Overstreet and Dean 87 



Retention of chloride and sulfate ions by soil 



The retention of chloride and sulfate ions by soil is not as readily 

 apparent as the phosphate retention. The mechanism by which these 

 ions are retained in acid soil systems in some respects parallels that for 

 phosphate. 



Toth (48) measured the adsorption of chloride by clays before and 

 after the free iron oxides had been removed (see Table II), and found 



TABLE II 

 Adsorption of Chloride Ion by Untreated and by Deferrated Colloids* 



*Adapted from Toth (48) 



the untreated clays to adsorb this ion. The decrease in chloride adsorp- 

 tion with increasing pH indicates the possibility that under acid con- 

 ditions CI ions replace OH ions associated with the free iron oxides. 

 Barbier and Chabannes (j) studied the retention of sulfate ions in 

 soils and reached the following conclusions. 



1. Sulfate ions are retained by soils more strongly than Cl ions but 

 less strongly than P0 4 ions. 



2. Calcium ion favored the retention of S0 4 ion independently of 

 the precipitation of CaS0 4 . 



3. Soils of average composition contain 10-20 mg. of sulfur per 

 kilogram in the adsorbed condition. 



Reitemeier (41), Kelley (28), and others have suggested sulfate adsorp- 

 tion to explain the increases in soluble sulfate on dilution of some soils. 



