OXIDATION PROCESSES IN THE SOIL 523 



Deh^rain and Demoussy 11 demonstrated that, in the process of 

 oxidation of organic matter, oxygen is always taken up and carbon 

 dioxide set free. They distinguished between microbial and chemical 

 oxidation. Microbial oxidation is most active at normal temperatures 

 and is favored by increased temperatures, 65° being the maximum; the 

 quantities of oxygen absorbed and C0 2 produced are found to differ 

 with the soil type, moisture, aeration. The volume of C0 2 produced 

 is usually smaller than that of oxygen absorbed. Chemical oxidation 

 is low at normal temperatures and increases with temperature eleva- 

 tion, reaching a maximum at 110°. The C0 2 produced chemically 

 often exceeds the oxygen absorbed. Russell 12 found that oxidation 

 increases with an increase in the fertility of the soil. The rate 

 of oxidation increased with temperature, amount of water (up to a 

 certain optimum) and amount of CaC0 3 . Heating of soil to 100°C. 

 or treatment with volatile antiseptics, which were subsequently re- 

 moved, brought about a great increase in the oxygen absorbed. 



Schreiner and Sullivan 13 used a solution of aloin (0.125 per cent) for 

 the study of soil oxidation, the change in color being taken as an index 

 of oxidation. As determined by this method, oxidation in soil was 

 found to be non-enzymatic in nature and was considered a result of 

 interaction between inorganic constituents and certain types of organic 

 matter. The addition of salts of Mn, Fe, Al, Ca and Mg increased 

 this type of oxidation. Factors decreasing oxidation in soils were found 

 to bring about conditions which decrease soil productivity and vice 

 versa. 



Oxidation of organic matter and the formation of nitrates are among 

 the most important oxidation processes in the soil. The evolution of 

 C0 2 is usually taken as an index of the first (p. 681). 



Source of nitrates in the soil. The decomposition of proteins and 

 of other nitrogenous organic substances leads to the formation and 

 often the accumulation of ammonia in the soil. Under favorable 

 conditions, this is rapidly oxidized to nitrites and then to nitrates. 

 Under certain conditions, when the nitrifying bacteria are killed, as 



11 Deh£rain, P. P., and Demoussy, E. Sur l'oxydation de la matiere organique 

 du sol. Ann. Agron., 22: 305-337. 1896. 



12 Russell, E. J. Oxidation in soils, and its connection with fertility. Jour. 

 Agr. Sci., 1: 261-279. 1905; Darbishire and Russell, 1908 (p. 752). 



11 Schreiner, O., and Sullivan, M. X. Studies in soil oxidation. Bur. Soils, 

 U. S. Dept. Agr. Bui. 73. 1910; Schreiner, O., and Reed, H. S. The role of 

 oxidation in soil fertility. Ibid., Bui. 56. 1909. 



