Greenhouse gas mitigation potential under different rice-crop rotation systems: from site experiment to model evaluation

Crop rotation systems in fields could improve crop production and indirectly affect carbon and nitrogen dynamics due to multiple fertilizer applications. Therefore, it is important to evaluate the impact of these crop rotation systems on greenhouse gas (GHG) emissions. Field experiments were conducted with three different rotation systems, and the DeNitrification–DeComposition (DNDC) model was applied to monitor and estimate crop yields and GHG emissions during three rice-upland crop rotational periods (from June 2013 to May 2016). Low methane (CH₄) and nitrous oxide (N₂O) emissions were observed in rice-Chinese milk vetch and single rice rotation systems. The simulated crop yields fit the observed data very well (d > 0.80, EF > 0.70) after the model was calibrated by adjusting the crop parameters. The model-simulated daily and annual CH₄ emissions agreed well with the field measurements (d > 0.7, EF = 0.41–0.98). The simulated N₂O (d = 0.01–0.70, EF < 0 or close to 0) of accumulated emissions and daily fluxes (d = 0.07–0.14, EF < 0) showed low levels of accuracy with field observations. The GHG emissions in Shanghai rice paddy were different under various rotation systems, with the following order: single rice rotation system < rice-Chinese milk vetch rotation system < baseline rotation system of Shanghai paddy < 1/3 (rice-Chinese milk vetch + single rice + rice-winter wheat rice-winter) rotation system < rice-winter wheat rotation system under the same nitrogen loading. The DNDC was able to predict rice yields and GHG emissions under different crop rotation systems. The results provide positive reliable indications that crop rotation systems have the potential to reduce GHG emissions; e.g., the rice-Chinese milk vetch rotation system could mitigate the CH₄ and N₂O emissions.