Study On The Effect Of Management Measures On N₂O Emission From Farmland In North China Plain

Global warming,which is caused by the sharp increase of greenhouse gas emissions,has become a major climate problem.Although N₂O is a trace greenhouse gas,its warming potential is much higher than CO₂.Farmland is the main source of N₂O emission.As the main grain producing area in China,North China Plain emitted a lot of N₂O during planting.Literature analysis and model simulation were adopted in this paper.Firstly,the database of N₂O emission from farmland in this area was established;and its emission law was analyzed;and N₂O emission factor and background emission were determined;and the influencing factors for background emission were discussed.Then,DNDC（De Nitrification-De Composition）model was used to simulate and verify the observation data of typical experimental sites;and different fertilization and irrigation scenarios were set for simulation;and the relationship between crop yield and N₂O emission and fertilization and irrigation in each typical site was analyzed.Quantitative guidance was put forward for farmland management measures to reduce N₂O emission on the premise of ensuring yield,so as to achieve the optimal management goal of stable yield,water saving,fertilizer saving and emission reduction.The main results were as follows:（1）N₂O emission from farmland in North China Plain had obvious temporal and spatial differences.When long-term fertilization rates were same in experimental sites,N₂O emissions were significantly different in different observation years.There were significant differences in N₂O emission in the same observation time with the same fertilization rate in different experimental sites.（2）N₂O emission from farmland was significantly related to fertilizer amount and fertilizer type.Nitrogen application rate significantly affected N₂O emission from farmland in North China Plain（p<0.05）.N₂O emission from fertilization treatment was much higher than that from no fertilization treatment,and N₂O cumulative emission increased with the increase of nitrogen application rate.If the total nitrogen application rate was constant,the N₂O emission of organic fertilizer treatment was significantly lower than that of single chemical fertilizer application.（3）Based on the measured data,a statistical model for estimating N₂O emission from farmland was established.The N₂O emission factor of nitrogen fertilizer in North China Plain was 0.6±0.1%;and the background N₂O emission from farmland was 0.298±0.145 kg N₂O-N·ha^-1yr^-1.Background emissions were linearly correlated with soil total nitrogen（p<0.05）and soil organic carbon（p<0.01）,which had a univariate quadratic nonlinear relationship with annual mean precipitation（p<0.01）,and which had a significant exponential relationship with annual mean temperature（p<0.01）.（4）DNDC model accurately simulated N₂O emission,soil temperature,soil moisture and crop yield at typical experimental sites.The evaluation consistency index d of N₂O emission at each site in the model was above 0.58;and the consistency index d of soil temperature（ST）and soil moisture（SM）at each site was between 0.73-0.92 and 0.57-0.93,respectively.The model had a good simulation effect.The overall fitting degree R~2 of the crop yield of each site in the model was above 0.88（p<0.05）,and the simulated value was in good agreement with the measured value.（5）The DNDC model was used to simulate and analyze different fertilization and irrigation scenarios.The suggestions for optimal management measures of farmland in North China Plain were as follows:the optimal proportion of organic fertilizer and inorganic fertilizer was organic fertilizer:inorganic fertilizer=2:3;the optimum fertilization rate was 162 kg Nha^-1 for wheat and 216-231 kg Nha^-1 for corn.The best irrigation amount of corn in season was about 210 mm.To sum up,the N₂O emission factor in North China Plain was0.6±0.1%,and the background N₂O emission from farmland was0.298±0.145 kg N₂O-N·ha^-1yr^-1.The amount and kind of fertilization significantly affected the N₂O emission from farmland.DNDC model was suitable for simulating N₂O emission from farmland in this area.Based on the simulation results of DNDC model,the suggestions for optimal management measures for the goal of stable yield,water saving,fertilizer saving and emission reduction of farmland in North China Plain were put forward as follows:（1）the optimal proportion of organic fertilizer and inorganic fertilizer was 2:3;（2）the optimum fertilization rates for wheat and corn were 162 kg Nha^-1 and 216-231 kg Nha^-1,respectively;（3）the optimum irrigation amount of corn was 210 mm.