Abstract: The role of upland crops in N₂O emission from farmland is evaluated by measuring N₂O flux from several farniland ecosystems with closed chamber method,comparing with N₂O flux from bare field.The effect of environmental factors on N₂O flux its investigated by experiments in field and laboratory.The results show that there exists an emission peak of diurnal N₂O flux both in the morning and in the afternoon from soybean field,but only one peak from spinach and spring wheat fields,which occurs in the afternoon and dusk,respectively.Plantation of soybean,which is less fertilized,strongly promotes the N₂Oemission from farmland with an average emission flux of 83.8 μg·m^-2·h^-1.Bare field is a weak N₂Osource,whose emission rate is 1.2 μg·m^-2· h^-1 in average,and can be a sink of atmospheric N₂O from September to October,the flux rate being-11.9μg·m^-2·h^-1.The variation of illumination has a significant influence on N₂O flux from crop.Higher emission of N₂O from aroid occurs under weak illumination.

Key words: Farmland, Crop, N₂O flux, N₂O sink, Illumination, alpine forest, simulated warming, altitude gradient, DOC, DON