ROCK PHOSPHATE SOLUBILIZATION BY ASPERGILLUS-NIGER ON OLIVE CAKE-BASED MEDIUM AND ITS FURTHER APPLICATION IN A SOIL-PLANT SYSTEM

A citric acid-producing strain of Aspergillus niger, grown on olive ca ke-based medium, was able to solubilize rock phosphate. Solubilization of insoluble phosphate increased during the solid-state fermentation process, reaching a maximum of 164 mu g/ml. Various combinations of ol ive cake and rock phosphate, previously treated or untreated by the fu ngus, were introduced into a calcareous, phosphorus (P)-deficient soil to improve the growth of Trifolium repens in a greenhouse experiment. Synergistic action of both the filamentous and arbuscular fungi cause d considerable improvement of growth and plant P uptake. Greater growt h and P uptake of mycorrhizal and non-mycorrhizal plants were achieved when microbe-treated olive cake and rock phosphate were applied to so il compared with all other treatments.