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Potassium Fixation Characteristics of Five Southern California Soils¹

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 BaCl₂. 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 CEC, the decreases in the initial cation exchange capacity (CEC_in). The difference between K_f and CEC 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⁺)/[(Ca²⁺)+(Mg²⁺)]^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 = A₂ + B₂ x 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.

¹ Contribution from the Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA. Financial support from BARD is gratefully acknowledged.

² Postgraduate Research Soil Scientist, Visiting Soil Scientist, Professor, and Assistant Professor of Soil Science, respectively. M. Mohsin is an Associate Professor, Universidad del Oriente, Cumana, Venezuela. The address for the senior author is now TECHNION, Dep. Soil Science, Haifa 32000, Israel.

Received for publication July 23, 1984. Accepted for publication March 26, 1985.