Modeling ammonia emissions and abatement potential from the rice-wheat rotation fields using the calibrated DNDC model: A case study in Shanghai, China

Abating ammonia (NH3) volatilization from intensive cropping system is of great importance for preventing the pollution of atmospheric environment and sustainable agriculture. Urea, a common nitrogen fertilizer, can convert to an unstable carbamate and further releases NH3 from the fields. However, few investigations of NH3 volatilization loss following fertilizer application to agricultural soils have been done using process-based models. In this study, a two-year field study was conducted to calibrate and evaluate the DeNitrification-DeComposition (DNDC) model for simulating NH3 volatilizations and crop production for the rice-wheat rota-tion system under four fertilizer regimes: control group without N fertilizer (CK), chemical fertilizer (CF), mixed application of inorganic and organic fertilizer (MF), and organic fertilizer (OF) treatments. The calibrated and modified DNDC performed effectively in simulating cumulative NH3 volatilization (coefficient of determination (R2) = 0.96 for rice and 0.92 for wheat field, relative deviation (RD) =-6.3% -2.1% for rice and-22.5 to-4.6% for wheat) and grain yields for both crops (R2 = 0.94 for rice and 0.91 for wheat, RD of rice: 4.94%- 9.59%; wheat: -1.84%-11.51%). The sensitivity analysis demonstrated that NH3 volatilization from rice-wheat rotation field was most sensitive to N application rate. Compared to CF and OF, MF treatments significantly mitigated NH3 volatilization and improved crop yield. Therefore, scenario simulation was conducted to confirm the optimal N application rate under MF. The results revealed that 250 kg N ha-1 and 112.5 kg N ha-1 in MF were recommended for rice-and wheat-growing, respectively. Compared to the current N fertilizer rate, the recommended rate saved 50 kg N ha-1 and mitigated NH3 volatilization loss by 28.31% from rice field and saved 37.5 kg N ha-1 and mitigated NH3 volatilization loss by 19.29% from wheat field. Overall, the calibrated DNDC model proved to be an effective tool to simulate NH3 volatilization from the rice-wheat rotation system and provides a promising fertilizer management strategy to decrease N input and mitigate NH3 volatilization.