396 



PRINCIPLES OF SOIL MICROBIOLOGY 



mum points at 9.4 and 7.6. Warington 21 believed that nitrification of 

 ammonia could take place only with ammonium carbonate and that 

 the function of carbonates in solution was to supply the ammonium 

 carbonate by interaction with the other ammonium salts. This was, 

 however, found to be incorrect by Bonazzi, 22 and others. According 

 to Bonazzi, the oxidation of ammonia can be considered to take place 

 in two steps: (a) respiration, with resultant gain in energy and syn- 

 chronous nitrogen absorption; (6) nitrogen assimilation (nitrification 



100 



90 



80 



13 



• 1-1 



3 



30 



20 



10 



/__ _._ . . - 



0,1 



0,3 



0,4 



0.6 



0,7 



0.8 



1 atmosphere 



Fig. 20. Influence of oxygen pressure upon the oxidation of nitrite to nitrate 

 (from Meyerhof). 



proper) whereby oxidation of the absorbed nitrogen takes place, the 

 utilized portion goes to make up the following cell generations, ni- 

 trous acid is split off and excreted as a non-utilizable product, and 

 energy is liberated. 



21 Warington, 1878-1891 (p. 63). 



22 Bonazzi, A. On nitrification. IV. The carbon and nitrogen relations of 

 the nitrite ferment. Jour. Bact., 6: 479-499. 1921. 



