ROTATION OF CROPS 2/5 



330. Deep- and Shallow-rooted Crops. --When deep- 

 and shallow-rooted crops alternate, the draft upon the 

 surface soil and subsoil is more evenly distributed and 

 the physical condition of the soil is improved. In many 

 soils, nitrogen and phosphoric acid are more abundant 

 in the surface soil while potash and lime predominate 

 in the subsoil. When such a condition exists the 

 alternating of deep- and shallow-rooted crops is very 

 beneficial, because the surface soil is gradually enriched 

 by accumulations of fertility from the subsoil, deposited 

 by decay of the residue of the deep-rooted crops. 



331. Humus- consuming and Humus-producing Crops. 



- When grain or hoed crops are grown continuously, 

 oxidation of the humus occurs, and the chemical and 

 physical properties of the soil are entirely changed by 

 loss of the humus. The rotating of grass and grain 

 crops and the use of stable manure serve to maintain 

 the humus equilibrium. On some soils lime may be re- 

 quired along with the humus to prevent the formation 

 of humic acid, and in such cases the best conditions 

 exist when both lime and humus materials are supplied. 

 Alternation of humus-producing and humus-consuming 

 crops is one of the essentials of a rotation. 



332. Crop Residues. Crop residues should always 

 be placed at the disposal of weak feeding crops. After 

 a light clover and timothy sod, wheat or flax should 

 be grown in preference to barley or mangels. The 



