The increasing population and global food demand require the maintenance of high agricultural productivity, especially for maize (Zea mays L.), an important crop both globally and in Brazil (FAO, 2025). In the 2024/2025 season, the planted area in Brazil reached 21.679 million hectares, with an estimated production of 137 million tons (CONAB, 2025). The off-season (second-crop maize) is the main maize cultivation cycle in Brazil, accounting for approximately 80% of national maize production (CONAB, 2025). This crop is typically established after soybean harvest and develops under transitional climatic conditions characterized by irregular rainfall. Short dry spells often occur early in the cycle, followed by a marked reduction in precipitation from mid- to late season, frequently coinciding with periods of high crop water demand. These conditions are commonly associated with elevated temperatures, an early onset of the dry season, and, in some regions, occasional frost events (Cunningham, 2020). Collectively, these climatic stresses restrict grain filling, disrupt photosynthetic processes, and reduce nutrient uptake, underscoring the importance of appropriate crop management strategies (Bigolin and Talamini, 2024; Moretti et al., 2026).

Maize productivity is strongly influenced by the availability of both nitrogen (N) and phosphorus (P) (Moreira et al., 2017, 2026). N is essential for the production of proteins, nucleic acids, chlorophylls, coenzymes, phytohormones, and secondary metabolites, all of which are critical for vegetative growth and grain formation (Govindasamy et al., 2023; Khan et al., 2023). Consequently, N is one of the most limiting nutrients for crop productivity. In tropical soils like those found in Brazil, low N use efficiency (NUE) is often caused by N losses through volatilization, leaching, or microbial processes such as denitrification (Ladha et al., 2022). These losses not only reduce crop productivity but also lead to emissions of nitrous oxide (N₂O), a potent greenhouse gas with a global warming potential approximately 300 times that of CO₂ (Butterbach-Bahl et al., 2013; Griffis et al., 2017). The Intergovernmental Panel on Climate Change (IPCC) has estimated that in humid climates, applied N has an average N₂O emission factor of 1.6% (De Klein et al., 2019), although field values can vary depending on fertilization type and management (Yang et al., 2022). Improving NUE is therefore crucial to maximize productivity while mitigating environmental impacts (Eagle et al., 2020; Ladha et al., 2022). P plays a central role in energy transfer through ATP, nucleic acid synthesis, membrane structure, root development, and early plant establishment (Khan et al., 2023; de Souza et al., 2025), and promoting P use efficiency (PUE) is critical for sustaining growth and yield under off-season conditions (Crusciol et al., 2022; Moreira et al., 2022).

A promising strategy to meet the nutritional demands of maize during critical growth stages is combining the foliar application of plant growth-promoting bacteria (PGPB) such as Azospirillum brasilense at the vegetative stage with P supplementation at the reproductive stage. A. brasilense can supplement the supply of N to maize by fixing atmospheric N₂ (Moretti et al., 2018; Fukami et al., 2018; Condori et al., 2024). In addition, foliar inoculation with A. brasilense has been shown to stimulate root development (van Loon et al., 1998; Doornbos et al., 2012), photosynthetic pigment synthesis, nutrient accumulation (Hungria et al., 2010), and tolerance to abiotic stress, ultimately boosting grain yield (Arzanesh et al., 2011; Alhammad et al., 2023). Foliar P supplementation enhances photosynthetic and antioxidant metabolism, physiological recovery under stress, and productivity (Viveiros et al., 2024, 2025; Rodrigues et al., 2025; de Souza et al., 2025). Together, these practices have the potential to improve nutrient use efficiency, sustain physiological processes, and enhance maize productivity under tropical conditions.

The objective is to develop a sustainable (green) management practice capable of reducing the carbon footprint while maintaining the same profitability and productivity. This can be achieved by lowering nitrogen fertilizer doses and improving nutrient use efficiency, specifically nitrogen use efficiency. This study aimed to evaluate the effects of foliar Azospirillum brasilense application at the V₃ growth stage and foliar soluble monoammonium phosphate application at the R₁ stage, applied individually or in combination, on nitrogen uptake efficiency, plant nutrition, and grain yield of off-season maize grown under field conditions.

For each treatment, we also compared two N doses (100% and 75%). For both N doses, standard soluble monoammonium phosphate (MAP) only at sowing served as a control. We hypothesized that foliar application of Azospirillum brasilense and/or P would enhance NUE, improve the nutritional status of the crop, and increase grain yield in off-season maize, even under reduced N fertilization (75% instead of 100%).

Maize production in Brazil contributes significantly to the global grain supply and the growing demand for animal feed, biofuels, and food (Cardozo et al., 2022). In Brazil, maize is predominantly cultivated as a second crop during the off-season, a period of high climatic variability, including water deficits and extreme heat (Santos et al., 2020; de Oliveira et al., 2025). The six sites in our study perfectly illustrate this variability: Santa Cruz do Rio Pardo, Sengés and Dourados experienced below-average, irregular rainfall in 2024 (226, 237 and 278 mm, respectively), whereas Jataí, Campo Verde and Primavera do Leste received adequate rainfall (894, 811 and 770 mm, respectively). GY was lower at the former three sites than at the latter three sites (Table 5), highlighting the importance of adequate water availability for maize, particularly during the tasseling stage (Bergamaschi et al., 2004).

High climatic variability in the off-season makes N management a critical factor for efficiently maximizing maize yield. Maize has a high requirement for N, but despite high N application rates (Hungria et al., 2022), NUE is usually low, emphasizing the need for strategies that improve nutrient uptake and yield (Galindo et al., 2019). Studies have shown that either foliar inoculation with PGPB or foliar P application alone can improve nutrient uptake and GY (Oliveira et al., 2017; Scudeletti et al., 2023; Viveiros et al., 2024, 2025; de Souza et al., 2025). In the present study, combined foliar A. brasilense inoculation and P application increased leaf N and P concentrations as well as GY under both 100% and 75% of the recommend N rate. Notably, under 75% N, the same foliar applications resulted in leaf N and P concentrations and GY similar to those obtained with the full N rate.

The increase in leaf N concentrations may be related to the ability of A. brasilense to synthesize phytohormones, particularly indole-3-acetic acid (IAA), which stimulates root growth and consequently improves the plant’s capacity to explore the soil and acquire nutrients (Fukami et al., 2018; Santos et al., 2021; Hungria et al., 2022). Azospirillum also fixes atmospheric N₂, directly supplementing the plant’s N nutrition (Fukami et al., 2018; Condori et al., 2024). Corroborating these findings, Galindo et al. (2019) and Condori et al. (2024) reported that, even without urea fertilization, plants inoculated with A. brasilense outperformed the control and reached leaf N concentration values comparable to those in fertilized treatments.

Both the direct effect of foliar P supply and the action of A. brasilense likely contributed to the increase in leaf P concentrations. A. brasilense promotes root proliferation through phytohormone synthesis (Hungria et al., 2022; Silva et al., 2022) and releases organic compounds in the rhizosphere that may enhance P solubilization and uptake (Moreira et al., 2016, 2018; Sithole et al., 2019; Kumar et al., 2022). Scudeletti et al. (2023) and de Souza et al. (2025) respectively reported that inoculation of sugarcane or foliar P supplementation of maize increased leaf P concentrations.

Despite the absence of significant differences in foliar N and P concentrations at the other sites, this likely reflects site-specific conditions that limited the expression of the treatment effect, such as baseline soil fertility, pH, microbial activity, or local climate. Soil P levels ranged from low to high across sites, with concentrations of 7 mg kg⁻¹; in Dourados (low), 23 mg kg⁻¹; in Sengés (medium), 29 mg kg⁻¹; in Campo Verde (medium), 59 mg kg⁻¹; in Primavera do Leste (high), 51 mg kg⁻¹; in Santa Cruz do Rio Pardo (high), and 77 mg kg⁻¹; in Jataí (high). These differences may have interacted with the foliar P treatment to modulate plant responses, helping to explain why some sites exhibited significant increases in foliar P whereas others did not. Regardless of treatment or site, the maize plants were not nutrient limited, as the leaf concentrations of N and P were within the ranges of maize sufficiency (25–35 and 1.9–3.5 g kg⁻¹, respectively; Cantarella et al., 2022).

In addition to enhancing nutrient uptake, foliar A. brasilense inoculation and P application promoted plant growth, as evidenced by increases in PH and SD. Yield components, including NRE, NGE, W100, and GY, were also enhanced (Díaz-Zorita et al., 2015; Barbosa et al., 2022; Cardozo et al., 2022). Maize plants produced more grains per plant with higher individual grain weight, directly reflecting more efficient nutrient uptake and potentially increased metabolic activity.

Excessive N application not only increases production costs but also damages the environment. In our study, the combined use of foliar A. brasilense inoculation and foliar P application enabled a 25% reduction in the N fertilization rate without significant yield losses, as evidenced by the comparable GYs of T8 and T1. This demonstrates that integrating inoculation and foliar supplementation may be a viable approach to improve nutrient use efficiency. Our findings are consistent with those of previous studies reporting that maize inoculation with A. brasilense strains Ab-V₅ and Ab-V₆ enhances N fertilizer efficiency (Hungria, 2011; Díaz-Zorita et al., 2015; Martins et al., 2018). Hungria et al. (2022) also observed positive responses to inoculation at 0, 75, and 100% of the recommended N rate but not at 50%. In that study, inoculated plants that received 75% of the N rate achieved an average 4.6% yield increase compared with non-inoculated controls and performed similarly to non-inoculated plants supplied with the full N dose. Taken together, these results and our findings indicate that inoculation can enable a 25% reduction in N fertilization without yield penalties, supporting a synergistic interaction between inoculation and N fertilization in optimizing maize productivity.

More than 85% of anthropogenic N₂O emissions are associated with N enrichment of agricultural soils (Arango and Rice, 2021). As expected, N₂O emissions were higher under the higher N rate in our study (Shcherbak et al., 2014). The observed reduction in N₂O emissions under the 25% lower N application rate can be attributed to the lower availability of mineral N, which limits substrates for nitrification and denitrification, the main processes responsible for N₂O formation. When larger amounts of mineral N (ammonium (NH₄⁺), and nitrate (NO₃⁻) are applied, nitrifying microbes increase the NO₃⁻ supply for denitrifying bacteria under partially anaerobic conditions, such as high soil moisture, thereby enhancing N₂O production (Li et al., 2025; Luo et al., 2025). The yield per N₂O emitted represents an integrative indicator of how efficiently a crop converts available N into economic yield while minimizing environmental losses. Higher values of this ratio indicate that more grain is produced per unit of N₂O emitted, reflecting both agronomic efficiency and reduced emission intensity. Here, this ratio was highest in T8, i.e., when a 25% reduction of the N application rate was combined with foliar inoculation and P application (Figure 3). These findings highlight that moderate reductions in the N rate can effectively lower N₂O emissions while maintaining GY, emphasizing the potential of optimized N management, including complementary practices such as foliar P application and A. brasilense inoculation, as a strategy for sustainable maize yield.

The combination of foliar Azospirillum brasilense inoculation and foliar P application effectively enhanced nutrient uptake and grain yield of off-season maize across Brazilian regions under both full and reduced N fertilization. Treatments integrating foliar inoculation and P, particularly T4 (TSP + 100% N + A. brasilense + foliar P), consistently achieved the highest grain yield, confirming the synergistic effects of these practices. Notably, grain yield under reduced N application in T8 (75% N + A. brasilense + foliar P) was comparable to that achieved under full N application, demonstrating the potential of inoculation and foliar P application to sustain productivity while reducing N inputs. This strategy also reduced estimated N₂O emissions, a major greenhouse gas associated with agricultural N use, highlighting both agronomic and environmental benefits. By enabling reductions in N fertilizer inputs without compromising grain yield, this management approach contributes to climate change mitigation and supports sustainable agriculture. Overall, the combined use of foliar Azospirillum brasilense inoculation and foliar P application represents a sustainable strategy to optimize nutrient use efficiency, reduce environmental impacts, and ensure stable off-season maize production.