The Elements of Agriculture Part 11

3. It gives it greater power to absorb moisture.

4. It renders it warmer.

1. Carbon (or charcoal) makes the soil retentive of manures, because it has in itself a strong power to absorb, and retain[R] fertilizing matters. There is a simple experiment by which this power can be shown.

Ex.--Take two barrels of pure beach sand, and mix with the sand in one barrel a few handfuls of charcoal dust, leaving that in the other pure.

Pour the brown liquor of the barn-yard through the pure sand, and it will pa.s.s out at the bottom unaltered. Pour the same liquor through the barrel, containing the charcoal, and pure water will be obtained as a result. The reason for this is that the charcoal retains all of the impurities of the liquor, and allows only the water to pa.s.s through.

Charcoal is often employed to purify water for drinking, or for manufacturing purposes.

[Will charcoal purify water?

If a piece of tainted meat, or a fishy duck be buried in a rich garden soil, what takes place?

What is the reason of this?

How does charcoal overcome offensive odors?

How can you prove that charcoal absorbs the _mineral_ impurities of water?]

A rich garden-soil contains large quant.i.ties of carbonaceous matter; and, if we bury in such a soil a piece of tainted meat or a fishy duck, it will, in a short time, be deprived of its odor, because the charcoal in the soil will entirely absorb it.

Carbon absorbs gases as well as the impurities of water; and, if a little charcoal be sprinkled over manure, or any other substance, emitting offensive odors, the gases escaping will be taken up by the charcoal, and the odor will cease.

It has also the power of absorbing _mineral_ matters, which are contained in water. If a quant.i.ty of salt water be filtered through charcoal, the salt will be retained, and the water will pa.s.s through pure.

We are now able to see how carbon renders the soil retentive of manures.

1st. Manures, which resemble the brown liquor of barn-yards, have their fertilizing matters taken out, and retained by it.

[How does charcoal in the soil affect the manures applied?

Why does charcoal in the soil cause it to appropriate the gases of the atmosphere?

What fertilizing gases exist in the atmosphere?

How are they carried to the soil?

Does the carbon retain them after they reach the soil?

What can you say of the air circulating through the soil?

How does carbon give the soil power to absorb moisture?]

2d. The gases arising from the decomposition (_rotting_) of manure are absorbed by it.

3d. The soluble mineral portions of manure, which might in some soils leach down with water, are arrested and retained at a point at which they can be made use of by the roots of plants.

2. Charcoal in the soil causes it to appropriate larger quant.i.ties of the fertilizing gases of the atmosphere, on account of its power, as just named, to absorb gases.

The atmosphere contains results, which have been produced by the breathing of animals and by the decomposition of various kinds of organic matter, which are exposed to atmospheric influences. These gases are chiefly ammonia and carbonic acid, both of which are largely absorbed by water, and consequently are contained in rain, snow, etc., which, as they enter the soil, give up these gases to the charcoal, and they there remain until required by plants. Even the air itself, in circulating through the soil, gives up fertilizing gases to the carbon, which it may contain.

3. Charcoal gives to the soil power to absorb moisture, because it is itself one of the best absorbents in nature; and it has been proved by accurate experiment that peaty soils absorb moisture with greater rapidity, and part with it more slowly than any other kind.

[How does it render it warmer?

Is the heat produced by the decomposition of organic matter perceptible to our senses?

Is it so to the growing plant?

What is another important part of the organic matter in the soil?]

4. Carbon in the soil renders it warmer, because it darkens its color.

Black surfaces absorb more heat than light ones, and a black coat, when worn in the sun, is warmer than one of a lighter color. By mixing carbon with the soil, we darken its color, and render it capable of absorbing a greater amount of heat from the sun's rays.

It will be recollected that, when vegetable matter decomposes in the soil, it produces certain gases (carbonic acid, etc.), which either escape into the atmosphere, or are retained in the soil for the use of plants. The production of these gases is always accompanied by _heat_, which, though scarcely perceptible to our senses, is perfectly so to the growing plant, and is of much practical importance. This will be examined more fully in speaking of manures.

[How is it obtained by the soil?

What offices does the organic matter in the soil perform?]

Another important part of the organic matter in the soil is that which contains _nitrogen_. This forms but a very small portion of the soil, but it is of the greatest importance to vegetables. As the nitrogen in food is of absolute necessity to the growth of animals, so the nitrogen in the soil is indispensable to the growth of cultivated plants. It is obtained by the soil in the form of ammonia (or nitric acid), from the atmosphere, or by the application of animal matter. In some cases, manures called _nitrates_[S] are used; and, in this manner, nitrogen is given to the soil.

We have now learned that the organic matter in the soil performs the following offices:--

Organic matter thoroughly decomposed is _carbon_, and has the various effects ascribed to this substance on p. 79.

Organic matter in process of decay produces carbonic acid, and sometimes ammonia in the soil; also its decay causes heat.

Organic matter containing _nitrogen_, such as animal substances, etc., furnish ammonia, and other nitrogenous substances to the roots of plants.

FOOTNOTES:

[Q] Produce.

[R] By absorbing and retaining, we mean taking up and holding.

[S] Nitrates are compounds of nitric acid (which consists of nitrogen and oxygen), and alkaline substances. Thus nitrate of potash (saltpetre), is composed of nitric acid and potash: nitrate of soda (cubical nitre), of nitric acid and soda.

CHAPTER III.

USES OF INORGANIC MATTER.

[What effect has clay besides the one already named?

How does it compare with charcoal for this purpose?]