OXIDATION PROCESSES IN THE SOIL 531 



very active, leading often to a rapid diminution of available nitrogen, 45 

 as shown in table 52. 46 



Influence of organic matter upon nitrate formation. It has been 

 pointed out that small amounts of soluble organic matter are found to 

 retard the activities of nitrite and nitrate forming bacteria. Glucose, 

 which is so important for the activities of the majority of microorgan- 

 isms, is injurious in concentrations of 0.025 to 0.05 per cent. In the 

 soil, however, the organisms can stand high concentrations of organic 

 matter. 47 Miintz and Laine 48 concluded that organic matter or humus 

 in the soil may even be distinctly favorable to the activities of the 

 nitrifying organisms. The greater the organic content of the soil, the 

 more abundant is its bacterial flora and the more rapid will be the 

 process of nitrification taking place. It was later found 49 that, 

 even in solution, impure cultures may be favored by soil extracts. 

 According to Barthel, 50 the easily soluble organic substances must be 

 mineralized in the soil before nitrate formation takes place, if no in- 

 jurious effect is to occur (figure 38). Difficultly soluble organic sub- 

 stances have little effect on the process. 



Influence of salts upon nitrate formation. Winogradsky 51 observed 

 that ammonium salt had a distinctly injurious action upon nitrate- 

 forming bacteria; this action was found to be due not to the salt itself 

 but to free ammonia. 52 At as low a concentration as 0.001 N of am- 



45 Arnd, Th. tlber schadliche Stickstoffumsetzungen in Hoehmoorboden als 

 Folge der Wirkung starker Kalkgaben. Landw. Jahrb., 47: 372-442. 1914; 

 49: 191-213. 1916; Tulin, A. F. The injurious action of high doses of lime on 

 podsol soils, in connection with the nature of the biological processes in them 

 (Russian). Trans. Institute Fertilizers No. 26, 1925. 



46 Willis, L. G. Nitrification and acidity in the muck soils of North Carolina. 

 Tech. Bui. 24, N. C. Agr. Exp. Sta. 1923. 



47 Stevens, F. L., and Withers, W. A. Studies in soil bacteriology. IV. The 

 inhibition of nitrification by organic matter, compared in soils and in solutions. 

 Centrbl. Bakt. II, 27: 169-186. 1910. 



48 Miintz, A., and Laine, E. Role de la matiere organique dans la nitrifica- 

 tion. Compt. Rend. Acad. Sci., 142: 430-435. 1906. 



49 Coleman, 1908 (p. 391); Maze— Compt. Rend. Acad. Sci., 152: 1625. 1911; 

 Fremlin— Jour. Hyg., 14: 149. 1914; Wright, 1916 (p. 552); Barthel —Centrbl. 

 Bakt. II, 49: 382. 1919; Greaves and Carter— Jour. Agr. Res., 6: 889. 1916; 

 Makrinow, J— Centrbl. Bakt. II, 24: 415. 1919; Lohnis and Green, 1914 (p. 

 579). 



60 Barthel, C. Die Einwirkung organischer Stoffe auf die Nitrifikation und 

 Denitrifikation im Ackerboden. Ztschr. Garungsphysiol., 4: 11-48. 1914. 



61 Winogradsky, 1890 (p. 389). 

 62 Meyerhof, 1916 (p. 390). 



