Effect of Plant Growth-Promoting Rhizobacteria at Various Nitrogen Rates on Maize Growth.

Plant growth-promoting rhizobacteria (PGPR) are capable of aggressively colonizing plants roots and promoting plant growth by producing and secreting various chemical regulators around the rhizosphere. With the recent interest in sustainable agriculture, an increasing number of researchers are investigating ways to maximize the efficiency of PGPR use while reducing chemical fertilizer inputs needed for crop production. Therefore, a greenhouse study was conducted to evaluate the impact of PGPR inoculants on biomass production and N content of maize (Zea mays L.) under different N levels. Treatments included three PGPR inoculants (2 PGPR strain mixtures and 1 control without PGPR) and five N levels at 0, 25, 50, 75, and 100% of the recommended N rate (135 kg N ha^-1). Results showed that inoculation of PGPR significantly increased maize growth parameters (e.g., plant height, stem diameter, leaf area, and root morphology) compared to no PGPR application under the same N levels at the V6 growth stage, but little difference was observed at the V4 stage. PGPR with 50% of the full N rate produced maize biomass and N content equivalent to or greater than that of the full N rate without inoculants at the VT stage. It could be concluded that PGPR inoculant mixtures could potentially reduce inorganic N fertilization without affecting maize plant growth parameters. Future research is needed under field conditions to determine if these PGPR inoculants could be integrated as a bio-fertilizer in crop production nutrient management strategies.