emain in the
country, and must supply the food, not only for themselves, but for all
the two-thirds who are not food producers, so that the food supply is
lagging far behind the demand. The price of corn has advanced from
twenty-five cents to sixty-five cents a bushel in ten years, and this in
turn raises the price of live stock. And so all along the line. Prices
are growing higher all the time because not enough food is being
produced to supply the demand.

So we can see that it is absolutely necessary that the soil be properly
cared for if we are to continue to increase and prosper, for as
Secretary Wilson has said, "Upon the fertility of the soil depends the
whole business of agriculture."

The soil is exhausted in two ways: (1) By erosion, or the carrying away
of the entire soil itself. (2) By so using the soil that one or more of
its principal elements are worn out. We shall consider this form of soil
exhaustion first, because it more directly concerns the work of every
farmer.

By a fertile soil is meant one that has an abundance of plant food in
the proper proportions. The soil contains all the elements that are
needed to support life, but they are in an inorganic form, that is, they
are lifeless. Plants alone can take these inorganic substances from the
soil, and change them into starch, sugar, fats, and protein. All
animals, including man, must get these substances through plants, or
through other animals that have already absorbed them from plants.

The soil contains ten elements that are absorbed or assimilated by
plants. These are: (1) lime, (2) magnesia, (3) iron, (4) sulphur, all of
which are found in most plants in very small proportions, and are
present in most soils in quantities far beyond the needs of crops for
ages to come; (5) carbon, which is obtained by plants through their
leaves directly from the air and the sunshine; (6) hydrogen and (7)
oxygen, which are taken from the water in the soil and carried to the
leaves, where they also help to take the carbon from the atmosphere.
With none of these elements, then, does the farmer need to concern
himself in regions where the water supply is abundant, as they are, and
will continue to be, plentifully supplied by nature. But the other
three, (8) nitrogen, (9) potassium, and (10) phosphorus, are needed by
plants in large quantities, and are taken from the soil far more rapidly
than nature can replace them.

All these elements are necessary to plant