172 



Bacteria in Relation to Country Life 



rod-shaped organisms. The demonstration was thus 

 furnished that the oxidation of ammonia to nitrites is 

 performed by two distinct groups of organisms found in 

 all soils. They seem to work in unison, since the nitrites 

 are changed into nitrates almost as fast as they are 

 formed. Under abnormal conditions favoring the growth 

 of the nitrous ferment, but not of the nitric ferment, 

 there may be an accumulation of nitrites. Recently 

 it was announced by Kaserer that he had isolated an 

 organism capable of changing ammonia directly into 

 nitrate. This discovery, if substantiated by other 

 investigators, promises important revelations concern- 

 ing the transformation of nitrogenous organic materials 

 in the soil. 



Importance of nitrification. The vast practical sig- 

 nificance of nitrification processes is apparent from the 

 fact that most of the nitrogen used 

 by crops is taken up in the nitrate 

 form. While there is much evi- 

 dence at hand to show that many 

 plants are capable of utilizing am- 

 monia as readily as nitrate nitrogen, 

 yet, because of the very rapid con- 

 version of ammonia into nitrate, the 

 latter is almost the exclusive source 

 of nitrogen. The rapidity with 

 which ammonia salts are changed 

 in the soil to nitrates is attested by the experience at 

 Rothamsted in England. It was the practice there to 

 apply the nitrogen on certain plots in the form of am- 

 monium sulfate in the fall. It was soon noticed, how- 



Fig. 28. Nitrite bacteria; 

 growth of the organ- 

 isms on the specially 

 prepared agar. 



