MIXED SOIL/CLINOPTILOLITE QUANTITY/INTENSITY BEHAVIOR IN BINARY AND TERNARY K-NH4-Ca EXCHANGE SYSTEMS

Abstract

Theoretical quantity/intensity (Q/I) analysis reveals that addition of a third cation (e.g., NH + [over] 4) to a heterovalent cation exchange system (e.g., K-Ca) under constant CEC and cation exchange selectivity coefficients decreases the apparent linear potential buffering capacity for K+ (PBCK) whereas labile K+ (ExK°) remains unaffected. However, ternary cation exchange reactions, K-NH4-Ca, in soils cannot always be predicted from binary exchange data. This study deals with Q/I relationships of K-Ca exchange, with and without added NH + [over] 4, and NH4-Ca exchange, with and without added K+ in the Ap and Bt horizons of a Greek soil (Typic Rhodoxeralf) amended with 0, 1%, 5%, and 10% of zeolite (clinoptilolite) on a weight basis. The experimental approach was based on the Q/I concept. In the case of K-Ca exchange in the Ap horizon, addition of solution NH + [over] 4 to soil samples with increasing quantities of zeolite increased PBCK, whereas in the case of NH4-Ca exchange, addition of solution K+ or zeolite had no particular influence on PBCNH4. In the case of K-Ca exchange in the Bt horizon, solution NH + [over] 4, as well as zeolite, had no apparent consistent influence on PBCK, whereas in the case of solution K+ and zeolite, PBCNH4 increased significantly. Labile K+ (ExK°) increased with addition of NH + [over] 4 and/or zeolite in K-Ca exchange, whereas ExNH4° behavior showed no particular pattern, perhaps because of the small quantity of residual ExNH4 in the systems. The above demonstrated an ion-selective sieving effect by soil and zeolite that was not consistent with theoretical ternary cation exchange behavior.