a solution kept at 10 deg. C. required ten days, while a solution kept at 30 deg. C. required only eight days for nitrification.

[118] In sixty-nine trials no failure to produce nitrification by seeding with soil from a depth, of 2 feet was experienced. Similarly in eleven trials only one failure took place with soil from a depth of 3 feet. With clay soil from a depth of 6 feet success took place to the extent of 50 per cent. No nitrification was obtained with clay from a depth of 8 feet. Entire failure was experienced with chalk subsoil. The process thus diminishes in activity the lower down we go.

[119] Koch has found that in soils he has examined few organisms were found at a depth below 3 feet.

[120] See Appendix, Note VI., p. 198.

[121] For full analytical results see Appendix, Note VII., p. 198.

[122] We find the least amount in the month of April. In the water, from a 20-and 60-inch gauge respectively, the amounts were 1.35 lb. and 1.61 lb. per acre (rainfall 2.25 inches). From then on to November the amount steadily increases. In the latter month it reaches its maximum—viz., 6.50 lb. (20-inch gauge) and 5.98 lb. (60-inch gauge) per acre (rainfall 2.30 inches). See Appendix to Chapter III., Note VIII, p. 160.



APPENDIX TO CHAPTER IV.

NOTE I. (p. 162).

OLD THEORIES OF NITRIFICATION.

According to the old theories, nitrification was regarded as a simple case of the oxidation of nitrogen by the oxygen of the air, or by ozone. The union of nitrogen and oxygen, however, probably takes place only at very high temperatures, such as are formed during electric discharges. It is needless to point out that the union of nitrogen and oxygen in this way is not likely to occur in soils. According to other theories, nitrification was effected by means of the oxidation of ammonia. Ammonia, however, can only be oxidised to nitric acid by means of certain powerful oxidising agents, such as ozone or hydrogen peroxide. As, however, these substances are not found in the soil, it is much to be doubted whether nitric acid is ever formed in the soil in this way. It is possible, however, as held by some, that ferric oxide is capable of inducing this conversion. On the whole, however, most evidence points to the conclusion that all nitric acid produced in the soil is formed through the agency of micro-organic life.

NOTE II. (p. 170).

The important fact that nitrification can take place in solutions practically devoid of organic matter, was first shown by Dr J. H. M. Munro ('Chemical Society Journal,' August 1886, p. 561). It was further corroborated by Warington and P. F. Frankland. Winogradsky, however, has carried out the most conclusive experiments on the subject. "He prepared vessels and solutions, carefully purified from organic matter, and these solutions he sowed with the nitrifying organism. Finding that under these conditions the nitrifying organism increased enormously and displayed its full vigour, he proceeded further to determine the amount of carbonaceous organic matter formed in solutions after the introduction of the organism. By making the nitrification intensive, he was able to obtain considerable quantities of carbon from the nitrified solutions by the process of wet combustion. In his third memoir he publishes figures which apparently show a close relation between the amount of nitrogen oxidised, and the amount of carbon assimilated; the ratio is about 35:1."—See Bulletin of U.S. Department of Agriculture, No. 8, containing Lectures on Rothamsted Experiments by R. Warington, F.R.S., p. 50.

NOTE III. (p. 170).

The oxidising power of the micro-organisms of soil is not confined to the oxidation of ammonia or of organic matter. Muentz has shown that soil is capable of oxidising iodides to hypo-iodides and iodates, and bromides to hypo-bromides and bromates. This is a very important result, and seems to indicate that nitrification is part of a general oxidising action, and that we must not assume that nitrites or nitrates are produced because they are in themselves of advantage to the organism.

NOTE IV. (p. 172).

"When urine in different degrees of dilution was treated with soil, 1 gram of soil being added to 100 c.c. of diluted urine, nitrification commenced in the 1-per-cent solution in 11 days, in the 5-per-cent solution in 20 days, in the 10-per-cent solution in 62 days, in the 12-per-cent solution in 90 days. The alkalinity of the last-named solution when nitrification commenced was equal to 447 mgs. of ammonia per litre. A solution with an alkalinity of 500 mgs. of ammonia per litre is apparently unnitrifiable."—American Department of Agriculture Bulletin, Warington's Lectures on Rothamsted Experiments, p. 51.

NOTE V. (p. 171).

Professor P. F. Frankland in his experiments used the following solutions:—

grms. NH{4}Cl .5 } H{3}PO{4} .1 } MgSO{4} .02 > In 1000 c.c. of distilled water. CaCl{2} .01 } CaCO{3} 5.00 }

NOTE VI. (p. 185).

Experiment by Boussingault on Rate of Nitrification.

Percentage of Nitrate 1857. of Potash. = lb. per acre. August 5 .01 34 August 17 .06 222 September 2 .18 634 September 17 .22 760 October 2 .21 728

NOTE VII. (p. 188).

NITROGEN AS NITRATES IN ROTHAMSTED SOILS AFTER BARE FALLOW IN LB. PER ACRE.

+ -+ -+ -+ Alternate Four-course rotation. Wheat + -+ -+ Depth of and Super- Claycroft Foster's Soil. Fallow. phosphate Mixed Manure. Field. Field. only. + -+ -+ -+ -+ -+ 1878. 1878. 1878. 1882. 1881. 1881. + -+ -+ -+ -+ -+ lb. lb. lb. lb. lb. lb. 1st 9 ins. 28.5 22.3 30.0 40.1 16.4 14.6 2d 9 ins. 5.2 14.0 18.8 14.3 26.5 24.6 3d 9 ins. - - - 5.5 15.9 17.3 + -+ -+ -+ -+ -+ Total 33.7 36.3 48.8 59.9 58.8 56.5 + -+ -+ -+ -+ -+



CHAPTER V.

THE POSITION OF PHOSPHORIC ACID.

We now come to consider the position of phosphoric acid in agriculture. The question is, however, very much simpler in its nature than that of nitrogen, and may be consequently discussed in a much shorter space.

Most soils, as we have already had occasion to point out, are better supplied with available ash-plant ingredients than available nitrogen compounds. The quantity of phosphoric acid absorbed by the plant is also less than that of nitrogen; and lastly, the different chemical compounds of phosphoric acid occurring in the soil are not nearly so numerous as those of nitrogen. Phosphoric acid, however, must be regarded as ranking next to nitrogen in its importance as a soil-constituent.

Occurrence of Phosphoric Acid in Nature.

That phosphoric acid is of universal occurrence may be assumed from the fact of the almost universal occurrence of vegetable life on the earth's surface; for plants are unable to grow without it. While thus of practically universal occurrence, its amount in most soils is very trifling. As the only source of it in the soil is from the disintegration of the different rocks, a short description of its occurrence in the mineral kingdom may first be given.

Mineral Sources of Phosphoric Acid.

It was first discovered in the mineral kingdom towards the close of last century; but we have only of late years ascertained any exact knowledge of its percentage in the different rocks out of which soils are formed. This has been shown in many cases to be very trifling. It most abundantly occurs as apatite, a mineral consisting of calcium phosphate, with small quantities of calcium fluoride or calcium chloride. This apatite, or phosphorite, is found in certain parts of the world in large masses; but as a rule, it only occurs in small quantities in most rocks. It may be stated that the older rocks are, as a general rule, richer in it than those of more recent formation; and Daubeny has drawn attention to this fact as furnishing a useful guide in estimating the probable richness of a soil in phosphoric acid. The older, therefore, a rock is, the richer it is likely to be in phosphoric acid.

Apatite and Phosphorite.

Of apatite there are a variety of kinds, which differ in their appearance as well as in their composition. It occurs chiefly in a crystalline form, and is found sometimes in regular crystals, but it also occurs in the amorphous form. In colour it may be white, yellow, brown, red, green, grey, or blue. Two classes of apatite are found. The first consists of calcium phosphate along with calcium fluoride; and in other kinds of apatite the calcium fluoride is replaced by calcium chloride. Phosphorite is another name for apatite, but is chiefly applied to impure amorphous apatite. The percentage of phosphate of lime in different kinds of apatite may be stated at from 70 to 90 per cent. It occurs in very large quantities in Canada, the Canadian apatite being very rich in phosphate of lime—80 to 90 per cent. In many parts of the world it forms portions of mountain-masses, and is quarried, crushed, and used for artificial manurial purposes. Further details of its occurrence and chemical composition will be found in the Appendix.[123]

Coprolites.

In many parts of the world round nodules, largely consisting of phosphate of lime, have been found, to which the name "coprolites" has been given, on the assumption that they consisted of fossilised animal excrements. These coprolites, or osteolites as they have also been called, vary in the percentage of phosphate of lime they contain. Sometimes this amounts to 80 per cent, but as a rule it is very much less. They also in the past have formed an important source of manure, and will be referred to subsequently.

Guano.

We have, lastly, phosphoric acid occurring in large quantities in guano-deposits, chiefly found on the west coast of South America. These deposits, which have been of enormous importance as a source of artificial manure, are of animal origin, and will be discussed at considerable length in a chapter specially devoted to the subject; so that we need do no more than mention them here.

Phosphoric acid is also found in the form of phosphate of lime in certain rocks as "layers" and "pockets."

Universal Occurrence in Common Rocks.

But while it is thus found in considerable quantities in various parts of the world, and while no anxiety need thus be felt as to its abundance for artificial manurial purposes, its occurrence in the common rocks, which, as we have already pointed out, is practically universal, is in many cases very minute.

Fownes first identified it in the felspathic rocks in 1844; and since then its percentage in granite, lava, trachyte, basalt, porphyry, dolomite, gneiss, syenite, dolerite, diorite, and a number of other rocks, has been determined by numerous investigators. For analyses of these rocks the reader is referred to the Appendix.[124]

Occurrence in the Soil.

That no soil is actually without phosphoric acid is highly probable, but in many soils it is present in the merest traces, and even in fertile soils it is rarely present in quantities over two-tenths of a per cent; while half that amount may be taken as an average for most fairly fertile soils. This would be about 3500 lb. per acre, calculating the soil to a depth of 9 inches. In exceptional cases it has been found to the extent of .3 per cent; and in the famous Russian black earth it has been found to amount to .6 per cent.[125] Like nitrogen, it is found in greatest amount in the surface portion of the soil, but its amount at different depths does not vary to the same extent as we have found to be the case with nitrogen.

Condition in which Phosphoric Acid is present in the Soil.

Unlike nitrogen, phosphoric acid occurs in the soil almost entirely in an insoluble form; and when applied to the soil in a soluble form, is speedily converted into an insoluble condition. Its most commonly occurring forms are as phosphates of lime, iron, and alumina. These facts are of importance to remember, as they explain why phosphoric acid is not found in drainage-water in any quantity. It also shows how little the risk of loss from drainage is in the application of artificial phosphatic manure to the soil.

Occurrence in Plants.

The percentage of phosphoric acid in plants, like other ash-constituents, is subject to considerable variation, and depends on a variety of conditions, such as the state of the plant's development, nature of soil, climate, season, treatment with manures, &c. All these conditions have a certain influence. The different parts of the plant have been found to contain it in different quantities. The tendency of phosphoric acid is to travel up to the higher portions of the plant with the progress of growth, and to finally accumulate in the seed. As illustrating this, it may be mentioned that the inner portion of the stalk of a ripe oat-plant has been found to contain only a seventeenth of the amount of phosphoric acid found in the same portion of the stalk of a young oat-plant. Similarly it may be mentioned that, while the ash of the grain of rye and wheat contains nearly half their weight of phosphoric acid, the percentage present in the ash of other parts of the plant amounts only to from 5 to 16 per cent. The percentage of phosphorus is greater in young plants than in mature plants; it is greater also in quickly developed plants than in slowly developed plants.

In the plant, phosphorus is present chiefly in the albuminoids; and its absorption from the soil takes place in greatest quantity during the period of maximum growth. In beans and peas an oil containing phosphorus has been found.

Occurrence in Animals.

That phosphorus in different forms exists in animal tissue is well known. It is found both in the brain and in the nerves, as well as in nearly all the fluids of the animal body. It is, however, in the bones that it is most abundant, the mineral portion of which is almost entirely made of phosphate of lime,—a fact which renders bones such a valuable artificial manure. Altogether, phosphoric acid occurs in the animal body to the extent of 2.3 per cent. There is a point which we shall have occasion to draw the student's attention to further on in discussing the nature of farmyard manure—and that is, that the urine of the common farm animals is practically devoid of phosphoric acid.

Sources of Loss of Phosphoric Acid in Agriculture.

As we have already done in the case of nitrogen, we may now attempt to form some conception of the sources of loss and gain of phosphoric acid in the soil. The sources of loss may be divided into natural and artificial. Of natural sources of loss we have only one, and that is loss by drainage.

Loss of Phosphoric Acid by Drainage.

We have already seen that the condition in which phosphoric acid is present in the soil is as insoluble phosphate. In drainage-water it occurs in mere traces. Minute though the amount seems when stated as percentage, and small as it appears beside the loss (from the same source) of nitrogen, it is yet, if considered for large areas, sufficiently striking. Thus it has been estimated that in the river Elbe there is carried off by drainage from the fields of Bohemia 2-3/4 million pounds (1200 tons) of phosphoric acid annually. This, it is true, is a very trifling amount compared with the annual loss of nitrogen from an equal area; but then it must be remembered, on the other hand, the sources of gain to the soil of this ingredient are not so numerous as are those of nitrogen, the only sources of phosphoric acid being in the manure applied to the soil, and that coming from the gradual disintegration of phosphatic minerals.

Artificial Sources of Loss.

The other sources of loss may be classed under the term artificial, and are connected with agricultural practice. Just as we have seen that in the case of nitrogen enormous quantities of that substance are constantly being removed from the soil in those crops which are consumed off the farm, so, too, enormous quantities of phosphoric acid are being removed in the same way. As illustrating this fact, it may be mentioned that Professor Grandeau has recently estimated that in the entire crops grown in France in one year there are about 298,200 tons of phosphoric acid; while the amount returned in the dung of farm animals is only 157,200, or only about one-half of what is removed in the crops, leaving a deficit of 147,000 tons to be made good by the addition of artificial phosphatic manures, if the fertility of the soil is to be maintained. The same authority has calculated that in the bones of the entire farm animals in France there is no less a quantity than 76,820 tons of phosphoric acid.

As an example of how, in many cases, the amount of phosphoric acid removed from the farm is very often much greater than that restored, a case quoted by Crusius may be cited. This was a farm of 670 acres (Saxon) which had received only farmyard manure, and from which, during sixteen years, 985.67 cwt. of phosphoric acid had been sold off in the crops; while only 408.33 cwt. had been restored in the manure, leaving a loss of 577.34 cwt.

Phosphoric Acid removed in Milk.

A further source of loss is the phosphoric acid removed in milk. In the total annual yield of milk from one cow there may be from 11 to 12 lb. of phosphoric acid.

Loss in Treatment of Farmyard Manure.

The risks of loss of phosphoric acid in the treatment of farmyard manure are not so great as in the case of nitrogen. There is, however, a considerable risk, through want of proper precautions, of the soluble phosphates being washed away by rain.

Loss in Sewage.

The loss of phosphoric acid incurred by the present method of sewage disposal is not so large as the loss of nitrogen, inasmuch as the quantity of phosphoric acid contained in human excreta is very much less. Roughly speaking, it may be said to amount to a little less than one-third of the nitrogen lost in this way.

Sources of Artificial Gain of Phosphoric Acid.

To balance these losses, we have a practically unlimited supply of mineral phosphates for application as artificial manure, as well as large quantities of other manures, many of them already mentioned in connection with nitrogen, such as bones and guanos of all kinds. Quite recently, also, a large source of phosphoric acid has been opened up in the basic slag, a rich phosphatic bye-product obtained in considerable quantity in steel-works from the basic process of steel manufacture. We have also large quantities of phosphoric acid in the imported feeding-stuffs, for statistics regarding which we would refer our readers to a previous chapter. The question of the actual amount contained in these sources is not of the same interest as in the case of nitrogen, and need not therefore detain us. We have sufficiently indicated the importance of phosphoric acid in agriculture by the statements above given. All further consideration of phosphoric acid must therefore be deferred to future chapters.

FOOTNOTES:

[123] See Appendix, Note I., p. 210.

[124] See Appendix, Note II., p. 211.

[125] These results, as indeed all soil percentages, are calculated on the soil in a dry condition.



APPENDIX TO CHAPTER V

NOTE I. (p. 201).

COMPOSITION OF APATITE (Voelcker).

(Krageroee, Norway.)

Lime 52.16 Phosphoric acid 41.25 Chlorine 4.10 Fluorine 1.23 Oxide of iron 0.29 Alumina 0.38 Potash and soda 0.17 Water 0.42 ——— 100.00 ======

Apatite is found in considerable quantities in America, Germany, France, Spain, Hungary, Norway, and Great Britain. According to Rose, apatite is made up of three molecules of tribasic calcium phosphate (Ca(PO4)2), combined with one molecule of calcium fluoride (Ca F2) or one molecule of calcium chloride (CaCl2) respectively.

The composition of the pure mineral should be—

Chlorapatite. Per cent. Calcium phosphate 89.38 Calcium chloride 10.62

Fluorapatite.

Calcium phosphate 92.31 Calcium fluoride 7.69

NOTE II. (p. 203).

The following is a list of the commoner rocks in which the percentage of phosphoric acid has been determined. The results are taken from analyses by Nesbit, Schramm, Bergemann, Rose, Deherain, Handtke, Petersen, Nessler, Muth, Fleischmann, Storer, and others:—

Per cent. Felspar 1.7 Granite 0.09 0.25 0.58 0.68 Lava 1.21 1.8 Trachyte 0.30 0.66 Basalt 0.50 1.11 Porphyry 0.26 Marl 1.45 2.31 3.8 Calcareous stones 0.064 0.176 Dolomite 1.24 Lias chalk 1.39 Gneiss 0.18 0.78 1.51 Syenite 0.10 Dolerite 0.3 1.1 1.2 Diorite 0.5 0.69



CHAPTER VI.

THE POSITION OF POTASH IN AGRICULTURE.

We may, lastly, consider the position of potash in agriculture, the only ash ingredient of the plant, in addition to phosphoric acid, which it is as a rule necessary to add as a manure.

Potash of less Importance than Phosphoric Acid.

It is of far less importance than phosphoric acid, from the fact of its much more abundant occurrence in the soil, as well as from the fact that under the ordinary conditions of agriculture, although removed from the soil in considerable quantities by crops, it finds its way back again in the farmyard manure; for it has not the same tendency to accumulate in large quantities in the grain or seed as we have seen to be the case with phosphoric acid. On this account straw contains a much greater proportion of potash than phosphoric acid, and hence farmyard manure may be regarded as fairly rich in potash.

Occurrence of Potash.

Of all sources of potash the ocean must be regarded as the chief. Millions and millions of tons are present in a state of solution in the salt water of the ocean.[126] Like phosphoric acid, its occurrence in the rocks forming the earth's crust may be said to be practically universal. Many of the commonly occurring rocks and minerals are extremely rich in it, and by their disintegration furnish large quantities to the soil. Some of these rocks contain it in such abundance that they have been tried as potash manures; and were other more valuable sources less available than they actually are, such a practice might well be recommended. A volcanic rock known as palagonite, and that most commonly occurring of all potash minerals—viz., felspar—have both been experimented with in this way with considerable success.

Felspar and other Potash Minerals.

That felspar should prove, when finally ground, a valuable source of potash, is not to be wondered at when we remember that some varieties of it contain over 16 per cent. It has been calculated that a single cubic foot of this mineral is sufficient to supply an oak-wood, covering a surface of 26,910 square feet, with potash for a period of no less than five years.[127] Some idea of the enormous potential fertility of a soil containing felspar, so far as potash is concerned, may be obtained from this statement. It must be remembered, however, that it is only the orthoclase or potash felspars which contain large quantities of potash—other felspathic rocks, such as oligoclase and labradorite, being comparatively poor in it. Another commonly occurring mineral which is rich in potash is mica, which has been found to contain from 5 to 13 per cent. From this it follows that rocks which have large amounts of these minerals in their composition—such as granite, for example, which often contains 5 or 6 per cent of potash—form by their disintegration soils rich in this ingredient.

Stassfurt Salts.

But in addition to the sources of potash already mentioned, it exists in other forms in the earth's surface. Till within recent years it was obtained for commercial purposes from the ashes of plants, which, as we shall immediately see, are extremely rich in this ingredient; from salt water—this source giving rise to the so-called "salt gardens" on the coast of France; and from nitre soils in different parts of India, referred to already at considerable length. Large mineral deposits, however, have been recently discovered in the neighbourhood of Stassfurt in Germany, and have since their discovery supplied all the potash required for manurial and other purposes. In these deposits (similar ones have also been found at Kalusz in the Carpathian Mountains) there are no less than five different minerals which contain potash. The form in which it is present is as sulphate or chloride, so that it is readily available for plants, and is of altogether very much greater value than the form in which it occurs in the minerals already mentioned—viz., as an insoluble silicate. Of the Stassfurt potash salts, the best known as a manure is kainit, which contains about 32 per cent of sulphate of potash. A list of the other potash minerals, with the particulars of their composition and the percentage of potash they contain, will be found in the Appendix.[128]

Occurrence of Saltpetre.

We have already had occasion, in Chapter IV., when discussing the question of nitrification, to refer to the occurrence of nitrate of potash in certain soils in India, which have formed a large source of saltpetre used in commerce in the past.

Occurrence of Potash in the Soil.

From what has been said regarding the richness in potash of certain commonly occurring minerals, such as felspar, it is only natural to infer that most soils must contain large quantities of this substance; and this is so. The wonder is that potash, when applied as an artificial manure, should have such a marked effect in increasing the fertility of the soil, as is often the case. We must remember, however, that although a soil may contain large quantities of potash, there may be a very small percentage of the whole in an available form for the plant's needs.

Potash chiefly in insoluble Condition in Soils.

Potash occurs almost entirely in soils in a very insoluble form—viz., combined with silica as a silicate of potash. It is only by the slow disintegration of potash rocks that the potash they contain is set free for plant uses. When it is applied as an artificial manure, on the other hand, it is in a soluble form. In most soils the amount soluble in water probably lies between .001 and .009 per cent; that soluble in dilute acid solutions from .1 to .5 per cent; and that insoluble from .2 to 3.5 per cent of the soil. It is highly probable that a certain quantity of potash in the soil may exist in combination with humic and ulmic acids, forming insoluble potassium humates and ulmates.

Potash in Plants.

Of all the ash ingredients of plants, potash is the most abundant, as it forms on an average about 50 per cent of the total ash of plants—about 90 per cent of the alkalies. The ash of plants, indeed, was for long the chief source of potash. Certain plants remove very large quantities from the soil. Of these roots, potatoes, the vine, the tobacco-plant, and hops may be mentioned as examples. It is present in large quantities in the grain of cereals, although, as we have already pointed out, not to the same proportional extent as phosphoric acid. It is found in the plant's extremities, such as twigs and new leaves, in greatest abundance.[129]

Potash in the Animal Tissue.

It is also found in all parts of the animal body. Especially rich in potash salts are the blood corpuscles, which contain about ten times the amount contained in the serum. It is found in especial abundance in the fleece of sheep, which may contain more potash than that in the whole body of the sheep. Animal urine also contains potash in considerable quantities.

Sources of Loss of Potash.

The capacity of the soil to retain soluble potash compounds, while not equal to its capacity for retaining phosphoric acid, is yet very much in excess of its capacity for retaining nitrates. The result is, that potash is only found in comparatively minute traces in drainage water.[130] Taking the same example as we already cited in illustration of the loss of phosphoric acid, we find that the amount carried away in the course of a year in the waters of the Elbe from Bohemia is 97,000,000 lb. (43,300 tons).

Potash removed in Crops.

The amount of potash removed by the different crops from the soil will be considered in a subsequent chapter. We need only say here that the class of crops which remove the largest quantity are the root crops, especially mangels. The loss is least in the case of the cereals. The amount of potash contained in the straw of cereals is about three times the amount of that removed in the grain.

Potash removed in Milk.

Lastly, we may refer to the potash removed in milk, which, on an average, may be taken at 10 lb. per annum for each cow.

Potash Manures.

Of potash manures the chief are the sulphate and the chloride, or, as it is commercially known, the "muriate." The chief source of potash manures are the Stassfurt deposits already referred to. Wood-ashes have also been used in large quantities in the past (chiefly as a potash manure), and in some parts of the world are still used. A considerable source of artificial potassic manures is the refuse manufacture of sugar-beet, such a large industry in Germany. Potash occurs as a constituent of certain other manures, more valuable for nitrogen and phosphoric acid, such as guano and dried blood.

FOOTNOTES:

[126] According to Boguslawski and Dittmar, the total amount of potash calculated as sulphate of potash in salt water equals 1141 x 10^{12} tons.

[127] See Storer's 'Agricultural Chemistry,' vol. ii. p. 291.

[128] See Appendix, Note I., p. 220.

[129] See Appendix, Note II., p. 220.

[130] According to Way, different samples of drainage waters were found only to contain from .00003 to .00031 per cent.



APPENDIX TO CHAPTER VI.

NOTE I. (p. 215).

AMOUNT OF POTASH IN DIFFERENT MINERALS.

Felspars— Percentage of potash. (a) Orthoclase { 9.11 10.28 11.07 12.12 12.47 { 13.49 14.35 15.21 16.7 (b) Oligoclase 0.50 (c) Labradorite 0.33 Mica { 5.61 6.20 7.23 8.26 8.95 { 9.00 10.25 12.40 13.15 Amphibole 0.25 2.96 Pyroxene 0.34 2.48 Leucite 13.60 18.61 Zeolites 0.30 9.35 0.98 4.93

Stassfurt potash salts— Per cent. (_a_) Polyhallite, _potassium sulphate_ 28 (_b_) Karnallite (KCl.MgCl_{2}6H_{20}), _potassium chloride_ 24 to 27 (_c_) Sylvin, pure _potassium chloride_. (_d_) Kainit (K_{2}SO_{4}MgSO_{4}MgCl_{2}6H_{2}O), _potassium sulphate_ 32 (_e_) Schoenite (K_{2}SO_{4}, MgSO_{4}, 6H_{2}O), pure _potassium magnesium sulphate_.

NOTE II. (p. 217).

The quantity of potash obtainable from various plants in the manufacture of potashes on a large scale is illustrated by the following statements. 1000 lb. of the following vegetative products yield the following quantities of potashes:—

lb. Old spruce-wood 1/2 Old poplar-wood 3/4 Old oak-wood 1-1/2 Corn-stalks 17-1/2 Bean-stalks 20 Grape-vine twigs 40

(Storer, 'Agricultural Chemistry,' vol. ii. p. 108.)



PART III.

MANURES



CHAPTER VII.

FARMYARD MANURE

Farmyard manure is the oldest, and is still undoubtedly the most popular, of all manures. It has stood the test of long experience, and has proved its position as one of the most important of all our fertilisers. It is highly desirable, therefore, to make a somewhat detailed examination of its composition, and to see on what the variation in this depends; and, finally, to examine into the mode of its action as a manure.

That it should prove a valuable manure is scarcely to be wondered at, as it is originally formed from vegetable substance, and as it therefore contains all the elements present in the plant itself.

Its composition is very variable, and probably no two samples would yield exactly similar analyses. In this fact lies one of the chief difficulties of the treatment of the subject, and all statements made in the following pages as to its chemical composition must be taken as only approximate.

We may divide its constituents into three classes.

1. That portion due to solid excreta.

2. The liquid portion, largely made up of dilute urine.

3. The straw, or other material, which is used as litter.

The composition of the manure will vary according to the proportion in which these three substances are present, as well as according to the composition of the substances themselves. It will consequently tend to a clearer apprehension of the subject if we first examine briefly the chemical composition of the solid excreta and urine of the farm animals.

1. Solid Excreta.

The manurial value of the solid excreta of animals—i.e., the proportion they contain of nitrogen, phosphoric acid, and potash—depends on a variety of conditions.

The solid excreta of horses, sheep, cows, and pigs, are well known to possess different properties, as well as to vary in their composition.

What, however, has a still greater influence is the nature of the food. This is owing to the fact that the solid excreta are made up of undigested food. We can scarcely expect the same quality of solid excreta from an animal fed on poor diet as from an animal fed on very much richer diet. Again, the percentage of the food voided in the solid excreta varies in the case of different animals.[131]

Another consideration which enters into the question is the age, as well as the treatment, of the animal. A young animal, during the period of its growth, absorbs from its food into its system a larger quantity of the three fertilising substances, nitrogen, phosphoric acid, and potash, than is the case with an adult animal whose weight is neither increasing nor diminishing. A working horse, similarly, will return more of the nitrogen, phosphates, and potash in its dung than one not at work and which is permitted to gain in weight. The nature of the composition of the solid excreta, therefore, will depend on the nature of the food, age, breed, condition, and treatment of the animal.

Let us now investigate shortly the influence of the above considerations. The solid excrements of the common farm animals are generally distinguished from one another according to the rate at which they decompose or ferment on keeping. Thus horse-dung is generally known as a "hot" dung; while cow-dung, on the other hand, is known as "cool." Why this should be so is not absolutely clear. Probably it is owing to the fact that the former contains less water, as well as to the fact (and this probably has more to do with it) that it contains a larger percentage of fertilising matter, especially nitrogen, thus affording conditions more favourable for rapid fermentation than in the case of the more moist and less rich cow-dung.

The composition of the solid excreta of various animals, as we have just said, varies with the nature of their food; so that it is impossible to take any analyses as absolutely representing its composition. It may be interesting, however, to compare the analyses of samples of horse-dung with those of some other of the commoner farm animals, with a view to obtaining an approximate idea of this difference.

Stoeckhardt has found that in 1000 lb. of the fresh solid excreta of the animals below mentioned, there were the following amounts of nitrogen, phosphoric acid, and alkalies:—

-+ + -+ -+ - PHOSPHORIC NITROGEN. ACID. ALKALIES. WATER. -+ -+ -+ -+ -+ - Reduced Reduced Reduced to to to -+ + -+ -+ -+ -+ -+ -+ - lb. per lb. per lb. per lb. per cent. cent. cent. cent. Horses (winter food) 760 76 5 .50 3-1/2 .35 3 .30 Cows (winter food) 840 84 3 .30 2-1/2 .25 1 .10 Swine (winter food) 800 80 6 .60 4-1/2 .45 5 .50 Sheep (2 lb. hay per diem) 580 58 7-1/2 .75 6 .6 3 .30 -+ + -+ -+ -+ -+ -+ -+ -

From the above table it will be seen that the sheep's dung contains the least percentage of water, and is richer in nitrogen and phosphoric acid than any of the other three. The percentage of alkalies, of which the most important is potash, is, however, not so large. This may be accounted for by the interesting and well-known fact that a large percentage of potash is to be found in the wool of sheep.[132]

The solid excrement of the sheep is, therefore, weight for weight, the most valuable as a manure, as it contains more nitrogen and phosphates than the others, and at the same time is much drier.

If, however, we compare the composition of the solid excreta in a dry state, we shall find that the following are the results (basing our calculation on Stoeckhardt's analyses):—

Nitrogen, Phosphoric acid, Alkalies, per cent. per cent. per cent.

Horse 2.08 1.45 1.25 Cow 1.87 1.56 0.62 Pig 3.00 2.25 2.50 Sheep 1.78 1.42 0.71

It will be seen from the above that the dry substance of the solid excreta of the pig is richest in fertilising substances. Too much stress, however, as has already been pointed out, must not be put on any single analysis, as so much depends on various conditions, especially the food.[133] The most reliable method of studying this question, therefore, is to study it in its relation to the food consumed. Wolff has calculated from numerous investigations that, with regard to the amount of solid excreta produced by the food, the following percentage of organic matter, nitrogen, and mineral substances, originally present in the dry matter of the food, is voided in the dung:—

Cow. Ox. Sheep. Horse. Average.

Organic matter 39.5 42.5 44.0 44.1 42.5 Nitrogen 47.5 33.9 46.7 32.4 40.1 Mineral substances 53.9 64.6 57.9 62.5 59.7

There is one fact to be borne in mind in estimating the manurial value of the dung of different animals—viz., that the quantity of dung voided by one animal is much greater than that voided by another. Thus the amount voided by the cow, for example, is much greater than that voided by the horse; so that, in this way, the inferior quality of the former is, to some extent, compensated for by its greater quantity.

2. Urine.

The solid excreta possess, however, very much less manurial value than the urine. The former, as already stated, are undigested food-substances: any fertilising matters which they contain are such as have failed to be digested or absorbed into the animal system. The urine, on the other hand, contains those fertilising substances which have been digested.

The amount of nitrogen and mineral matter, however, in the urine, does not represent necessarily the total amount of these substances. Thus, in the case of a growing or fattening animal, there is always a certain amount of these substances being absorbed to build up the animal tissue and put on flesh.

In this respect it will be seen that the composition of urine will vary in the same way as that of the dung. In the case of the urine, however, there is a compensating influence to be taken into account. Urine is a waste product, and there is more waste in a young than in an adult animal.

Another very important condition which determines the composition of urine is the nature of the food, especially the quantity of water drunk. This, of course, is obvious: the more water drunk, the poorer must the composition of the urine be. But here again, as in the case of the dung, this is largely compensated for by the total quantity voided—the more dilute the urine, the larger will its quantity be; so that the inferior quality is in this way made up for by its increased quantity.

Keeping in mind, then, the fact we have just stated—viz., that the composition of urine will vary according to different conditions—we may obtain an approximate idea of what its composition is from the following results of analyses by Stoeckhardt. In 1000 parts the following quantities of water, nitrogen, phosphoric acid, and alkalies were found to be present.

From the following table it will be seen that the urine of swine (containing 97 per cent of water) is much poorer in nitrogen and alkalies than is the case with the urine of the sheep, horse, or cow.[134] While this is the case, the amount of phosphoric acid it contains is greater than that contained in the sheep's urine.

-+ + -+ Phosphoric Water. Nitrogen. Acid. Alkalies. + + -+ + -+ + -+ + - Per Per Per Per Per Per Per Per 1000 cent. 1000 cent. 1000 cent. 1000 cent. parts. parts. parts. parts. -+ + -+ + -+ + -+ + - Sheep (2 lb. hay } 865 86.5 14 1.4 .5 .050 20 2.0 per diem) } Swine (winter food) 975 97.5 3 .3 1.25 .125 2 .2 Horses (hay and } 890 89.0 12 1.2 - - 15 1.5 oats) } Cows (hay and } 920 92.0 8 .8 - - 14 1.4 potatoes) } -+ + -+ + -+ + -+ + -

Phosphoric acid is present in the urine of the farm animals in the most minute traces: practically, it may be considered to be wanting in the urine of the horse and the cow, and is present only in small quantities in sheep's urine. The pig's urine, indeed, contains it in larger quantities; but the percentage is still so small as to justify the statement that the urine of the common farm animals is not a complete manure, and must be supplemented by phosphates, if it is to be used alone. The incomplete nature of urine as a manure constitutes a strong argument in favour of its being applied along with the solid excreta, which contain, as we have seen, considerable quantities of phosphoric acid. It is on this account that the drainings of rotten manure-heaps are more valuable, from a manurial point of view, than urine itself, since these contain the soluble portion of the phosphates in the solid excreta.[135] The urine of all animals, however, is not equally poor in phosphates. In the case of flesh-eating animals, such as the dog, the urine is found to contain them in considerable quantities.

The above tables show that the most valuable urine, weight for weight, is that of the sheep, as it contains the largest amount of alkalies (including potash) and nitrogen; that the urine of the horse comes next; then that of the cow; while, as has already been pointed out, that of the pig is the poorest.

In order to make our survey of the composition of urine uniform with that of the dung, let us see how the urine of the common farm animals compares in the matter of the composition of its dry substance. The following results (basing our calculations on Stoeckhardt's figures, previously given) show this:—

Nitrogen, Phosphoric acid, Alkalies, per cent. per cent. per cent.

Pig 12.0 5 8 Horse 10.9 trace 13.6 Sheep 10.4 3.7 14.9 Cow 10.0 trace 17.5

From these figures we see that the dry substance of the urine of the pig is richest in nitrogen and phosphoric acid, but poorest in alkalies, of the four common farm animals; that of the horse comes next in the amount of nitrogen it contains, but that, on the whole, there is very little difference between the horse, cow, and sheep in this respect.[136]

As in the case of the dung, this subject is best studied in relation to the food consumed. We are again indebted to Wolff's investigations for valuable information on this point. He has found that the following percentages of organic matter, nitrogen, and mineral substances, originally present in the dry matter of the food, are voided in the urine:—

Cow. Ox. Sheep. Horse. Average

Organic matter 4.0 4.4 2.0 3.3 3.4 Nitrogen 31.0 54.8 42.3 60.7 47.2 Mineral substances 43.1 34.3 41.0 37.5 39.0[137]

We have now considered briefly the composition of the solid excrements and urine of the common farm animals, and have also enumerated some of the principal causes of the variation in their composition.

The solid excreta consist, as we have seen, of undigested food, while the urine contains the manurial ingredients of the food which have been digested by the animal system.[138] The latter is, weight for weight, as a rule, very much more valuable as a manure than the former. From the table given in the Appendix[139] it will be seen that the proportions of the nitrogen and ash-constituents originally present in the food consumed, which are voided in the excrements, vary with different circumstances. Wolff, in summarising his results, points out that, as a rule, the solid and liquid excrements will contain about 46 per cent of the organic matter, 87.3 of the nitrogen, and 98.7 of mineral matter; while the experiments of Lawes and Gilbert at Rothamsted show that, with fattening oxen and sheep and with horses, more than 95 per cent of the nitrogen and 96 per cent or more of the ash-constituents are voided in the manure. The pig retains a larger proportion of the nitrogen—about 85 per cent appearing in the manure—while in the milking-cow only about 75 per cent is returned in the excrements. Generally speaking, we may say that the nitrogen originally present in the food suffers very little loss in passing through the animal system, and that, practically speaking, the ash-constituents suffer no loss whatever.

As to the distribution of the manurial ingredients, much will depend on the nature of the food. Almost invariably more than a half of the total nitrogen excreted will be found in the urine, in many cases very much more.[140] Of the mineral constituents, about a third on the average may be said to be excreted in the urine. Of this mineral matter it may be noted that nearly all the alkalies (potash and soda), or about 98 per cent, are found in the urine. Of phosphoric acid and lime, on the other hand, there are the merest traces in the urine. Horse-urine, however, is an exception with regard to lime, as it contains about 60 per cent of the lime consumed in the food. For information on the subject of pig-manure the reader is referred to Appendix, Note V.[141]

Before passing from this part of the subject, it may be desirable to place before our readers the composition of the dung and urine taken together, so that we may be able to form some idea of their relative value, weight for weight. As the nitrogen constitutes by far the most valuable portion of the manurial ingredients, it will be sufficient if we compare them as to their percentage of this ingredient.

Water, Nitrogen, Calculated on per cent. per cent. dry substance, Analyses by per cent. Sheep 67 .91 2.7 Juergensen. Horse 76 .65 2.7 Boussingault. Pig 82 .61 3.4 Boussingault. Cow 86 .36 2.6 Boussingault.

From these figures we see that, in their natural condition, the excreta of the sheep are the most valuable; those of the horse and pig coming next; while those of the cow are the poorest, containing one-third as much nitrogen as those of the sheep, and one-half as much as those of the horse and pig. This difference, however, is due almost entirely to the different percentage of water the excreta of the various animals contain in their natural state; for in the dry state they are seen to contain, with the single exception of the pig, practically the same amount.

In conclusion, then, the important points to be noticed are—

1. That in the passage of the food through the system of the common farm animals, only a very small percentage of the fertilising substances, nitrogen, phosphoric acid, and potash, is assimilated and retained in the animal body; and that, therefore, theoretically at least, the excreta should contain nearly the same amount of fertilising matter as the food originally did.

2. That even in the case of a fattening animal, the loss of fertilising matter sustained by the food in passing through the system is not great.

3. That with regard to the total amount of solid excreta and urine voided, the latter contains, as a rule, more nitrogen than the former; the nitrogen in the urine, further, being more valuable, as it is in a soluble condition.

4. That as regards the distribution of the ash-constituents, lime, phosphoric acid, and magnesia are almost entirely found in the solid excrements; while the urine contains nearly all the potash.

5. That the best results can be expected only when the liquid and solid excreta are used together as a manure.

As the composition of the manure depends so largely on the nature of the food, a table will be found in the Appendix, Note VI.,[142] containing the manurial composition of some of the commoner feeding-stuffs.

3. Litter.

We have now to consider the third constituent of farmyard manure—viz., the litter, which generally consists of straw.

The uses of the litter, in addition to providing a dry and comfortable bed for the animal, may be briefly summed up as follows:—

1. To absorb and retain the liquid portion of the excreta.

2. To increase the quantity of the manure, and thus secure its more equal distribution when applied to the field than could otherwise be done.

3. To add to its value as a manure, both physically and chemically.

4. To retard and regulate the decomposition of the excreta.

Of course litter also performs a very useful function sanitarily, inasmuch as it serves to keep the stall or byre fresher and cleaner, and more free from noxious gases, which it absorbs, than would otherwise be the case.

Straw is almost universally used for this purpose. Besides being one of the bye-products of the farm, it is admirably suited in many ways, both owing to its peculiar shape—its tubular structure being excellently adapted for this purpose—as well as on account of its composition, being largely composed of cellulose, a very absorptive substance. Straw thus possesses considerable absorptive power. In manurial ingredients it is not very rich; for, of the various parts of the ripened plant, straw contains the least percentage of nitrogen and phosphates. This is due to the fact that, as the straw ripens, a considerable proportion of these ingredients passes up from the stalk to the seeds, where they are retained.

Generally speaking, straw may be said to contain not more than a half per cent of nitrogen—i.e., 11.2 lb. per ton. Its percentage of nitrogen varies, of course; the recorded analyses[143] for wheat-straw ranging from .22 to .81 per cent, or furnishing an average of .48 per cent—i.e., 10.75 lb. per ton. Barley-straw is somewhat richer in nitrogen, the recorded analyses ranging from .41 to .85 per cent, or giving an average of .57 per cent—i.e., 12.76 lb. per ton; while oat-straw is the richest of the commoner straws, ranging from .32 to 1.12 per cent, an average of .72 per cent—i.e., 16.12 lb per ton.

Of mineral matter, however, straw contains a very much larger percentage, proportionally, than of nitrogen; for, with the exception of phosphates, there is a considerable quantity of inorganic fertilising matter, in the shape of potash, lime, &c., present in

Composition of Straw.[144] -+ -+ + Ash. Composition of Ash. + + + + Lb. per ton. Lb. -+ + - Number Per per Potash. Phosphoric Lime. of cent. ton. Acid Analyses -+ + + -+ + -+ Wheat (winter) 5.54 124.09 18.61 5.05 7.18 8 Wheat (summer) 5.14 115.13 25.76 6.47 7.12 6 Rye (winter) 5.33 119.39 20.61 5.89 9.73 8 Rye (summer) 6.14 137.53 42.41 6.73 10.53 1 Barley 4.90 109.76 26.83 5.75 8.73 8 Oats 5.09 114.01 26.22 4.17 9.12 4 -+ + + -+ + -+

it. Of total ash ingredients, on an average, there are generally about 5 per cent—or 112 lb. per ton. The largest percentage of the fertilising matter in this 5 per cent is potash, which varies in the ashes of the straws of the commoner crops from 30 to 15 per cent. The above table will show the variation in composition of the straws of some of the commoner farm crops, and may be valuable for purposes of reference. The crops are wheat (winter and summer), barley, oats, and rye (winter and summer), and the amount is also calculated in lb. per ton. The results represent the average of a number of analyses.[145] From the table it will be seen that the percentage of phosphates is, as has already been noticed, very small.

But while straw is well adapted for the purposes for which litter is used, it is not the only substance. Its almost exclusive use as litter is largely owing to the fact that it is a bye-product of the farm.

Loam as Litter.—Generally speaking, any substance which has great absorptive as well as retentive powers for nitrogen and the soluble fertilising matters present in farmyard manure, and whose price is nominal, is well suited for acting as litter. Ordinary loamy soil possesses the above qualifications, and is, besides, a substance to be had for nothing, and, under certain circumstances and in certain countries, is actually used for this purpose, often along with straw. A great objection against loam, however, is that it forms a dirty litter. Moreover, it possesses a very small percentage of fertilising matter. The tendency, consequently, in using ordinary loam, would be to dilute the manure too much, besides retarding fermentation to an undesirable extent. Except, therefore, under very exceptional circumstances, loam is not to be regarded as a good litter.

Peat as Litter.—Some kinds of soil, however, are well suited for this purpose. Of these, the best are those rich in organic matter, the so-called peaty soils. Peat, when dried and freed from any earthy matter, forms an excellent absorbent of the liquid portion of the manure, surpassing in this respect straw itself. It is, further, generally very much richer in nitrogen—some peats having been found to contain between 4 and 5 per cent of nitrogen. In some thirty samples of peat analysed by Professor S. W. Johnson, the percentage of nitrogen varied from .4 to 2.9, giving an average of 1.5 per cent.

While it has a very great capacity for absorbing liquids, it possesses in an unequalled degree the power of retaining the soluble nitrogen compounds. This is undoubtedly one of the most important properties which recommend peat for the purposes of litter.[146]

Some interesting experiments on the value of peat-moss as a litter have been recently carried out by Dr Bernard Dyer.[147] From these experiments Mr Dyer has found that both its liquid-absorbing and liquid-retaining powers are very much greater than those of straw. While straw was only able to absorb three times its weight of water, peat-moss was found to absorb nearly ten times its weight. With regard to its water-retaining power, this was also found to be in excess of that of straw. Both these properties are, it need scarcely be pointed out, of very great value in a litter. Another point of interest in these experiments was the respective amounts of nitrogen absorbed and retained by the peat-moss and the straw. It was found that, in this respect, the peat-moss had again an advantage over the straw. Lastly, the manure produced by the peat-moss was shown to be richer in fertilising matter than that produced by the use of straw.[148] These experiments are interesting as demonstrating the fact that in peat-moss we have a substance which is capable of acting as an excellent substitute for the more costly straw, and which might increasingly be used as a fodder with great benefit to the farmer.

Another substance which has been suggested as an excellent litter is the common bracken-fern. According to some analyses made by Mr John Hughes, the bracken, especially if cut in a young state, is a substance of considerable manurial value. When dried, it is very much richer in nitrogen, potash, and lime than straw. Its absorbent properties, however, are probably not so great. Where it can easily and cheaply be had, as in many parts of Scotland and Ireland, it might well be used for littering purposes.[149]

Dried leaves have also been used as a litter. Autumn leaves, however, contain a very small percentage of fertilising matter. This is due to the fact that the most of their potash, phosphoric acid, and nitrogen pass into the body of the trees at the approach of winter. According to Professor Storer, dried leaves only contain from .1 to .5 per cent potash,.006 to .3 per cent phosphoric acid, and about .75 per cent of nitrogen. Leaves, however, besides being poor in manurial ingredients, make a bad litter, as they ferment but slowly. There is in this fermentation a large quantity of cold sour humic acid formed, which seriously impairs the value of the manure.[150]

Having now considered the composition of the three separate ingredients of farmyard manure—viz., the dung or solid excreta, the urine, and the litter—we are in a position to consider the composition of farmyard manure. In this connection it will be well to consider separately the manures produced by the different farm animals.

1. Horse-manure.

The composition of horse-manure is perhaps the most uniform of all the manures produced by the different farm animals. This is due to the fact that the food of the horse is generally of the same kind, consisting of oats, hay, and straw.

The total excrements voided by a horse in a day have been calculated, according to the average of experiments by Boussingault and Hofmeister, at 28.11 lb., of which only 6.37 lb. consisted of dry matter.[151] These 28.11 lb. contained .18 lb. of nitrogen and .92 lb. of mineral matter. The amount of straw necessary to absorb this amount of excrement may be stated at from 4 to 6 lb. The amounts of nitrogen and mineral matter in 4 lb. of straw are .01 and .23 lb. respectively. The total amount of nitrogen and ash, therefore, in the farmyard manure produced by a horse in one day, would be .19 lb. nitrogen and 1.15 lb. mineral matter; or, if we take the larger quantity of straw, somewhat more.

Taking these figures, we find that the amount of manure produced by a horse in a year will be from 11,720 to 12,450 lb. (i.e., from 5-1/4 to 5-1/2 tons),[152] containing from 69 to 73 lb. nitrogen, and from 420 to 460 lb. mineral matter.[153]

A word or two may be of value regarding the treatment in the stable of horse-manure. The great object to be aimed at is the prevention of loss of valuable fertilising constituents. This loss may be due to two causes. It may be, in the first place, caused by drainage of the soluble matter of the manure; or secondly, it may be due to volatilisation of the volatile constituents.

The first of these two sources of loss depends on the precautions taken in the way of providing a proper impervious flooring to the stable. This source of loss is extremely difficult to prevent, inasmuch as nearly all materials used for flooring absorb a certain percentage of urine. The judicious use of litter, however, will minimise this loss to within a trifling extent.

Dr Heiden states that the amount of straw used as litter for the horse in Germany is from 4 to 6 lb. per day. The quantity should be regulated according to the percentage of water the excreta contain; the more watery excreta requiring naturally a larger quantity of litter. The most eminent authorities on this subject recommend that the amount of litter should equal one-fourth of the food in its natural state, or about one-third of its dry substance.

The second source of loss, which is due to volatilisation of the volatile ingredients, may be largely prevented by the use of certain preservatives.

Horse-dung being, comparatively speaking, of a dry nature, it is extremely difficult to effect its thorough mixture with the litter. For this reason the manure formed from horse excreta is particularly liable to rapid fermentation.[154] In the process of fermentation, as will be seen more in detail further on, the nitrogen is converted into carbonate of ammonia. As nitrogen in this form is of an extremely volatile nature, the risks of loss from this source are considerable. As illustrating this fact, it may be mentioned that Boussingault has found by experiment that the total percentage of nitrogen contained by fresh horse-manure might be reduced in the process of fermentation to one-half of its original amount by loss from this source.

The preservatives used to prevent this volatilisation are technically known as "fixers." This they do by chemically combining with the volatile ammonia and forming non-volatile compounds with it.

Of the acid fixers, hydrochloric and sulphuric acids have been recommended. The former, however, is not well suited for this purpose. It is a strongly fuming acid, and when brought into contact with ammonia forms dense white fumes. The use of sulphuric acid is not open to this objection. Sulphate of ammonia, the salt formed in this case, is one of the most stable (or least volatile) of the compounds of ammonia. If used, it should be largely diluted with water, and the whole mixed with sand. Such a mixture, when sprinkled over the stable-floor in even very small quantities, has been found to effectually prevent any loss of the volatile carbonate of ammonia.

It is not, however, on the whole advisable to use an acid substance as a fixer, since such a substance may act deleteriously on the horses' hoofs.

Such substances as gypsum, copperas, and sulphate of magnesia, while equally efficient, are not open to this objection. The above-mentioned substances owe their efficacy to the fact that they are compounds of sulphuric acid, which, by combining with the volatile ammonia and forming sulphate of ammonia, prevent its escape.

Gypsum, or sulphate of lime, although, comparatively speaking, an insoluble substance, when brought in contact with carbonate of ammonia has been proved to effect the conversion of the ammonia into sulphate of ammonia. It is also believed to retard the decomposition of the manure.[155] Copperas, or ferrous sulphate, while a soluble salt, and while thus acting in a more speedy manner in fixing the ammonia, is not so well suited, owing to the hurtful influence it is well known to possess on plant-life. It is only right to remember that there may be circumstances in which copperas may, in small quantities, act even beneficially as a manure, as Griffiths' experiments would seem to indicate. The above objection, however, cannot be urged against sulphate of magnesia. In addition to fixing the ammonia, sulphate of magnesia may very probably fix the soluble phosphoric acid. Kainit, which consists of a mixture of sulphates and chlorides of potassium and magnesium, has also been suggested for this purpose. By using such a fixer, the value of the resulting manure would be much enhanced. In conclusion, it must be remembered that all the above-named fixers act very much in the same way—viz., by converting the volatile carbonate of ammonia into sulphate of ammonia.[156]

2. Cow-manure.

The composition of the manure formed from the excrementitious matter of the cow is very much less constant than is the case in the horse-manure. An average statement of that composition is therefore very much more difficult to obtain. The number of analyses available for the purpose of forming this average is, however, very large. The manure produced by cows contains a large percentage of water. This is due to the large quantity of water they drink. It has been estimated that milch-cows drink along with their winter food, for every pound of dry substance, 4 lb. of water, and in summer about 6 lb.

According to some experiments by Boussingault, the excrements of a cow in a day amounted to 73.23 lb., of which only 9.92 lb. were dry matter.[157] These excrements contained .256 lb. of nitrogen and 1.725 lb. of mineral matter. The amount of straw necessary to use as litter for this amount of excrements may be taken at 6 to 10 lb. The manure, therefore, formed by a cow per day, would contain from .274 to .286 lb. of nitrogen, and from 2.046 to 2.278 lb. of mineral matter. In a year this would amount to from 100 to 104.4 lb. of nitrogen, and from 746.8 lb. to 831.5 lb. of mineral matter; or from 6 cwt. 75 lb. to 7 cwt. 47 lb.

Cow-dung is, owing to its more watery nature and poorer quality, very much slower in its fermentation than horse-dung. When applied alone, cow-manure is very slow in its action, and makes its influence felt for at least three or four years. It is difficult to spread it evenly over the soil, owing to the fact that, when somewhat dried, it has a tendency to form hard masses, which, when buried in the soil, may resist decomposition for a very long period. The cause of this is due to the presence of a considerable amount of mucilaginous and resinous matter in the solid excreta, which prevents the entrance of moisture and air into the centre of the mass. This tendency of cow-manure to resist decomposition will be greatly lessened in the case of the excrements of a cow richly fed.

The risks of loss of volatile ammonia are, therefore, in its case not so great as we have seen them to be in the case of the "hot" horse-dung. Notwithstanding this fact, much of what has been said on the use of preservatives for horse-manure may be also applied to the cow-dung. This is owing to the fact that the dung is allowed to accumulate in the court for some time. The amount of straw it is advisable to use as litter varies, as has been said, from 6 to 10 lb. per day. The best method of calculating this amount, according to Dr Heiden, is by taking one-third of the total weight of the dry substance of the food. The above authority also recommends that the straw is best applied in blocks of about one foot in length; and this for the following reasons:—

1. The strewing of it is more convenient.

2. The absorption of the fluid portion is more complete.

3. The cleaning out of the manure from the byre is easier.

4. The manure is more easily distributed when applied to the field.

Among the advantages incidental to allowing the manure to accumulate in the court may be mentioned the following:—

1. The more thorough absorption of the urine by the straw, and, consequently, the more uniform mixture which will be thus effected of the more valuable urine with the less valuable solid excreta.

2. A certain retardation of decomposition effected by the treading under foot of the manure.

3. The protection of the manure from rain and wind, and the securing of a uniform temperature.

Against those advantages must be placed the risk of seriously affecting the health of the animal. Although this is a point of very great importance, it scarcely falls within the scope of this work. It may be pointed out, however, that the judicious use of some of the chemical fixers previously referred to may do much to keep the air of the byre or court free of noxious gases.[158]

3. Pig-manure.

The food of the pig is so very variable in its character that it is wellnigh impossible to obtain anything like an average analysis of its excrements. When the food of the pig is rich, then the manure may be quite equal in quality to the other manures. According to Boussingault, the total amount of excrements, on an average, voided by a pig in twenty-four hours is about 8.32 lb., of which 1.5 lb. is dry matter.[159] The amount of nitrogen these excrements contain is only .05 lb., and of mineral ingredients .313 lb. If we take the amount of straw most suitable for absorbing this quantity of excrementitious matter at from 4 to 8 lb., then we shall find that the manure produced by a pig will contain from .06 to .074 lb. nitrogen and .545 to .772 lb. mineral matter. These quantities, calculated for a year, give from 22 to 27 lb. of nitrogen, and from 1 cwt. 87 lb. to 2 cwt. 57 lb. of mineral matter. That is about as much nitrogen as would be contained in 1-1/4 to 1-1/2 cwt. of nitrate of soda (95 per cent purity); or from slightly less than 1 cwt. to slightly over 1 cwt. of sulphate of ammonia (97 per cent purity).