ILLINOIS FIELD EXPERIMENTS 



471 



surface 6f inches of an acre about five times as much nitrogen as 

 the early Wisconsin black clay loam prairie. In phosphorus con- 

 tent these two soil types are about equal, but the peat contains 

 less than one tenth as much potassium as the black clay loam. 

 Thus, the total supply of potassium in the peat to a depth of 6| 

 inches (2930 pounds) would be equivalent to the full potassium re- 

 quirement (75 pounds) of a hundred-bushel crop of corn for only 

 39 years, or if the equivalent of only one fourth of i per cent 

 of this is annually available in accordance with the rough estimate 

 previously suggested, about 7 pounds of potassium would be liber- 

 ated annually, or sufficient for about 10 bushels of corn per acre. 



In Table 91 are given all results obtained from the Manito 

 (Mason County, Illinois) experiment field on deep peat, which was 

 begun in 1902 and discontinued after 1905. The plots in this field 

 were one acre l each in size, being 2 rods wide and 80 rods long, 

 and untreated half-rod division strips were left between the plots, 

 which, however, were cropped the same as the plots. 



TABLE 91. CORN YIELDS PER ACRE IN ILLINOIS SOIL EXPERIMENTS : MANITO 

 FIELD: TYPICAL DEEP PEAT SOIL 



1 In 1904 the yields were taken from quarter-acre plots because of severe insect 

 injury on the other part of the field. 



2 Estimated from 1903; no yield was taken in 1902 because of misunderstanding. 



