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 pa.s.s _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 a.n.a.lysis_; 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 CHARACTER OF SOILS.

[What is the first office of the soil?

How does it hold water for the uses of the plant?

How does it obtain a part of its moisture?]

The mechanical character of the soil is well understood from preceding remarks, and the learner knows that there are many offices to be performed by the soil aside from the feeding of plants.

1. It admits the roots of plants, and holds them in their position.

2. By a sponge-like action, it holds water for the uses of the plant.

3. It absorbs moisture from the atmosphere to supply the demands of plants.

[How may it obtain heat?

What is the use of the air circulating among its particles?

Could most soils be brought to the highest state of fertility?

What is the first thing to be done?

Should its color be darkened?]

4. It absorbs heat from the sun's rays to a.s.sist in the process of growth.

5. It admits air to circulate among roots, and supply them with a part of their food, while the oxygen of that air renders available the minerals of the soil; and its carbonic acid, being absorbed by the water in the soil, gives it the power of dissolving, and carrying into roots more inorganic matter than would be contained in purer water.

6. It allows the excrement.i.tious matter thrown out by roots to be carried out of their reach.

All of these actions the soil must be capable of performing, before it can be in its highest state of fertility. There are comparatively few soils now in this condition, but there are also few which could not be profitably rendered so, by a judicious application of the modes of cultivation to be described in the following chapters.

The three great objects to be accomplished are:--

1. To adopt such a system of drainage as will cause all of the water of rains to pa.s.s _through_ the soil, instead of evaporating from the surface.

2. To pulverize the soil to a considerable depth.

3. To darken its color, and render it capable of absorbing atmospheric fertilizers.

[Name some of the means used to secure these effects.

Why are under-drains superior to open drains?]

The means used to secure these effects are _under-draining, sub-soil and surface-plowing, digging, applying muck, etc._

CHAPTER II.

UNDER-DRAINING.

The advantages of _under_-drains over _open_ drains are very great.

When open drains are used, much water pa.s.ses into them immediately from the surface, and carries with it fertilizing parts of the soil, while their beds are often compacted by the running water and the heat of the sun, so that they become water-tight, and do not admit water from the lower parts of the soil.

The sides of these drains are often covered with weeds, which spread their seeds throughout the whole field. Open drains are not only a great obstruction to the proper cultivation of the land, but they cause much waste of room, as we can rarely plow nearer than within six or eight feet of them.

There are none of these objections to the use of under-drains, as these are completely covered, and do not at all interfere with the cultivation of the surface.

[With what materials may under-drains be constructed?

Describe the tile.]

Under drains may be made with brush, stones, or tiles. Brush is a very poor material, and its use is hardly to be recommended. Small stones are better, and if these be placed in the bottoms of the trenches, to a depth of eight or ten inches, and covered with sods turned upside down, having the earth packed well down on to them, they make very good drains.