Stationary observation was performed during the period from October, 2006 to October, 2007 of N₂O emissions from a field under wheat-maize rotation and a field under vegetable cultivation for over 20 years, using the static chamber method/gas chromatograph technique. Characteristics of the emissions from the two ecosystems were analyzed for differences between the two and effects of the participating factors, such as N application, soil temperature, soil moisture and crops on the emissions. Results show that in CK (No N applied) the mean N₂O emission flux was 17.8?5.6 and 50.7?13.3 ?g m^-2 h^-1, respectively, from the wheat-maize ecosystem and the vegetable ecosystem. Clearly the flux from the latter was 3.1 times higher than that from the former. When N was applied at N150 kg hm^-2, the N₂O emission coefficient in the vegetable field was 39.0% higher than that in wheat-maize field. Plant participation was not responsible for higher N₂O emission from the vegetable ecosystem. The difference in N₂O emission flux between the two ecosystems in different crop growing seasons was attributed to the fact that the difference in life cycle between the crops led to difference in intensity of N application per unit time. Therefore, N₂O emission from the agro-ecosystems may be cut down by regulating N application rate in light of characteristics of the crop growing season, which vary sharply especially of vegetables. If precise fertilization can be adopted for vegetables, the potential of the vegetable field in reducing N₂O emission would be greater than that of the upland farm field.