The major objective of this study is to find a feasible management practice to mitigate the cumulative global warming potential (GWP) from CH4 and N2O emission in an irrigated rice field. Nonflooding (but wet) conditions reduced CH4 emission by 79 and 71% from the fields with and without organic matter (OM) addition, respectively. This was mainly due to the desirable soil redox status in the nonflooded fields with less CH4 production and more CH4 oxidation when CH4 diffused up the soil profile. Increase in N2O emission from the nonflooded fields offset part of the reduction in CH4 emission, especially when OM was not added. Thus the nonflooding treatment reduced the cumulative GWP by 72% in the OM-added field but only 46% in the field without OM addition. Under flooding conditions, no OM addition reduced CH4 emission by 57%, but rice yield was decreased by 16% in comparison with the OM-added fields. The best management practice proposed from this study is to keep the fields nonflooded but wet with OM addition, which largely reduced the GWP from the fields with no decrease in rice yield.