For five million dollars we export to Europe each year enough phosphorus for 1,400,000,000 bushels of wheat, or twice the average crop of the entire United States.  Meanwhile our ten-year-average yield of wheat is 14 bushels an acre, while Germany’s yield has gone up to 29, Great Britain’s to 33, England’s to 37-1/2 and Denmark’s to more than 40 as the average for a decade.

Potato Yield Twice Doubled

There is only one place in the world where we can go for the results of soil improvement for more than a quarter of a century in connection with the growing of potatoes.  Of course this place is Rothamsted, England, where as an average for twenty-six years the yield of potatoes was 51 bushels an acre on unfertilized land and exactly 102 bushels where only a phosphate fertilizer was applied.  Where the same amount of phosphorus—­29 pounds of the element per acre per annum—­was used in connection with other minerals—­300 pounds of potassium sulfate and 100 pounds each of the sulfates of magnesium and sodium—­the average yield of potatoes was 109 bushels.  Where 86 pounds of nitrogen was applied in sodium nitrate the average yield was 79 bushels; but where the nitrogen, phosphorus and other minerals were all applied the average yield for the twenty-six years was 203 bushels.

At 50 cents a bushel for potatoes, the investment in phosphorus alone paid 600 per cent net profit; and even the complete fertilizer, including 392 pounds of acid phosphate, 550 pounds of sodium nitrate and 500 pounds of alkali salts, aggregating 1442 pounds, and costing at moderate prices $24.28 an acre per annum, paid back $76 a year as a twenty-six year average, thus making 300 per cent even on an investment of nearly $25 an acre a year.

Phosphorus Helps Good Farming

There is also but one place in the world where we can learn the results secured from the application of phosphorus for a period of thirty-six years in a good system of farming; and again this place is Rothamsted.

In 1848 Sir John Lawes and Sir Henry Gilbert began investigations on Agdell Field.  The Norfolk rotation, already known at that time as one of the best rotation systems, was turnips, barley, clover, and wheat; and in these practical field experiments the turnips were fed on the land and the animal fertilizer thus produced was returned to the soil, which was well supplied with limestone.

During the next thirty-six years $29.52 worth of phosphorus per acre was applied to one part of the field; and in comparison with another part of the same field cropped and managed similarly, except that no phosphorus was applied, the $29.52 worth of phosphorus produced $98.02 increase in the value of the turnips, $37.45 in barley, $48.93 in clover (and beans) and $45.99 in wheat.

The total value of the crops grown on the land not receiving phosphorus during the thirty-six years was $432.43 an acre, while on the phosphated land the crop values amounted to $662.82, an increase of $230.39 from an investment of $29.52, the turnips being figured at $1.40 a ton, barley at 50 cents a bushel, clover hay at $6 a ton, beans at $1.25 a bushel, wheat at 70 cents a bushel, and phosphorus at 12 cents a pound.  As a general average at these conservative prices, the investment of $3.28 an acre every four years paid back $25.60 in the four crops.