166 TRANSFORMATION OF MINERAL SUBSTANCES 



makes the soil strongly buffered and prevents rapid changes in 

 reaction. 



2CH3CHOHCOOH + CaCOa 



= Ca(CH3 ■ CHOH • C00)2 + CO2 + H2O. 



Calcium lactate 



The acid may become neutrahzed by interacting with calcium car- 

 bonate. When the lactate is decomposed by other organisms, the 

 calcium carbonate is regenerated : 



Ca(CH3- CHOH -000)2 + 6O2 = CaCOs + 5CO2 + 5H2O 



4 3 2 0LogCKc. o,Mg 



Solution of Minerals — Increase 



Fig. 67. — The influence of acidity created by growth of Azotobacter on solu- 

 tion of potassium, calcium, and magnesium from the mineral biotite (after 



Wright). 



During the weathering of rocks, which are composed for the 

 most part of minerals made up of strong bases (as calcium, potas- 

 sium, magnesium, sodium) bound to a weak acid (silicic), there is a 

 tendency for the development of an alkaline reaction. This is 

 what happens in regions of deficient rainfall where the limited 

 amount of drainage waters fails to remove the soluble salts as 

 rapidly as they are formed. In the reclamation of alkali soils, 

 the injurious effects of the basic reaction and high content of basic 

 salts may be partly overcome by the addition of sulfur, which is 

 oxidized by bacteria to sulfuric acid, as will be discussed later. 

 In humid regions the weathering processes are accelerated by the 



