ILLINOIS FIELD EXPERIMENTS 



459 



TABLE 86. LATEST COMPARABLE CORN YIELDS FROM THE UNIVERSITY OF 

 ILLINOIS EXPERIMENT FIELD AT URBANA: TYPICAL BROWN 



SILT LOAM PRAIRIE SOIL 

 Three -year Averages: Bushels per Acre 



AVERAGE OF THREE CORN CROPS IN CORN-OATS-CLOVER ROTATION: 

 13-YEAR EXPERIMENTS 



1 Legume catch crops and crop residues. 



2 Manure applied in proportion to previous crop yields. 



addition to this, the development of corn insects in soil on which 

 their favorite crop is grown every year is sometimes an important 

 factor in reducing the yield. 



Where corn is followed by oats in a 2-year rotation the average 

 yield of the three crops of corn is 46 bushels in the 29-year experi- 

 ments, whereas in the 13-year experiments the average yield for 

 the same three years is 62 bushels of corn per acre. In this case the 

 destruction of humus is less rapid, and the development of the corn 

 insects is discouraged by changing to oats every other year, so that 

 the decrease in yield is less marked during the early years, although 

 the reduction continues persistently with passing years. During 

 the first ii years the yield decreased from more than 70 bushels to 

 62 bushels, and during the next 16 years a further reduction of 16 

 bushels has occurred. 



