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.

But this progressive, practical farmer is only putting into profitable practice the results of the long-continued careful investigations with raw phosphate conducted by such public-service institutions as the agricultural experiment stations of Pennsylvania, Maryland, Rhode Island, Massachusetts, Ohio and Illinois.  He knows also that on four different fields of typical Corn-Belt land in McLean county, Illinois, the total crop values per acre for a period of ten years were $148.75 $151-30, $149.43 and $149.96, respectively, and that on four other adjoining or intervening fields, which differed only by two liberal additions of phosphorus during the ten years, the respective crop values for the same time were $229,37, $221.30, $229.20 and $225.57.

Of course, Mr. Mann does not buy nitrogen, but be takes it from the inexhaustible supply in the air by means of clover and alfalfa or other legumes.  He does not buy potassium because he knows how to liberate it from the inexhaustible supply contained in the soil, and because he knows that in the Illinois investigation just cited the crop values from four different fields not receiving potassium were $148.75, $151.30, $229.37 and $221.30; while four other adjoining fields, which differed only by liberal applications of potassium, produced during the same ten years $149.43, $149.96, $229.20 and $225.57, respectively.

Thus, as a general average, phosphorus increased the crop values by $76.50 an acre, which amounts to more than 300 per cent on the investment, and at the end of the ten years the soil on the best treated and highest yielding land was 10 per cent richer in phosphorus than at the beginning; while the crops from the unfertilized land removed an amount of phosphorus equal to nearly one-tenth of the total supply in the plowed soil.  But a similar general average shows that potassium produced increased crop values worth only 86 cents, or 3 per cent of its cost.