Effect of water-saving irrigation on CH_4 emissions from rice fields

摘要

Although water saving irrigation (WSI) has been widely used in China, there is limited understanding on the effect of such a practice on the CH_4 emission in rice fields. Consequently it is difficult to estimate the regional distribution of CH_4 emissions in space and time from rice fields across China. Two water treatments (controlled irrigation (CI), a routine WSI practice in China, and a traditional continuous flooded irrigation (CI)) were used to examine diurnal and seasonal variations of CH_4 emissions in field experiments in Kunshan, east China. The heavy loams in the site have organic matter content of 30.3 g/kg while percolation rates in the shallow groundwater range from 2 to 10 mm per day. Gas samples were collected and analyzed using a static chamber technique and a Gas Chromatograph system respectively. The results show that under WSI conditions, the diurnal variation of CH_4 emissions presented regular afternoon-maximum mode during the initial and middle tillering stage, which mainly depends on air temperature. Only one peak of CH_4 emission occurred in initial/middle tillering growth stage of rice season under CI conditions, which is mainly regulated by drainage or water layer receding. For CI, seasonal CH_4 emission is 2.4g·m~(-2)～24.5g·m~(-2), and the seasonal average flux is 0.8 mg·m~(-2)·h~(-1)～8.15 mg·m~(-2)·h~(-1), which is 39-85% lower than that for FI. CI has more mitigation potential than midseason drainage. Furthermore, CI significantly reduces irrigation water use while maintains rice yields, even increases yields under atrocious weather conditions. A hydrologic characterization and spatial distribution of rice field in China is needed to assess the extent and magnitude of potential emission reduction in the region.