life, but some plants require
a large amount of one element, others a small proportion of that, but a
large amount of some of the others. No two varieties of plants require
exactly the same proportions, so it is easy to see that the plant that
takes out of the soil any one element makes the soil less capable each
year of producing a good crop of the same kind.

In the early days of farming in this country, it was the custom to grow
a single crop, which had been found to give good results, year after
year in the same field. In Virginia and other near-by states nearly all
the best land was given every year to the cultivation of tobacco, which
exhausts the soil rapidly. In the states farther north other crops were
planted in the same way. As a result, some of the most fertile soil in
Virginia, the Carolinas, Massachusetts, and other eastern states has
been so exhausted that it is no longer worth cultivating. Everywhere
throughout the New England states are to be found these worn-out farms,
and, while they were never so fertile as the lands of the Mississippi
Valley, each one was rich enough to support a family in comfort, with
something left to sell; but because they were required to produce the
same crops, and so take the same element from the soil, year after year,
they have become so lacking in one of the essential elements that they
are unfit for cultivation, and have been abandoned.

It is wisdom and good business policy for farmers to study carefully
this question of plant food and to learn what each crop is taking from
the soil, so that it may be replaced. It has been found by long and
careful experiments, that when land has been "single cropped," as this
abuse of the land is called, for a long time, the soil has been almost
entirely deprived of its nitrogen. As you know, nitrogen is one of the
elements of the air, so that there is a never-ending supply, but most
plants are unable to take it from the air, and until the last few years
the task of replacing nitrogen in the soil was considered impossible.
Recent discoveries, however, have shown that there are two ways in which
it may be done. By means of electricity, nitrogen may be directly
combined with the other elements of the soil. The other method is
nature's own plan, and so is easier and cheaper. It has been found that
while most plants exhaust the nitrogen from the soil, one class of
plants, the legumes, of which beans, peas, clover, and alfalfa are the
best