50 



Effective Farming 



been found, however, that, if the soil is kept in good physical 

 condition and is well drained, denitrification probably will 

 not occur. This, then, is another reason for handling the soil 



in a manner to keep 

 it in good tilth. 



As stated in para- 

 graph 24, bacteria 

 that live on the roots 

 of legumes are able 

 to take nitrogen from 

 the air and convert 

 it into a soluble 

 form. On the roots 

 of legumes that are 

 growing under f avor- 

 able conditions, 

 there are tubercules, 

 'or knots (Fig. 20). 

 In these live the bac- 

 teria that do the 

 work of changing the 

 nitrogen into a solu- 

 ble form. The bac- 

 teria receive food 

 from the plant on 

 which they are found 

 and in turn benefit 

 their hosts by mak- 

 ingthenitrogensolu- 

 ble. If the legumes are properly inoculated with bacteria, some 

 of the nitrogen may remain for crops that grow later in the soil. 

 Thus the land on which clovers or other legumes are growing 

 is richer in nitrogen than before the crop was planted. This 

 accounts for the good crops that usually follow legumes on 

 a field. Legumes are often planted and, instead of being 



FIG. 20. Cowpea root showing tubercles. 



