known, have the power of drawing large stores of nitrogen from the
air, and, by means of bacteria attached to their roots, restoring it to
the ground.

So farmers have learned that if they plant corn one year, it is wiser
not to plant corn in the same field the next year, but to sow wheat,
which requires less nitrogen, and the following year to sow clover, so
that the nitrogen which the corn and wheat have taken from the soil, may
be put back into it. If the land be naturally fertile, and has been well
cared for, the soil is then ready to produce a good crop of corn again.

If the soil has become worn-out and the farmer is trying to improve its
general condition, he can gain better results by keeping the field in
clover a second year, when a profitable crop of clover seed may be had
from the land. This system of changing each year, and alternating cereal
crops, which take the nitrogen from the soil, with leguminous plants,
which restore it to the soil again, is called "rotation of crops," and
if regularly followed will preserve a proper balance of nitrogen in the
soil.

In some parts of the West there is a lack of decaying vegetable matter
in the soil, because the few plants which naturally grow there have
small roots, and leave little vegetable material behind when they decay.
For this condition one of the best crops to employ in rotation is
sugar-beets, because they strike many small roots deep into the earth.
As these decay, each leaves behind a tiny load of vegetable mold deep in
the earth, and also makes the soil more porous. As the principal
elements of the soil needed by sugar-beets are carbon and oxygen, which
are absorbed from the air and sunshine, and as the beets can be sold at
a good profit, it is an excellent crop to employ in rotation. In the
United States records in various states show that where sugar-beets are
used in rotation, the wheat and corn yield is increased from two to four
times, and in Germany they are largely used to restore the fertility of
the land, even if the sugar-beets themselves are sold at a loss.

It is most important that farmers should understand the principle of
rotation of crops, because nothing is taken from the soil so quickly or
in such large quantities as nitrogen, and nothing is so easily put back;
while, if it is not so replaced, the land becomes worthless.

A comparison of the results of single cropping and the rotation of crops
has been clearly shown at the Experimen