NITRIC ACID IN THE SOIL 



161 



Stoklasa reported a case where distilled water dissolved only 0.07 

 gm. of phosphate (calculated as P2O5) from 1 gm. of di-calcium 

 phosphate, while carbonated water dissolved 0.26 gm. The 

 solvent action of carbonated water on various phosphates is quite 

 pronounced, as evidenced by the data shown in Table 40. In 

 general, its action is considerably weaker than that of the organic 

 acids. 



TABLE 40 



SoL\'ENT Action of Weak Acids on Pho.sphates (from Stoklasa) 



In the vicinity of growing roots of plants, considerable amounts 

 of carbonic acid appear as a product of respiration of the root 

 tissues; this is further increased by the microorganisms in their 

 decomposition of the organic materials originating from the roots. 

 The solvent action of this carbonic acid in the vicinity of root 

 absorption is an important factor in the nutrition of plants in an 

 environment such as soils where the inorganic nutrients occur 

 in low concentrations. 



Nitric Acid in the Soil. — The amount of nitrate which occurs 

 at any one time in soils supporting plant growth is comparatively 

 small. This may occasionally be as much as 100 pounds, calcu- 

 lated as nitrogen, or 450 pounds, calculated as nitric acid, per acre. 

 Generally the nitrate in soils would be a small fraction of this. 

 The significance of nitrate formation lies not so much in the fact 

 that certain amounts exist in soils at any one time combined with 

 basic substances, but that nitric acid is formed continuously. Its 



