608 



PRINCIPLES OF SOIL MICROBIOLOGY 



Soluble 



Sulfates 



inlOOCC 



Mg. of SO 4 



150 



OH 



2.4 



3.4 



120 



100 



4.4 



70 



5.4 60 



Soluble 



Phosphates 



inlOOCC 



Mcj. of: p 

 240 



200 



160 



120 



80 



40 



Days 



15 



5 10 



Incubation period 



Fig. 44. Course of sulfur oxidation and transformation of insoluble phosphate 

 into soluble forms by Th. thiooxidans in liquid media (from Waksman and Joffe). 



The addition of CaC0 3 frequently stimulates sulfur oxidation in the 

 soil; 20 it also prevents the injurious effect of sulfur oxidation upon the 



20 Brown, H. D. Sulfofication in pure and mixed cultures with special refer- 

 ence to sulphate production, hydrogen-ion concentration and nitrification. Jour. 

 Amer. Soc. Agron., 15: 350-3S2. 1923. 



