THE SOIL AS A SOURCE OF MINERAL SALTS 



137 



sodium in the soil solution tend to increase to a relatively smaller 

 extent than do the concentrations of chloride, nitrate or calcium, 

 suggesting that the amount of univalent cations in solution decreases 

 with increasing concentration, through equilibration with the solid 

 phase. At very low soil moisture content, the concentrations of all 

 ions except phosphate increase with decreasing volume of soil 



Table 13. The Composition of Soil Solutions. 

 A. Analyses of soil solutions displaced from a cropped soil in California at the 

 beginning and end of one growing season and at the beginning of the next. 



(Burd and Martin, 1924). 



Date 



m eq./l. of displaced solution 



NO, 



HCO, 



SO. 



PO4 



30.4.1923 



4.4.1923 



28.4.1924 



2-23 

 0-21 

 2-71 



1-75 7-10 

 2-88 I 4-36 

 2-33 : 9-56 



Ca 



Mg 



Na 



K 



05 

 008 

 04 



6-75 

 4 00 

 8-45 



B. Analyses of soil solutions extracted from 4 soils. 

 (Reitemeier and Richards, 1944). 



solution more rapidly than can be accounted for, assuming that all 

 the water in the soil contains dissolved salts. It appears that some 

 of the soil water, bound to colloidal particles, is unavailable to salts. 



C. Exchangeable ions 

 1. Anion Exchange Capacity 



Anions are present only to a limited extent, in undissolved, but 



