Impact of nitrogen fertilizer sustainability on corn crop yield: the role of beneficial microbial inoculation interactions

Background: Considering the challenges posed by nitrogen (N) pollution and its impact on food security and sustainability, it is crucial to develop management techniques that optimize N fertilization in croplands. Our research intended to explore the potential benefits of co-inoculation with Azospirillum brasilense and Bacillus subtilis combined with N application rates on corn plants. The study focused on evaluating corn photosynthesis-related parameters, oxidative stress assay, and physiological nutrient use parameters. Focus was placed on the eventual improved capacity of plants to recover N from applied fertilizers (AFR) and enhance N use efficiency (NUE) during photosynthesis. The two-year field trial involved four seed inoculation treatments (control, A. brasilense, B. subtilis, and A. brasilense + B. subtilis) and five N application rates (0 to 240 kg N ha^−1, applied as side-dress). Results: Our results suggested that the combined effects of microbial consortia and adequate N-application rates played a crucial role in N-recovery; enhanced NUE; increased N accumulation, leaf chlorophyll index (LCI), and shoot and root growth; consequently improving corn grain yield. The integration of inoculation and adequate N rates upregulated CO₂ uptake and assimilation, transpiration, and water use efficiency, while downregulated oxidative stress. Conclusions: The results indicated that the optimum N application rate could be reduced from 240 to 175 kg N ha⁻¹ while increasing corn yield by 5.2%. Furthermore, our findings suggest that replacing 240 by 175 kg N ha⁻¹ of N fertilizer (-65 kg N ha⁻¹) with microbial consortia would reduce CO₂ emission by 682.5 kg CO₂^−e ha⁻¹. Excessive N application, mainly with the presence of beneficial bacteria, can disrupt N-balance in the plant, alter soil and bacteria levels, and ultimately affect plant growth and yield. Hence, highlighting the importance of adequate N management to maximize the benefits of inoculation in agriculture and to counteract N loss from agricultural systems intensification.