Potassium Fixation Characteristics of Five Southern California Soils

Abstract

Abstract Potassium 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 BaCl 2 . Potassium fixation, K f , 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 (CEC in ). The difference between K f 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 K f with E P (the ratio of adsorbed K to adsorbed Ca and Mg) and with PAR = {(K + )/[(Ca 2+ )+(Mg 2+ )] 1/2 } were found for each depth for each soil. Potassium fixation also increased with increasing depth. Relating the fractional fixation FK f = (K f /CEC in ) to E P and PAR, a more general representation of K fixation was obtained. Fractional fixation and E P showed a linear relationship as FK f = A 2 + B 2 × E P . Such a correlation resulted in one or two regression lines representative of fixation through a given soil profile to the 105‐cm depth.