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

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... howed 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.