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
hand, intelligent attention to these same factors will bring
restoration and high productive power to such lands.

England's Best Lesson in Farming

Where these five elements were supplied regularly to land on the
Rothamsted Experiment Station the average yield of wheat for the
thirty years, 1852 to 1881, was 35.9 bushels an acre, while 13.6 was
the average yield of similar unfertilized land; and during the next
thirty years--1882 to 1911--the corresponding average yields were 38