The Elements of Agriculture Part 34

CHAPTER IV.

SUB-SOIL PLOWING.

[Describe the Mapes plow.

Why is the motion in the soil of one and a half inches sufficient?

How does the oxidation of the particles of the soil resemble the rusting of cannon b.a.l.l.s in a pile?]

The _sub-soil plow_ is an implement differing in figure from the surface plow. It does not turn a furrow, but merely runs through the subsoil like a mole--loosening and making it finer by lifting, but allowing it to fall back and occupy its former place. It usually follows the surface plow, entering the soil to the depth of from twelve to eighteen inches below the bottom of the surface furrow.

The best pattern now made (the Mapes plow) is represented in the following figure.

[Ill.u.s.tration: Fig. 8.

The Mapes plow and its mode of action. _a_--Shape of the foot of the plow, _b_--Its effect on the soil.]

The sub-soil plows first made raised the whole soil about eight inches, and required very great power in their use often six, eight, or even ten oxen. The Mapes plow, raising the soil but slightly, may be worked with much less power, and produces equally good results. It may be run to its full depth in most soils by a single yoke of oxen.

Of course a motion in the soil of but one and a half inches is very slight, but it is sufficient to move each particle from the one next to it which, in dry soils, is all that is necessary. Whoever has examined a pile of cannon-b.a.l.l.s must have observed that at the points where they touch each other, there is a little rust. In the soil, the same is often the case. Where the particles touch each other, there is such a chemical change produced as renders them fit for the use of plants. While these particles remain in their first position, the changed portions are out of the reach of roots; but, if, by the aid of the sub-soil plow, their position is altered, these parts are exposed for the uses of plants. If we hold in the hand a ball of dry clay, and press it hard enough to produce the least motion among its particles, the whole ma.s.s becomes pulverized. On the same principle, the sub-soil plow renders the compact lower soil sufficiently fine for the requirements of fertility.

[Why are the benefits of sub-soiling not permanent on wet lands?

Does sub-soiling overcome drought?

How does it deepen the surface soil?]

Notwithstanding its great benefits on land, which is sufficiently dry, sub-soiling cannot be recommended for wet lands; for, in such case, the rains of a single season would often be sufficient to entirely overcome its effects by packing the subsoil down to its former hardness.

On lands not overcharged with water, it is productive of the best results, it being often sufficient to turn the balance between a gaining and a losing business in farming.

It increases nearly every effect of under-draining; especially does it overcome drought, by loosening the soil, and admitting air to circulate among the particles of the subsoil and deposit its moisture on the principle described in the chapter on under-draining.

It deepens the surface-soil, because it admits roots into the subsoil where they decay and leave carbon, while the circulation of air so affects the mineral parts, that they become of a fertilizing character.

The deposit of carbon gives to the subsoil the power of absorbing, and retaining the atmospheric fertilizers, which are more freely presented, owing to the fact that the air is allowed to circulate with greater freedom. As a majority of roots decay in the surface-soil, they there deposit much mineral matter obtained from the subsoil.

[Why is the retention of atmospheric manures ensured by sub-soiling?

Why are organic manures plowed deeply under the soil, less liable to evaporation than when deposited near the surface?

How does sub-soiling resemble under-draining in relation to the tillering of gra.s.ses?

When the subsoil consists of a thin layer of clay on a sandy bed, what use may be made of the sub-soil plow?]

The retention of atmospheric manures is more fully ensured by the better exposure of the clayey portions of the soil.

Those manures which are artificially applied, by being plowed under to greater depths, are less liable to evaporation, as, from the greater amount of soil above them, their escape will more probably be arrested; and, from the greater prevalence of roots, they are more liable to be taken up by plants.

The subsoil often contains matters which are deficient in the surface-soil. By the use of the sub-soil plow, they are rendered available.

Sub-soiling is similar to under-draining in continuing the tillering of gra.s.ses, and in getting rid of the poisonous excrement.i.tious matter of plants.

When the subsoil is a thin layer of clay on a sandy bed (as in some plants of c.u.mberland Co. Maine), the sub-soil plow, by pa.s.sing through it, opens a pa.s.sage for water, and often affords a sufficient drainage.

[To how great a depth will the roots of plants usually occupy the soil?

What is the object of loosening the soil?

How are these various effects better produced in deep than in shallow soils?]

If plants will grow better on a soil six inches deep than on one of three inches, there is no reason why they should not be benefited in proportion, by disturbing the soil to the whole depth to which roots will travel--which is usually more than two feet. The minute rootlets of corn and most other plants, will, if allowed by cultivation, occupy the soil to the depth or thirty-four inches, having a fibre in nearly every cubic inch of the soil for the whole distance. There are very few cultivated plants whose roots would not travel to a depth of thirty inches or more. Even the onion sends its roots to the depth of eighteen inches when the soil is well cultivated.

The object of loosening the soil is to admit roots to a sufficient depth to hold the plant in its position--to obtain the nutriment necessary to its growth--to receive moisture from the lower portions of the soil--and, if it be a bulb, tuber, or tap, to a.s.sume the form requisite for its largest development.

It must be evident that roots, penetrating the soil to a depth of two feet, anchor the plant with greater stability than those which are spread more thinly near the surface.

The roots of plants traversing the soil to such great distances, and being located in nearly every part, absorb mineral and other food, in solution in water, only through the _spongioles at their ends_.

Consequently, by having these ends in _every part_ of the soil, it is _all_ brought under contribution, and the amount supplied is greater, while the demand on any particular part may be less than when the whole requirements of plants have to be supplied from a depth of a few inches.

[May garden soils be profitably imitated in field culture?]

The ability of roots, to a.s.sume a natural shape in the soil, and grow to their largest sizes, must depend on the condition of the soil. If it is finely pulverized to the whole depth to which they ought to go, they will be fully developed; while, if the soil be too hard for penetration, they will be deformed or small. Thus a carrot may grow to the length of two and a half feet, and be of perfect shape, while, if it meet in its course at a depth of eight or ten inches a _cold, hard_ subsoil, its growth must be arrested, or its form injured.

Roots are turned aside by a hard sub-soil, as they would be if received by the surface of a plate of gla.s.s.

Add to this the fact that cold, impenetrable subsoils are _chemically_ uncongenial to vegetation, and we have sufficient evidence of the importance, and in many cases the absolute necessity of sub-soiling and under-draining.

It is unnecessary to urge the fact that a garden soil of two feet is more productive than a field soil of six inches; and it is certain that proper attention to these two modes of cultivation will in a majority of cases make a garden of the field--more than doubling its value in ease of working, increased produce, certain security against drought, and more even distribution of the demands on the soil--while the outlay will be immediately repaid by an increase of crops.

[Is the use of the sub-soil plow increasing?

Will its use ever injure crops?]

The subsoil will be much improved in its character the first year, and a continual advancement renders it in time equal to the original surface-soil, and extending to a depth of two feet or more.

The sub-soil plow is coming rapidly into use. There are now in New Jersey more foundries casting sub-soil plows than there were sub-soil plows in the State six years ago. The implement has there, as well as in many other places, ceased to be a curiosity; and the man who now objects to its use, is cla.s.sed with him who sh.e.l.ls his corn on a shovel over a half-bushel, instead of employing an improved machine, which will enable him to do more in a day than he can do in the "good old way" in a week.

Had we s.p.a.ce, we might give many instances of the success of sub-soiling, but the agricultural papers of the present day (at least one of which every farmer should take) have so repeatedly published its advantages, that we will not do so.

In no case will its use be found any thing but satisfactory, except in occasional instances where there is some chemical difficulty in the subsoil, which an a.n.a.lysis will tell us how to overcome.

As was before stated, its use on wet lands is not advisable until they have been under-drained, as excess of water prevents its effects from being permanent.

CHAPTER V.