ROTATION OF CROPS 2/7 



tion, but other bacterial changes are also affected. The 

 entire bacterial flora of a soil may be changed by 

 modifications of systems of cultivation, cropping, and 

 manuring. By means of rotating nitrogen-producing 

 and nitrogen-consuming crops, grain can be sold from 

 the farm without purchasing nitrogenous manures. 

 Conservation of the nitrogen and humus of the soil 

 is one of the most important points to consider in the 

 rotation of crops. 



334. Influence of Rotation upon the Mechanical Con- 

 dition of Soils. - - With different kinds of crops the 

 mechanical condition of soils is constantly undergoing 

 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 rotation the action of the 

 crop upon the mechanical condition of the soil should 

 be considered, otherwise the soil may get into poor 

 condition to retain water or become so loose that heavy 

 losses occur through wind storms. Sandy soils are 

 improved by methods of cropping which compact the 

 soil, while heavy clays require the opposite treatment. 

 The rotation should be made to conform to the re- 

 quirement of the soil. 



335. Economic Use of Soil Water. The rotation 

 should not be of such a nature as to make excessive 



