"Yes, I believe you are right in this matter, Mr. Johnston, but I
have never been able to see how we could apply the figures reported
from chemical analysis."

"Neither do I see how any one but a chemist could make much use of
the reports which the analyst usually publishes. Such reports will
usually show the percentages of moisture and so-called 'phosphoric
acid,' for example, in a sample of clover hay, and perhaps the
percentages of these constituents in a sample of soil; but to
connect the requirements of the clover crop with the invoice of the
soil demand more of a mental effort than I was prepared for before I
went to the agricultural college.

"On the other hand we were taught in college that the plowed soil of
an acre of our most common Illinois corn belt land contains only
1200 pounds of phosphorus, and that a hundred-bushel crop of corn
takes twenty-three pounds of phosphorus out of the soil. Furthermore
that about one pound of phosphorus per acre is lost annually in
drainage water in humid regions. By dividing 1200 by 24 it is easy
to see that fifty corn crops such as we ought to try to raise would
require as much phosphorus as the present supply in our soil to a
depth of about seven inches. Of course there is some phosphorus
below seven inches, but it is the plowed soil we must depend upon to
a very large extent. The oldest agricultural experiment station in
the world is at Rothamsted, England. On two plots of ground in the
same field where wheat has been grown every year for sixty years,
the soil below the plow line has practically the same composition,
but on one plot the average yield for the last fifty years has been
thirteen bushels per acre, while on the other the yield of wheat has