242 SOILS AND FERTILIZERS 



rotation of crops, because it is the most expensive ele- 

 ment and is the most liable to be deficient. 



313. Influence of Rotation upon the Mechanical 

 Condition of Soils. — With different kinds of crops, 

 the mechanical conditions of soils are constantly under- 

 going change. Grain crops and hoed crops tend to 

 make the soil open in texture. Grass crops have the 

 opposite effect. All soils should undergo periodic 

 compacting and loosening. Some require more of one 

 treatment than of the other. In a good rotation the 

 mechanical action of the crop upon the soil should be 

 considered, otherwise the soil may get into poor condi- 

 tion to retain water or become so loose that heavy 

 losses occur through wind storms. Sandy soils are 

 improved by those methods of cropping which compact 

 the soil, while heavy clays require the opposite treat- 

 ment. The rotation should be made to conform to 

 the requirements of the soil. 



314. Economic Use of Soil Water. — The rotation 

 should not be of such a nature as to make excessive 

 demands upon the soil water. For example, after a 

 grain crop has been produced, it is best in regions of 

 scant rainfall to plow the land and get it into condi- 

 tion to conserve the water for the next year's crop, 

 rather than to attempt to raise a catch crop the same 

 year. Crops removing excessive amounts of water 

 should not be grown too frequently. Sunflowers, for 

 example, remove twenty times more water than grain 



