Manures have two distinct classes of action in the soil, namely, chemical and mechanical.

Chemical manures are those which enter into the construction of plants, or produce such chemical effects on matters in the soil as shall prepare them for use.

Mechanical manures are those which improve the mechanical condition of the soil, such as loosening stiff clays, compacting light sands, pulverizing large particles, etc.

Manures are of three distinct kinds, namely, Organic, mineral, and atmospheric.

Organic manures comprise all vegetable and animal matters (except ashes) which are used to fertilize the soil. Vegetable manures supply carbonic acid, and inorganic matter to plants. Animal manures supply the same substances and ammonia.

Mineral manures comprise ashes, salt, phosphate of lime, plaster, etc. They supply plants with inorganic matter. Their usefulness depends on their solubility.

Many of the organic and mineral manures have the power of absorbing ammonia arising from the decomposition of animal manures, as well as that which is brought to the soil by rains—these are called absorbents.

Atmospheric manures consist of ammonia, carbonic acid, oxygen and water. Their greatest usefulness requires the soil to allow the water of rains to pass through it, to admit of a free circulation of air among its particles, and to contain a sufficient amount of absorbent matter to arrest and retain all ammonia and carbonic acid presented to it.

Manures should never be applied to the soil without regard to its requirements.

Ammonia and carbon are almost always useful, but mineral manures become mere dirt when applied to soils not deficient of them.

The only true guide to the exact requirements of the soil is chemical analysis; and this must always be obtained before farming can be carried on with true economy.

Organic manures must be protected against the escape of their ammonia and the leaching out of their soluble parts. One cord of stable manure properly preserved, is worth ten cords which have lost all of their ammonia by evaporation, and their soluble parts by leaching—as is the case with much of the manure kept exposed in open barn-yards.

Atmospheric manures cost nothing, and are of great value when properly employed. In consequence of this, the soil which is enabled to make the largest appropriation of the atmospheric fertilizers, is worth many times as much as that which allows them to escape.

SECTION FOURTH.