Abstract

The use of plant growth-promoting diazotrophic bacteria as an alternative to increase nitrogen (N) availability and contribute to its use by corn can be a less costly and ecologically more viable option. Thus, this study aimed to evaluate the effects of the inoculation with Azospirillum brasilense and Herbaspirillum seropedicae in association with N fertilization on the N use efficiency and its biological fixation by corn, in field conditions, using the ¹⁵N-isotope technique. A randomized-block design was used, with nine treatments and six replicates. The following parameters were evaluated: grain productivity, dry matter production, accumulated N in plant, percentage of N from the fertilizer, total N from the fertilizer, use efficiency of N applied as fertilizer and percentage of biological N fixation. Results show that N fertilization associated with A. brasilense and H. seropedicae inoculations influences positively grain productivity in corn. The inoculation with A. brasilense and H. seropedicae combined with 30 and 120 kg ha^-1 of N promotes a reduction of N percentages in corn grains and shoot. The increase in N dose associated with the inoculation of A. brasilense and H. seropedicae promotes an increase in the N from the fertilizer in corn grains and shoot and reduces the N use efficiency by the crop. Using the ¹⁵N natural abundance technique, it was found that the inoculation with A. brasilense and H. seropedicae contributed, respectively, with in average 19.40% and 9.49% of the N required for the development of corn plants.

Key words: Zea mays L., Azospirillum brasilense, Herbaspirillum seropedicae, ¹⁵N, biological nitrogen fixation.