550 PRINCIPLES OF SOIL MICROBIOLOGY 



to nitrite; the latter is then reduced to atmospheric nitrogen and NO. 

 This process was rather slow and independent of the oxygen supply. 

 Tacke 28 found that thirty-eight per cent of the gas mixture formed dur- 

 ing the process of nitrate reduction by bacteria may consist of N 2 0. 

 The formation of nitric oxide in the reduction of nitrates has also been 

 demonstrated by other investigators. 29 



The free nitrogen may, of course, be a result of the chemical interac- 

 tion of the oxides of nitrogen with ammonia : 



NH 4 N0 2 = N 2 4- 2 H 2 



Formation of nitrogen gas from organic compounds. To make the 

 study of formation of nitrogen gas in microbiological reactions complete, 

 attention should be called to the possibility of its formation in the 

 decomposition of organic compounds, especially as a result of rapid 

 oxidation of ammonia which is formed from those compounds: 



4 NH 3 + 3 2 = 6 H 2 + 2 N 2 

 2 NH 3 4- 3 H 2 2 - 6 H 2 + N 2 



These two processes may play an important part causing a loss of nitro- 

 gen in the decomposition of manure. 30 Nitrogen gas may also be formed 

 by the interaction of nitrites with amino compounds ; both of these may 

 be formed in the decomposition of organic matter rich in nitrogen 

 accompanied by the incomplete liberation of ammonia. 



-CH 2 -NH 2 + HN0 2 = -CH 2 -OH 4- H 2 + N 2 



Denitrification in the soil. Denitrification takes place in an entirely 

 different manner in soil than in solution. 31 In solution and in the presence 



28 Tacke, 1888 (p. 184). 



29 Lebedeff, A. J. tlber die Bildung des Stickoxyds bei dem durch Bac. 

 hartlebri eingeleiteten Denitrifikationprozess. Ber. deut. bot. Gesell., 29: 327- 

 329. 1911; Suzuki, S. Uber die Entstehung der Stickoxyde im Denitrifikations- 

 prozess. Centrbl. Bakt. II, 31: 27-49. 1911; see also Acklin, O. Zur Biochemie 

 des Bacterium pyocyaneum. Ein Beitrag zur Frage seines Stoffwechsels und 

 dessen Beziehungen zur intramolecularen Atmung. Biochem. Ztschr., 164: 

 312-370. 1925. 



30 Pfeiffer, Th., Franke, F., Gotze, C, and Thurmann, H. Beitriige zur 

 Frage uber die bei den Faulnis stickstoffhaltiger organischer Substanzen ein- 

 tretenden Umsetzungen. Landw. Vers. Sta., 48: 1S9-245. 1897; Street, J. P. 

 A review of the investigations concerning denitrification. N. J. Agr. Exp. Sta. 

 14th Ann. Rept.: 183-210. 1901; Lohnis, 1910, p. 488 (p. xiii). 



31 Koch, A., and Pettit, H. Uber den verschiedenen Verlauf der Denitrifika- 

 tion im Boden und in Fliissigkeiten. Centrbl. Bakt. II, 26: 335-345. 1910. 



