ROTATION OF CROPS 24I 



then with barley, and finally with flax, because the 

 flax would be placed at a serious disadvantage follow- 

 ing two strong feeding crops. If reversed, the crops 

 would be placed in order of assimilative power, and the 

 best use would be made of the sod crop residue. 

 When crops of dissimilar feeding habits follow each 

 other in rotation not only are the crop residues used to 

 the best advantage, but the soil is relieved of excessive 

 demands on special elements. For example, wheat 

 and clover take different amounts of potash and lime 

 from the soil. Wheat has the power of feeding upon 

 silicates of potash which clover cannot assimilate, 

 hence wheat and clover in rotation relieve the soil of 

 excessive demands on the potash. 



312. Nitrogen-consuming and Nitrogen-producing 

 Crops. — It is possible in a five-course rotation to main- 

 tain or even increase the nitrogen of the soil without 

 the use of nitrogenous manures. In Section 131 an ex- 

 ample is given of a rotation which has left the 

 soil with a better supply of nitrogen than at the begin- 

 ning. When a soil produces a good clover crop once 

 in five years, and stable manure is used once during 

 the rotation, the soil nitrogen is not decreased. By 

 means of rotating nitrogen-producing and nitrogen- 

 consuming crops it is possible to sell nitrogenous grain 

 products from the farm without purchasing nitroge- 

 nous manures. The conservation of the nitrogen of 

 the soil is the most important point to consider in the 



