il, such as loosening stiff clays, compacting light sands,
pulverizing large particles, etc.

[What are the three kinds of manures?

What are organic manures, and what are their uses? Mineral?
Atmospheric?]

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.

[What rule should regulate the application of manures?

How must organic manures be managed? Atmospheric?]

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.

MECHANICAL CULTIVATION.

CHAPTER I.

THE MECHANICAL CHAR