CHAPTER XII 



CROPPING SYSTEM IN RELATION TO MAIN- 

 TAINING THE YIELD OF CORN 



The discussion so far, on the adaptation of soil for corn 

 growing, brings out -the fact that the constant growing 

 of corn involves the development of a cropping system 

 by which, with the least cost, the organic matter can be 

 maintained and the most profitable use made of any 

 fertilizing material that it may be necessary to add. 



90. Cropping systems in the United States undergo evo- 

 lution from the time when new land is opened up to the 

 time when it reaches a permanent agricultural basis. 



When new land is first brought under cultivation, grain 

 farming is the general custom. Often a single crop is 

 cultivated, as wheat in the Northwest. In a few years 

 the single crop becomes unprofitable, due to the coming of 

 insect pests or plant diseases, or to the decreasing avail- 

 ability of some mineral element in the soil. Then cul- 

 tivated crops are introduced to alternate with the small 

 grain. 



In many regions of the Corn Belt, corn was continu- 

 ously raised until it became necessary to introduce small 

 grain culture. After a time, however, the continuous 

 rotation of grain crops alone no longer gave paying crops. 

 In general, this appears to be due to : — 



1. Exhaustion of actual organic matter resulting in 



(a) Decrease in availability of some necessary 



element as phosphorus, or 



(b) Poor physical condition of the soil. 



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