Enhanced Soil Fertility and Baby Maize Yield Through Bacillus megaterium CM2 under Reduced Nitrogen Input

This present study evaluated the effectiveness of Bacillus megaterium CM2 (strain CM2) as a biofertilizer for the enhancement of soil fertility and baby maize (Zea mays L.) productivity under reduced nitrogen (N) input in the Mekong Delta, Vietnam. A field experiment was conducted using a randomized complete block design (RCBD) featuring five treatments combining strain CM2 inoculation and varying nitrogen fertilizer rates. Each treatment was replicated four times. The treatments included a non-inoculated control receiving the full recommended N rate (350 kg urea ha−1) and four strain CM2-inoculated treatments supplied with 100%, 75%, 50%, and 25% of the recommended N dose (350, 262.5, 175, and 87.5 kg urea ha−1, respectively). Laboratory characterization demonstrated that strain CM2 possessed high nitrogenase activity, strong thermotolerance, and broad adaptability, confirming its suitability for field application. In comparison with the non-inoculated control, strain CM2 inoculation under reduced N regimes significantly improved soil chemical properties, including soil pH, cation exchange capacity, soil organic matter, total nitrogen, available phosphorus, and exchangeable potassium. This present study revealed overall soil fertility indicators exhibited an increase by approximately 10–95%, with the lowest responses as observed in under treatments subjected to 25% and 57% reductions in nitrogen fertilizer application. Whilst the most pronounced enhancement were recorded at the 50% N reduction level, particularly for pH (6.99), CEC (14.8 cmol+ kg−1), and SOM (2.99%). Thirty days after sowing, CM2-inoculated plants exhibited substantial increases in leaf number (32%), chlorophyll content (17%), and plant height (19%) relative to uninoculated control. Furthermore, yield performance was also substantially enhanced, with total edible cob yield reaching 2.98 t ha−1 and the proportion of grade-1 cobs increasing to 65.8%, corresponding to yield gains of 12.9% and 27.6%, respectively. The enhancement observed were attributed to enhanced biological nitrogen fixation, phytohormone-mediated growth promotion, and improved nutrient acquisition efficiency. The integration of strain CM2 with 25–50% reduced N fertilization-maintained yield and improved soil fertility, highlighting its potential as an eco-friendly microbial inoculant for sustainable baby maize cultivation.