462 INVESTIGATION BY CULTURE EXPERIMENTS 



on these fields, it has not nearly paid its cost. The most profitable 

 yields are the go-bushel average in the grain farming or the 93- 

 bushel average in the live-stock system. The effect of limestone 

 has not yet been sufficiently uniform to recommend its use on 

 this soil, but marked profit has resulted from the addition of 

 phosphorus, which is applied in sufficient amount actually to en- 

 rich the land, and not as a stimulant. Phosphorus has been ap- 

 plied since 1902. 



Table 87 gives results obtained during seven years (1902 to 1908) 

 from the Sibley soil experiment field, located in Ford County, on 

 typical brown silt loam prairie of the Illinois corn belt. 



TABLE 87. CROP YIELDS IN ILLINOIS SOIL EXPERIMENTS: SIBLEY FIELD 



The standard applications for this and other Illinois soil experi- 

 ments are 100 pounds of nitrogen (in dried blood), 25 pounds of 

 phosphorus (in steamed bone meal), and 42 pounds of potassium (in 

 potassium sulfate), per acre per annum, but the phosphorus and 

 potassium are usually applied in correspondingly heavier applica- 

 tions once for the rotation. 



It is not necessary to take space here for a complete discussion 

 of the data in Table 87. 



Previous to 1902 this land had been cropped with corn and oats 



