MANURES. Substances added to the I soil, with a view of accelerating vegeta tion, and increasing the production of the crops. Animal, vegetable, and mineral substances are used for this purpose. Decomposing animal matter of any kind forms one of the most powerful manures, and in many instances accelerates the decay and decomposition of inert vege table matters mixed with it ; as in the mixture of dung and straw which forms the common offal of stables. All animal excrements are also powerful manures, and, when duly applied to the soil, soon exhibit their influence by the luxuriance of the crop. It, however, often happens, in respect to esculent vegetables, that their quality is deteriorated, and that they acquire a coarse and rank flavor if over-manured ; as is the case with much of the produce of the market-gardens near large cities, where in consequence of the vicinity, manure is abundant, and luxuriant and fine-looking vegetables in great request for the table.
In all cases where animal manures are used, care should be taken that they are brought into action upon the soil as soon as they begin to decompose, or as soon as possible afterwards, and not suffered to rot, and exhale their best constituent parts while lying in the farm-yard. The drainings and the exhalations of a com mon dung-heap contain its most effective ingredients ; and these are often suffered to go to waste, or to contaminate the air and collect in pools of filth. The fresh and the old manure of this decomposi tion are known to farmers under the terms long and short dung : the advan tages and economy of the former, when properly applied, cannot be doubted. Those animal manures which are slow of decornpositon are most durable, and gen erally most effective in their operation. Of these, the best is ground bones, the animal part of which is very gradually dissolved out by moisture ; so that their effect is long-continued, and their earthy matter is also, probably, beneficial, at least to many crops. Vegetable manures are often very effective,. especially as in the case of ploughing in a green crop, where all the soluble matters are brought into action ; and inert vegetable sub stances may be rendered active by mix ture with those which easily putrefy, or with animal matter. Some vegetables, such as cabbages and many other cruci form plants, approximate to animal mat ter in their composition, and are propor tionately good manures. Mineral man urea act in two ways : either by their causticity, as is the case with quicklime, by which they decompose most organic bodies, such as roots, fibres, &c., and render them soluble and nutritious to the growing crop ; or they alter the texture of the soil. Thus, sand may be called a manure for clayey lands, and clay and loam for those that are sandy. Upon the same principle, stiff soils are improved by paring and burning, by which a superficial sandiness is produced, and the texture of the soil rendered more appro priate for vegetation.
The principle on which manures act has only been fully understood since chemistry has lent its aid to agriculture. When crops grow upon soils they re move a certain portion of mineral mat ters, which, if not replaced, leave that ground deficient, and a constant course of cropping with one plant will remove nearly, if not all, the substances which the plant requires out of the soil. The crop will every year diminish, till ulti mately it does not return its seed. Such is the case of Virginia with tobacco cul tivation, and many parts of the south with cane culture. The ground so treat ed is not perfectly barren, for it will grow other crops •, and if these be planted and removed without any addition to the ground, the latter becomes permanently sterile. This is the condition of much of the land in Europe, which is cultivated by those who have no real interest in the good of the soil; and it is the condition toward which much of the land of New England and the Atlantic States is ap proaching from ignorance and careless farming. Now, to restore those mineral
substances, which have been removed by a crop or a rotation, is the object of manuring, and a manure ought always be looked upon as certain substances added for the supply of the wants of the crop. The soil does not require addition or improvement, except so far as it min isters to the wants of the plant. Hence the folly of using only one variety of manure for various kinds of crops. All plants do not require lime ; hence con stant liming is unnecessary, and constant farm manure, withont other additions, is equally absurd. The manure should Con tain those things which the crop or the ro tation requires. It should contain the ex act chemical salts, and sufficient to supply the deficiency which the crop produces. To know what manures to apply, it is necessary to know what minerals plants abstract, and this is learned by a chemical analysis of the crop. There are now an alyses made of most of the cultivated plants, from which data special manures may be deduced—the application of which is more certain and economical than the old fashioned mode. This sub ject of special manures is but in its in fancy ; and analyses of American plants, made by trustworthy chemists, are ex tensively required, until which be done little absolute exactitude can be obtained. It is in this line that a bureau of agricul ture at Washington could act most effici ently. Plants do not remove more than 14 elements out of the soil, and, there fore, comparatively few substances are required to be added as manure. These are silica, lime, magnesia, oxide of iron, potash, soda, ammonia, sulphuric, phos phoric, and carbonic acids. To supply i these in the cheapest and most effective forms is the object of the farmer. Silica i always exists in ground in sufficient quantity. Lime is added either as caustic hme, or as compost with farm sweepings, or as marl, which is an impure carbonate, with a little phosphate and sulphate. Gypsum supplies lime with sulphuric acid, and bones or yhosphorite supplies lime with phosphonc acid, as phosphate of lime. Guano also supplies phosphate of lime, but the chief object of guano is to supply ammonia by decomposition. The value of bones is much increased by acting on it with sulphuric acid, forming i what is called dissolved bones. The use of bones and guano are the two greatest modern improvements in agriculture. Potash is absolutely required by some plants, as maize and oats, and may be added in the form of pearlash or nitre. Cow-dung contains salts of potash, and much of it depends upon the presence of the potash. Some plants prefer potash when they can have a selection, otherwise they appear to thrive just as well on soda. This fact of substitution is not fully understood in agriculture ; in prac tice we do know that one substance will replace another in the plant without in jury. This resembles isomorphism in minerals very much. Potash and soda have a remarkable effect in developing the leaf and other green parts of plants. The nitrates of potash and soda exert a wonderful influence in this way. It is not easy to say how much is due to the acid, and how much to the alkaline element. Unleached ashes is always preferable to the leached. Ammonia is the most pow erful stimulant to all plants, and is requir ed by them. The salts of ammonia are gen erally too expensive, and hence the use of those substances which supply it by decomposition. Animal matters, urine, i excrement, wool, hair, horn, guano, and the gelatine in bones all act in this way, and that is the most efficient manure which decomposes most readily, and affords the ammonia most quickly. Night-soil is a most powerful manure, but it is disliked on account of its un pleasant odor—this, however, is gotten rid of by mixing it with fresh burned charcoal. Fish, along shore, forms a most valuable manure for corn or potatoes, and is fully equal to guano. Sea-weed is ben eficial on account of the large quantity of saline matters which it adds to the ground.