162 



TRANSFORMATION OF MINERAL SUBSTANCES 



absorption by plants or removal in drainage waters keeps the 

 concentration of nitrate low in humid regions. Soon after its 

 formation it reacts with soil constituents, such as the insoluble car- 

 bonates, phosphates, and silicates, and, over a period of time, 

 dissolves large amounts of insoluble substances forming salts of 

 potassium, sodium, magnesium, calcium, and iron. It has been 

 stated that, in the conversion of organic nitrogen to nitrate suffi- 

 cient for a hundred bushel crop of corn, there will be produced 

 sufficient acid to convert seven times as much insoluble tri-calcium 

 phosphate into soluble mono-calcium phosphate as would be 

 required to supply the phosphorus for the same crop. Of course, 

 the larger part of the nitric acid would take part in other reactions, 

 and only a small portion of the acid would react with the phos- 

 phates. Nitrification of ammonium sulfate is responsible for 

 greater acid formation than nitrate formation from nitrogen origi- 

 nally contained in organic combination. The solvent action 

 accompanying nitrification in laboratory cultures containing tri- 

 calcium phosphate is shown in Table 41. 



TABLE 41 



Solution of Phosphate and Calcium from Tri-calcium Phosphate by 

 Nitrification of Ammonium Sulfate in Solution Cultures (from 

 Hopkins and Whiting) 



The reaction concerned in this process may be expressed as 

 follows: 



Ca3(P04)2 + (NH4)2S04 + 402 = 



Ca(H2P04)2 + Ca(N03)2 + CaS04 + 2H2O 



