Simulation of Water Saving and Methane Mitigation Potential of Paddy Fields under Alternate Wetting and Drying Irrigation Regime in China

Paddy fields are the main consumption of agricultural water and the main source of greenhouse gas methane (CH 4 ). Water use in paddy fields accounts for about 70% of agricultural water worldwide. 9%-19% of CH 4 in the atmosphere comes from rice season around global. As the largest rice producer, China’s rice planting area and production account for more than 23% and 30% of the world total respectively. Reducing irrigation water and methane emissions from paddy fields can effectively alleviate pressure on water shortage and climate change. Therefore, the alternate wetting and drying (AWD) irrigation regime is currently used in rice cultivation. It has been widely promoted in major rice-producing countries in Asia. Compared with continuous flooding (CF), AWD saves water by alternate flood and drainage in different rice growth stages. However, the current research experiment only has conducted at several specific sites and them show that AWD can mitigate CH 4 emissions while reducing water consumption in paddy fields. More importantly, there is no significant change in rice yield under moderate AWD. Our study intends to quantify the reduction potential of irrigation water and CH 4 at the regional level by coupling model. DSSAT (Decision Support System for Agrotechnology Transfer), DNDC (Denitrification Decomposition) and AEZ (Agro-ecological Zone) are widely used agricultural models at different research scales. The corresponding parameters transferring between them can reduce the uncertainty of the simulation process. The inputs of model included rice observation, climate data and soil information. After integrating the basic data, we calibrated rice genetic parameters by DSSAT and simulated rice yield, irrigation water and CH 4 emissions by DNDC at 24 agro-meteorological observation sites in China. Based on the AEZ ecological zone division, the site scale results are upscaled to the spatial scale under AWD and CF irrigation scenarios. Due to differences in environmental conditions, we divided the study region into two parts, the northeast and south. The simulation results show that compared with CF, the water-saving ratio in the northeast rice area is 23%-34%, and that in the southern rice area is 18%-50% The emission reduction ratio of CH 4 in Northeast is 60% -71%, and it in South is 34% -65%. In general, the CH 4 emission mitigation effect in the northeast rice area and the water-saving effect in the southern rice area are better. It is mainly caused by the different texture of the paddy soil. At the same time, the simulation results of rice yield are consistent with the experimental results, without significant changes. This study can provide references for water-saving rice cultivation in China.