118 



ELEMENTS OF AGRICULTURE 



cicola) that enters the roots of the legume. These bacteria 

 are able to use the free nitrogen of the soil air. After they 

 have used the nitrogen, it is left in compounds that the 

 plant can make use of, so that a legume can grow with no 



FIG. 53. Nodules on the roots of hairy vetch 



nitrogen in the soil if other conditions are favorable. The 

 legume roots furnish a home for the bacteria and in return 

 are supplied with nitrogen. These bacteria do not live on 

 the roots of any other farm crops. 



Most soils contain the bacteria, so that all we need to 

 do is to sow the legume seed; but, if the bacteria are ab- 

 sent, we must sow them also. In much of the eastern part 

 of the United States, bacteria need to be supplied for 

 the growth of alfalfa. The best way of supplying them is 

 to scatter a bushel or more of soil from a successful alfalfa 

 field on each acre of land that needs to be inoculated. 

 Soy-beans, cowpeas and vetches often need to be inocu- 

 lated when they are grown on a soil for the first time. 



Legumes are also abJe to take nitrogen from the soil 



