ich water is
composed. Water is taken into the plant through the roots, carried
through the stems to the leaves, and there, under the influence of
chlorophyll, sunlight and the life principle, the carbon, oxygen and
hydrogen are made to unite into some of the most important plant
compounds, such as the sugars, which are later transformed into
starch and fiber.

Though these three elements constitute the larger part of the mature
agricultural plant they are no more necessary for plant growth than
the seven which are supplied by the soil. Iron is one of the
essential elements of plant food; but the amount required by plants
is so small and the amount contained in the soil is so large that
soils have never been known to become deficient in iron. Though
sulfur is found in plants in very appreciable amounts and is known
to be essential to plant growth, it is evident that plants do not
need so much sulfur as they often contain, some of it being taken up
and merely tolerated, as is the case with all of the sodium and
silicon found in plants, neither of these being required for normal
growth, although commonly found in plants in very considerable
amounts. The supply of sulfur in normal soils is not large; but,
with the combustion and decay of organic materials--coal, wood,
grass, leaves, and so forth--sulfur passes into the air and is
brought back to the soil dissolved in rain or absorbed by direct
contact of soil and air. Thus under normal conditions the supply of
sulfur naturally provided is ample to meet the needs of the staple
farm crops, although there are some plants, such as cabbage, for
example, which may possibly be benefited by fertilizing with sulfur.

But there are five other essential elements of plant food, and these
require special consideration in connection with permanent soil
fertility. They are potassium, magnesium, calcium, phosphorus and
nitrogen. There are also five important points to be kept in mind in
relation to each of these elements: (1) the soil's supply, (2) the
crop requirements, (3) the loss by leaching, (4) the methods of
liberation, and (5) the means of renewal.

The neglect of one or more of these important points in relation to
one or more of these five elements has reduced the fertility of most
cultivated soils in the United States, has greatly impoverished the
older farm lands, and has brought agricultural abandonment to
millions of acres in the original thirteen states. On the other
h