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THE ESSENTIALS OF AGRICULTURE 



97. The use of green manure. A green-manure crop is one 

 which is grown and turned under for the purpose of enriching 

 the soil in organic matter. The most profitable crops for this 

 purpose are usually the legumes, because of the nitrogen they 

 secure from the air. In the case of clover about two thirds of 

 the total nitrogen of the plant is in the tops, which are removed 

 as hay if the crop is harvested, while one third is in the roots 



FIG. 39. Cowpeas in rotation with grain crops help maintain soil fertility 

 Photograph from Missouri Experiment Station 



and stubble. On average soils the clover plant gets about one 

 third of the nitrogen from the soil and about two thirds from 

 the air. Hence, where a clover crop is removed from the land 

 for hay and only the stubble and roots are left as a fertilizer, 

 the gain of nitrogen by the soil is small. If the crop is fed 

 and the manure is carefully saved and applied to the soil, about 

 70 per cent of the nitrogen in the hay can be thus returned, 

 and the soil will be made richer in nitrogen than before the 

 clover was grown upon it. The greatest gain to the soil from 



