ENHANCED DISSOLUTION OF PHOSPHATE ROCKS IN THE RHIZOSPHERE

Dissolution of two phosphate rocks (PRS) which vary in their chemical reactivity was examined using two soils in the absence (closed-incubat ion and open-leaching) and presence (thin-layer) of plants. Greater di ssolution was obtained in the presence than in the absence of plants. In the absence of plants, open-leaching resulted in higher dissolution than the closed-incubation system. Removal of the dissolved Ca from t he zone of PR dissolution is considered to be the main reason for the increased dissolution in the open-leaching columns. In the case of the thin-layer experiment, removal of Ca and P through plant uptake and t he supply of protons (H+) through the release of organic acids are con sidered to be the main reasons for the enhanced dissolution of PRs in the rhizosphere.