The distribution of potassium and sodium between the solution and the solid phase in a ternary (K–Na–Ca) system

Abstract

Reduction of sodicity hazards in soils irrigated with waste water can be achieved through the replacement of the Na salts (mainly NaCl), used in water softening and other industrial processes, with potassium salts. We studied the effect of equilibrating a grumusol (Typic Chromoxerert) with solutions of differing potassium adsorption ratio (PAR) and sodium adsorption ratio (SAR), within the range expected in waste water, on the distribution of K and Na between the solution and the solid phase. The K distribution did not depend on the level of Na in the solution, but the distribution of Na between the 2 phases depended strongly on the PAR of the solution. For SAR 10 solutions, ESP decreased from 11.1 to 7.8 as PAR increased from 0 to 4. Gapon selectivity coefficients for Na, calculated separately for each PAR level, also decreased with increasing PAR. The Na distribution between solution and solid phase in a ternary (K–Na–Ca) system could not therefore be predicted from the Gapon selectivity coefficient obtained from a binary (Na–Ca) system.