Effect of plant types on release of mineral potassium from gneiss

The ability of plant types to release mineral K from little weathered gneiss for a mixture of particle size fractions of less than 10 mm, as well as for two separated size fractions (2 mm < D < 5 mm, and 1 mm < D < 2 mm) were compared in pot experiments with maize (Zea mays L. cv. ND60), pak-choi ( Brassica campestris L. ssp.chinensis (L.) Mokina. var. cammunis Tsen et Lee, cv. Wuyueman) and two alfalfa cultivars (Medicago sativa L. cv. Asta and Haifei). Release of mineral K was significantly stimulated by maize, pak-choi and ryegrass, implying a direct mobilization of mineral K by plant roots. The net release of mineral K was greatly influenced by plant species. Among these, the more profound release of mineral K was observed with maize and ryegrass. Besides, the mobilization of mineral K was negatively correlated with the particle size of gneiss. The difference in net release of K from gneiss between two size fractions decreased in the order: maize > ryegrass > pak-choi.