Estimation of Potassium Availability by Incremental Additions of K to K-Fixing Soils.

Potassium fixation has been identified as a property of concern in managing certain soils in the San Joaquin Valley of California, particularly those formed from granitic alluvium with vermiculite in the silt and fine sand fractions (Murashkina et al., 2007). In order to better estimate the fate of K applied to K-fixing soils, incremental additions of K were made to soil materials from six profiles representing a range of K-fixation potential (Kfix), with air drying steps between each addition. An additional treatment was made adding a symmetry of K (K applied= CEC). K pools were then measured using three lab methods: NH₄OAc extraction of exchangeable K, NaBPh₄ extraction of “plant-available” K, and measurement of Kfix by the procedure of Murashkina et al. Results show the changes within these pools with additional levels of K applied, and provide an approximate maximum K fixation value for these soils, as opposed to the percentage or relative values given by the Kfix method.