MANURE: 



291 



(2) To prevent loss of plant food by leaching. The soil is 

 covered with a crop instead of being left bare. The crop takes 

 up most of the plant food in solution and prevents it being washed 

 out of the soil. 



(3) To secure nitrogen from the air for the use of succeeding 

 crops. For this purpose, leguminous crops should be grown, and 

 they must be infected with the proper organism. 



Green manures should, if possible, be allowed to mature before 

 being plowed under. A large mass of easily decaying matter 

 may sour the soil and injure it for some years. Lands which are 

 decidedly wet are also not benefited by green manures, as they 

 may denitrify. An acid condition of the soil may be corrected by 

 lime. 



As a rule, it is best to follow green manures with cultivated 

 crops. The tillage of such crops hastens the decay of the 

 vegetable matter, and by aerating the soil, favors additional nitro- 

 gen fixation by the soil bacteria. Corn, cotton, potatoes, and 

 heavy tobacco derive great benefit from green manures. 



The following table shows the effects of green manures on 

 crops compared with crops on the same soil which had no green 

 manure. 



Fallen leaves and stubble have some fertilizing value, even 

 when the crop is cut for hay. For example, at the Alabama Ex- 

 periment Station, 36.6 of the entire weight of the cowpea plant 

 was found to be in the fallen leaves and stubble. The hay in one 

 experiment contained 55.8 pounds nitrogen per acre, the fallen 

 leaves and stubble 31.4 pounds. 



