Methane emission and its relationship with soil temperature and moisture during rice growth in film mulching upland rice field in South China

Abstract: To investigate methane fluxes in traditional paddy field and film mulching upland for late rice growth in South China, field experiment were conducted and gas sampling the closed-chamber technique were applied. The methane cumulative fluxes and global warming potential (GWP) from film mulching upland and traditional paddy field during rice growth were compared to estimate the contribution of methane fluxes from film mulching upland to greenhouse effect. Soil samples in 0-20 cm layer were collected to measure the soil water content (w/w). The thermometer was buried at 5cm soil depth in closed-chamber for gas sampling after rice transplanting. Soil temperature was obtained by the thermometer when methane was sampled. The relationships of soil moisture and soil temperature with methane fluxes were studied. Results showed that methane emitted were concentrated during the vegetative growth stage of rice both paddy field and film mulching upland. However methane emission in paddy field concentrated in former 35 days after rice transplanting with methane cumulative flux of 14 779.97 mg/m2. Methane emission in film mulching upland concentrated in former 25 days after rice transplanting with methane cumulative flux of 2 372.27 mg/m2. The percentage of CH4 cumulative flux in emission peak period and total cumulative flux in the paddy field and film mulching upland were 72% and 97%, respectively. Methane fluxes in film mulching upland were significantly lower than that in traditional paddy fields. Methane cumulative flux in film mulching upland declined by 88% compared to paddy field due to the fact maximum emission peak reduced and the emission peak period shortened. The GWP (CO2 equivalent fluxes) of methane was 468.72 g/m2 in paddy field, but 56.48 g/m2 in film mulching upland. Thus the contribution of methane fluxes to greenhouse effect in film mulching upland was lower than that in paddy field. Soil temperature and soil moisture at 5 cm soil depth had significant positive correlation with methane fluxes during the rice growth stage, respectively. The area of methane flux more than 1.0 mg·m-2·h-1 existed in the area of the soil water content (w/w) higher than 36.25%, and few methane in both paddy field and film mulching upland was emitted when soil water content was less than 36.25%.