616 PRINCIPLES OF SOIL MICROBIOLOGY 



potassium when introduced into the soil is readily assimilated by 

 plants. 41 



Another interesting process in which the oxidation of sulfur may 

 be utilized is the neutralization of the alkalinity of black alkali soils. 

 In view of the fact that the alkalinity of such soils is due not only 

 to the presence of sodium carbonate but to the fact that sodium 

 forms the saturating base in the zeolitic silicates, large quantities of 

 sulfur have to be applied before any marked effect is observed. The 

 sulfur is readily oxidized and the sulfuric acid changes the carbonates to 

 bicarbonates and then to sulfates. However, when insufficient amounts 

 of sulfur are used, the zeolitic sodium will soon form fresh carbonates 

 and the reaction of the soil will again become markedly alkaline. The 

 acid not only neutralizes the carbonates, but coagulates the colloids, 

 thus making the soil more permeable and allowing leaching to take 

 place. 42 



An increase in the acidity of the soil which results from the applica- 

 tion of sulfur can be utilized for the control of organisms which cause 

 plant diseases, such as Act. scabies causing potato scab. However, 

 an increased acidity may prove injurious to microorganisms whose 

 activities are essential for the normal biochemical soil processes, such 

 as the bacteria concerned in the process of nitrification, etc. 43 The 

 practical application of sulfur must, therefore, always be accompanied 

 by a careful study of the reaction of the soil. 



41 Rudolfs, W. Sulfur oxidation in inoculated and uninoculated greensand 

 mixtures and its relation to the availability of potassium. Soil Sci., 14: 307- 

 319. 1922. 



42 This process was studied in detail by Hibbard, P. L. Sulfur for neutralizing 

 alkali soil. Soil Sci., 11: 385-387. 1921; Rudolfs, W. Sulfur oxidation in 

 "Black alkali" soils. Soil Sci., 13: 215-229. 1922; Joffe, J. S., and McLean, H. C. 

 Alkali soil investigations. Soil Sci., 17: 395-409. 1924; 18: 13-30, 133-149, 237- 

 251. 1924. 



43 The influence of sulfur oxidation upon microbiological activities in the 

 soil is discussed in detail by Vogel, J. Die Einwirkung von Schwefel auf die 

 bakteriellen Leistungen des Bodens. Centrbl. Bakt. II, 40: 60-83. 1914. 



