"I think you should keep in mind, however, that, for every twenty-five bushels of corn you wish to produce, you should return to the soil one ton of clover or four tons of average farm manure, and that for one ton of produce hauled to the barns and fed, you will probably not return to the land more than one ton of manure." CHAPTER XXX "STONE SOUP" THE next forenoon Percy and Mr. West spent some time making some further tests with hydrochloric acid and litmus paper in different places on the farm; but the result only confirmed the previous examinations. "I never before saw any such light as now appears," said Mr. West. "It seems to me that for the first time in the history of Westover, covering about two centuries, a real plan can be intelligently made based upon definite information looking toward the positive improvement of the soil. While you have been away, I have been looking up the lime matter. I find that a lime is being advertised, and sold in small amounts, that is called hydrated lime, and it is especially prepared as an agricultural lime. It is recommended by some dealers as being fully equal to the ordinary commercial fertilizer which sells at about $25 a ton, while this hydrated agricultural lime can be bought for $8 a ton, and I think for a little less in larger amounts. You mentioned also that you had seen some one who had used hydrated lime, but it didn't seem to make much of a clover crop. Of course, I understand from what you said that his soil contained only one hundred and sixty pounds of phosphorus, and I take it that lime alone could not markedly improve his soil; but still I would like to know why, if he has one hundred and sixty pounds of phosphorus in his plowed soil, he could not produce a few good crops of clover. HOW much phosphorus does it require for a ton of clover?" "One ton of clover contains only five pounds of phosphorus," Percy replied, "and of course the roots must also require some phosphorus, although after the crop is produced and removed, the phosphorus contained in the roots remains for the benefit of subsequent crops. Thus we might suppose the land which contains one hundred and sixty pounds of phosphorus ought to furnish the phosphorus needed for a three ton crop of clover every year for ten years; but in actual practice no such results are secured. The invoice of the plant food in the soil is a matter of very great importance, for it reveals the mathematical possibilities, but another matter of almost equal importance is the problem of liberating plant food from this supply sufficient for the crops to be produced year by year.