OXIDATION PROCESSES IN THE SOIL 539 



tion water has an appreciable influence upon the process of nitrate 

 formation in arid and semi-arid soils. 80 



Air drying has a favorable effect upon the formation of nitrates in 

 the soil; this effect is noticeable even after spreading out the soil for 

 twenty-four hours and then remoistening. 81 Freezing of the soil in 

 winter was also found to improve the nitrifying power of the soil. 82 

 According to Mtintz and Gaudechon, 83 maximum nitrifying activities 

 take place in spring (March 28 to April 25). 



Conditions which tend to promote nitrate formation in the soil are: 84 

 (1) temperature of 37.5°C, (2) an abundant supply of air (oxygen), 

 (3) proper moisture supply, (4) a favorable reaction (pH greater than 

 4.6), (5) presence of carbonates or other buffering agents, and (6) 

 absence of large quantities of soluble organic matter in the soil. The 

 nature of the crop grown also influences the nitrate content of the soil, 

 as shown in figures 37 and 38. 



Further information on the influence of soil treatment upon nitrate 

 formation in the soil and on the correlation between nitrate formation 

 and other microbiological activities in the soil is given elsewhere (p. 715). 

 The formation of nitrates from organic and inorganic nitrogenous 

 fertilizers can be used as an index of the availability of the nitrogen 

 for the growth of higher plants. 85 



rado soils. Colo. Agr. Exp. Sta. Bui. 193. 1914; Science, 42: 452. 1914; Head- 

 den, W. P. The excessive quantities of nitrates in certain Colorado soils. Jour. 

 Ind. Engin. Chem., 6: 5S6-590. 1914; also Col. Agr. Exp. Sta. Bui. 155, 160, 178, 

 179, 183, 184, 186, 193; Kelley, 1916 (p. 532) ; Stewart, R., and Greaves, J. E. The 

 production and movement of nitric nitrogen in soil. Centrbl. Bakt. II, 34: 

 115-147. 1912. 



80 McBeth and Smith, 1914 (p. 536). 



81 Buddin, W. Note on the increased nitrate content of a soil subjected to 

 temporary drying in the laboratory. Jour. Agr. Sci., 6: 452-455. 1914. 



82 Lyon, T. L., and Bizzell, J. A. Some relations of certain higher plants to 

 the formation of nitrates in soils. N. Y. (Cornell) Univ. Agr. Exp. Sta. Mem. 1. 

 1913. 



83 Miintz, A., and Gaudechon, H. Le reveil de laterre. Compt. Rend. Acad. 

 Sci., 154: 163-8. 1912. 



"Owen, 1908 (p. 535). 



86 Withers, W. A., and Fraps, G. S. The rate of nitrification of some fertil- 

 izers. Jour. Amer. Chem. Soc, 23: 31S-326. 1901; also Ibid., 28: 213-233. 

 1906; Lipman, C. B. Some observations on the present status of the subject of 

 the availability of nitrogen in fertilizers. Jour. Ind. Engin. Chem., 9: 189. 

 1917: Cal. Agr. Exp. Sta. Bui. 260. 1915; Lipman, J. G., Brown, P. E., and 

 Owen, I. L. Relative availability of nitrogenous materials as measured by 

 nitrification. N. J. Agr. Exp. Sta., 31st Ann. Rept., 152-155. 1910. 



