

UTILIZATION OF NITROGEN-FIXING POWERS OF LEGUMES. 105 



species grow better in some climates than others, and certain soils 

 seem to be, for some reason, better adapted for particular species, 

 quite independent of the question of the presence of the proper soil 

 bacteria. By the proper consideration of the facts of his experience 

 the farmer can, without much difficulty, determine what species of 

 legume grows best in his soil. The most vigorously growing 

 legume is the best. In clay soils red and yellow clover, lupin, sera- 

 dilla, horse beans, and 'vetches are successfully grown. Which of the 

 varieties is to be selected must be determined by the conditions of 

 the soil and the needs of the farmer for the particular crop which he 

 raises. The essential feature must be that the species selected 

 should be one that will grow well in the soil in question, otherwise 

 the advantage of the nitrogen fixation will not be obtained. 



2. Insuring Presence of Proper Bacteria. In order that the soil 

 may increase its nitrogen store it is evidently necessary for tubercles 

 to develop in large numbers on the roots of the legumes. For this 

 purpose, of course, it is necessary that the proper variety of bacteria 

 shall be present in the soil, otherwise no tubercles will be formed, or 

 the tubercles formed will be few and small. To insure this result 

 may sometimes require a little experimenting and observation. 

 Some species of legume find in a certain soil the tubercle organism 

 adapted to them, while other species of legume may not find the 

 proper organisms in the same soil. The soy bean is a most excellent 

 crop for nitrogen gathering since it is an extremely luxurious grow- 

 ing legume, producing abundant tubercles and a large fixation of 

 nitrogen when supplied with the organisms which produce tubercles. 

 But in order to make use of this crop it may be necessary to import 

 the proper bacteria from other soils. On the other hand, there are 

 some species of legumes, like most kinds of peas, which are capable 

 of growing in most soils and producing an abundance of tubercles. 



Further, a legume, which, during the first season produces only a 

 small number of tubercles, may succeed better the second year than 

 the first and may fix more nitrogen. The growth of the crop in the 

 soil during the first year apparently either increases the number of 

 soil organisms appropriate to this particular legume or produces 

 such changes in the physiological character of the bacteria present 



