DRY-LAND CROPS 



which, while feeding on the legume, pro- 

 vide it with nitrogen drawn from the air. 

 These nitrifying bacteria vary in size 

 and shape according to the plant. Thus, 

 while in red clover, they are usually small 

 and round, on the bean they may reach 

 the size of a pigeon's egg. Again, every 

 legume has its own special strain of bac- 

 teria. For example, the germ on the 

 lucern root is different from that on the 

 clover plant and that on the cow pea is 

 distinct from that of the soy bean. Land 

 may be inoculated with the legume or- 

 ganisms by scattering soil from a field 

 where the crop has been recently grown, 

 or by using artificial cultures of the 

 proper bacteria. According to Piper, 

 there are in the United States fifteen 

 leguminous field crops which are grown 

 more or less extensively for feeding pur- 

 poses or for green manuring. In the 

 approximate order of their importance 

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