172 MINERALIZATION AND SOLVENT BACTERIA 



Calcium and magnesium occur in soils mainly as carbonate, sul- 

 phate, silicate, and as the cation in the salts of organic acids which 

 have resulted during the breaking down of the organic plant and 

 animal residues. 



Soil bacteria in their life processes are continually forming large 

 quantities of carbon dioxid, nitrous, nitric, and sulphuric acid, 

 together with organic acids which are in the main combined with 

 calcium or magnesium of the soil, with the formation, often, of a 

 soluble compound. The waters carry these to the lakes, seas, and 

 oceans there to be taken up by marine life. In the course of time 

 these are deposited as coral reefs, chalk cliffs, and marl beds. At 

 times the speed with which the lime is taken from the waters by 

 marine life is faster than it is carried into a lake by its tributaries. 

 The result is that, in spite of the evaporation and concentration 

 which is going on, the main body of water contains less lime than 

 does its tributaries. This is the case with Bear Lake, Utah, the 

 tributaries of which have an average lime content of 101.7 parts 

 per million, whereas the lake contains only 13.2 parts per million. 



Calcium Carbonate. The loss of calcium carbonate from a soil 

 varies with (1) the methods of agriculture, intense methods increas- 

 ing the loss; (2) with the application of animal manures and green 

 manures, which increases the bacterial activity and also the solubility 

 of the calcium carbonate; (3) with the addition of commercial fertil- 

 izers added to a soil which hasten the loss of calcium in drainage 

 water. 



The carbon dioxid generated by bacteria reacts with the calcium 

 carbonate forming the much more soluble calcium bicarbonate: 

 or 



CaCO 3 + COa ' + H 2 O = Ca(HCO 3 ) 2 



Ammonium sulphate resulting either from ammonification or from 

 the addition of a fertilizer changes the calcium from an insoluble 

 to a soluble form : 



(NH 4 ) 2 SOi + 2CaCO 3 + 4O 2 = Ca(NO 3 ) 2 + CaSO 4 + 4H 2 O + 2CO 2 

 (NH 4 ) 2 SO 4 + CaCO 3 = (NH 4 ) 2 CO 3 + CaSO 4 



The addition of acid phosphate or potassium chlorid also helps 

 deplete the soil of its calcium carbonate: 



CaH 4 (PO 4 ) 2 + 2CaCO 3 = Ca 3 (PO 4 ) 2 + 2H 2 O + 2CO 2 

 2KC1 + CaCOs = K 2 CO 3 + CaCl 2 



The absolute amount of calcium and magnesium lost from a soil 

 varies with the aridity of a region as well as with the composition 

 of the soil. Hall estimates that the annual loss from the Rotham- 

 sted soil, which contains about 3 per cent, of calcium carbonate, is 

 from 800 to 1000 pounds an acre annually, whereas in some parts 



