THE NITROGEN CYCLE 



449 



experiments show that in the same soil nitrites may 

 sometimes accumulate, indicating conditions more favor- 

 able to the development of the Nitrosomonas bacteria. 



To tzntmaf 



; Free wrrope/? ~ a . a 



^rt/TG/F/flAT/ON 



\. ... -..-.-. xr*^--:- : r 

 .-/.. : .>>>^ 



FIG. 61. Diagrammatic representation of the movements of nitrogen 

 between soil, plant, animal, and atmosphere. This has been termed 

 the nitrogen cycle. 



The formation of nitrates usually follows closely on the 

 production of nitrites, so that there is rarely more than 

 a trace of the latter to be found in soils. A soil favorable 

 to the process of nitrification is usually well adapted to 

 all the processes of nitrogen transformation. 



Marked differences have been found in the nitrifying 

 power of bacteria from different soils. Highly productive 

 soils have generally been found to contain bacteria having 

 greater nitrifying efficiency than those from less produc- 

 tive soils, but this may not always be the case, as other 

 factors may limit the productiveness. 



369. Effect of organic matter on nitrification. A 

 peculiarity in the artificial culture of nitrifying bacteria 



2G 



