Abstract: Soil N2O flux was measured for a whole year in winter wheat-summer maize rotation system in the North China Plain to determine its sources and changes in the soil,by using close chamber method.The relationships between soil N2O flux and soil temperature,moisture and available nitrogen content were analyzed after getting rid of the influence of fertilization.The results indicated that the winter wheat and summer maize fields were sources of N2O.Soil N2O fluxes both in wheat and maize fields showed obvious seasonal variations because of the influence of fertilization.Soil N2O flux in wheat field ranged from-36 to 835μg m-2 h-1,and in the maize field ranged from-1 to 263μg m-2 h-1.The seasonal average soil N2O flux in wheat field with 80.5μg m-2 h-1 was smaller than in maize field with 90.5μg m-2 h-1.The total soil N2O emission in wheat field with 4.2 kg hm-2 was higher than in maize field with 2.7 kg hm-2.Annual soil N2O emission was with 6.9 kg hm-2.Soil N2O flux increased exponentially with the soil temperature(P<0.01).Its seasonal Q10 was 2.2,and the diurnal Q10 were from 3.8 to 4.5.There was no obvious correlation between the soil N2O flux and the soil moisture.During main growing seasons(from April to October) the soil N2O flux increased with soil NH+4-N contents(P<0.05).There was no obvious correlation between the soil N2O flux and the NO-3-N and content.During main growing seasons,the comprehensive influence of soil temperature,moisture and NO-3-N and NH+4-N contents on the soil N2O flux was significant(P<0.01).Soil moisture and soil NH+4-N contents were the main factors controlling soil N2O emission.

Key words: Soil N2O flux, Soil N2O flux, North China Plain, Q10, Winter wheat-summer maize rotation system