NOVEMBEB 8, 1912] 



SCIENCE 



619 



and 4), either for one year or for five 

 years, was secured after potatoes had been 

 grown on the same land for more than 

 fifteen years. 



On permanent meadow land at Rotham- 

 sted, the average yield of hay for fifty 

 years was 1| tons per acre on unfertilized 

 land, and more than 4 tons per acre on 

 land heavily fertilized with commercial 

 plant food. During the last ten years of 

 this fifty-year period the unfertilized land 

 has produced an average yield of 1,863 

 pounds of hay, while the fertilized land 

 has produced 8,490 pounds per acre. 



On Barn Field at Rothamsted, mangels 

 were grown for thirty years. The average 

 yield per acre was 4J tons on unfertilized 

 land, 19| tons where farm manure had 

 been applied, and 29 tons per acre where 

 the farm manure had been reinforced with 

 nitrogen and phosphorus in commercial 

 form. 



In 1902 the University of Illinois began 

 a series of experiments on the common 

 corn-belt prairie land in McLean County, 

 on a field which had grown no wheat for 

 thirty-two years. We first grew wheat in 

 1905. Four plots not receiving phosphorus 

 produced, respectively, 28.8 bushels, 30.5 

 bushels, 33.2 bushels and 29.5 bushels of 

 wheat per acre; while four other plots 

 which differed from these only by the addi- 

 tion of phosphorus, at the rate of 25 

 pounds of that element in 200 pounds of 

 steamed bone meal per acre per annum, 

 produced 39.2 bushels, 50.9 bushels, 37.8 

 btishels and 51.9 bushels, respectively, per 

 acre. Six years later wheat was again 

 grown on this land, when the four plots 

 not receiving phosphorus produced, re- 

 spectively, 22.5 bushels, 25.6 bushels, 21.7 

 bushels and 27.3 bushels per acre, and the 

 other four plots, which differ from these in 

 treatment only by the phosphorus applied 

 during the ten years, produced 57.6 bush- 



els, 60.2 bushels, 54.0 bushels and 60.4 

 bushels, respectively, of wheat per acre, 

 this being the second crop of wheat grown 

 on this land in forty years. 



This most common prairie land of the 

 Illinois com belt contains 600 pounds of 

 phosphorus and 18,000 pounds of potas- 

 sium per million of surface soil, while one 

 million pounds of the subsoil contains 450 

 pounds of phosphorus and 27,000 pounds 

 of potassium. This is the type of soil on 

 which, as an average of four different tests 

 each year under four different conditions 

 of soil treatment, the addition of phos- 

 phorus produced an increase in yield per 

 acre of 9.6 bushels of corn in 1902, of 17.8 

 bushels of corn in 1903, of 14.8 bushels of 

 oats in 1904, of 14.4 bushels of wheat in 

 1905, of 1.46 tons of clover^ in 1906, of 

 18.8 bushels of corn in 1907, of 17.3 bushels 

 of corn in 1908, of 15.2 bushels of oats in 

 1909, of 2.56 tons of clover^ in 1910 and 

 an average increase of 33.8 bushels of 

 wheat per acre in 1911. 



As an average of four similar tests dur- 

 ing the ten years, applications of potas- 

 sium (costing the same as the phosphorus) 

 increased the yield of corn by 3.1 bushels, 

 decreased the yield of oats by 2.3 bushels, 

 decreased the yjeld of clover by 70 pounds 

 per acre and increased the yield of wheat 

 by 0.1 bushel per acre, these being the gen- 

 eral average results from four years of 

 corn and from two years each of oats, 

 clover and wheat. 



If now we turn to the extensive peaty 

 swamp soil of northern and north-central 

 Illinois, we find by analysis that it con- 

 tains in one million poimds of the surface 

 soil 1,960 pounds of phosphorus and 2,930 

 pounds of potassium, or more than three 

 times as much phosphorus and less than 

 one sixth as much potassium as the com- 



' Average of two tests (see Illinois Soil Eeport 

 No. 2, pp. 17, 39). 



