538 



PRINCIPLES OP SOIL MICROBIOLOGY 



form of ammonium sulfate and cottonseed meal change into nitrates 

 more rapidly in arid soils, while dried blood and the soil's own 

 nitrogen change into nitrates with greater vigor in humid soils. 78 



Days o 



.■3 1000 



a 



3 



"8 



o 

 S 



a 



3 



Fig. 38. Influence of organic matter upon the formation of nitrate in the soil: 



a, soil receiving 0.2 per cent ammonium sulfate, — — nitrate N, ammonia 



N; b, soil receiving 0.25 per cent peptone,—"— nitrate N, ammonia N; 



c, soil receiving 1 per cent peptone, nitrate nitrogen, ammonia N; 



d, soil receiving 1 per cent dextrose •••• nitrate N, ammonia N (after 



Barthel and de Rossi). 



Abundant nitrate formation and even extensive accumulation may 

 take place in semi-arid soils. 79 The amount and application of irriga- 



78 Lipman, C. B., Burgess, P. S., and Klein, M. A. Comparison of nitrifying 

 powers of some humid and some arid soils. Jour. Agr. Res., 7: 47-82. 1916. 



79 Stewart, R. The intensity of nitrification in arid soils. Centrbl. Bakt. 

 II, 36: 477-490. 1913; Sackett, \V. G. The nitrifying capacity of certain Colo- 



