CHAPTER IV.

SUB-SOIL PLOWING.

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 sub-soil like a moleloosening 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.

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-balls 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 mass becomes pulverized. On the same principle, the sub-soil plow renders the compact lower soil sufficiently fine for the requirements of fertility.

Describe the Mapes plow.

Why is the motion in the soil of one and a half inches sufficient? How does the oxydation of the particles of the soil resemble the rusting of cannon balls in a pile?

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 sub-soil 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 sub-soil 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 surfacesoil, they there deposit much mineral matter obtained from the sub-soil.

The retention of atmospheric manures is more

Why are the benefits of sub-soiling not permanent on wet lands? Does sub-soiling overcome drought?

How does it deepen the surface soil?

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 sub-soil 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 grasses, and in getting rid of the poisonous excrementitious matter of plants.

When the sub-soil is a thin layer of clay on a sandy bed (as in some plants of Cumberland Co. Maine), the sub-soil plow, by passing through it, opens a passage for water, and often affords a sufficient drainage.

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.

Why is the retention of atmospheric manures ensured by subsoiling?

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 grasses?

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

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 assume the form requisite for its largest develop

ment.

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

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 ?