Abstract: The reuse of treated wastewater in agricultural systems could partially help alleviate water resource shortages in developing countries. Treated wastewater differs from fresh water in that it has higher concentrations of salts, E. coli and presence of dissolved organic matter and inorganic N after secondary treatment, among others. Its application could thus cause environmental consequences such as soil salinization, ammonia volatilization and greenhouse gas emissions. However, the effect of irrigation with treated wastewater on N₂O and CO₂ emissions is not well known. In an incubation experiment, we evaluated the characteristics and effects of water filled pore space and N inputs on greenhouse gas emissions from silt loam soil receiving treated wastewater. Irrigation with treated wastewater (vs. fresh water) significantly increased cumulative N₂O emission in unamended soil (32.5 μg N kg^-1 dry soil). N₂O emissions caused by irrigation with treated wastewater combined with urea fertilization did not simply add linearly, but significant interaction (P<0.01) caused lower emissions than the additive effects of the two treatments alone. However, no significant impact on cumulative CO₂ emission and emission rate was measured in soil irrigated with treated wastewater. Significant interaction between water filled pore space and N inputs was shown in soil to which treated wastewater was applied. Cumulative N₂O emissions showed an exponential relationship with increasing water content.