TRANSFORMATION OF MINERALS IN THE SOIL 663 



in a manner similar to that of the phosphates. The calcium is made 

 soluble much more easily than the phosphate, since organic and inor- 

 ganic acids interact very readily with calcium carbonate and silicates 

 in the soil with the formation of soluble calcium compounds. 



Nadson 50 found that soil bacteria may bring about the formation of 

 calcium carbonate by means of ammonium carbonate which is formed 

 in the decomposition of organic matter: 



CaS0 4 + (NHO2CO, = CaC0 3 + (NH 4 ) 2 S0 4 (1) 



The formation of calcium carbonate was also observed in the de- 

 composition of organic compounds containing calcium. Nadson even 

 reported the formation of dolomite, or a mixture of calcium and magne- 

 sium carbonates, in media containing bacterial mixtures or a pure cul- 

 ture of Bad. vulgare. According to Molisch, 51 various bacteria, yeasts 

 and actinomyces are capable of causing the precipitation of calcium 

 salts; but his use of the term "calcium bacteria" is not justified. 



Kellerman and Smith 49 suggested that calcium carbonate precipita- 

 tion takes place in any of the following ways: (1) Nitrates are reduced 

 to nitrites and ammonia; the ammonia unites with C0 2 to form 

 (NH 4 ) 2 C0 3 which reacts with CaS0 4 to form CaC0 3 . (2) Ammonia 

 itself may act upon calcium bicarbonate and precipitate CaC0 3 : 



Ca(HC0 3 )2 + 2 NH 4 OH = CaC0 3 + (NH 4 ) 2 C0 3 + 2 H £ 



(3) The bacteria utilize organic acids as source of energy; the calcium, 

 with which the organic acids were combined in the form of salts, is thus 

 liberated and reacts with the free C0 2 to give precipitated CaC0 3 . 



The dissolution of calcium in the soiL whether present in the form of 

 carbonates or as an absorbed base, is brought about by the various 

 organic and inorganic acids formed by the activities of microorganisms. 

 The calcium thus dissolved is either removed by the plant or is lost 

 in drainage waters. The washing out of the calcium from the soil is 

 sometimes so great that some soils of calcareous origin are practically 



60 Nadson, G. Mikroorganismi kak geologitscheskie dieinteli. St. Peters- 

 burg. 1903. 



51 Molisch, H. tlber Kalkbakterien und andere kalkfallende Pilze. Centrbl. 

 Bakt. II, 65: 130-139. 1925. 



