Effects of Priestia megaterium Inoculation on Growth and Yield of Adzuki Bean (Vigna angularis) Under Reduced Nitrogen and Phosphorus Fertilization

Nitrogen (N) and phosphorus (P) are critical nutrients governing legume growth and productivity, while excessive dependence on mineral fertilizers can reduce nutrient use efficiency and environmental sustainability. This study evaluated the agronomic effects of Priestia megaterium inoculation on the growth and yield of adzuki bean (Vigna angularis L.) under different nitrogen (N) and phosphorus (P) fertilizer reduction regimes. Two independent field experiments were conducted using a 2 × 4 factorial design to assess bacterial inoculation combined with graded reductions in N or P fertilization. Inoculation increased fresh pod yield from 4.55 to 4.68 t ha−1 under different N fertilization treatments and from 4.61 to 4.80 t ha−1 under different P fertilization treatments, representing increases of 2.9% and 4.1%, respectively. Under reduced N fertilization, yield declined from 5.12 t ha−1 with full N application to 4.00 t ha−1 under a 75% reduction. Similarly, a 75% reduction in P fertilization decreased fresh pod yield by 28.0%, from 5.33 to 3.84 t ha−1, whereas a 25% reduction maintained yield statistically comparable with full P fertilization. The novelty of this study lies in evaluating the agronomic effects of P. megaterium inoculation under field conditions across graded N and P fertilizer reduction levels in adzuki bean. The findings highlight the potential of bacterial inoculation to support adzuki bean production under reduced mineral fertilizer inputs and contribute to more sustainable nutrient management.