环境地球化学国家重点实验室知识库

Fluxes of nitrous oxide (N₂O) from different land use patterns (matured forest, secondary forest, grassland and cropland) in a subtropical karst region of Guizhou Province, Southwest China, were measured for one year with a closed static chamber technique and by gas chromatography. The results showed that soil under different land uses was a source of atmospheric N₂O. The cropland was a source with relatively high N₂O as compared to forest and grassland, but no significant differences were observed. N₂O emissions from soils varied with land use change and fertilizer application. There were two peaks of N₂O flux occurred following the combination of two obvious precipitation and fertilizer events in the cultivated land. Converting from the matured forest to secondary forest tended to increase annual emissions of N₂O (from 1.40 to 1.65 kg N ha⁻¹ a⁻¹), while changing land use from secondary forest to scattered grassland tended to decrease annual emissions of N₂O slightly (from 1.65 to 1.45 kg N ha⁻¹ a⁻¹). Our range of cumulative annual N₂O emission across different land uses (1.40–1.91 kg N ha⁻¹ a⁻¹) in a karst region is in general agreement with previously published data in a non-karst region. However, in the maize field, N₂O emission factor (EF) was 0.34% for fertilizer application, which is about 71.2% lower than the IPCC default value. It is suggested that current IPCC (Intergovernmental Panel on Climate Change) EF methodology could overestimate N₂O emission from the karstic cropland. Anyway, the N₂O emission from cropland in the karst region would contribute significantly to the global N₂O budget, so reducing fertilization frequency during the crop growing season could lead to a decrease in N₂O emission in the whole year.