Abstract:This study was conducted to determine the effect of different N fertilization rates on N2O emissions from a loamy fluvo-aquic soil in North China Plain in 2009. Fluxes of N2O were measured on greenhouse cropped with tomatoes (Lycopersicon esculentum) with split application of 675 or 900 kg/hm2 N from Aug 7th to Dec 25th. An unfertilized plot planted with tomatoes as control was also set up. The results indicated that total emission increased with the N application rate. The mean N2O emission rate from the differently management plots was closely correlated to the mean soil nitrate content in surface soil after topdressing (R2=0.810). The peak of N2O emission generally occurred within 3–5 days after N application, and more than 50 per cent of total N2O emissions occurred over the first 7 days after fertilization. The N emission from the unfertilized treatment was N 0.56 kg/ha. Total N2O emission from the fertilized crops for the low and the conventional rates of N fertilization were N 3.616 and 5.304 kg/ha,respectively. The high N2O emissions from greenhouse tomatoes plots were due to high N2O losses from the fertilized treatments during the summer and early autumn (Aug, Sept and Oct) and high soil nitrate contents after the N application. The reduction of N fertilization resulted in decreased N2O emissions during the warmly period. However, the emissions during the winter were not affected by the rate of N fertilization. The results show that the N application management in greenhouse had a great influence on the N2O emissions. It also affected the emissions per unit N fertilizer applied (low and the conventional rates of N fertilization were 0.45and 0.53).