Amal A. Ali and Wafaa A. Hafez( 2018). Phosphate solubilizing bacteria (rhizobium and azotobacter chroococcum) and their environmental effects with compost on growth promotion of wheat under saline soil conditions N. Egypt. J. Microbiol. Vol. 51, September, 2018
Abstract: Phosphorus (P) is one of the major essential macronutrients for plants. But its availability in soil is relatively low due to the high rate of P fixation. Phosphate solubilizing microorganism (PSM) used to solubilize the fixed form of P for economically reasonable and ecologically safe as compared to chemical phosphatic fertilizers. In this study Strain of Azotobacter chroococcum and four effective rhizobial strains of R. leguminosarum bv. Viceae strains 481, 441, 202, 207 were used in to examine their phosphate-solubilizing ability on Pikovskaya’s agar medium. Azotobacter chroococcum was able to solubilize phosphate effectively and recorded higher solubilization efficiency up to (150 %) Followed by Rhizobium sp. strain 441(109 %). The activity of Rhizobium sp. strain 441 was further screened with different sources of carbon and nitrogen for their ability to solubilize tricalcium phosphate (TCP). Maximum phosphate solubilization (323 mg/ml) was observed in mannitol and potassium nitrate as carbon and nitrogen sources respectively. Furthermore incubation period of 5 days was adequate for attaining maximum phosphate solubilization. A field study was conducted to test the effects of phosphate-solubilizing modified rhizobium sp. strain 441 and Azotobacter chroococcum with or without compost on wheat by comparing with chemical fertilizers. Inoculation of phosphate solubilizing bacteria (PSB) together with compost increased the crop growth in terms of shoot height, shoot biomass, amount of chlorophyll, Carbohydrates, grain yield and total nitrogen and P uptake in wheat crops compared to the other treatments. The results obtained revealed that applying of PSB (modified rhizobial strain combined with Azotobacter sp.) in presence of compost led to improve many of soil variables such as, soil pH, EC, O.M and NPK concentrations.
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