Nano-Hydroxyapatite Improves Drought Resilience in Soybean: Coordinated Physiological Adaptation and Soil Phosphorus Management for Sustainable Cropping Systems

Under global warming scenarios, where drought and water scarcity are becoming more prevalent, this study investigated the efficacy of the nanophosphorus material (n-P) in enhancing soybean resilience under soil water restriction. Compared to conventional ionic phosphate fertilizer (i-P), n-P application significantly improved soybean growth under water-limited conditions, achieving a near-normal growth status. The n-P treatments increased plant fresh weight by 21.2–30.2% relative to i-P, demonstrating superior growth promotion. Physiological analysis revealed that n-P enhanced stress adaptation through the modulation of antioxidant enzyme activities, indicating improved oxidative stress management. Importantly, n-P application boosted reproductive success with 62.0% higher pod fresh weight and 21.5% increased total protein content compared to i-P. Postharvest soil analysis showed additional benefits of n-P fertilization, including 69% lower residual Olsen-P and ameliorated soil acidification compared with the i-P group. These findings provide mechanistic insights into nanofertilizer-mediated plant stress adaptation and highlight the dual benefits of n-P in sustainable crop production and soil health maintenance.