[Nitrous Oxide Emissions and Its Influencing Factors from an Agricultural Headwater Ditch During a Maize Season in the Hilly Area of Central Sichuan Basin].

Agricultural headwater ditches, the important locations for retaining and transforming nitrogen derived from the adjacent farmlands, have been regarded as the potential source of nitrous oxide (NO) emission. In this study, NO emissions from a typical agricultural ditch in the Hilly Area of Central Sichuan Basin, were observed by closed static chamber-GC technique during the maize season (rainy season), from June to the end of September. During the study period, cumulative NO emissions in the sediment-water interface without vegetation (NV) and the ditch ecosystem with natural vegetation (V) were 0.07 and 0.43 kg·hm, respectively. Meanwhile, the mean NO flux from the agricultural headwater ditch ecosystem[14.7 μg·(m·h)] was comparable to the magnitude of direct NO flux from the maize cropland in this region. Nitrate concentration in the overlying water could be the main factor governing NO emission from the ditch, especially in the rainy season. The existence of vegetation increased the indirect NO emission factor (V:0.05% .NV:0.01%). The indirect NO emission factor from this field investigation was much lower than the default value proposed by the Intergovernmental Panel on Climate Change (IPCC, 2006) for assessing indirect agricultural NO emissions. More attention should be paid to measurements to reduce uncertainty of NO estimation calculated by only applying the default value for emission factor from the IPCC.