Study On Soil CO₂ And N₂O Emissions In Agro-ecosystem And Regional Model-based Evaluation In Huang-huai-hai Plain

Greenhouse gases (GHGs) emitted from agro-ecosystems have been becoming one of the main causes which result in the global warming. CO₂ and N₂O, as the main greenhouse gases, have attracted more and more attentions from the international scientists and governments of many countries. This paper are focusing on: (1) the greenhouse gas fluxes (CO₂ and N₂O) from the typical upland soils (field experiments were set in Quzhou county) under winter wheat - summer corn rotation, cotton, fallow field in Huang-huai-hai Plain were measured, and the relevant factors were analyzed, such as soil temperature, soil moisture, soil organic matter content, and fertilization, irrigation etc. (2) the DNDC model was tested by the experimental data to confirm whether the simulated results can capture the seasonal change character of CO₂ and N₂O emission or not. (3) The regional CO₂ and N₂O emitted from cropland soils in the Huang-huai-hai Plain were also simulated by using DNDC model with the support of GIS database, and some possible suggestions to reduce the emissions of GHGs were proposed based on analyzing the simulated results. The main research results listed as the follows:CO₂ and N₂O emission from the upland soils in the winter wheat-summer corn rotation, cotton, and fallow fields changed regularly with the change of the season, the gas fluxes reached the highest value in the summer and the lowest value in the winter. The maximum value of CO₂ emission fluxes was 2324mgCO₂·m^-2·h^-1 in winter wheat-summer corn rotation fields, 1111.9 mgCO₂·m^-2·h^-1 in cotton fields and 436.07 mgCO₂·m^-2·h^-1 in fallow fields. The CO₂ emission was exponentially correlated with the 5cm soil temperature, but there was no obvious relation between CO₂ emission and soil moisture. The fields under the same crop with higher soil organic matter content can emit more CO₂. But it was different in N₂O emissions, the peak value of N₂O emission flux appeared in July with 433.5μgN₂O·m^-2·h^-1in winter wheat-summer corn rotation fields, 146.5 μgN₂O·m^-2·h^-1 in cotton fields and 175.16 μgN₂O·m^-2·h^-1 infallow fields. The N₂O emission was exponentially correlated with the soil moisture, but it did not happen in wheat-summer corn rotation field. The more N₂O emissions also occurred in the fields with higher soil organic matter content.The DNDC model simulated results captured the seasonal change character of CO₂ and N₂O emissions with good matching the field data, so it demonstrated that the DNDC model is applicable which can be used to estimate the regional emissions with the support of GIS database. The geographical characteristics of GHGs in Huang-huai-hai Plain simulated by using DNDC model illustrated: the total CO₂ and N₂O emissions were found differently in different regions, the total emissions in northwest areas were lower than that in the southeastern of the Plain. The soil CO₂ emission amount will be increased with temperature rising, fertilizer and straw-returned increasing, but it will be decreased under no-tillage cropping system. The N₂O emission will be decreased, while improving crop straw return proportion, decreasing fertilizer, choosing no-tillage. The fertilizer had made great impacts on CO₂ and N₂O emissions. When fertilizer added was reduced by 30% and 50%, the CO₂ emission will be reduced by 8.7% and 10.1% respectively, and the N₂O emissions will bereduced at 29.8% and 47.3%. So in this region it was very important to reduce fertilizer addition rationally. It will not only decrease the costs of production, but also improve the environment and increase the accumulation of soil organic carbon.