386 



THE PRINCIPLES OF SOIL MANAGEMENT 



Table LX 



Red or mammoth clover 



Crimson clover 



Alsike clover 



Alfalfa 



Cowpeas 



Soy beans 



Field peas 



Nitrogen 

 per acre 



Pounds 

 GO 

 54 

 50 

 112 

 48 

 60 

 55 



Not all of the nitrogen contained in these crops is 

 taken from the air. On soils rich in nitrogen, a consider- 

 able proportion may be obtained from the soil. On poor 

 soils, the proportion derived from the atmosphere is 

 considerably larger. The soils needing the nitrogen 

 most are those that benefit most largely. 



As the legumes need other fertilizing material in an 

 available form to produce a good yield, mineral ferti- 

 lizers or farm manure should be added to the soil. 

 Especially on run-down land this treatment is profitable. 



The crops should be plowed under while green and 

 succulent, as they decompose most readily at that stage. 

 On sandy soils and in dry regions, the soil may be 

 rendered so porous by plowing under a crop of dry 

 vegetation that the capillary rise of water is greatly 

 decreased, and the movement of air through the soil 

 causes it to become very dry. 



The perennial clovers (red, mammoth and alsike) 

 and alfalfa do not make a rapid growth after seeding, 

 which is a disadvantage when quick results are desired, 



