Maize seed inoculated with Azospirillum brasilense as strategy to improve photosynthetic nitrogen use efficiency in the Amazonian periphery

In the Amazonian region of Brazil, the combination of different inoculation forms of Azospirillum brasilense and N rates has not been studied for its effect on photosynthetic N use efficiency and yield in maize plants. The effects of inoculation forms of A. brasilense and N rates on photosynthetic N use efficiency and maize yield were evaluated. Two field trials were conducted, combining four N rates (0 to 180 kg ha(-1)) with different inoculation forms of A. brasilense (seed, leaf, or control). Photosynthetic N use efficiency (photosynthesis per unit leaf N) was taken at the beginning of tasseling stage, while yield and N use efficiency components were evaluated at physiological maturity. Photosynthesis and specific leaf N increased with increasing N rates, regardless of inoculation forms. Azospirillum-inoculated seeds, along with 114 kg ha(-1) of N provided the maximum yield (6.0 Mg ha(-1)). Without N, seed inoculation increased yield by 33% and photosynthesis by 31% compared to the control. Averaged across N rates, seed inoculation increased photosynthetic N use efficiency by 17%-24% compared to the control. Azospirillum-inoculated seeds improved N use efficiency compared to the control under low N available. The results show that the Azospirillum-inoculated seeds could potentially decrease N rates from 180 to 114 kg ha(-1) of N, while increasing yield by 9%. Besides, Azospirillum-inoculated seeds could enhance photosynthetic N use efficiency in a sustainable manner on low-fertility soils. Therefore, the benefits of the A. Brasiliense drive a sustainable agriculture by improving yield and reducing the need for N inputs.