TRANSFORMATION OF MINERALS IN THE SOIL 653 



saccharides and ammonium salts are better sources of nitrogen than 

 other nitrogenous substances. The soluble bases (especially Ca) pre- 

 vent the solubility of phosphates; iron oxide influences the process 

 least. This would seem to indicate definitely that this process is rather 

 secondary in nature and depends upon the action of the products of 

 carbon and nitrogen metabolism upon the insoluble phosphate. 



The production of soluble phosphates was reported 28 to be associated 

 with the vital function of microorganisms. However, the existence of 

 specific enzymes capable of bringing into solution insoluble phosphates 

 has been questioned by Bazarevski, 29 who submitted evidence to show 

 that this process is chiefly a result of acid production by microorganisms. 

 Even if the organism does not form any acid in the medium, a part of 

 the phosphate may be assimilated by it, either by the action of carbon 

 dioxide or as a result of basic exchange between the soluble products 

 formed and certain soil constituents. The continuous removal of the 

 soluble phosphate by the growing organism and its synthesis into or- 

 ganic matter may sometimes bring about appreciable transformation. 

 The greatest amount of dissolution of the phosphate has been obtained 

 with ammonium salts and the least with nitrate ; this substantiates the 

 claim that the acids formed in the metabolism of the organisms, rather 

 than any enzymatic phenomena, are responsible for the process. In the 

 case of ammonium salts, the organisms remove the ammonium as a 

 source of nitrogen, leaving the S0 4 in the medium, while in the case 

 of the nitrate, the acid-ion is removed and the alkaline is left. 30 



The growing organism is capable of forming large quantities of 

 carbon dioxide and often appreciable quantities of organic acids, both 

 under aerobic and anaerobic conditions. One gram of bacterial cells 

 produces 0.25 to 0.5 mgm. of C0 2 in twenty-four hours and 1 gram of 

 fungus mycelium produces 0.13 to 0.18 mgm. C0 2 . As much as 6000 

 pounds of C0 2 may be given off in 200 days by one acre of normal soil, 

 on a 2,000,000 pounds basis. The soil atmosphere may contain 0.6 



28 Pozerski, E., and Levy, M. M. Sur l'exretion de composes phosphor's par 

 les microbes. Compt. Rend. Soc. Biol., 87: 1157-1159. 1922. 



29 Bazarevski, S. On the question of mobilization of phosphoric acid in the 

 soil by the agency of microorganisms (Russian). Moskau. 1916. 



30 Haselhoff, E. Untersuchungen iiber die Zersetzung bodenbildender Ges- 

 teine. Landw. Vers. Sta., 70: 53-143. 1909; Stalstrom, A. Beitrag zur 

 Kenntnis der Einwirkung steriler und in Garung befindlicher organischer Stoffe 

 auf die Loslichkeit der Phosphorsiiure des Tricalciumphosphats. Centrbl. 

 Bakt. II, 11: 724-732. 1904. 



