Potassium Fixation Characteristics of Five Southern California Soils

Abstract

AbstractPotassium fixation in five southern California soils, sampled at 15‐cm depth increments down to a depth of 105 cm, is reported. The objective was to develop quantitative relationships between K fixation and other soil and solution properties. The experiments were conducted under wet conditions only and the exchangeable cation removal done by BaCl2. Potassium fixation, Kf, was calculated by the difference between total initial K and total final exchangeable plus soluble K in a given system and compared to ΔCEC, the decreases in the initial cation exchange capacity (CECin). The difference between Kf and ΔCEC appeared small, inferring that under wet field conditions, fixation mainly occurred via the mechanism of K entrapment between clay plates. Linear increases of Kf with EP (the ratio of adsorbed K to adsorbed Ca and Mg) and with PAR = {(K+)/[(Ca2+)+(Mg2+)]1/2} were found for each depth for each soil. Potassium fixation also increased with increasing depth. Relating the fractional fixation FKf = (Kf/CECin) to EP and PAR, a more general representation of K fixation was obtained. Fractional fixation and EP showed a linear relationship as FKf = A2 + B2 × EP. Such a correlation resulted in one or two regression lines representative of fixation through a given soil profile to the 105‐cm depth.