Optimizing Nitrogen Management for Sustainable Peanut Production on Subtropical Sloping Red Soils

Balancing high yield, nitrogen use efficiency, and environmental sustainability is a central challenge around the world. A ¹⁵N tracing and a gradient nitrogen application experiment was taken at 12 runoff plots with four treatments, i.e. 0, 90, 120, and 150 kg ha⁻¹ on subtropical sloping red soils of southern China. Effects of N rate on peanut yield, N losses, and soil N balance were systematically evaluated in different growth stages. Results showed that an appropriate N rate (90 kg ha⁻¹) effectively synchronized N supply with crop demand across growth stages: it met early-stage N requirements for vigorous growth while preserving rhizobial N fixation capacity, thereby maintaining a stable N source during pod-filling and achieving a pod yield of 3,866 kg ha⁻¹. In contrast, excessive N application (150 kg ha⁻¹) disrupted this balance, leading to early-stage N surplus, excessive vegetative growth, suppressed nodulation, and a late-season N shortfall, which reduced the harvest index without increasing yield. Environmentally, deep leaching was the primary pathway of N loss, accounting for 67.5% of the total loss. The 90 kg ha⁻¹ treatment significantly reduced N loss while maintaining soil N balance, whereas the high N treatment increased loss by 93.8%. These findings demonstrate that effective N management in peanut systems on sloping red soils should tailor N supply to crop demand patterns rather than simply increasing input. The 90 kg ha⁻¹ rate is recommended to sustain productivity while minimizing environmental risk, providing a scientific basis for sustainable peanut production in the region.