Evaluation of Azotobacter and Azospirillum as biofertilizers in aquaculture.

摘要

A preliminary comparative evaluation of the two commonly encountered free-living nitrogen fixers in the aquatic system, Azotobacter and Azospirillum was carried out in the laboratory for use as biofertilizers in aquaculture considering the importance of eco-friendly and econo-friendly productivity optimization of freshwater aquaculture. The ammonium-nitrogen levels in water media in Azotobacter treatment varied in the range 2.59-34.34 micro g-N/l and was found to be significantly different from that of Azospirillum treatment (p<0.05). The viable population of the respective nitrogen fixers as colony forming units (c.f.u.) in water media in charcoal-immobilized Azotobacter treatment ranged from 0.39 to 2.48x103 c.f.u./ml and were significantly higher (p<0.05) than the counterparts. The nitrogenase activity in the same treatment similarly remained higher, at 8.3-12.15 nmol of ethylene/ml water/h followed by the alginate-immobilized Azotobacter treatment which was at 7.2-11.40 nmol of ethylene/ml water/h compared to 5.8-7.8 and 4.65-4.83 in the respective Azospirillum-treated counterparts. Hence, better performance of Azotobacter sp. over Azospirillum sp., and of charcoal immobilization over alginate immobilization were observed..