Effect of phlogopite on plant growth under phosphorus deficiency

The release of potassium (K) from a K-bearing trioctahedral mica (phlogopite, <0.25 mm), was investigated in pot experiments with pak-choi, maize and radish under different phosphorus (P) regimes. In the nutrient solution culture, where phlogopite was the sole K source, P-starvation led to a significant increase in the total K uptake in pak-choi and radish plants, and. the net release of K from phlogopite was significantly stimulated. The x-ray diffractometry showed that the degree of vermiculitization induced by these two species under P deficiency was much stronger than that found in normal growth conditions. Similar results were obtained in a pot experiment with soil and application of phlogopite as K fertilizer, where three treatments were prepared: A control without K application, a KCl treatment (100 mg K kg(-1) soil) and a phlogopite treatment (50 g phlogopite kg(-1) soil, yielding 100 mg exchangeable-K kg(-1) soil). Maize and pak-choi were grown in triplicated pots for 5 weeks. After 3 weeks, no further P was supplied to half of the pots of the phlogopite treatment. The shoot dry weight of plants grown in the control and phlogopite treatments were similar, but they were significantly lower than the KCl treatment. The total K uptake in plants grown in phlogopite treatments reached the 70% of that supplied with KCl. Therefore, phlogopite could be used as a slow-release K fertilizer to a certain extent.