Percy laughed.  “You see,” he said, “you have more figures in your head than I have in mine.  You have mentioned twice as many right here, without a moment’s hesitation, as I try to remember for the plant food contained in clover.  I like to keep in mind the requirements of large crops, such as it is possible to raise under our climatic conditions if we will provide the stuff the crops are made of, so far as we need to, and do the farm work as it should be done.  I never try to remember how much plant food is required for twenty-two bushels of corn per acre, which is the average yield of Virginia for the last ten years, while an authentic record reports a yield of 239 bushels from an acre of land in South Carolina.  On our little farm in Illinois we have one field of sixteen acres, which was used for a pasture and feed lot for many years by my grandfather and has been thoroughly tile-drained since I was born, that has produced as high as 2,015 bushels of corn in one season, thus making an average of 126 bushels per acre.

“What I try to remember is the plant food requirements for such crops as we ought to try to raise, if we do what ought to be done.  I try to remember the plant food required for a hundred-bushel crop of corn, a hundred-bushel crop of oats, a fifty-bushel crop of wheat, and four tons of clover hay.  It is an easy matter to divide these amounts by two, as I have really been doing here in the East where it is hard for people to think in terms of such crops as these lands ought to be made to produce.

“The requirements of the clover crop I certainly want to have in mind as a part of my little stock of ever-ready knowledge.  It is not very hard to remember that a four-ton crop of clover hay, which we ought to harvest from one acre in two cuttings, contains: 

160 pounds of nitrogen, 31 pounds of magnesium, 20 pounds of phosphorus, 120 pounds of potassium, 117 pounds of calcium.

“It is just as easy to think in these terms as in per cent. or pounds of butter fat, which I understand is the basis on which you sell your cream.”

“Yes, I believe you are right in this matter, Mr. Johnston, but I have never been able to see how we could apply the figures reported from chemical analysis.”

“Neither do I see how any one but a chemist could make much use of the reports which the analyst usually publishes.  Such reports will usually show the percentages of moisture and so-called ’phosphoric acid,’ for example, in a sample of clover hay, and perhaps the percentages of these constituents in a sample of soil; but to connect the requirements of the clover crop with the invoice of the soil demand more of a mental effort than I was prepared for before I went to the agricultural college.