NBPT-DCD co-application mitigates dual nitrogen losses in AWD paddies without yield trade-off

Urease and nitrification inhibitors effectively mitigate nitrogen (N) losses in paddy ecosystems, yet their efficacy and interactive effects under alternate wetting and drying (AWD) with fluctuating soil moisture remain poorly understood. Here, we conducted a three-year field-based lysimeter experiment (2021–2023) with five treatments: continuous flooding irrigation (CF) with no inhibitor (I CF A 0 ), AWD with no inhibitor (I AWD A 0 ), AWD with a nitrification inhibitor dicyandiamide (DCD) (I AWD A N ), AWD with a urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) (I AWD A U ), and AWD with both inhibitors (I AWD A N+U ). AWD had no significant effect on NH 3 volatilization compared to CF, but it increased total N leaching by 15.1%-26.5% over three years. The sole application of NBPT under AWD significantly reduced NH 3 volatilization and N leaching by 19.1–43.2% and 1.3–14.1%, respectively. However, DCD significantly increased NH 3 volatilization by 5.8–25.1% and N leaching by 15.2–27.9% under AWD. Notably, the combined application of two inhibitors (NBPT and DCD) under AWD decreased NH 3 volatilization by 6.0–38.5% and N leaching by 3.5–28.3%. Soil NH 4 + availability and urease activity jointly regulated NH 3 volatilization and N leaching under AWD conditions. Neither inhibitors nor AWD significantly affected grain yields. Our findings demonstrate that no single inhibitor regime is universally optimal under AWD: dual application balanced N leaching control, while NBPT alone achieved stronger NH 3 volatilization mitigation. These results emphasize the need to tailor inhibitor strategies to specific N loss mitigation targets in AWD rice systems.