The oldest direct comparison between these two systems of farming, so far as the writer has learned, is on the experiment fields of the University of Illinois, where as an average of six years the yield of corn has been 87 bushels an acre in grain farming and 90 bushels in live-stock farming, the same crop rotation being practiced. Where wheat was introduced the average yield for six years was 43.1 bushels in grain farming and 43.5 in live-stock farming.
No nitrogen was purchased in any form in either of these systems; but clover is grown in the rotation to secure nitrogen from the air and then the crop residues or farm manure is returned to the soil to provide sufficient nitrogen for the grain crops. In all cases phosphorus was used for these yields.
Even more encouraging than these six-year average results from Illinois are the results of sixty years from Agdell Field at Rothamsted.
Where mineral plant food was regularly applied, and where all the manure produced by feeding the turnips was returned to the soil, in a four-year rotation of turnips, barley, clover (or beans) and wheat, with no other provision made for supplying nitrogen, the yields per acre were as follows:
Turnips, 24,724 lbs. in 1848, and 26,410 in 1908.
Barley, 42.8 bushels in 1849 and 22.1 in 1909
Clover, 5586 pounds in 1850 and 7190 in 1910.
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.
PHOSPHORUS: THE MASTER KEY
The greatest economic loss that America has ever sustained has been the loss of energy and profit in farming with an inadequate supply of phosphorus. Phosphorus is a Greek word which signifies “light-bringer”; but it is a light which few Americans have yet seen, else we should not permit the annual exportation of more than a million tons of our best phosphate rock, for which we receive at the mines the paltry sum of five million dollars, carrying away from the United States an amount of the one element of plant food we shall always need to buy, which if retained in this country and applied to our own soils would be worth not five million but a thousand million dollars for the production of food for the oncoming generations of Americans.