"In the legume system the minerals applied have more than doubled the value of the crops produced, have paid their cost, and made a net profit of one hundred and forty per cent. on the investment, in direct comparison with the unfertilized land.
"If we compare the average yield of turnips, barley, clover, and wheat of the last twenty years with the yield of turnips in 1848, barley in 1849, clover in 1850 and wheat in 1851 we find that on the unfertilized land in this rotation of crops in fifty years the yield of turnips has decreased from ten tons to one-half ton, and the yield of barley has decreased from forty-six to fourteen bushels, the yield of clover has decreased from two and eight-tenths tons per acre to less than one-half ton, while the yield of wheat has decreased only from thirty bushels to twenty-four bushels. As a general average the late yields are only one-third as large as they were fifty years before on the same land. Wheat grown once in four years has been the only crop worth raising on the unfertilized land during the last twenty years, and even the wheat crop has distinctly decreased in yield; although where mineral plant food was applied the yield has increased from thirty bushels, in 18851 to thirty-eight bushels as an average of the last twenty years. In the fallow rotation on the unfertilized land the yield of wheat averaged thirty-four and five-tenths bushels during the first twenty years (1848 to 1867) and twenty-three and five-tenths bushels during the last twenty years.
"On another Rothamsted field the phosphorus actually removed in fifty-five crops from well-fertilized land is two-thirds as much as the total phosphorus now contained in the plowed soil of adjoining untreated land.
"In the early 80's the Pennsylvania Agricultural Experiment Station began a four-year crop rotation, including corn, oats, wheat, and mixed clover and timothy.
"There are five plots in each of four different fields that have received no applications of plant food from the beginning. Thus, every year the crops are carefully harvested and weighed from twenty measured plots of ground that receive no treatment except the rotation of crops. The difference between the average of the first twelve years and the average of the second twelve years should represent the actual change in productive power during a period of twelve years. These averages show that the yield of corn has decreased from forty-one and seven-tenths bushels to twenty-seven and seven-tenths bushels; that the yield of oats has decreased from thirty-six and seven-tenths bushels to twenty-five bushels; that the yield of wheat has decreased only from thirteen and three-tenths bushels to twelve and eight-tenths bushels; and that the yield of hay has decreased from three thousand seventy pounds to two thousand one hundred and eighty pounds.
"As a general average of these four crops the annual value of produce from one acre has decreased from $11.05 to $8.18. Here we have information which is almost if not quite equal in value to that from the Agdell rotation field at Rothamsted. While the Rothamsted experiments cover a period of sixty years, each crop was grown but once in four years; whereas, in the Pennsylvania experiments, there have been four different series of plots, so that in twenty-four years there have been twenty-four crops of corn, twenty-four crops of oats, twenty-four crops of wheat, and twenty-four crops of hay.
"Under this four-year rotation the value of the crops produced has decreased twenty-six per cent. in twelve years. What influence will impress that fact upon the minds of American landowners? A loss amounting to more than one-fourth of the productive power of the land in a rotation with clover seeded every fourth year! This one fact is the mathematical result of four hundred and eighty other facts obtained from twenty different pieces of measured land during a period of twenty-four years.
"As an average of these twenty-four years, the addition of mineral plant food produced increases in crop yields above the unfertilized land as follows:
Corn increased forty-five per cent.
Oats increased thirty-two per cent.
Wheat increased forty-two per cent.
Hay increased seventy-seven per cent.
"As a general average of the four crops for the twenty-four years, the produce where mineral plant food is applied, was forty-nine per cent. above the yields of the unfertilized land, although the same rotation of crops was practiced in both cases."