"Many of them try it many times," replied Percy, "and the yield is about twenty bushels per acre, whereas the virgin soil easily produced sixty to eighty bushels."
"And they can't grow wheat as they once did?"
"No, wheat after timothy or red top now yields from five to twelve bushels per acre, while they once grew twenty to thirty bushels of wheat per acre year after year.
"If they rotate their crops, they would probably yield as well as ever," said the Chief.
"No, that, too, has been tried," replied Percy. "The Illinois Experiment Station has practiced a four-year rotation of corn, cowpeas, wheat, and clover on an experiment field on the common prairie soil down in 'Egypt,' and the average yield of wheat has been only twelve bushels per acre during the last four years, but when legume crops were plowed under and limestone and phosphorus applied, the average yield during the same four years was twenty-seven bushels per acre."
"Probably the increase was all produced by the green manure," suggested the Chief. "Organic matter has a great influence on the control of the moisture supply."
"That was tested," said Percy. "The green manure alone increased the average yield to only fourteen bushels while the green manure and limestone together raised the average wheat yield to nineteen bushels, the further increase to twenty-seven bushels having been produced by the addition of phosphorus."
"Well, Sir," said the Chief, "we have made both extensive intensive investigations concerning the chemistry of the soil solution by very delicate and sensitive methods of analysis we have developed, and we have also conducted culture experiments for twenty-day periods with wheat seedlings in the water extract of soils from all parts of the United States, and the results we have obtained have changed the thought of the world as to the cause of the infertility of soils."
"But you have not made analyses for total plant food in the soils or conducted actual field experiments with crops grown to maturity?" asked Percy.
"No, we have not done that," answered the Chief. "Those are old methods of investigation which have been tried for many years and yet no chemist can tell in advance what will be the effect of a given fertilizer upon a given crop on a given soil."