| Nitrogen application rate and nitrogen fertilization method can significantly influence N2O flux. In this study, the field experiment was carried out at the experimental station of China Agricultural University, which is located in Quzhou County, Hebei Province, to investigate the chamber model and computing method effect on N2O flux from winter wheat-summer maize rotation on the North China Plain (NCP), to precise quantization N2O flux, in2012and2013. In2013and2014, five treatments were designed to study the effect of nitrogen application rate on N2O emission, and to calculate the emission factor. The five nitrogen fertilizer rates are nitrogen application at the rate of0kg N ha-1, nitrogen application at the local farmers traditional nitrogen application rate, optimized nitrogen application rate, optimized nitrogen application rate multiply by1.3and optimized nitrogen application rate multiply by0.7. In2013and2014summer maize top dressing times three treatments were designed to study the impacts of nitrogen fertilization method on maize yield, soil NH3volatilization and N2O emission, and to investigate the mechanism. The three nitrogen fertilizer methods are local farmers’ traditional practices which broadcasting urea on soil surface, broadcasting urea on soil surface and followed by the application of nitrification inhibitor on soil surface, band application of urea in the middle of two adjacent maize rows and backfilled with soil. In2014summer maize top dressing time, to study the impacts of simulated strong rainfall on soil O2content, to investigate the relationships between soil WFPS and soil O2content, and between soil O2content and soil N2O concentration. The results were summarized as follows:(1) There was no significant difference between four N2O fluxes, which achieved by big and small chamber models with liner and curve fitting methods, the N2O flux and emission of small chamber model with curve fitting method was the biggest, in the maize season, on NCP.(2) Soil N2O emission was caused by fertilization, the N2O emission was large in the maize season, small in the wheat season. The four treatments with fertilizer had the same N2O emission tendencies, the more nitrogen fertilizer put, the bigger N2O emission. Alternation of wetting and drying, alternate freezing and thawing, management practices in farmland lead to N2O emission change, on NCP.(3) The best relationship between nitrogen fertilizer rate and N2O emission was quadratic exponential correlation; compared with traditional nitrogen fertilizer rate, the optimized nitrogen application rate assured yield and reduce N2O emission. Grain-yeild scaled N2O emission increase with nitrogen fertilizer rate increase. The N2O emissions per unit was0.3g N2O-N kg-1or so during corn season while it was not more than0.1g N2O-N kg-1during wheat season in normal years. N2O emission factor was1.2%in2012on NCP, and the emission factor was0.7%in2013, the two years emission factor was1.0%.(4) North China Plain was hot and rainy during corn season, application of nitrogen fertilizer was the main controlling factor to N2O emissions during corn season. North China Plain was cold and dry during wheat season, N2O emissions are low even with the application of nitrogen fertilizer, and the temperature and moisture were the main controlling factor to N2O emissions during wheat season.(5) After application nitrogen fertilization to farmland soil on North China Plain during season maize, a large amount of N2O emissions was produced, accompanied by a certain amount of nitrite accumulation. Nitrification inhibitor (DCD) reduced soil N2O emissions and slightly promoted soil NH3volatilization. Applying nitrogen fertilizer and covering it with soil could significantly reduce soil NH3volatilization, but this caused a large accumulation of nitrite in fertilizer strip and promoted N2O emissions.(6) Soil O2content was controlled by soil moisture, when the soil WFPS was greater than60%the soil O2content decreased rapidly which resulted in a large number of N2O production. During the24hours and7days after fertilization and saturated irrigation, the soil O2content was negatively linear correlation with soil N2O concentration. And soil WFPS and O2was negatively exponential correlated within15days. |
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