Leaching and ammonia emissions in rice fields exhibit greater influences by seasons than management

Estimation of ammonia (NH₃) emissions requires calculation of emission factors (EFs) based on experimental data that reflects seasonal and climatic variability, particularly in an annual triple cropping system. However, data on season-specific EFs under varying climate regimes are required to develop the management strategies that help mitigate nitrogen (N) loss via volatilization. A large portion of N releases into atmosphere from rice soils causing both economic and environmental costs since farmers indiscriminately use N fertilizers for rice production. Ammonia emissions and EFs were assessed in two different rice growing sites with an annual Boro–Aus–Aman sequence. Two sets of treatments were used: two residue treatments (no residue incorporation, NR; and 30 %, by height, crop residue incorporation, CR); and four N levels (control, CL; farmers' practice, FP; recommended nitrogen dose, RD; and 125 % of RD, 125RD). Crop residue incorporation significantly elevated NH₃ emissions. CR coupled with 125RD exhibited 10–27 %, 6–7 % and 6–9 % higher NH₃ emissions than NR-125RD in Boro, Aus and Aman seasons, respectively. Although the recommended N rate was higher in Boro, NH₃ emission was higher in Aman rice (28–34 kg NH₃-N ha⁻¹) suggesting that climatic conditions are the most influential driver rather than the N rate. Likewise, NH₃ EFs in RD ranged from 11 to 18 %, 16–33 % and 28–34 % in Boro, Aus and Aman seasons, respectively. Our results indicate that NH₃ emissions do not only depend on N rate but also on seasons where consideration of seasonal EFs is required to improve NH₃ and N budget. By contrast, N rate and crop residue did not influence N leaching but leaching was a considerable part of N loss from rice fields. Overall, our findings underscore the critical need for season-specific N fertilizer management including crop residue incorporation in multi-cropped rice systems to effectively mitigate NH₃ emissions while maintaining productivity.