Enhancing agronomic efficiency and maize grain yield with Azospirillum brasilense inoculation under Brazilian savannah conditions

In view of ecological and economic costs of nitrogen (N) fertilization, measures are needed to enhance the sustainability of cereal production in tropical savannah regions. In this context, we investigated the combined effects of N application levels and inoculation with Azospirillum brasilense on maize plant biomass, grain yield, agronomic efficiency (AE), and N content in plants, focusing on the economic feasibility of maize production systems. The field trial involved four N application levels (control, low, average and high, i.e., 0, 50, 100 and 200 kg ha(-1), respectively, applied as sidedress) either with seed inoculation with A. brasilense or without inoculation. Inoculation with A. brasilense enhanced AE and N uptake in maize plants with increased shoot, root and grain N accumulation, augmenting grain yield by 7%. The increase in total N accumulation was mainly the result of improved N-NH4+ accumulation in plant roots and shoots. Our results showed that it is possible to reduce the N fertilization level by 50% while increasing the operating profit by 11% with A. brasilense inoculation. Additionally, when inoculation was performed in the presence of a high N level, the operating profit was 11% higher than that for the same N level in the absence of inoculation. Therefore, in view of the low economic cost, ease of application, and high probability of a positive response by maize crops, even in the presence of different N application levels, inoculation with A. brasilense has the potential to be a key technology for improving plant-soil N management, leading to more sustainable maize production under tropical conditions. (AU)