Three-year field evaluation of a rhizobacterial consortium improving maize growth and yield under reduced N-fertilization and modulating soil respiration.

Ensuring global food security while protecting soil health requires sustainable agricultural innovations, such as the use of plant growth-promoting rhizobacteria (PGPR). However, excessive nitrogen fertilization in semi-arid maize systems contributes to soil salinization, groundwater contamination, and declining nutrient efficiency, underscoring the need for field-validated microbial strategies that reduce fertilizer inputs without compromising yield. This study presents the results of a three-year field trial (2023-2025) conducted under semi-arid maize production conditions, evaluating a functionally selected microbial consortium (Priestia megaterium and Enterobacter cloacae) on three maize hybrids (Hipopótamo, C3, and C4) under a reduced N rate of 51 kg N ha-1 (≈25% of the regional recommendation of 200 kg N ha-1), compared to non-inoculated controls receiving 102 kg N ha-1 (≈50% of the regional recommendation). Inoculation increased root volume and nitrate reductase activity, accelerating nitrogen assimilation and sustaining vegetative development. Treated plants maintained photosynthetic rates exceeding 43 μmol CO2 m-2 s-1, chlorophyll content above 60 SPAD units, and NDVI values exceeding 0.83 through reproductive stages, delaying canopy senescence and effectively extending the grain-filling period. Consequently, inoculated hybrids achieved grain yields exceeding 14 t ha-1, comparable to those obtained with the higher experimental N rate (102 kg N ha-1), while soil CO2 fluxes increased above 2.5 μmol CO2 m-2 s-1, confirming active rhizosphere microbial activity. This multi-year study demonstrates that microbial-assisted management can sustain maize productivity under reduced nitrogen inputs, enabling a 50% reduction in N fertilizer use relative to the conventional experimental rate (from 102 to 51 kg N ha-1) without yield penalty. No significant treatment × year interaction was detected, indicating consistent effects across growing seasons. Future work should validate these findings across diverse agro-ecological zones and elucidate the molecular mechanisms underlying the observed phenotypic stability and plant-microbe interactions.