Nitrogen (N) fertilization is one of the highest costs in the production process of cereal crops such as maize. Developing management practices which minimize the reliance on chemical N inputs are essential for global food security and environmental sustainability. Recent research has shown the potential for utilization of plant growth promoting rhizobacteria (PGPR) to enhance N use efficiency (NUE) in non-leguminous cropping systems, reducing N losses to the environment. Detailed studies with more accurate techniques such as isotopic techniques (15N) are needed to provide an in-depth approach regarding PGPR potential, such as Azospirillum brasilense and Bacillus subtilis for improving N recovery and accumulation from applied N-fertilizer, as well as the N contribution from atmosphere by biological N fixation (BNF), benefiting plant growth and development. This study was performed under greenhouse condition and aimed to evaluate the N accumulation in maize plants and N-fertilizer recovery as a function of seed inoculation with A. brasilense and B. subtilis, in single or combined (co-inoculation) application, coupled with 15N-urea rates. The following evaluations will be performed: Shoot and root N accumulation (total N, N-NO3- e N-NH4+), the percentage and total amount of N derived from labeled fertilizer and other sources (e.g. atmosphere - contribution from BNF, soil, organic matter and others) and the N recovery from applied fertilizer. In addition, shoot and root biomass and lead chlorophyll, flavonols and N balance index were determined. These activities were already approved as stated in the "schedule of activities" in the project "Recuperação do nitrogênio aplicado via fertilizantes e contribuição da fixação biológica de nitrogênio em função da inoculação com bactérias promotoras de crescimento de plantas associado a doses de 15N-ureia na cultura do milho" Process Number FAPESP (2021/10347-4). The isotopic analyses (performed with 2 isotopic techniques - 15N isotopic dilution and 15N natural abundance techniques ´15N 0) will be performed at College of Food, Agricultural and Natural Resource Sciences, University of Minnesota, under supervision of Prof. PhD Paulo H. Pagliari with collaboration of Prof. PhD Fabian G. Fernandez. The overall hypothesis of this study is that A. brasilense and B. subtilis coupled with N rates would enhance NUE by increasing N uptake from applied fertilizer with a contribution from BNF, providing greater maize growth and biomass yield. The data coming from this project will be an excellent tool to the understanding of the role of A. brasilense and B. subtilis on NUE and BNF in the same study approach. Also, the potential benefits that will arise from this research can be related to lower amounts of chemical fertilizers (specifically N) needed to grow maize for an ever-growing global population.
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