A field experiment was conducted to investigate gaseous losses from N fertilizers applied to a tomato field and affecting factors.Ammonia volatilization was measured by the enclosure chamber method.Denitrification loss(N₂+N₂O)was measured by the acetylene inhibition-intact soil core technique,and N₂O emission was also measured in the absence of acetylene.Results show that ammonia volatilization was not detected in all the treatments during the tomato growing season.It was presumed that ammonia partial pressures on the surface soil were lower than the detection limit of the method,as a result of the low ammonical N concentration and low pH in the surface soil.During the tomato growing season,in the CK treatment denitrification loss and N₂O emission were relatively high,which amounted to 29.6 kg hm^-2 and 7.76 kg hm^-2,respectively.Application of N fertilizer significantly increased denitrification loss up to the range of N 40.8~46.1 kg hm^-2,or 5.50%~6.01% of the applied N;and N₂O emission up to the range of N 13.6~17.6 kg hm^-2,or 2.62%~4.92% of the applied N in the three fertilized treatments.Application of polymer coated urea didn't show any significant effect on reducing denitrification loss and N₂O emission in comparison with urea.In the two urea treatments soil nitrate peaks were observed after each topdressing event, and subsequent flux peaks of denitrification loss and N₂O emission were found.There was a significant positive correlation between denitrification fluxes and wate-rfilled pore space(WFPS).It is concluded that ammonia volatilization is negligible,where-as nitrification-denitrification is an important pathway of N losses during the tomato growing season.