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Agricultural liming materials are broadly utilized in the world to ameliorate soil acidity. Crushed limestone (CaCO3) and dolomite (MgCo3 center dot CaCO3) are most common liming materials. The CO2 emission coefficient was proposed as 0.12 Mg C per Mg for CaCO3 by the Intergovernmental Panel on Climate Change (IPCC), which indicates that 100% of C in CaCO3 is eventually released to the atmosphere in the form of CO2. However, this assumption appears unlikely based on current knowledge of the very low solubility of CaCO3 and carbonate transport through soil. To develop the direct CO2 emission factor from the C-containing liming materials applied in moderately acidic soil, CaCO3 was applied in a typical temperate upland soil at different levels (0-2 Mg ha(-1) yr(-1)), and the CO2 emission rates were determined using the closed chamber method for two years. The direct CO2 emission factor from CaCO3 was estimated using (CO2)-C-13 fluxes from C-13-CaCO3 applied soils. Approximately 0.026 Mg C per Mg of CaCO3 was emitted as CO2 from CaCO3 in cropping lands. This value was much lower than the IPCC default value (0.12 Mg C per Mg of CaCO3). The current CO2 emission coefficient was comparable with the United States Environmental Protection Agency (EPA) emission factor (0.046 Mg C per Mg of CaCO3) from the agricultural field. If the EPA emission factor from the ocean (0.013 Mg C per Mg of CaCO3) is added to the currently developed CO2 emission factor of the inner agricultural field, the total CO2 emission factor from lime may be close to 0.039 Mg C per Mg of CaCO3 in the selected upland soil. Therefore, we propose that the current IPCC guideline value of the CO2 emission factor from lime should be revised as 0.039 Mg C per Mg of CaCO3 for Korean upland soils.