Potassium Release and Fixation Related to Illite and Vermicultie as Single Minerals and in Mixtures

Abstract Fixation and release of K were studied under moist and dry equilibrium conditions. Clay and silt fractions of illite and vermiculite, as single minerals and in mixtures, were used in the experiments. Nonaqueous solutions were compared with aqueous solutions as K extractants to evaluate the effect of rehydration upon K release. The drying of illite increased the amounts of K removed by aqueous solutions and decreased the amounts removed by nonaqueous solutions. Illite fixed no applied K against aqueous extraction, even after drying, but vermiculite fixed large amounts. Silt fractions of illite were nearly as efficient in K release as were the clay fractions. Mixtures of illite and vermiculite showed increased exchangeable K upon drying, reversion of this K upon remoistening, and fixation of applied K. These effects were not all present when the minerals were tested singly. The “Attoe effects” were induced in vermiculite‐free soil clays by an addition of vermiculite to the sample.