658 



PRINCIPLES OF SOIL MICROBIOLOGY 



fore, very limited. Nitrification of organic nitrogenous compounds like 

 dried blood does not increase the amount of citrate-soluble phosphate 

 when rock phosphate is added to the soil. The nitrification of ammo- 

 nium sulfate in normal soils does not have any appreciable effect upon the 

 solubility of rock phosphate. However, the concentration of the water- 

 soluble calcium is increased in both instances, due largely to the action 

 of the acid upon the calcium present in the soil in the form of silicates. 40 



TABLE 73 

 Effect of nitrification on the solubility of tricalcium phosphate in soil* 



* The ammonium sulfate was added at the rate of 0.01 gram of nitrogen per 

 100 grams of soil; an equal quantity of nitrogen was added in the form of dried 

 blood; tri-calcium phosphate — 0.10 gram and calcium carbonate — 0.25 gram per 

 100 grams of soil. 



The transformation of rock phosphate into soluble forms by sulfuric 

 acid formed from the oxidation of sulfur by microorganisms is very 

 similar to its transformation by the nitrous acid. In pure culture or 

 in composts, the transformation of the phosphate is rapid and almost 

 complete. In the soil, the sulfuric acid tends to transform the calcium 



*° Ames, J. W. Solvent action of nitrification and sulfofication. Ohio Agr. 

 Exp. Sta. Bui. 351. 1921. 



