农田周边的排水沟渠不仅是农田养分迁移的重要通道，也是氮转化非常活跃的场所和潜在的氧化亚氮（N₂O）排放源.本研究以川中丘陵区农田源头沟渠为对象，在6~9月的玉米季（雨季），采用静态箱-气相色谱法对其N₂O排放开展原位观测.结果表明，在整个观测期有自然植被覆盖的沟渠生态系统（V）N₂O累积排放量（以N计）为0.43 kg·hm^-2，而无自然植被覆盖的对照处理（NV，代表沟渠中的沉积物-水界面系统）则为0.07 kg·hm^-2.该沟渠生态系统的N₂O平均排放通量[14.7 μg·（m²·h）^-1]已达到本地区玉米农田直接排放的水平，表明玉米季中农田源头沟渠是不容忽视的N₂O源.川中丘陵区雨季丰富的降雨径流携带大量农田硝态氮进入沟渠，促进N₂O产生和排放，此外，植物的存在可大幅度提高农田沟渠的N₂O间接排放系数（V：0.05% vs. NV：0.01%）.由于本研究的N₂O间接排放系数远低于2006年IPCC建议的缺省值（0.25%），如果仅采用IPCC缺省值来估算本地区沟渠生态系统的N₂O排放，可能导致较大误差.未来研究中应对原位观测多予以重视，为进一步修正其缺省值提供理论依据.

 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.