Inoculation with Stenotrophomonas maltophilia LIMN and Enterobacter roggenkampii LCMG Enhances Maize (Zea mays L.) Yield and Reduces Nitrogen Fertilizer Dependence in Nutrient-Limited Soils of Semi-Arid Regions

Excessive nitrogen (N) fertilization in maize (Zea mays L.) production causes environmental degradation, particularly in semi-arid regions where high chemical inputs are necessary to maintain crop production. Plant growth-promoting rhizobacteria (PGPR) could reduce the optimal N fertilization doses. This investigation aimed to isolate bacteria, screen them for plant growth-promoting traits, and evaluate their potential effects on maize grain under different chemical N fertilization doses. Isolates Stenotrophomonas maltophilia LIMN and Enterobacter roggenkampii LCMG demonstrated multifunctional growth-promoting traits in vitro, including N2 fixation, indole-3-acetic acid and siderophore production, potassium solubilization, and desiccation tolerance, with E. roggenkampii LCMG also solubilizing inorganic phosphate. A field trial across four chemical N fertilization rates (0, 40, 80, and 120 kg N ha−1) revealed that single bacterial inoculation without N fertilizer matched or exceeded uninoculated controls receiving up to 80 kg of N ha−1 (the standard recommendation). Specifically, S. maltophilia LIMN combined with the recommended rate of 80 kg N ha−1 achieved the maximum grain yield (4601.2 kg DM ha−1), outperforming uninoculated controls (without PGPR) receiving excessive fertilization at 120 kg N ha−1 (3760.4 DM ha−1). Although maize plants benefited from inoculation with S. maltophilia LIMN or E. roggenkampii LCMG, achieving similar or better yields than crops fertilized with high chemical N inputs under stress factors such as deficiency of moisture, low-nutrient soils, and high temperatures, the present study did not test the pathogenicity and biosecurity of S. maltophilia or E. roggenkampii in crops; therefore, the results are not a direct recommendation of their use as biofertilizers before novel studies to assess all the limitations and the potential to reduce N dependency in order to design novel sustainable strategies for crop production.