Ammonium and nitrate levels of soil inoculated with Azospirillum brasilense in maize

Azospirillum brasilense is a nitrogen fixing bacteria used in maize crop production due to its high capacity for plant growth promotion and yield increase. The present study aimed to evaluate ammonium and nitrate levels from soil inoculated with A. brasilense in maize crop production. The experiment was carried out in greenhouse conditions, using randomized blocks with split plots for 20 days with four replicates and two treatments where ammonium and nitrate levels were measured daily. The numbers of colony forming units of diazotrophic bacteria at initial and final stages of the experiment were counted in addition to the shoot and root dry mass measurement. The results were analyzed using F, Scott and Knott tests. The treatment which received inoculation did not show any statistically significant difference in the ammonium, nitrate levels either root or shoot dry mass as compared to the control. Also, there was no increase in the colony counts of diazotrophic bacteria. Taken together, the results showed that A. brasilense was not able to promote ammonium and nitrate levels after 20 days of its inoculation, suggesting that the plant growth promoting effect  are not by fixing nitrogen during the initial plant development period and this period would be not appropriate for the plants to receive the inoculation. Key words: Azospirillum brasilense, maize, nitrogen fixer.