TRANSFORMATION OF MINERALS IN THE SOIL 661 



content of bacterial cells contains 4.0 to 25.6 per cent K 2 and of fungus 

 mycelium 8.7 to 39.5 per cent. The activities of bacteria may lead 

 to an increase in the available potassium, as in the decomposition 

 of organic matter by microorganisms and in the formation of acids 

 which liberate potassium from zeolites. Microbial activities may also 

 lead to a decrease of the available potassium through processes of 

 assimilation and transformation into organic materials. Orthoclase, 

 for example, may interact with acids formed by microorganisms or 

 with the calcium bicarbonate formed from insoluble calcium phosphate 

 by the action of carbon dioxide, to give, in both cases, soluble potas- 

 sium salts: 



Al 2 3 -K 2 0-6Si0 2 + 4H 2 S0 4 = Al 2 (SO«)» + K 2 S0 4 + 6Si0 2 + 4H 2 

 Al 2 3 -K 2 0-6Si0 2 + Ca(HCO s ), = Al 2 3 -CaO-6Si0 2 + 2KHC0 3 



The process of replacement of basic ions in the zeolitic part of the 

 soil is of common occurrence, the hydrogen ion acting also as a base. 

 The solubility of the potassium, often ascribed to the action of acids, 

 may be due merely to the replacement of the potassium in the zeolitic 

 complexes by the calcium or magnesium salts of organic or inorganic 

 acids added to the soil. However, when feldspar, glauconite or other 

 silicates rich in potassium are composted with substances which result 

 in the formation of acid (e.g., sulfur), a great deal of the potassium 

 may go into solution (p. 615). 



By composting greensand, sulfur, manure and soil, 9.1 to 41.3 per 

 cent of the total initial potassium present can be made soluble. 45 The 

 results of Wright cited previously on the action of organic acids upon 

 silicates containing potassium tend to confirm this assumption. This 

 process will take place only very slowly in normal soils. According to 

 Ames, 46 the liberation of potassium in the soil is brought about by the 

 salts formed rather than by the direct action of acidity on insoluble 

 potassium compounds, although he found that both nitrification of 

 organic and inorganic nitrogen compounds and oxidation of sulfur 

 in the soil increased the amount of water-soluble potassium. 



The available potassium compounds are also readily assimilated 

 by the heterotrophic bacteria and fungi and stored away in their 



45 McCall, A. G., and Smith, A. M. Effect of manure-sulfur composts upon 

 the availability of the potassium of greensand. Jour. Agr. Res., 19: 239-256. 

 1920; also Jour. Assoc. Offic. Agr. Chem., 5: 133-136. 1921. 



« Ames, 1921 (p. 658). 



