N₂O Flux And CH₄ Uptake Of Soil In Winter Wheat And Summer Maize Rotation System

North China Plain is one of the most important cereal crops production regions in China. Excessive N fertilization is a common problem in winter wheat and summer maize rotation system in this region. It not only decreases the nitrogen use efficiency, but also may stimulates N2O emission and inhibits CH4 uptake and oxidation. In this study, a N2O /CH4 continuous automatic measurement system was built, and measurements of N2O emission and CH4 uptake of conventional and optimized N fertilization treatments were conducted during winter wheat and summer maize rotations of 2001-2002 and 2002-2003 using this automatic system, to study N2O emission and CH4 uptake patterns. The results showed as followed:For N2O emission and as well as CH4 uptake measurements, 20 flux rates each day and each treatment could be obtained by using this N2O/CH4 continuous automatic measurement system, the diurnal change of N2O emission and CH4 uptake and every emission peak during the whole winter wheat and summer maize rotation period could be measured accurately.Using this continuous automatic system, the diurnal, seasonal variation, and the influences of sampling time during the daytime, sampling frequencies on the simulated results were studied. The results of the N2O emissions which were based on the different sampling time and sampling frequencies showed, the sampling time during the daytime strongly affect the calculated N2O emission amount, and mainly because of the diurnal variation of N2O emission. The calculated highest N2O emission was occurred when sampling at 14:30, which was 3.54 times of the calculated lowest emission when sampling at 7:20.Under conventional N fertilization and irrigation condition, N2O emissions during 2001-2002 and 2002-2003 in winter wheat and summer maize rotation system were 1959 g N hm-2 and 1250 g N hm'2, respectively; and 68%-86% of N2O emission occurred in summer maize growth season, the emissions mainly occurred in 2 weeks after N fertilization and irrigation. The highest flux rates were 5.06 mg m-2 d-1 and 5.60 mg m-2 d-1 in the rotation period of 2001-2002 and 2002-2003, which were happened at the ten-extended leaf stage in summer maize season when top-dressing N fertilizer was applied.The soil in winter wheat and summer maize rotation system in the North China Plain was a net sink of CH4. Under conventional N fertilization and irrigation condition, CH4 uptake during the measuring period in 2001-2002 and 2002-2003 were 2303 g C hm-2 and 1468 g. C hm-2, respectively . Furthermore, the ambient concentration of CH4 was an important environmental factor which affectedits uptake by soil.Compared with the convention N fertilization treatment, the optimized N fertilization treatment which based on the real-time nutrient monitoring and regulation technique could saved 70.8% - 76.4% N fertilizer but maintained same yield levels, but it reduced N2O emission by 61%-71%, and enlarged the CH4 uptake by 7.7%-24.6%.The calculated Global Warming Potential in the optimized N fertilization treatment was 1027 kg (CO2 equ) hm-2, which was reduced by 72.9% compared with the conventional N fertilization treatment. The contributions of N2O emission, CH4 uptake and reduced N fertilizer on GWP decreasing is as following: N-fertilizer(75.0%)>N2O flux(24.5%)>CH4 uptake(0.5%).