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.