In vitro nitrogen fixation, phosphate solubilization, survival and nutrient release by Azotobacter strains in an aquatic system

In vitro nitrogen fixation, phosphate solubilization, survival and nutrient release by the three strains of Azotobacter (Mac-27, nitrogen fixer; PS-21, phosphate solubilizer and MSX-9, a phytohormone producer) in an aquatic system using three different organic substrates (cow-dung, piggery and poultry waste/excreta) were studied. It was shown that Azotobacter can grow and multiply in an aquatic system when fertilized either with cow-dung (100 mgl−1), poultry (50 mgl−1) or piggery (25 mgl−1) waste/excreta. Mac-27 and MSX-9 strains of Azotobacter fixed higher quantities of nitrogen (0.03–0.12 mgl−1 d−1) in aquaria water treated with cow-dung, while with poultry and piggery excreta, the three strains of Azotobacter fixed 0.03–0.09 mgl−1 d−1 of nitrogen. O-PO4 concentration was also high in microbial-inoculated aquaria as compared to the controls which decreased with respect to time. Similarly, a decrease in total nitrogen concentration was also observed in the aquaria water after the maximum levels of fixation had been reached. Concomitant with the decrease in total nitrogen concentration, a simultaneous increase in NO3-N, NO2-N and NH4-N was observed. Maximum phytoplankton population was observed in MSX-9, while the population of zooplankton was maximum in Mac-27 inoculated aquaria. These studies indicated that Azotobacter can be used as a biofertilizer for enhancing nitrogen input and phosphate solubilization in fish ponds. Microbial inoculation along with organic substrate, however, has to be repeated at least at biweekly intervals.