Typical Farmland N₂O And CH₄ Net Exchange Characteristics Of Different Nitrogen Management

North China Plain （NCP） is an important grain producing area, which is commonly associated with excessive inputs of nitrogen fertilizer in the winter wheat/summer maize rotation system. The excess nitrogen inputs will not only reduce the use efficiency of nitrogen fertilizers, but also cause large emissions of N₂O from farmland soil and inhibit the CH₄ oxidation by soil. Therefore, optimizing N inputs and using control-released N fertilizers （CRU） that can adjust N release according to the requirement by crops are promotive strategies to improve N use efficiency, reduce N₂O emission and enhance CH₄ uptake. Furthermore, static chamber technique is being used to measure trace gas exchange among soil and atmosphere. However, large difference among different calculation methods for gas fluxes exists, which give rise to the large difficultry to directly compare the results by various researchers. Therefore, in this study, the difference of three calculation methods were firstly examined and corrected with TFU technique. Then the static chamber/gas chromatograph techniques were used to characterize N₂O emissions and CH₄ oxdation of 6 N management systems including no fertilizer （CK）, farmers conventional treatment （Nc）, optimized N （No）, CRU1（100% CRU）, CRU2（67%CRU+33% urea）, and CRU3（33% CRU+67% urea） in order to clarify the impact factors and emission reduction potential. The main findings are as follows:（1） In this study, the impact of LR, Quad and HM calculation techniques on the N₂O fluxes were examined through measuring N₂O fluxes from winter wheat soil with static chamber technique in one week after the N fertilization at shooting stage, and the impacts of N fertilization on both fluxes were examined as well. It was found that large variance among the N₂O fluxes and patterns obtained with different calculation techniques were observed when using the same dataset, and the greatest coefficient of variation （C.V.） was up to 71%; in comparison with the C.V. of 29% before the correction, it was reduced to be 13% after the performance of TFU technique; it was also obtained that the N₂O fluxes were all underestimated, where the underestimation of N₂O fluxes by the LR, Quad and HM methods were 14-31%, 5-48% and 3-62% for the N fertilized soil, and 14.9-16.0%, 15.5-35.2% and 8.4-57.2% for the unfertilized soil, respectively. Therefore, the performance of the TUF technique has a great potential to minimize the difference of trace gas fluxes calculated with different techniques and the uncertainty associated with N₂O fluxes.（2） During the summer maize growing season in 2011, all the N treatments perofmred as a source of N₂O emissions. Compared with Nc management, the both No treatment and CRU treatments significantly reduced N₂O emission in the summer maize season. The total N₂O soil emissions in the summer maize season was in an order of Nc> No> CRU3> CRU2> CRU1> CK, the corresponding total emissions were 9072.12 g N /ha, 4070.12 g N/ha, 3628.20 g N/ha, 3974.14 g N/ha, 4216.00 g N/ ha and 1183.79 g N/ha for Nc, No, CRU1, CRU2 and CRU3 treatments, respectively, and the emission factor were 1.60%, 2.63%, 1.36%, 1.54% and 1.68%, respectively.（3） It was also indicated that all of the N treatments performed as a sink of atmospheric CH₄, and the uptake of the summer maize season ranged from 19.19 mg C/m2 to 31.38 mg C/m2; the inhabitation of CH₄ uptake by N fertilization were observed. Furthermore, soil water content might be the major factor reducing the soil CH₄ oxidation.