Wheat, 32 bushels in 1851 and 37.8 in 1911.

Here we have data which span a period of sixty years and which show
that where mineral plant food has been provided the clover in
rotation and the manure produced by the feeding of only one of the
four crops have maintained the yield of all crops except the
barley-the third crop after clover-and without the application of
nitrogen in any other form. If the clover and straw had been
returned to the land either directly or in farm manure the
additional nitrogen thus provided would have been sufficient both to
maintain the yield of barley and to prevent the moderate decrease
which has occurred in the nitrogen content of the soil.






CHAPTER III

PHOSPHORUS: THE MASTER KEY

TO PERMANENT AGRICULTURE





THE greatest economic loss that America has ever sustained has been
the loss of energy and profit in farming with an inadequate supply