ys beneficial. The plants most used for this purpose, in our
country, are clover, buckwheat, and peas. These plants have very long
roots, which they send deep in the soil, to draw up mineral matter for
their support. This mineral matter is deposited in the plant. The leaves
and roots receive carbonic acid and ammonia from the air, and from
water. In this manner they obtain their carbon. When the crop is turned
under the soil, it decomposes, and the carbon, as well as the mineral
ingredients obtained from the subsoil, are deposited in the surface
soil, and become of use to succeeding crops. The hollow stalks of the
buckwheat and pea, serve as tubes, in the soil, for the passage of air,
and thus, in heavy soils, give a much needed circulation of atmospheric
fertilizers.

[What office is performed by the straw of the buckwheat and
pea?

What treatment may be substituted for the use of green crops?

Which course should be adopted in high farming?

Why is the use of green crops preferable in ordinary cultivation?

Name some other valuable manures.]

Although green crops are of great benefit, and are managed with little
labor, there is no doubt but the same results may be more economically
produced. A few loads of prepared muck will do more towards increasing
the organic matter in the soil, than a very heavy crop of clover, while
it would be ready for immediate cultivation, instead of having to lie
idle during the year required in the production and decomposition of
the green crop. The effect of the roots penetrating the subsoil is, as
we have seen, to draw up inorganic matter, to be deposited within reach
of the roots of future crops. In the next section we shall show that
this end may be much more efficiently attained by the use of the
sub-soil plow, which makes a passage for the roots into the subsoil,
where they can obtain for themselves what would, in the other case, be
brought up for them by the roots of the green crop.

The offices of the hollow straws may be performed by a system of ridging
and back furrowing, having previously covered the soil with leaves, or
other refuse organic material.

In _high farming_, where the object of the cultivator is to make a
profitable investment of labor, these last named methods will be found
most expedient; but, if the farmer have a large quantity of land, and
can afford but a limited amount of labor, the raising of green crops, to
be plowed under in the fall, will probably