Emissions of CH(4) and N(2)O under Different Tillage Systems from Double-Cropped Paddy Fields in Southern China

Understanding greenhouse gases (GHG) emissions is becoming increasingly important with the climate change. Most previous studies have focused on the assessment of soil organic carbon (SOC) sequestration potential and GHG emissions from agriculture. However, specific experiments assessing tillage impacts on GHG emission from double-cropped paddy fields in Southern China are relatively scarce. Therefore, the objective of this study was to assess the effects of tillage systems on methane (CH(4)) and nitrous oxide (N(2)O) emission in a double rice (Oryza sativa L.) cropping system. The experiment was established in 2005 in Hunan Province, China. Three tillage treatments were laid out in a randomized complete block design: conventional tillage (CT), rotary tillage (RT) and no-till (NT). Fluxes of CH(4) from different tillage treatments followed a similar trend during the two years, with a single peak emission for the early rice season and a double peak emission for the late rice season. Compared with other treatments, NT significantly reduced CH(4) emission among the rice growing seasons (P<0.05). However, much higher variations in N(2)O emission were observed across the rice growing seasons due to the vulnerability of N(2)O to external influences. The amount of CH(4) emission in paddy fields was much higher relative to N(2)O emission. Conversion of CT to NT significantly reduced the cumulative CH(4) emission for both rice seasons compared with other treatments (P<0.05). The mean value of global warming potentials (GWPs) of CH(4) and N(2)O emissions over 100 years was in the order of NT<RT<CT, which indicated NT was significantly lower than both CT and RT (P<0.05). This suggests that adoption of NT would be beneficial for GHG mitigation and could be a good option for carbon-smart agriculture in double rice cropped regions.