124 



COBN C'BOPS 



Cropping systems may then be classed as : — 



(1) Those that decrease productivity. 



(2) Those that maintain productivity. 



(3) Those that increase productivity (or in most cases 

 merely restore it) . 



Experiments demonstrating the above cases have been 

 made in a number of States where corn was used as one of 

 the crops in the system. 



MAINTAINING PRODUCTION 



92. Results are reported from the Illinois station/ where 

 corn has been grown in three systems of cropping, for 13 

 years in one case and for 29 years in the other. 



TABLE XXII 



Illinois Corn Yields where Three Systems of Cropping 

 ARE Compared. Average Yield for Last Three Years 



The land on which these experiments were conducted 

 originally produced more than 70 bushels per acre. There 

 has been some decrease in yield in all cases, but less de- 

 crease where rotation was practiced. Yield cannot be 

 maintained by rotation alone ivhere the crops are removed. 



In a second series of plots a corn-oats-clover rotation was 

 practiced, where all was returned to the land except the 

 grain and clover seed harvested. In one case, the straw, 



'lU. Agr. Exp. Sta., Bui. 125 : 324. 1908. 



