Eleven (11) rhizobacteria identified as Azospirillum sp. isolated from the rhizosphere of maize plants grown in Ibadan, Oyo State, Nigeria were evaluated for ammonia production and nitrogen fixation. The micro-Kjeldahl method was used for the screening of the isolates for nitrogen fixation. Nitrogenase activity ranging from 1.20 to 10.60% was detected in seven of the eleven isolates. Results show that treatments with the application of organic fertilizers enhanced bacterial population and also showed higher nitrogenase activity in rhizosphere soil compared to inorganic fertilizer and control treatments. This showed that organic manure would be a better alternative to chemical fertilizers in maize farming. It was also observed from this study, that Azospirillum possess high nitrogenase activity allowing for the possibility of using this bacteria as a biofertilizer to improve soil fertility for improved and efficient farming.
Key words: Rhizobacteria, rhizosphere, nitrogen fixation, nitrogenase activity, biofertilizer.
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