Production of nitrogen fixing Azotobacter (SR-4) and phosphorus solubilizing Aspergillus niger and their evaluation on Lagenaria siceraria and Abelmoschus esculentus

Aims: Current study was aimed to produce nitrogen fixing Azotobacter sp. (SR-4) and phosphorus solubilizers Aspergillus niger (A. niger) and to evaluate their efficiency as biofertilizers for agricultural practices. Methods: Two biofertilizer including nitrogen fixing and phosphorus solubilizing were grown. The nitrogen fixing efficiency of Azotobacter (SR-4) was determined by Kjeldahl method. Similarly, Vanadomoybdate method was used to measure the soluble phosphorus while Heinonen method was used to analyze concentration of phytase and phosphatase in the cultures. Furthermore, both biofertilizers were tested in a field trail on Lagenaria siceraria (bottle gourd) and Abelmoschus esculentus (okra). Results: The Azotobacter (SR-4) strain was found efficient nitrogen fixer as 35.08 mg of nitrogen per gram of carbon was produced after 72 h of fermentation. Similarly, A. niger strain excrete extracellular phosphate solubilizing enzymes such as phytase (133UI in 48 h of fermentation) and phosphatase (170UI in 48 h of fermentation) which can solubilize the rock phosphate and make it available to plants. In field trials on selected plants (L. siceraria and A. esculentus), both biofertilizers showed significant increase in plant height, leaf length/width, fruit size and number of fruits per plant when compared with controls/untreated plants. Furthermore, plants co-inoculated with both the N fixing Azotobacter and phosphorus solubilizing A. niger have enhanced performance than those treated with each biofertilizer alone. Conclusion: The inoculation of seeds with A. niger and Azotobacter may replace costly and environment toxic chemical fertilizers with environment friendly and cost effective biofertilizers. Keywords: Biofertilizers, Azotobacter, A. niger, Bottle gourd and okra