SECTION II.—OF DIGESTED ANIMAL MANURES.
Practical men have long been of opinion that the digestion of food, either animal or vegetable,—the passing of it through the bodies of animals,—enriches its fertilizing power, weight for weight, when added to the land. Hence, in causing animals to eat up as much of the vegetable productions of the farm as possible, it is supposed that not only is so much food saved, but that the value of the remainder in fertilizing the land is greatly increased. In a subsequent section we shall see how far theory serves to throw light upon these opinions. ([See Section IV., p. 182 to 186].)
I. LIQUID EXCRETIONS.
The digested animal substances usually employed as manures are, the urine of the cow and the sheep, the solid excrements of the horse, the cow, the sheep, and the pig, the droppings of pigeons and other birds, and night-soil. The liquid manures act chiefly through the saline substances they hold in solution, while the solid manures contain also insoluble matters, which decay slowly in the soil, and there become useful only after a time. The former, therefore, will influence vegetation more powerfully at first; the action of the latter will be less evident, but will continue to operate for a much longer period.
Urine.—Human urine consists, in 1000 parts, of
| Water, | 932 |
| Urea, and other organic matters containing nitrogen, | 49 |
| Phosphates of ammonia, lime, soda, and magnesia, | 6 |
| Sulphates of soda and ammonia, | 7 |
| Sal ammoniac and common salt, | 6 |
| 1000 |
A thousand pounds of urine therefore contain 68 lbs. of dry fertilizing matter of the richest quality, worth, at the present rate of selling artificial manures in this country, at least 20s. a cwt. As each person voids almost 1000 lb. of urine in a year, the national waste incurred in this form amounts, at the above valuation, to 12s. a head. And if five tons of farm-yard manure per acre, added year by year, will keep a farm in good heart, four cwt. of the solid matter of urine would probably have an equal effect; or the urine alone discharged into the rivers by a population of 10,000 inhabitants would supply manure to a farm of 1500 acres, yielding a return of 4500 quarters of corn or an equivalent produce of other crops.
The urine of the cow is said to contain less water than that of man, though of course much must depend upon the kind of food with which it is fed. Reckoning, then, the large quantity of liquid manure that is yielded by the cow (2000 or 3000 gallons a year), we may safely estimate the solid matter given off by a healthy animal in this form in twelve months at 1200 to 1500 pounds weight, worth, if it were in the dry state, from £10 to £12 sterling. In the liquid state, the urine of one cow collected and preserved as it is in Flanders, is valued in that country at about £2 a year. Any practical farmer may calculate for himself, therefore, how much real wealth, taking it even at the Flemish value, is lost in his own farm-yard—how much of the natural means of reproductive industry passes into his drains or evaporates into the air.
This liquid manure is invaluable, when collected in tanks, for watering the manure and compost heaps, and thus hastening their decomposition; but great part of it may also be sprinkled directly upon the fields of grass and upon the young corn, with the best effects. It must, however, be permitted to stand till fermentation commences, and afterwards diluted with a considerable quantity of water, before it will be in the best condition for laying on the land.
Urate.—In order to obtain the virtues of animal urine in a concentrated form, the custom has been adopted of mixing burnt gypsum with it, in the proportion of 10 lbs. to every 7 gallons, allowing the mixture, occasionally stirred, to stand some time, pouring off the liquid, and drying and crushing the gypsum. This is sold by manure manufacturers under the name of urate. It never can possess, however, the virtues of the urine, since it does not contain the soluble saline substances, which the gypsum does not carry down with it. Except the gypsum, indeed, 100 lbs. of urate contain no greater weight of saline and organic matter than 10 gallons of urine. If it be true, then, as the manufacturers state, that 3 or 4 cwt. of urate are sufficient manure for an acre, the practical farmer will, I hope, draw the conclusion,—not that it is well worth his while to venture his money in trying a portion of it upon a piece of his land,—but that a far more promising adventure will be to go to some expense in saving his own liquid manure, and, after mixing it with burned gypsum, to lay it abundantly upon all his fields.
II. SOLID EXCRETIONS.
Cow and Horse Dung.—So much of the saline, nutritive, and soluble organic matters from the cow pass off in the liquid form, that cow dung is correctly called cold, since it does not readily heat and run into fermentation. Mixed with other manures, however, or well diffused through the soil, it aids materially in promoting vegetation. The horse being fed generally on less liquid food, and discharging less urine, yields a hotter and richer dung, which, however, answers best also when mixed with other varieties. The dung of the swine is soft and cold, like that of the cow, containing, like it, at least 75 per cent. of water. As this animal lives on more varied food than any other reared for the use of man, the manure obtained from it is also very variable in quality. Applied alone, as a manure to roots, it is said to give them an unpleasant taste, and even to injure the flavour of tobacco. It answers best for hemp, and, it is said, also for hops; but, mixed with other manures, it may be applied to any crop.
Night-soil is probably the most valuable, and yet, in Europe at least, the most disliked and neglected of all the solid animal manures. It varies no doubt in richness with the food of the inhabitants of each district,—chiefly with the quantity of animal food they consume,—but when dry, no other solid manure, weight for weight, can probably be compared with it in general efficacy. It contains much soluble and saline matter, and as it is made up from the constituents of the food we eat, of course it contains most of those elementary substances which are necessary to the growth of the plants on which we principally live.
Attempts have been made to dry this manure also, so as to render it more portable,—to destroy its unpleasant smell, so as to reconcile practical men to a more general use of it,—and by certain chemical additions, to prevent the waste of ammonia and other volatile substances, which are apt to escape and be lost when this and other powerful animal manures begin to putrify through decay. In Paris, Berlin, and other large cities, the night-soil, dried first in the air with or without a mixture of gypsum or lime, then upon drying plates, and finally in stoves, is sold under the name of poudrette, and is extensively exported in casks to various parts of the country. In London also it is dried with various mixtures, while in others of our large towns an animalized charcoal is prepared by mixing and drying night-soil with gypsum and ordinary wood charcoal in fine powder.
The half-burned peat above described ([p. 80],) would answer well for such a purpose, while few simple and easily attainable substances would make a better compost with night-soil, and more thoroughly preserve its virtues, than half-dry peat or rich vegetable soil, mixed with more or less marl or gypsum. It is impossible to estimate the proportion of waste which this valuable manure undergoes by being allowed to ferment, without mixture, in the open air.
Taffo.—In China it is kneaded into cakes with clay, which are dried in the air, and, under the name of taffo, form an important article of export from all the large cities of the empire.
Pigeons’ Dung.—The dung of all birds is found to possess eminent fertilizing virtues. Some varieties are stronger than others, or more immediate in their action, and all are improved for the use of the farmer by being some time kept, either alone or in compost. In Flanders the manure of one hundred pigeons is considered worth 20s. a year for agricultural purposes.
Guano is the name given by the natives of Peru to the dung of sea-fowl, which in former periods used to be deposited in vast quantities on the rocky shores and isles of the Peruvian coast. The numerous shipping of modern times has disturbed and driven away many of the sea-fowl, so that comparatively little of their recent droppings is now preserved or collected. Ancient heaps of it, however, still exist in many places, more or less covered up with drifted sand, and also more or less decomposed. These are now largely excavated for exportation, not only to different parts of the coast of Peru, as seems to have been the case from the most remote periods, but also to Europe, and especially to England. It is at present sold at 20s. a cwt. in this country, and is capable of entirely replacing farm-yard dung,—that is to say, turnips may be manured successfully with guano alone;—but it has not yet been satisfactorily determined that the English farmer can afford to use it in this way to any extent, at the price now asked for it.
The dung of birds possesses the united virtues of both the liquid and solid excretions of other animals. It contains every part of the food of the bird, with the exception of what is absolutely necessary for the support and for the right discharge of the functions of its own body. It is thus fitted, therefore, to return to the plant a greater number of those substances on which plants live, than either the solid or the fluid excrements of other animals; in other words, to be more nourishing to vegetable growth.
SECTION III.—OF THE RELATIVE GROWTH OF
THE DIFFERENT ANIMAL MANURES.
The fertilizing power of animal manures, in general, is dependent, like that of the soil itself, upon the happy admixture they contain of a great number, if not of all, those substances which are required by plants in the universal vegetation of the globe. Nothing they contain, therefore, is without its share of influence upon their general effects, yet the amount of nitrogen present in each affords the readiest and most simple criterion by which their agricultural value, compared with that of vegetable matters and with that of each other, can be pretty nearly estimated.
In reference to their relative quantities of nitrogen, therefore, they have been arranged in the following order, the number opposite to each representing the weight in pounds which is equivalent to or would produce the same sensible effect upon the soil as 100 lbs. of farm-yard manure.
It is probable that the numbers in this table do not err very widely from the true relative value of these different manures, in so far as the organic matter they severally contain is concerned. The reader will bear in mind, however,
1. That the most powerful substances in this table, woollen rags, for example,—2½ lbs. of which are equal in virtue to 100 lbs. of farm-yard manure,—may yet shew less immediate sensible effect upon the crop than an equal weight of sheep’s dung, or even of urine. Such dry substances are long in dissolving and decomposing, and continue to evolve fertilizing matter, after the softer and more fluid manures have spent their force. Thus, while farm-yard manure or rape dust will immediately hasten the growth of turnips, woollen rags will come into operation at a later period, and prolong their growth into the autumn.
2. That besides their general relative value, as represented in the above table, each of these substances has a further special value not here exhibited, dependent upon the kind and quantity of saline and other inorganic matter which they severally contain. Thus three of dry flesh are equal to five of pigeons’ dung, in so far as the organic part is concerned; but the latter contains also a considerable quantity of bone-earth and of saline matter scarcely present at all in the former. Hence pigeons’ dung will benefit vegetation in circumstances where dry flesh would in some degree fail. So the liquid excretions contain much important saline matter not present in the solid excretions,—not present either in such substances as horn, wool, and hair,—and, therefore, each must be capable of exercising an influence upon vegetation peculiar to itself.
Hence the practical farmer sees the reason why no one simple manure can long answer on the same land; and why in all ages and countries the habit of employing mixed manures and artificial composts has been universally diffused.
SECTION IV.—NATURAL DISTINCTION OR DIFFERENCE
BETWEEN ANIMAL AND VEGETABLE MANURES,
AND THE CAUSE OF THIS DIFFERENCE.
In what do animal manures differ from vegetable manures,—what is the cause of this difference,—how does the digestion of vegetable matter improve its value as a manure?
1. The characteristic distinction between animal and vegetable manures is this,—that the former contain a much larger proportion of nitrogen than the latter. This will be seen at once, by comparing together the tables given in the two preceding sections, in which the numbers represent the relative agricultural values of certain animal and vegetable substances compared with farm-yard manure. The lowest numbers represent the highest value, and the largest amount of nitrogen, and these low numbers are always opposite to the purest animal substances.
2. In consequence of containing so much nitrogen, animal substances are further distinguished by the rapidity with which, when moist, they putrify or run to decay. During this decay the nitrogen they contain gradually assumes the form of ammonia, which is perceptible by the smell, and which, when proper precautions are not taken, is apt in great part to escape into the air. Hence the loss by fermenting manure too completely,—or without proper precautions to prevent the escape of volatile substances. And as animal manure, when thus over-fermented, or permitted to lose its ammonia into the air, is found much less active upon vegetation than before; it is reasonably concluded, that to this ammonia, chiefly, their peculiar virtue, when rightly prepared, is in a great measure to be ascribed.
Vegetable substances do not decay so rapidly,—do not emit the odour of ammonia when fermenting,—nor, when prepared in the most careful way, does vegetable manure exhibit the same remarkable action upon vegetable life as is displayed by almost every substance of animal origin.
3. Whence do animal substances derive all this nitrogen? Animals live only upon vegetable productions containing little nitrogen; can they then procure all they require from this source alone? Again, does the act of digestion produce any chemical alteration upon the food of animals, that their excretions should be a better manure,—should be richer in nitrogen than the substances on which they feed? Does theory throw any light upon the opinion generally entertained among practical men upon this point?
These two apparently distinct questions will be explained by a brief reference to one common natural principle.
Animals have two necessary vital functions to perform,—to breathe and to digest. Both are of equal importance to the health and general welfare of the animal. The digester (the stomach) receives the food, melts it down, extracts from it what is best suited to its purposes, and conveys it into the blood. The breathers (the lungs) sift the blood thus mixed up with the newly digested food, combine oxygen with it, and extract carbon,—which carbon, in the form of carbonic acid, they discharge by the mouth and nostrils into the air.
Such is a general description of these two great processes,—their effect upon the food that remains in the body and has to be rejected from it, is not difficult to perceive.
Suppose an animal to be full grown. Take a full grown man. All that he eats as food is intended merely to renovate or replenish his system, to restore that which is daily removed from every part of his body by natural causes. In the full grown state, every thing that enters the body must come out of the body in one form or another. The first part of the food that escapes is that portion of its carbon that passes off from the lungs during respiration. This quantity varies in different individuals—chiefly according to the quantity of exercise they take. From 5 to 9 ounces a day is the average quantity, though in periods of violent bodily exertion 13 to 15 ounces of carbon are breathed out in the form of carbonic acid.
Suppose a man to eat a pound and a half of bread and a pound of beef in 24 hours, and that he gives off by respiration 8 ounces of carbon (3500 grains) during the same time. Then he has
| Carbon. | Nitrogen. | |||
| Taken, in his food, | about | 4500 | grains, and | 500 grs. while |
| He has given off in |  | 3500 | and little | or no nitrogen, |
| respiration, | ||||
| Leaving to be converted |  | 1000 | grs. and | 500 grs. |
| into food, or to | ||||
| be rejected, | ||||
Our two conclusions, therefore, are clear. The vegetable food, by respiration, is freed from a large portion of its carbon, which is discharged into the air,—nearly the whole of the nitrogen remaining behind. In the food consumed the carbon was to the nitrogen as 9 to 1; in that which remains, after respiration has done its work, the carbon is to the nitrogen in the proportion of only 2 to 1.
It is out of this residue, rich in nitrogen, that the several parts of animal bodies are built up. Hence the reason why they can be formed from food poor in nitrogen, and yet be themselves rich in the same element.
It is this same residue also which, after it has performed its functions within the body, is discharged again in the form of solid and liquid excretions. Hence the greater richness in nitrogen,—the greater fertilizing power of the dung of animals than of the food on which they live.
Two other remarks I shall add for the benefit of the practical man.
1. The manure of the cow, taking it mixed, is not so rich in nitrogen as that of man,—because the cow in the stall, large though it be, and great the bulk of food it consumes, does not give off much more carbon by respiration than an active full grown man. Hence the proportion of carbon in the excretions of this animal is greater than in those of man. The dry manure is richer than the dry food, weight for weight, but not in the same proportion as if the cow respired a quantity of carbon more nearly corresponding to its bulk, when compared with the weight of carbon thrown off from the lungs of man.
2. Since the parts of animals—their blood, muscles, tendons, and the gelatinous portion of the bones—contain much nitrogen, young beasts which are growing, must appropriate to their own use, and work up into flesh and bone, a portion of the nitrogen contained in the non-respired part of their food. But the more they thus appropriate, the less will pass off into the fold-yard; and hence it is natural to suppose that the manure, either liquid or solid, which is prepared where many growing cattle are fed, will not be so rich as that which is yielded by full grown animals. I am not aware how far this deterioration has been observed in practice, but it may with some degree of certainty be expected to take place,—unless by giving a richer food to the young cattle, the difference to the farm-yard be made up.[18]