above, and they may be accepted with confidence for use in economic
systems of farming on normal soils.






CHAPTER II

THE NITROGEN PROBLEM AND

ITS ECONOMICAL SOLUTION





IN THE previous chapter emphasis has been laid upon the fact that
plants as well as animals must have food, and that the neglect or
ignorance of this factor in American agriculture has led to soil
depletion and land ruin on vast areas, especially in the older
states.

It has been shown that of the ten essential elements of plant food,
five are provided by natural processes without the intervention of
man; that, of the remaining five, potassium is the most abundant in
normal soil, but requires liberation by good systems of farming;
that ground natural limestone is the ideal material with which to
supply calcium and to prevent or correct soil acidity; and that if