Potassium 36,250 pounds
Magnesium 8,790 pounds
Calcium 11,450 pounds
Phosphorus 1,190 pounds

The older gray silt loam prairie, the most extensive soil of
Southern Illinois, contains in two million pounds of soil:

Potassium 24,940 pounds
Magnesium 4,690 pounds
Calcium 3,420 pounds
Phosphorus 840 pounds

These data represent averages involving hundreds of soil analyses,
and they emphasize the fact that normal soils are rich in potassium
and poor in phosphorus. This is to be expected, for most soils are
made from the earth's crust, and normal soils should bear some
relation in composition to the average of the earth's crust, which
contains in two million pounds 49,200 pounds of potassium and 2,200
pounds of phosphorus, as shown by the weighted averages of analyses
involving about two thousand samples of representative rocks,
reported by the United States Geological Survey.

Measuring Fertility Losses

The plant food required for one acre of wheat yielding 50 bushels,
one acre each of corn and oats yielding 100 bushels, and one acre of
clover yielding four tons, includes for the total crops: