hich appear during
the growing season. They are more commonly formed on the roots within
the cultivable area, and therefore are easily accessible to the roots of
the plants which immediately follow. Clovers are not equally capable of
thus drawing nitrogen from the air, nor are the same varieties equally
capable of doing this under varying conditions. The relative
capabilities of varieties to thus deposit nitrogen in the soil is by no
means equal, but up to the present time it would seem correct to say
that relative capability in all of these has not yet been definitely
ascertained. With reference to the whole question much has yet to be
learned, but it is now certain that in all, or nearly all, instances in
which clovers are grown on land, they leave it much richer in nitrogen
than it was when they were sown upon the same.

They also add to the fertility of the surface soil by gathering plant
food in the subsoil below where many plants feed. They have much power
to do this, because they are deep rooted and they are strong feeders;
that is, they have much power to take up food in the soil or subsoil.
Part of the food thus gathered in the subsoil helps to form roots in the
cultivable area and part aids in forming top growth for pasture or for
hay. If grazed down or if made into hay and fed so that the manure goes
back upon the land the fertility of the same is increased in all leading
essentials. This increase is partly made at the expense of the fertility
in the subsoil. But the stores of fertility in the subsoil are such
usually as to admit of thus being drawn upon indefinitely.

Clovers improve soils mechanically by rendering them more friable, by
giving them increased power to hold moisture, and by improving drainage
in the subsoil. Of course, they have not the power to do this equally,
but they all have this power in degree and in all the ways that have
been named.

Clovers send down a tap root into the soil and subsoil as they grow.
From the tap roots branch off lateral roots in an outward and downward
direction. From these laterals many rootlets penetrate through the soil.
When the plants are numerous, these roots and rootlets fill the soil.
When it is broken up, therefore, particles of soil are so separated that
they tend to fall apart, hence the soil is always made more or less
friable, even when it consists of the stiffest clays. The shade
furnished by the clover also furthers friability. This friability makes