TRANSFORMATION OF PHOSPHORUS BY SOIL MICROBES 175 



eral way as follows, where C refers to carbon in organic combina- 

 tion: 



2H3PO4 + C = 2H3PO3 + CO2 



Phosphoric 

 acid 



Phosphorous 

 acid 



H3PO4 + C = H3PO2 + CO2 



Hypophos- 

 phorous acid 



H3PO4 + 2C = PH3 + 2CO2 



Phosphine 



The possible significance and importance of these reactions in the 

 movements of phosphorus in arable soils are unknown. However, 

 since these processes are favored only by rather extreme reduction 

 conditions, it seems likely that phosphate reduction is not respon- 

 sible for very extensive changes under most soil conditions. The 

 extent of reduction of phosphates to the various substances by 

 bacteria under conditions favorable to the changes is shown in 

 Table 43. 



TABLE 43 



Reduction Products of Phosphate Formed by a Bacterium 

 (from Rudakov) 



The insoluble inorganic calcium phosphate may be present in 

 the soil in the native rock constituents or occur there subsequent to 

 the addition of various fertilizer mixtures. This form of phos- 

 phate is available to plants only in very limited amounts. How- 

 ever, as a result of interaction with the various organiis and inor- 

 ganic acids formed by microbes, the phosphate becomes changed 



