OXIDATION PROCESSES IN THE SOIL 



535 



concentration of oxygen for nitrate formation was found 68 to be 35 

 per cent. Similar observations were made for the influence of CO2 con- 

 centration. 69 Some believed that a supply of this gas is very important 

 both for the nitrite and nitrate forming organisms. Owen, 70 however, 

 found that C0 2 (above a certain concentration) has no effect on nitrate 

 formation in the soil. In view of the fact that the C0 2 is used by the 

 organism for the building up of its cells chemosynthetically, its presence 

 is necessary for growth. But since the organism produces only a 

 limited amount of growth, only small amounts of C0 2 are required 



Parts per 

 million of 

 nitrates 



Percentage 

 of oxygen 10 20 30 40 50 60 70 80 90 roo 



Fig. 35. Influence of oxygen tension upon nitrate formation in the soil (from 

 Plummer). 



even for the maximum nitrification. Larger amounts seem to act 

 merely as an inert gas. In general, while only small amounts of C0 2 

 are required, an excess of oxygen is essential and a lack of this gas 

 will produce anaerobic conditions which will lead to nitrate reduction 

 until all the nitrates are destroyed. 



ts Plummer, J. K. Some effects of oxygen and carbon dioxide on nitrification 

 and ammonification in soils. N. Y. (Cornell) Univ. Agr. Exp. Sta. Bui. 384. 

 1916. 



"Coleman, 1908 (p. 391). 



70 Owen, W. L. Effect of carbonates upon nitrification. Georgia Agr. Exp. 

 Sta. Bui. 81. 1908. 



