478 INVESTIGATION BY CULTURE EXPERIMENTS 



green manure, the average yield of wheat during the four years was 

 27 bushels; and where potassium also was included, the average 

 yield was 29! bushels of wheat per acre. 



These results are quite in harmony with what might be expected 

 from the chemical composition of the soil. If, however, we con- 

 sider the corn crops in the same rotation, we have a somewhat 

 different set of results. 



The average yield of corn for the four years on the untreated 

 rotated land was 38 bushels per acre; with legume treatment 

 (cowpeas turned under), 41 bushels; with legume and lime treat- 

 ment, 45 bushels; with legume, lime, and phosphorus, 46 bushels; 

 and with legume-lime-phosphorus-potassium treatment the average 

 yield of corn for four years was 61 bushels per acre. 



For more convenient comparison, these results are shown in 

 Table 94. 



TABLE 94. CROP YIELDS IN ILLINOIS SOIL EXPERIMENTS: ODIN FIELD 



These results are four-year averages. They were made in dupli- 

 cate each year. They are representative and trustworthy. They 

 have also been confirmed by results from other experiment fields 

 on the same type of soil. 



The effects upon corn of the green manure alone and with lime 

 are about the same as upon wheat, but the effects produced by 

 phosphorus and potassium are very different with the two crops, 

 phosphorus producing the largest increase in wheat, while potas- 

 sium is much more effective with corn, although potassium without 

 phosphorus (in other experiments) produces less increase in corn 

 than when applied in addition to phosphorus. 



