Soil inoculation with nitrogen-fixing bacteria to supplement maize fertilizer need

Nitrogen (N) is an essential plant nutrient, but low and variable plant-available N levels in agricultural soils often limit maximum grain production. The objective of this study was to determine if a free-living nitrogen-fixing bacterial inoculant (NFI) could supply biologically-fixed N as an additional N source and if this enhances maize (Zea mays L.) N uptake and grain yield. Maize was grown at four site-years in Illinois during 2019–2021. The NFI, a mixture of edited Klebsiella variicola and Kosakonia sacchari, was applied in furrow at planting with urea-N rates from 0 to 225 kg N ha⁻¹. Using quadratic regression models, across N rates, the NFI supplemented the fertilizer-N equivalent of 38.5 or 12.1 kg N ha⁻¹ at V8 or R1, respectively. Increases in N accumulation were observed in all plant fractions, and δ¹⁵N abundance measurements confirmed that some of this additional N was derived from biological N fixation. The NFI treatment increased N accumulation by an average of 4.8% and 3.7% at V8 and R1, respectively, which was the result of greater biomass, with no effect on plant N concentration. Application of NFI resulted in an average of 1.5% more kernels m⁻² and 0.11 Mg ha⁻¹ more grain yield. This work reveals that NFI can provide an additional source of N for maize production but identifies that the season-long benefit of fixed-N from an NFI is yet to be fully optimized.