ORGANISMS IN THE SOIL 439 



cium phosphates insoluble. He would limit the solvent 

 action of bacteria to the effect of the acids they produce. 



Sackett, Patten, and Brown * have in a measure repeated 

 Stoklasa's experiments and obtained somewhat similar 

 results, which lead them to conclude that there is a 

 solvent agent other than the acids produced by the 

 bacteria. 



It would appear from these experiments that bacteria, 

 and possibly fungi, commonly found in soils act on tri- 

 calcium phosphate in such a manner as to render a part 

 of it soluble. Nevertheless, experiments that have been 

 conducted for the purpose of ascertaining whether tri- 

 calcium phosphate in soils is rendered more readily avail- 

 able to plants when large quantities of decomposing organic 

 matter are present than when this is not the case, have 

 not, in the main, indicated that the decomposing organic 

 matter increases availability of the phosphorus (par. 439). 

 An explanation of this may possibly be found in the 

 occurrence of a reverse biological process which results 

 in the transformation of soluble phosphates into insoluble 

 ones, the occurrence of such a process having been found 

 by Stoklasa 2 and others. 



The carbon dioxide produced by bacteria is a solvent 

 for many of the silicates of the soil, and may free calcium 

 and potassium from hornblende and feldspar. 



Various groups of sulfur bacteria, through the produc- 

 tion of H 2 S and H 2 S0 4 , act on iron in the soil and con- 

 vert it into sulfide and sulfate. Carbon dioxide also 



1 Sackett, W. G., Patten, A. J., and Brown, C. W. The 

 Solvent Action of Soil Bacteria upon the Insoluble Phosphates 

 of Raw Bone Meal and Natural Rock Phosphate. Michigan 

 Agr. Exp. Sta., Special Bui. 43. 1908. 



2 Stoklasa, J. Biochemischer Kreislauf des Phosphat-Ions 

 imBoden. Centrlb. f. Bakt., II, Band 29, Seite 385-519. 1913. 



