CROP ROTATION 



17 



but the reduction in the last 16 years has been going on 

 much slower than at first. 



UNIVERSITY OF ILLINOIS EXPERIMENT FIELD AT URBANA, ILL. 

 TYPICAL CORN BELT PRAIRIE SOIL 



(Three years' averages : bushels per acre) 



IOWA AGRICULTURAL EXPERIMENT STATION, AMES, IOWA. 

 TYPICAL CORN BELT PRAIRIE SOIL 



(Figures give bushels per acre) 



Rotation of corn, corn, oats, clover, compared with continuous 



corn 



The results from nine years of experiments at the Iowa 

 station are even more striking than those from Illinois. 

 They show that, while each system started out with a 

 yield of approximately 75 bushels of corn per acre, con- 

 tinuous cropping never after the first year produced as 

 much by ten bushels per acre as in a four-year rotation 

 c 



