Co-inoculation maintains yields and lowers N2O emission by affecting rhizosphere bacterial diversity in common bean grown on a C-rich clayey Ferralsol

Despite being a N-fixing legume, common bean ( Phaseolus vulgaris ) cultivation using diazotrophic bacteria is not commonly adopted by Brazilian farmers, who instead rely on mineral nitrogen sources like urea, increasing environmental and economic costs. Diversified systems that enhance soil quality may improve the crop’s ability to depend solely on biological nitrogen fixation. This study investigated how co-inoculation with Rhizobium spp. and Azospirillum brasilense (+I or -I), with or without mineral N (+N or -N), affects N 2 O–N fluxes, yield, and rhizospheric community of common bean. A trial was established within a 20-year-old integrated crop-livestock system (ICLS) over the 2019/2020 (Y1) and 2021/2022 (Y2) crop years. Soil and plant variables were assessed throughout both years. N 2 O–N fluxes were measured using manual static chambers targeting days following co-inoculation and N fertilization applications, while the 16S rRNA microbiome composition was assessed by metabarcoding samples collected during flowering. Yields (∼3000 kg ha −1 ) were relatively high and similar among treatments. Co-inoculation alone (+I-N) led to reduced N 2 O–N fluxes (yearly average of 43.8 ± 16.0 µg/m²/h). Co-inoculation reduced the N 2 O emission intensity of common bean; however, its effectiveness was limited when applied in conjunction with urea. Regardless of year and co-inoculation, N 2 O–N fluxes remained high when N fertilizer was used (averaging 108.3 ± 30.3 µg/m²/h). Microbial diversity was generally lower under N fertilization, with shifts in the abundance of nitrogen-related functional groups, particularly in the second year. Despite seasonal variations, results indicate that co-inoculation can mitigate N₂O emission while maintaining crop yield and soil organic matter (∼4 %) in this biodiverse ICLS system.