We focused on and verified the efficacy of loss with the ignition method and the colorimetric method as applied to humic substances extracted using an alkaline medium. These are simplified methods of measuring organic (i.e. carbon) content and require no specialized equipment but they are rarely utilized in the field of forest soils and afforestation. Applying the ignition temperature at 600°C and the ignition time at 30 minutes, the ignition loss and the carbon content in the surface soils of the organic layer in the forest show a positive correlation (R²=0.998). Applying 0.5g of air-dried sample for each 20mL of the alkaline medium, we found a positive correlation between the carbon content in the soil and the absorbance (A₆₀₀) of the humic substance extracted, using the alkaline medium in the surface layer at the wavelength 600 nm (R²= 0.833). Therefore, both ignition loss and A₆₀₀ can be utilized in the simple measurement of the carbon content (i.e. organic matter content) of the sample.