Nitrogen use efficiency in high soil-plant nitrogen pool: Fertilizer management optimization via the DNDC model in rice fields

Enhancing the soil-plant nitrogen (N) pool (SPNP) in paddies system can mitigate environmental N pollution. However, a larger SPNP does not inherently improve N use efficiency (NUE), strategies to enhance NUE under high SPNP remain poorly understood. This study employed the DeNitrification-DeComposition model to evaluate fertilizer practices: single chemical N (SCN), SCN combining with green manure (GM), straw incorporation (SI) or manure fertilizer (MF), aiming for high NUE under elevated SPNP paddies in paddy systems. Results indicated that plant and soil microbial N fixation, soil organic and inorganic N, NH 3 volatilization, and N leaching were key factors affecting both SPNP and NUE. Among the practices, SCN at 100–150 kg N ha −1 minimized organic and inorganic N loss and increased soil and plant N fixation, but yielded the lowest SPNP and NUE. Combining GM with SCN at 50–100 kg N ha −1 (GMN50-100) increased soil organic N by 67 % and soil microbial N fixation by 5 %, while reducing NH3 volatilization by 20–30 kg N ha −1 . This significantly enhanced NUE under elevated SPNP. Similarly, SI combined with SCN (SIN) at 100–150 kg N ha −1 or MF combined with SCN (MFN) at 50–100 kg N ha −1 both increased soil organic N by over 20 % and reduced NH 3 volatilization. However, the SIN strategy resulted in lower SPNP but higher NUE, while the MFN treatment yielded the highest SPNP but comparatively lower NUE. Consequently, superior GMN50-100 proved the most effective approach for sustaining high NUE under high SPNP conditions. • Chemical N had lower N use efficiency (NUE) and soil-plant N pool (SPNP). • Chemical N combined with straw incorporation had lower SPNP and higher NUE. • Chemical N combined with manure fertilizer had the highest SPNP but lower NUE. • Chemical N combined with green manure had higher NUE and SPNP. • Chemical N combined with green manure reduced NH 3 and increased soil organic N.