Nitrogen-loss reduction efficiencies of field–ditch–pond systems under different water management strategies in rice-growing regions of China

Field–ditch–pond (FDP) systems alleviate nitrogen (N) loss from rice production through interception and purification; however, optimal strategies for N-loss regulation remain unclear. Therefore, we evaluated different water management strategies for N-reduction efficiency under FDP systems using FDP-NPS model in typical rice-growing regions of China. The ditch–pond proportions were 1.87–6.91%, and annual rainfall was 228.0–2713.2 mm. The “low‑water-level management” strategy for FDP system, consisting of water‑saving irrigation in fields and low‑water‑level regulation in ditch–ponds, synergistically intercepted over 93.72% of runoff from rainfall events. The N reduction efficiencies ( IR Nload ) were 42.68–89.55% in Northeast Plain, 46.01–85.94% in Mid-lower Yangtze River Basin, 27.18–76.44% in Southeast Coast, and 13.85–38.82% in Upper Yangtze River Basin. Adjusting the effective water depth of ditch–pond systems increased the high-intensity regulation of IR Nload by 7.74–36.23% over low- and medium-intensity regulation. The flexible regulatory strategies can further adapt to diverse rainfall events across dry, normal, and wet years while maintaining stable IR Nload with slight nationwide fluctuations (0.22–14.57%). Thus, region-specific optimization of water regulation should be prioritized over blind ditch–pond expansion for N pollution control and high-standard farmland construction.