ROTATION OF CROPS 231 



314. Principles Involved in Crop Rotation, In 



the systematic rotation of crops there are a few funda- 

 mental principles with which all rotations should con- 

 form. Briefly stated these principles are : 



1. Deep and shallow rooted crops should alternate. 



2. Humus-consuming and humus-producing crops 

 should alternate. 



3. Crops should be rotated so as to make the best 

 use of the preceding crop residue. 



4. Crops should be rotated so as to secure nitrogen 

 indirectly from atmospheric sources. 



5. Crops should be rotated so as to keep the soil in 

 the best mechanical condition. 



6. In arid regions crops should be rotated so as to 

 make the best use of the soil water. 



7. An even distribution of farm labor should be se- 

 cured by a rotation. 



8. Farm manures and fertilizers should be used in 

 the rotation where they will do the most good. 



9. Rotations should be planned so as to produce 

 fodder for stock, and so that every year there will be 

 some important crop to be sold. 



315. Deep and Shallow Rooted Crops. When 

 deep and shallow rooted crops alternate, the draft upon 

 the surface soil and subsoil is more evenly distributed. 

 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 re- 



