MANURE. Every substance which has been used to improve the natural soil, or to restore to it the fertility which is diminished by the crops annually carried away, has been included in the name of manure. Thus chalk, marl, clay, and even sand, when added to the soil for the purpose of improving its texture, have been called manures ; and some confusion has arisen in our ideas in consequence of applying the same word to signify things which are essentially different. The French have a term by which they distinguish the substances which merely improve the mechanical texture of the soil from those which act more directly in nourishing the plants which grow in it. The former of these they call amendments, and the latter morals.
It is well known to all practical agriculturists that the texture of the soil and the proportions of the earths of which it is composed are the first and most important conditions of its productive powers. When there is a good natural loam which retains moisture without becoming wet or overcharged with it, and permits the influence of the atmos pheric air to pervade it, the crops cannot fail to be more certain and remunerating than in loose sands or tenacious clays, however rich they may be in those substances which are supposed to supply the elements from which the juices of plants are chiefly composed. But, at the same time, it is equally true that tho best textuio of soil will not pro duce good crops for any length of time without the help of some other rich manure to recruit the loss produced by vegetation.
The various means of improving the texture, such as tillage and the mixture of earths, are treated of separately. [LOAM; MARL; SOIL; TILLAGE.] We shall here confine our observations to that class of manures which stimulate or enrich the soil.
There are some substances which evidently belong to both classes of manure. Of these, lime, either in its caustic state of quick-lime or its milder form of a carbonate or chalk, is the principal. Lime, being an earth less porous than sand, and more so than clay, has an improving effect on soils in which either sand or clay prevails ; but it has also a chemical effect as an alkaline earth ; and, considered in this light, it acts on the soil in a peculiar manner, and greatly assists the effect of enriching manures, which are all of animal or vegetable Lime as a manure acts most powerfully in its caustic state—that is, when deprived of the carbonic acid which is generally united with it. The carbonic acid is expelled by the heat of the kiln, and limestone is by this means reduced to the state of quick-lime, in which it has so strong an attraction for moisture and carbonic acid, that, if it be left exposed to the atmosphere for any length of time, it absorbs both from it, and gradually returns to the state of hydrate and carbonate, or lime united with water and carbonic acid, with this difference, that it is now a fine impalpable powder, instead of a bard stone.
Among the purposes it serves, and besides its use as a direct food of plants, are those comprised in its relations to the dormant and mis chievous ingredients of soils ; its power to detach serviceable alkaline matters from useless positions in the soil ; its power to induce the decomposition of vegetable matter there ; its power to decompose and render harmless mineral and metallic salts of a mischievous character ; its uses in detaching ammonia from comparatively insoluble compounds of it, and so presenting portions ready for immediate use by the plant ; its influence in possibly increasing the power of soils to absorb ammonia from the air.
Besides all this, its influence on the texture of the soil, on the growth of weeds, on the general fertility of the land, on the growth especially of particular crops, on the health and soundness more especially of the turnip crop, should be also named.
The use of frequent limings in small doses, as compared with larger dressings at longer intervals, depends on the quantity of vegetable matter in the soil, but the larger dressings are generally to be preferred, on the grounds that in practice the full influence of a liming is not seen until after several • years, and that the abundant fertility which, when lime is properly used, is consequent upon its use, may, when rightly managed, be made to reproduce itself, and so become permanent. The abuses to which it is liable are, chiefly, its application to soils deficient in vegetable matter, and its application along with manure rich in ammoniacal matters. But a distinction may be drawn between rotten dung and recent farm manure in this respect,—the application of hot lime along with the former being waste ful, but along with the latter by no means uneconomical. There are many modes of applying lime, as slaked or unslaked,—in compost with vegetable matter of any kind, or directly to the land, ploughed in deep or shallow, in quantities of 40 or of 240 bushels per acre,—pre viously to a corn crop or a green crop,—on a corn or clover stubble, etc. One of the best rules of practice is, to apply it where thee is the -greatest quantity of undecomposed vegetable fibre in the soil ; and, acting on this rule, the best time in the rotation for the application of lime is on the clover stubble or the grass layer previous to ploughing it up for a grain crop.