[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 (N₂O) emission. In this study, N₂O 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 N₂O 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^-2, respectively. Meanwhile, the mean N₂O flux from the agricultural headwater ditch ecosystem[14.7 μg·(m²·h)^-1] was comparable to the magnitude of direct N₂O flux from the maize cropland in this region. Nitrate concentration in the overlying water could be the main factor governing N₂O emission from the ditch, especially in the rainy season. The existence of vegetation increased the indirect N₂O emission factor (V:0.05% vs.NV:0.01%). The indirect N₂O 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 N₂O emissions. More attention should be paid to in situ measurements to reduce uncertainty of N₂O estimation calculated by only applying the default value for emission factor from the IPCC.