OXIDATION PROCESSES IN THE SOIL 527 



proper aeration of the culture, the nitrate forming organisms, in liquid 

 culture, may oxidize 4 to 5 grams NaN0 2 per liter in 24 hours. 



According to Miyake, 27 nitrification in the soil obeys the law of 

 autocatalysis; i.e., the reaction is at first slow, then becomes more 

 rapid and finally comes to a standstill, as a result of accumulation of 

 nitrates. The relation between nitrite oxidation and concentration of 

 substrate is given in figure 18, which shows a rapid increase in oxida- 

 tion with an increase in nitrite concentration up to 0.05 per cent. An 

 optimum is reached with 0. 1 per cent of substrate, with a slow decrease 

 to 0.3 per cent. This is followed by a gradual drop, so that in a 4 per 

 cent solution of nitrite, oxidation is only 26 per cent of the optimum. 

 A detailed discussion of the oxidation process, especially from the 

 point of view of growth and respiration is given elsewhere (p. 388). 



Nitrate formation from inorganic salts and from organic nitrogenous 

 compounds. Schloesing 28 compared the formation of nitrates from 

 various ammonium salts added to the soil and found that the following 

 relative amounts of nitrogen (in milligrams) are nitrified per day: 



NH 4 C1 - 3.4, (NHO2SO4 - 9.0, (NH 4 ) 2 C0 3 - 4.0 



Ammonium salts of organic acids are also nitrified rapidly. 29 



It was thought at first that organic matter can be nitrified directly. 

 However, Miintz 30 has shown that organic matter has to be decomposed 

 first and ammonia liberated, before nitrates can be formed. Omeli- 

 ansky 31 later obtained negative results also for urea, asparagine, methyl- 

 amine, dimethylamine and egg-albumin, so that he concluded that all 

 forms of organic nitrogen have to be transformed first into ammonia be- 

 fore they can be nitrified. The same was found to hold true for calcium 

 cyanamide. 32 When the processes of nitrate formation from ammo. 



11 Miyake, K. On the nature of ammonification and nitrification. Soil 

 Sci., 2: 481-192. 1916; Miyake, K., and Soma, S. Jour. Biochem. Tokio, 1: 

 123-9. 1922. 



28 Schloesing, 1885 (p. 525). 



29 Boullanger, E., and Massol, L. Etudes sur les microbes nitrificateurs. 

 Ann. Inst. Pasteur., 18: 181-196. 1904; Lohnis, F., and Blobel, S. Die Ursachen 

 der Wirkungsunterschiede von Schwefelsaurem Ammoniak und Chilesalpeter. 

 Fuhlings landw. Ztg., 57: 385^02. 1908. 



30 Miintz, A. Sur la decomposition des engrais organiques dans le sol. 

 Compt. Rend. Acad. Sci., 110: 1206-1209. 1890. 



Jl Omelianski, \V. Uber die Nitrifikation des organischen Stickstoffes. 

 Centrbl. Bakt. II, 5: 473^90. 1899; 9: 63-65. 1902. 



32 de Grazia, S. Sulla nitrificazione della cianamide di calcio in diversi tipi 

 di terreno. Staz. sper. agr. ital. Modena, 41: 241-257. 1908. 



