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102 



Nature-Study Agriculture 



Four 



advantages 



arising 



from 



rotation 



u. s. D. A. 



FIG. 81. A catch crop of cowpeas in corn. The cowpeas will furnish feed 

 for stock, and, being legumes, they will improve the soil. 



Rotation of crops. Raising different crops in suc- 

 cession on the same land (rotation) is better than raising 

 one crop continuously, for several reasons : (i) Insects 

 and fungous diseases die out of the soil where the crop 

 upon which they live is changed. (2) If wheat or other 

 small grain is raised continually for several years, the 

 land becomes foul with weeds which ripen seed after 

 the grain is cut. A cultivated crop such as corn, rotated 

 with wheat, gives an opportunity to kill the weeds. 

 (3) Crops like wheat remove large quantities of nitro- 

 gen and other plant-food materials from the soil. Rotat- 

 ing such crops with legumes (as clover) will restore 

 nitrogen and allow some of the other plant foods to 

 accumulate. 



The following diagram indicates the manner in which 



