And, if we again double the yield, making it 80 bushels an acre, the value of the land becomes not $87.24, and not $232.72; but easy computation will show that the gross receipts from an 80-bushel crop will pay $7.20 an acre for soil enrichment, $4 for raising the crop, $4 for harvesting and marketing, $1.53 for taxes and 5 per cent interest on a valuation of $305.45 an acre. The average yield of corn in the United States is only 25 bushels an acre, and the average net returns even from the farms of the Corn Belt will not pay 4 per cent interest on their present market value. But the intelligent investment of $2 an acre annually in positive soil enrichment will increase the crop yield by two bushels of corn each year--or by equivalent amounts of other crops grown in the rotation--and will maintain this increase for at least a dozen years on the average land now under cultivation in the United States; and no other safe investment can be named that will pay so great returns. Of course, the cost is $1 a bushel for the first year's increase, and even the second year the 4 bushels of corn cost $2; but what is the cost per bushel of the increase the tenth year? It is 10 cents; and the twelfth year the 24 bushels of increase cost only 8-1/3 cents a bushel, with a return of nearly 500 per cent on the annual investment in soil improvement. And this is not based on mere theoretical considerations. The average Corn-Belt land is producing only 40 bushels of corn to the acre; while a six-year average yield of 90 bushels has been produced on the common Corn-Belt land with proper and profitable soil treatment. Thus is it too much for any farmer to adopt a definite system based upon established practical scientific information which makes it possible for his yield to increase from 40 bushels to an average of 64 bushels an acre? But let him make sure that the system he adopts is cumulative and truly permanent, and not merely stimulating and temporary. What Phosphorus Did on One Farm On his 500-acre farm near Gilman, in the heart of the Illinois Corn Belt, Mr. Frank I. Mann has produced a 70-bushel average yield of corn for a five-year period, and with 200 acres of land in corn annually. It cost him only $1 an acre a year in fine-ground natural rock phosphate to produce increased yields of 16 bushels more corn, 23 bushels more oats and 1 ton more clover than the average yields secured without adding phosphorus.