Ability of alfalfa (Medicago sativa L.) to take up potassium from different micaceous minerals and consequent vermiculitization

Nonexchangeable soil K trapped between interlayers of clay minerals is an important source of K for plants grown on many soils. In this study, the ability of alfalfa, as the most important forage crop worldwide, to take up K from some micaceous minerals and to promote the transformation of micaceous minerals were investigated. Alfalfa was cultivated in pots that consisted of a mixture of Hamadan quartz sand and Amlash biotite, Hamadan muscovite and Hamadan phlogopite. Plants were irrigated with distilled water and complete or K-free nutrient solutions. After 90 days, K uptake by plants was measured by flame photometer. Also, the clay size particles in each pot were analyzed using x-ray diffraction. It was found that alfalfa was able to induce a significant release of interlayer K during cropping. The amount of K taken up by alfalfa was significantly higher for Hamadan phlogopite. X-ray diffractometry showed a strong vermiculitization of Hamadan phlogopite and Amlash biotite, but no X-ray detectable transformation of muscovite was recognized.