CHAPTER VII. 

 CROP ROTATION AND IRRIGATION 



CROP ROTATION. 



The Effects of Continuous Cropping. Different crops re- 

 move from and contribute to the soil elements of different 

 kinds or in different proportions. The availability of plant 

 food is also influenced. Continuously raising one crop tends to 

 exhaust the soil of the food elements available for that crop. 

 In a rotation of crops these effects are not so manifest. Some 

 crops also contribute to the soil elements needed by others, as, 

 for example, leguminous plants fix nitrogen which becomes 

 available for wheat the next year. A rotation involves differ- 

 ent methods of cultivation, which are often very effective in 

 eradicating certain weeds. Continuous cropping and culti- 

 vation change the physical condition of the soil. This often 

 results, particularly in prairie regions, in the soil blowing and 

 drifting. Rotation of crops, especially N when grass is intro- 

 duced, will soon return the soil to its proper physical condition 

 and prevent blowing. There is little profit in using commercial 

 fertilizers unless rotation of crops is practiced. 



Comparative Utility of Crop Rotation. As a rule the pioneei 

 farmer in a new country never practices much rotation of 

 crops. This is one of the factors of high and intensive farm- 

 ing, which is never found on the frontier. The main reason 

 for this is that land, being plentiful, is cheap, while all other 

 forms of capital, as well as human labor, are comparatively 

 scarce and high. It is but natural for the pioneer to endeavor 

 to diminish those elements entering into the cost of production 

 which are most expensive by substituting others less expensive. 

 Land is the cheapest factor, so he uses this more lavishly, not 

 to say recklessly, and saves the labor and other capital re- 

 quired to farm intensively, which is to cultivate more care- 

 fully, to rotate and diversify crops, to keep stock, to fertilize, 

 to irrigate, and to follow many other practices requiring addi- 

 tional labor and capital. This fundamental advantage of ex- 

 tensive farming due to the cheapness and abundance of land 



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