The Effect of Drainage Systems on Methane Emission Reduction from Paddy Fields

Global warming، as a consequence of greenhouse gases accumulation، has exerted significant impacts on biosphere. Methane، a product of reduction processes of organic carbon in anaerobic conditions، is mainly emitted from paddy fields. The aim followed in this research is to evaluate the impact of midseason drainage on methane emission from paddy fields. The research was conducted with three treatments of traditional، surface، and subsurface drainages in a CBD in Sari region. Gas sampling was done weekly following the first week of transplanting till harvest time. Twenty five days after planting، irrigation was ceased for a week، which caused lowering of water table depth to 0. 03، 0. 1، and 0. 7m for traditional، surface، and subsurface drainages، respectively. Methane emission decreased as subsurface water table dropped. Gas emission reduction and the return period to before drainage practice were significantly higher in subsurface drainage. The lowest methane emission occurred two weeks after midseason drainage، as compared with the other two. where emission was reduced by 25، 45 and 315 percent in traditional، surface، and subsurface drainages، respectively. In conclusion، based on the obtained results، water table drawdown، and thus change in anaerobic conditions of root zone to an aerobic one could reduce methane emissions from paddy fields. Abstract Global warming، as a consequence of greenhouse gases accumulation، has exerted significant impacts on biosphere. Methane، a product of reduction processes of organic carbon in anaerobic conditions، is mainly emitted from paddy fields. The aim followed in this research is to evaluate the impact of midseason drainage on methane emission from paddy fields. The research was conducted with three treatments of traditional، surface، and subsurface drainages in a CBD in Sari region. Gas sampling was done weekly following the first week of transplanting till harvest time. Twenty five days after planting، irrigation was ceased for a week، which caused lowering of water table depth to 0. 03، 0. 1، and 0. 7m for traditional، surface، and subsurface drainages، respectively. Methane emission decreased as subsurface water table dropped. Gas emission reduction and the return period to before drainage practice were significantly higher in subsurface drainage. The lowest methane emission occurred two weeks after midseason drainage، as compared with the other two. where emission was reduced by 25، 45 and 315 percent in traditional، surface، and subsurface drainages، respectively. In conclusion، based on the obtained results، water table drawdown، and thus change in anaerobic conditions of root zone to an aerobic one could reduce methane emissions from paddy fields.