Evaluation of Phosphate Solubilizing and Potassium Releasing Ability of Some Trichoderma Species under in-vitro Conditions

The deficiency of macro-nutrients such as phosphorus and potassium is very important due to vital roles of these elements. Although the total amount of phosphorus and potassium in the soil is high, the formation of insoluble forms of phosphorus, as well as the stabilization of potassium in silicates, has led to the shortage of these essential elements. The use of microorganisms, having the ability to dissolve insoluble phosphate forms and potassium fixed in silicates, can be effective in reducing the deficiency of these elements for the plant. In this research, 7 species of Trichoderma fungis were selected and their effects on the release of phosphorus and potassium were evaluated in Pikovskaya’s, Alexandrov’s and modified Pikovskaya’s media. The results showed that in Pikovskaya’s broth medium, phosphorus release rate by different species of fungi was consistent with decreasing pH. Trichoderma koningii, T.harzianum, T.citrinoviride and T.viridescens had the most phosphate solubilizing ability and increased soluble phosphorus by 244, 205, 191 and 190%, respectively. In both Aleksandrov’s and modified pikovskaya’s media, which contain both insoluble inorganic phosphate and potassium as biotite, it was observed that the dissolution rate of tri-calcium phosphate was lower than that of pikovskaya’s medium which has available potassium. T.koningii in Aleksandrov’s medium and T.harzianum in modified Pikovskaya’s medium had the highest ability to release potassium from biotite. These species increased potassium in solution by 123 and 20% compared to control, respectively. In general, the results showed that Trichoderma fungi has the ability to solubilize phosphate from tri-calcium phosphate and release potassium from biotite under in-vitro conditions.