2,000,000 pounds--corresponding to about 6-2/3 inches to the
acre--1000 pounds of phosphorus and 35,000 of potassium, while an
acre of plowed soil of the same weight at State College,
Pennsylvania, contains 1100 pounds of phosphorus and 50,700 of
potassium.

In a word, normal soils are deficient in phosphorus, and the
application of phosphorus in good systems of farming produces marked
and profitable increases in crop yields. But what form of phosphorus
shall we apply? This is a very important question in agricultural
economics, for we have many different kinds of fertilizing materials
that contain phosphorus, and one may cost ten times as much as
another as a source of phosphorus. Thus 250 pounds of phosphorus in
a ton of finely ground natural rock phosphate can be purchased at
the mines in Tennessee and delivered at the farmer's railway station
in the heart of the Corn Belt for $8. Or the ton of raw phosphate
may be mixed with a ton of sulfuric acid in the fertilizer factory,
and the two tons of acid phosphate may be sold to the same farmer
for $32. Or the fertilizer manufacturer may mix the two tons of acid
phosphate with two tons of "filler," containing a little nitrogen
and potassium, and then sell the same farmer the four tons of
so-called "complete" fertilizer for $80; and the farmer gets no more
phosphorus in the four tons of "complete" fertilizer for $80 than in
the one ton of natural phosphate for $8.

The Pennsylvania State College conducted an experiment for twelve
years--1884 to 1895--in which $1.05 an acre was invested in ground
raw rock phosphate with a rotation of corn, oats, wheat and hay
(clover and timothy), and the value of the increase produced by the
phosphorus amounted to $5.85 as an average for the twelve years, and