SOIL BACTERIOLOGY AS A FACTOR IN CROP PRODUCTION. 



9 



fating or complementary action of the different groups of soil bacteria 

 which transform nitrogen compounds is more clearly expressed by a 

 diagram. Figure 1, which is self-explanatory, shows the relation of 

 bacteria to some of the most essential changes. Since the study of 

 the nitrogen-accumulating power of legumes bearing root nodules 





BAC TERIA 



CHANGE 



NITROGEN GAS INTO 



PFtOTED NITROGEN 



BACTERIA OF LEGUME 



AND NON-LEGUME 



ROOT NODULES 



CHANGE 



NITROGEN GAS INTO 



PROTEID NITROGEN 



DENITRIFYING 



BACTERIA 



<-««<C/-/A/VGC-<— m 



AMMONIA TO 

 NITROGEN GAS 





//I 





<&*> 



o 



o 



y 



# 





Fig. 1.— Diagram showing the nitrogen changes produced in the soil by the action Of bacteria. The arrows 

 indicate the course of the changes which various groups of bacteria may produce in the n it r< men compounds 

 of the soil. 



deals with a definite and comparatively simple relation of a single 

 type of organism to a single type of plant, it has been possible to 

 develop these investigations upon a pure-culture basis; in other 

 words, it has been possible to isolate the nitrogen-fixing organism 

 from nodules of leguminous plants and with these cultures produce 

 77106°— Cir. 113—13 2 



