CHAPTER XVIII 

 GREEN-MANURES 



Crops that are grown primarily for the purpose of being 

 plowed under to improve the soil are called green-manures. 

 They may benefit the soil in one or more of four ways : (1) By 

 utilizing soluble plant-food material that would otherwise 

 leach from the soil ; (2) by incorporating vegetable matter 

 with the soil ; (3) leguminous crops, when used, add to the 

 available nitrogen of the soil ; (4) plant-food materials from 

 the lower soil may be brought tfcrthe surface soil. 



A large number of crops may be used for this purpose, 

 while the climate determines to some extent which crops 

 should be used. Crops that can be planted in the fall to 

 grow during the cool weather may be utilized when otherwise 

 the land would frequently lie bare. Leguminous crops have 

 the great advantage of acquiring nitrogen from the air. Deep- 

 rooted crops usually accumulate a large amount of nutriment 

 from the soil and considerable from the lower depths. They 

 are therefore useful in bringing plant-food material to the 

 upper layers of soil. Succulent crops decompose easily, and 

 dry out the soil less, when plowed under, than do woody crops. 

 Crops with extensive root- systems prevent loss of soluble 

 matter more thoroughly than do plants with small root 

 systems. 



294. Protective action of green-manures. — It has been 

 shown in section 121 that the growth of crops on land may 

 prevent a large loss of plant-food material, especially nitrogen 



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