COEN, WHEAT, OATS, BARLEY, RYE 



55 



that continuous cropping of a soil to one crop depleted tlie fer- 

 tility of the soil. This is very definitely shown by exi^erimental 

 results for eighteen years from the Ohio Station as given in the 

 following table : 



Very similar results have been secured at various experiment 

 stations. Continuous cropping of land causes a depletion of 

 organic matter, nitrogen and mineral elements, and finally a 

 poor physical condition of the soil. It is due to these facts 

 chiefly that rotations have been developed. 



The advantages of a crop rotation are listed below: 



1. Helps maintain organic matter and nitrogen content of the 



soil. 



2. Keeps soil in good physical condition. 



3. IIelj)s control weed, insect and fungus pests. 



4. Helps to make available more mineral matter. 



5. Distributes man, horse and machine labor so as to make 



it more efficient. 



6. Lessens risk of complete failure. 



The effect of crop rotation on yield of corn may be illustrated 

 l)y data from the Illinois Experiment Station. 



Although there has been considerable decrease in all cases, 

 the decrease has been very much greater under continuous crop- 

 ping than Avhere the crops are rotated. The effect of a legume 

 in the rotation is also very apparent. Likewise the data show 

 conclusively that rotations alone where the crops are all removed 

 will not maintain fertility. Fertility can be maintained where 

 mineral fertilizers are emplo^^ed in connection mth a rotation 

 including legumes and green manures. 



