Human urine has been accurately examined by Berzelius, although his estimate of the proportion of urea is generally admitted to be above the average. His analysis gives the following numbers:—

Among the special organic constituents of the urine are three substances, urea, uric acid, and hippuric acid, which are of much importance in a manurial point of view. The first of these is found in considerable quantity in the urine of all animals, but is especially abundant in the carnivora. Uric acid is found only in these animals, and is the most remarkable constituent of the excrement of birds, serpents, and many of the lower animals. Hippuric acid is most abundant in the herbivora. These substances are all highly nitrogenous. They contain—

They are extremely prone to change, and in presence of animal matters readily ferment, and are converted into salts of ammonia. Thus human urine, which, at the time of emission is free from smell of ammonia, and has a slightly acid reaction, becomes highly ammoniacal if it be kept for a few days. This is due to the conversion of urea into carbonate of ammonia; and the same change takes place, though more slowly, with uric and hippuric acids.

It is obvious, from the foregoing analyses, that great differences must exist in the manurial value of the urine of different animals. Not only do they vary greatly in the proportion of solid matters which they contain, but also in the kind and quantity of their nitrogenous constituents. They differ also in regard to their saline ingredients; and while salts of potash and soda form the principal part of the ash of the urine of the ox, sheep, goat, and horse, and phosphoric acid and phosphates are entirely absent, that of the pig contains a considerable quantity of the latter substances, and in this respect more nearly resembles the urine of man. Human urine is also much richer in urea and nitrogenous constituents generally, and has a higher value than any of the others.

It is especially worthy of notice that the urine of the purely herbivorous animals (with the exception of the sheep, which contains a small quantity), are devoid of phosphates and urea; and consequently, when employed alone, they are not general manures—a matter of some importance in relation to the subject of liquid manuring, which will be afterwards discussed.

Dung.—The solid excrement of animals is equally variable in composition. That of the domestic animals which had the ordinary winter food was found to have the following composition:—

100 parts of ash contained—

Human fæces contain about 75 per cent of water; and their dry residue was found by Way to have the following composition:—

In a sample analyzed by myself there were found—

It is to be observed that the urine and dung of animals differ conspicuously in the composition of their ash, the former being characterized by the abundance of alkaline salts, while the latter contains these substances in small proportion, but is rich in earthy matters, and especially in phosphoric acid. Salts of potash, for example, form nine-tenths of the inorganic part of the urine of the ox, while less than three per cent of that alkali is found in its dung. Phosphoric acid, on the other hand, is not met with in the urine, but forms about ten per cent of the dung. Silica is the most abundant constituent of the dung, but a large proportion of that found on analysis has been swallowed in the shape of grains of sand and particles of soil mechanically mixed with the food, although part is also derived from the straw and grains, which contain that substance in great abundance. The difference in the quantity of nitrogen they contain is also very marked, and is distinctly shown by the following analyses by Boussingault, which give the quantity of carbon, hydrogen, nitrogen, oxygen, and ash in the dung and urine of the horse and the cow in their natural state, and after drying at 212°.

Hence, weight for weight, the urine of the horse, in its natural state, contains three times as much nitrogen as its dung; that of the cow twice as much; and the difference, especially in the horse, is still more conspicuous when they are dry.

It is obvious that the quality of farm-yard manure must depend—1. On the kind of animal from which it is produced; 2. On the quantity of straw which has been used as litter; 3. On the nature of the food with which the animals have been supplied; 4. On the extent to which its valuable constituents have been rendered available by the treatment to which it has been subjected; and 5. On the care which has been taken to prevent the escape of the urine, or of the ammonia produced by its decomposition.

The composition of farm-yard manure has engaged the attention of several chemists; but there are still many points on which our information regarding it is less complete than might be desired. Its investigation is surrounded with peculiar difficulties, not merely on account of its complexity, but because its properties render it exceedingly difficult to obtain a sample which fairly represents its average composition. In the case of long dung, these difficulties are so great that it is scarcely possible to overcome them; and hence, discrepancies are occasionally to be met with in the analyses of the most careful experimenters. The most minute and careful analyses yet made are those of Voelcker, who has compared the composition of fresh and rotten dung, and studied the changes which the former undergoes when preserved in different ways. He employed in his experiments both fresh and rotten dung, and subjected them to different methods of treatment. His analyses are given in the accompanying table, in which column 1 gives the composition of fresh long dung, composed of cow and pig dung. 2. Is dung of the same kind, after having lain in a heap against a wall, but otherwise unprotected from the weather for three months and eleven days in winter, during which time little rain fell. 3. The same manure, kept for the same time under a shed. 4. Well rotten dung, which had been kept in the manure heap upwards of six months. 5. The same, after having lain against a wall for two months and nine days longer.

On examining and comparing these analyses, it appears that the differences are by no means great, although, on the whole, they tend to show that, weight for weight, well-rotten dung is superior to fresh, provided it has been properly treated. Not only is the quantity of valuable matters existing in the soluble state materially increased, whereby the dung is enabled to act with greater rapidity, but, owing to evaporation and the escape of carbonic acid, produced by the decomposition of the organic substances, the proportion of those constituents which are most important to the plant is increased. This is particularly to be noticed, in regard to the nitrogen, which has distinctly increased in all cases in which the dung has been kept for some time; and the practical importance of this observation is very great, because it has been commonly supposed that, during the process of fermentation, ammonia is liable to escape into the air. It would appear, however, that there is but little risk of loss in this way, so long as the dung-heap is left undisturbed; and it is only when it is turned that any appreciable quantity of ammonia volatilizes. It is different, however, with the action of rain, which soon removes, by solution, a considerable quantity of the nitrogen contained in farm-yard manure; and the deterioration must necessarily be most conspicuous in rotten dung, which sometimes contains nearly half of its nitrogen in a soluble condition. The effect produced in this way is conspicuously seen, by the results of weighings and analyses of small experimental dung-heaps, made by Dr. Voelcker at different periods. The subjoined table shows the composition of the heap, lying against a wall, and exposed to the weather at different periods:—

In this case, during the winter six months, which were very dry, the manure lost 541·8 lbs. of water and 270·2 lbs. of dry matter, but the nitrogen remained completely unchanged. But during the succeeding semi-annual period, when rain fell abundantly, the quantity of nitrogen is diminished by nearly a third, while the water has increased, and the loss of dry matter by fermentation, notwithstanding the high temperature of the summer months, was only 182·4 lbs. The soluble mineral matters also, which increased during the first period, are again reduced during the second, until they also fall to about two-thirds of their maximum quantity. That this effect is to be attributed to the solvent action of rain is sufficiently obvious, from a comparison of the results afforded by the other heaps, which had been kept under cover during the same period, as shown below.

The loss of nitrogen is here comparatively trifling, and during the whole year, but little exceeds two pounds, of which the greater part escapes during the first six months, and the soluble inorganic matters are almost unchanged. The total weight of the manure, however, undergoes a very great reduction, due chiefly to evaporation of water, but in part also to the loss of organic matters evolved in the form of carbonic acid during fermentation.

When the manure is spread out, as it is usually found under cattle in open yards, the deterioration is very great, a quantity thus treated having lost, in the course of a year, nearly two-thirds of its nitrogen, and four-fifths of its soluble inorganic matters.

The general conclusion deducible from these analyses is that, provided it be carefully prepared, farm-yard manure does not differ very largely in value, although the balance is in favour of the well-rotten dung. This result is in accordance with that obtained by other experimenters, who have generally found from 0·5 to 0·6 per cent of nitrogen, and 1 or 2 per cent of phosphates. But when carelessly managed, it may fall greatly short of this standard, as is particularly seen in a sample examined by Cameron, which had been so effectually washed out by the rain, as to retain only 0·15 per cent of ammonia. These cases, however, are exceptional, and well made and well preserved farm-yard manure will generally be found to differ comparatively little in value; and when bought at the ordinary price, the purchaser, as we shall afterwards more particularly see, is pretty sure to get full value for his money, and the specialities of its management are of comparatively little moment to him. But the case is very different when the person who uses the manure has also to manufacture it. The experiments already quoted have shown that, though the manure made in the ordinary manner may, weight for weight, be as valuable as at first, the loss during the period of its preservation is usually very large, and it becomes extremely important to determine the mode in which it may be reduced to the minimum.

In the production of farm-yard manure of the highest quality, the object to be held in view is to retain, as effectually as possible, all the valuable constituents of the dung and urine. But in considering the question here, it will be sufficient to refer exclusively to its nitrogen, both because it is the most important, and also because the circumstances which favour its preservation are most advantageous to the other constituents. In the management of the dung-heap, there are three things to be kept in view:—First, To obtain a manure containing the largest possible amount of nitrogen; secondly, To convert that nitrogen more or less completely into ammonia; and thirdly, To retain it effectually.

As far as the first of these points is concerned, it must be obvious that much will depend on the nature and quantity of the food with which the animals yielding the dung are supplied, and the period of the fattening process at which it is collected. When lean beasts are put up to feed, they at first exhaust the food much more completely than they do when they are nearly fattened, and the manure produced is very inferior at first, and goes on gradually improving in quality as the animal becomes fat.

When the food is rich in nitrogenous compounds, the value of the manure is considerably increased. It has been ascertained, for instance, that when oil-cake has been used, not less than seven-eighths of the valuable matters contained in it reappear in the excrements; and as that substance is highly nitrogenous, the dung ought, weight for weight, to contain a larger amount of that element. That it actually does so, I satisfied myself by experiments, made some years since, when the dung and urine of animals fed on turnips, with and without oil-cake, were examined; but unfortunately, no determination of the total quantity of the excretions could be made, so that it was impossible to estimate the increased value. It has been commonly supposed that when cattle are fed with oil-cake, the increased value of the manure is equal to from one-half to two-thirds the price of the oil-cake; but this is a rather exaggerated estimate as regards linseed-cake, although it falls short of the truth in the case of rape, as we shall afterwards more particularly see.

Although it may be possible, in this way, to increase the quantity of nitrogen as a manure, there is a limit to its accumulation, due to the fact, that it is contained most abundantly in the urine, which can only be retained by the use of a sufficient supply of litter. Where that is deficient, the dung-heap becomes too moist, and the fluid and most valuable part drains off, either to be lost, or to be collected in the liquid manure-tank. In the well managed manure-heap, the quantity of litter should be sufficient to retain the greater part of the liquid manure, and to admit of only a small quantity draining from it, which should be pumped up at intervals, so as to keep the whole in a proper state of moisture. Attention to this point is of great moment, and materially affects the fermentation. When it is too moist or too dry, that process is equally checked; in the former case by the exclusion of air, which is essential to it; and in the latter, by the want of water, without which the air cannot act. The exact mode in which the manure is to be managed must greatly depend on whether the supply of litter is large or small. In the latter case the urine escapes, and is collected in the liquid manure-tank, and must be used by irrigation, and in some cases this mode of application has advantages, but in general, it is preferable to avoid it, and have recourse to substances which increase the bulk of the heap sufficiently to make it retain the whole of the liquid. For this purpose, clay, or still better, the vegetable refuse of the farm, such as weeds, ditch cleanings, leaves, and, in short, any porous matters, may be used. But by far the best substance, when it can be obtained, is dry peat, which not only absorbs the fluid, but fixes the ammonia, by converting it more or less completely into humate. Reference has been already made to the absorbent power of peat in the section on soils, but it may be mentioned here that accurate experiment has shown that a good peat will absorb about 2 per cent[L] of ammonia, and when dry will still retain from 1 to 1·5 per cent, or nearly twice as much as would be yielded by the whole nitrogen of an equal weight of farm-yard manure. Peat charcoal has been recommended for the same purpose, but careful experiment has shown that it does not absorb ammonia, although it removes putrid odour; and though it may be usefully employed when it is wished to deodorize the manure heap, it must not be trusted to for fixing the ammonia.

Much stress has frequently been laid on the advantage to be derived from the use of substances capable of combining chemically with the ammonia produced during the fermentation of dung and gypsum, sulphate of iron, chloride of manganese, sulphate of magnesia, and sulphuric acid, have been proposed for this purpose, and have been used occasionally, though not extensively. They all answer the purpose of fixing the ammonia, that is, of preventing its escaping into the air; but the risk of loss in this way appears to have been much exaggerated, for a delicate test-paper, held over a manure-heap, is not affected; and during fermentation, humic acid is produced in such abundance, as to combine with the greater part of the ammonia. The real source of deterioration is the escape of the soluble matters in the drainings from the manure-heap, which is not prevented by any of these substances; and where no means are taken to preserve or retain this portion, the loss is extremely large, and amounts, under ordinary circumstances, to from a third to a half of the whole value of the manure. Manure, therefore, cannot be exposed to the weather without losing a proportion of its valuable matters, depending upon the quantity of rain which falls upon it. Hence it is obvious that great advantage must be derived, especially in rainy districts, from covered manure-pits. This plan has been introduced on some farms with good effect; but the expense and doubts as to the benefits derived from it, have hitherto prevented the practice becoming general. The principal difficulty experienced in the use of the covered dung-pit is, that, where the litter is abundant, the urine does not supply a sufficiency of moisture to promote the active fermentation of the dung, and it becomes necessary to pump water over it at intervals; but when this is properly done, the quality of the manure is excellent, and its valuable matters are most thoroughly economized.

Although covered dung-pits have been but little used, their benefits have been indirectly obtained by the method of box-feeding, one of the great advantages of which is held to be the production of a manure of superior quality to that obtained in the old way. In box-feeding none of the dung or urine is removed from under the animals, but is trampled down by their feet, and new quantities of litter being constantly added, the whole is consolidated into a compact mass, by which the urine is entirely retained. Whatever objection may be taken to this system, so far as the health of the animals is concerned, there is no doubt as to the complete economy of the manure, provided the quantity of litter used be sufficient to retain the whole of the liquid. But its advantage is entirely dependent on the possibility of fulfilling this condition.

Whether box manure is really superior to that which can be prepared by the ordinary method is very questionable, but it undoubtedly surpasses a large proportion of that actually produced. It is more than probable, however, that the careful management of the manure-heap would yield an equally good product. It is manifest that the same number of cattle, fed in the same way, on the same food, and supplied with the same quantity of litter, must always excrete the same quantities of valuable matters; and the only question to be solved is, whether they are more effectually preserved in the one way than the other? It will be readily seen that this cannot be done by analysis alone, but that it is necessary to conjoin with it a determination of the total weight of manure produced; for though, weight for weight, box manure may be better than ordinary farm-yard manure, the total quantity obtained by the latter method, from a given number of cattle, may be so much greater, that the deficiency in quality may be compensated for. At the present time our knowledge is too limited to admit of a definite opinion on this subject, but it is highly deserving of the combined investigation of the farmer and the chemist.

Supposing the conditions which produce the manure containing the largest quantity of nitrogen to have been fulfilled, we have now to consider those which affect its evolution in the form of ammonia. This change is effected by fermentation. When a quantity of manure is left to itself it becomes hot, and gradually diminishes in bulk, and if it be turned over after some time, the smell of ammonia may be more or less distinctly observed. This ammonia is produced, in the first instance, from the urine, the nitrogenous constituents of which are rapidly decomposed, and the fermentation thus set up in the mass of manure extends first to the solid dung, and then to the straw of the litter, and gradually proceeds until a large quantity of ammonia is produced.

When fresh manure is deposited in the soil, the same changes occur, but they then proceed more slowly, and experience has shown that a much smaller effect is produced on the crop to which it has been applied than when it has been well fermented in the heap. This effect is consistent with theory, which would further indicate that well-fermented dung must be especially advantageous when applied to quick-growing crops, and less necessary to those which come slowly to maturity. As a rule, well fermented manure is to be preferred, provided it has been well managed and carefully prepared; but when this has not been done, and the manure has been exposed to the weather, or made in open courts or hammels, the economic advantages are all on the side of the fresh dung. It may be questioned also whether, now that there are so many other available sources of ammonia, it may not in many instances be advantageous to use the dung fresh, conjoined with a sufficient quantity of some salt of ammonia, or other substance fitted to supply the quantity of that element necessary for the requirements of the crop.

After the farm-yard manure has been prepared at the homestead, it is often necessary to cart it out to the field some time before it is to be applied, and it is a question of some importance to determine how it may be best preserved there. The general practice is to store it in heaps in the corners of the fields, but some difference of opinion exists as to whether it should be lightly thrown up so as to leave it in a porous state, and so promote its further fermentation, or whether it should be consolidated as much as possible by driving the carts on to the top of the heap during its construction. Considering the risks to which the manure is exposed on the field, the latter plan would appear to be the best. It is advisable also to interstratify the dung with dry soil, so as to absorb any liquid which may tend to escape from it, and it should also be covered with a well-beaten layer of earth, in order to exclude the rain. Although these precautions must not be omitted if the manure is to be stored in heaps, it will probably be often found quite as advantageous to spread it at once, and leave it lying on the surface until it is convenient to plough it. The loss of ammonia by volatilization will, under such circumstances, especially in the cold season of the year, be very trifling, and the rain which falls will only serve to incorporate the soluble matters with the soil, where they will be retained by its absorptive power.

In the actual application of the manure to the crop, several points require consideration. It is especially important to determine whether it ought to be uniformly distributed through the soil, or be kept near the roots of the plants. Both systems have their advocates, and each has advantages in particular cases. The choice between the two must greatly depend upon the nature of the crop and the soil. When the former is of a kind which spreads its roots wide and deep through the soil, the more uniformly the manure can be distributed the better; but when it is used with plants whose roots do not travel far, it is more advantageous to accumulate it near the seeds. Obvious advantages also attend this practice in soils which are either too heavy or too light. When, for example, it is necessary to cultivate turnips in a heavy clay, the manure put into the drills produces a kind of artificial soil in the neighbourhood of the plants, in which the bulbs expand more readily than in the clay itself. On the other hand, when a large quantity of dung, in a state of active fermentation, comes into immediate contact with the roots, its effect is not unfrequently injurious. These and many other points, which will readily suggest themselves to any one who studies the composition and properties of farm-yard manure, belong more strictly to the subject of practical agriculture, and need not be enlarged on here.

In the present state of agriculture, a proper estimate of the money value of farm-yard manure is of much importance in an economic point of view, and many matters connected with the profitable management of a farm must hinge upon it. If an estimate be made upon the principle which will be explained when we come to treat of artificial manures, it appears that fresh farm-yard manure of good quality is worth from 12s. to 15s. per ton, and well-rotted dung rather more. It is questionable, however, whether the system of valuation which is accurate in the case of a guano or other rapidly acting substance, is applicable to farm-yard manure, the effects of which extend over some years. A deduction must be made for the years during which the manure remains unproductive, and also for the additional expense incurred in carting and distributing a substance so much more bulky than the so-called portable manures, and it would not be safe to estimate its value at more than 7s. or 8s. per ton.

Liquid Manure.—This term is applied to the urine of the animals fed on the farm, and to the drainings from the manure-heap, which, in place of being returned to it, are allowed to flow away, and collected in tanks, from which they are distributed by a watering-cart, or according to the method recently introduced in Ayrshire, and since adopted in other places, by pipes laid under-ground in the fields, and through which the manure is either pumped by steam-power, or, where the necessary inclination can be obtained, is distributed by gravitation. That liquid manure must necessarily be valuable, is an inference which maybe at once drawn from the analyses of the urine of different animals already given, and of which it chiefly consists. In addition to the urine, however, it contains also the soluble organic and mineral matters of the dung, as well as a quantity of solid matters in suspension, among which phosphates are found, and thus it possesses a supply of an element which would be almost entirely deficient if it were composed of urine alone. In the following analyses by Professor Johnston, No. 1 is the drainings of the manure-heap when exposed to rain; and No. 2 the same, when moistened with cows' urine pumped over it, the results being expressed in grains per gallon:—