Experimental Study On Greenhouse Gas Emissions From Rice Fields In Arid Areas Based On DNDC Model

In recent years,with the development of high-quality rice areas in Xinjiang and the development of sea rice cultivation experiments,rice cultivation in Xinjiang has moved toward large-scale,standardized and intensive development.In the context of China's greenhouse gas emission reduction target,namely,carbon dioxide emissions,to achieve carbon peak before 2030 and to achieve carbon neutrality before 2060,it is particularly important to carry out research on greenhouse gas emissions of paddy fields in arid areas,which has practical significance for agricultural carbon emission reduction and optimization of irrigation conditions in Xinjiang.In this study,greenhouse gas emission and simulation of paddy fields under different water control conditions in arid areas were studied,providing theoretical support and practical basis for agricultural greenhouse gas emission reduction in arid areas.This study selected Urumqi Midong District,one of the rice growing regions in Xinjiang,and observed the rice growing season in 2019 and 2020 for two consecutive years.The experimental plan was developed by referring to domestic and foreign literatures,and the experimental plan was modified based on the observed data in 2019to develop the experimental plan suitable for the arid area.In this study,the methane emission flux of irrigated paddy fields under different water control conditions was observed,and the diurnal and seasonal variation characteristics of methane emission and its influencing factors were analyzed.By modifying Denitrification-Decompositiond Model parameters,measured and simulated values of methane emissions from rice fields were compared and analyzed to explore the adaptation of DNDC Model in the study area.The yield and quality of rice were measured under different water control conditions,and economic benefits and agricultural carbon emission reduction were considered comprehensively.The main results are as follows:1.Diurnal variation characteristics of methane emission in rice fields The methane emission rate in the afternoon was higher than that in the morning.Shallow water(lt;The methane emission rate of 3cm paddy field increased with the increase of temperature,and the methane emission reached the highest value when the temperature reached the highest temperature.Deep water(>;The relationship between methane emission and temperature was not obvious,and there was no significant change with the increase of temperature.In the same growing period,the daily methane emission was affected by the water depth.Under the shallow water condition,the daily methane emission was larger,while under the deep water condition,the daily methane emission was smaller.In the yellow ripening stage,there was no water in the field,and the diurnal trend of methane emission in the experimental field was similar.2.The seasonal variation of methane emission from paddy fields in the study area showed a single peak mode during the growth season,and the methane peak appeared at the tillering stage of rice growth.Under the irrigation of 5cm water depth,the peak value appeared in the middle and late tillering period,the peak duration was the shortest and the peak value was the highest,the maximum emission flux was 26.20 mg·m²·h^-1,and the total emission was 83.50kg/hm².Under 10cm water irrigation and conventional irrigation experiment,the methane emission rate increased continuously from the early tillering period to the middle and late tillering period,and the maximum emission fluxes were 20.58 mg·m²·h^-1 and 20.32 mg·m²·h^-1,respectively.The total emissions were122.29 kg/hm² and 107.47 kg/hm²,respectively.The methane emission characteristics of the two places were similar,and the total methane emission was similar.Under the condition of long and deep water under 15cm water irrigation,there was obvious methane emission from the early tillering stage,and the methane emission peak lasted until the late tillering stage.The methane emission peak lasted for a long time,but the peak value was low.The maximum emission flux was 7.57 mg·m²·h^-1,and the total emission flux was 42.29 kg/hm².3.The relative errors of the DNDC model for the simulation results of#1-#4experiments are 17.4%,9.2%,0.49%,and 129.4%,respectively.The DNDC model has a good simulation effect on#1-#3 experiments,and the relative errors are all within20%.4.In this study,5cm water depth irrigation significantly affected the total dry matter,plant height and tiller number of rice.Under 5-15cm water irrigation,the dry matter weight of stem and leaf increased with the increase of water depth,which was significantly related to rice yield.Different water depths had great effects on the brown rice rate and protein content of rice.Irrigation with 5cm water significantly reduced the brown rice rate and protein content of rice.5.In this study,paddy yields higher rice under 15 cm deep water irrigation,and has the least methane emission flux per unit yield.It is the best choice under comprehensive consideration of economic benefits and agricultural carbon emission reduction.5.In this study,rice yield under 15cm depth water irrigation was higher and methane emission flux per unit yield was the least,which was the best choice for comprehensive consideration of economic benefits and agricultural carbon emission reduction.