250 



FIELD CROP PRODUCTION 



ment, from one place to another, of hay and seeds to 

 which the bacteria may cling, is also an important agency 

 in their distribution. 



249. Inoculation. In sections of the country where a 

 legume has been grown for many years, the bacteria that 

 work upon its roots may usually be found in almost all 

 soils. Thus, when red clover has been grown for years 



in a community, no 

 difficulty is usually ex- 

 perienced from a lack 

 of the proper variety 

 of bacteria. Some- 

 times, however, the 

 bacteria of certain 

 crops are not generally 

 distributed, especially 

 in sections of the 

 country where the 

 legume is a new crop. 

 Thus the variety that 

 forms the nodules upon 

 the roots of alfalfa is 

 not generally distributed in all parts of the country. When 

 they are not present, if the best results from the crop are 

 to be secured, they must be supplied artificially. While 

 the crop may sometimes be grown without the aid of the 

 bacteria, it is not usually desirable to do so, because the 

 plants then must draw upon the nitrogen supply of the 

 soil, and, like non-leguminous plants, they then become 

 soil exhausters instead of soil builders. Supplying the 

 bacteria artificially is called inoculation. 



250. Methods of inoculation. The general methods 

 employed in inoculation are : by applying prepared cul- 



FIG. 88. Nodules on the roots of soy 

 beans. 



