60 THE BOOK OF ALFALFA ,' 



that these nodules are the homes of bacteria, microscopic 

 vegetable organisms obtaining their sustenance from 

 the nitrogen of the air and the starch of the plant ; that 

 they collect much more nitrogen than they need, the 

 over-supply being taken up by the alfalfa, which, after 

 these nodules are formed and occupied, takes no more 

 nitrogen from the soil, but annually stores about its roots 

 more from the air, thus adding to the nitrogen supply 

 in the soil instead of taking from it as do all other farm 

 crops except the legumes. Each legume — clover, alfalfa, 

 cowpeas, etc. — has a distinct species of bacteria, or at 

 least bacteria with a distinct development, excepting, 

 as has been found, that Sweet clover (Melilotus alba) 

 and Bur clover {Medicago denticulata) develop the same 

 species as does alfalfa. 



BUYING INFECTED SOIL 



Several methods of preparing land for alfalfa by 

 introducing its peculiar bacteria have been suggested, 

 and practiced to some extent. Many farmers and experi- 

 menters have used with success infected soil upon their 

 lands; soil from established alfalfa fields, or that from 

 along the roads or creeks where the Sweet clover or Bur 

 clover has been growing. This soil is spread upon the 

 field or sown with alfalfa just before the seeding. If 

 the drill is to be used the inoculated soil is spread on and 

 harrowed in. If the seed is to be broadcasted, the 

 infected soil may be harrowed in with the seed. It is 

 better, however, to harrow this infected soil in thor- 

 oughly before seeding. Experiment stations recommend 

 an application of two hundred pounds of such soil to 



