In order to estimate the gas diffusion flux through the soil surface to the atmosphere, it is important to know spatial variability of soil gas behavior. The gas diffusion flux is derived from the gas diffusivity of soil and the gradient of gas concentration. This study is carried out to clarify the effect of the spatial variability of the gas diffusivity of soil and the gradient of gas concentration on gas flux from the soil surface. CO2 and O2 gas flux have been measured by close chamber method. Soil gas samples were taken from at 5 cm and 0 cm (soil surface) depth and CO2 and O2 gas concentrations were measured by GC. Undisturbed soil samples were taken and gas diffusion coefficients of O2 gas were measured. The measurements of gas flux and samplings of soil gas and undisturbed samples were carried out at the same place, 10 points along the straight line with 3 m interval. The gas flux measured by closed chamber method (qmes)is larger than the gas flux calculated from the values of gas diffusion coefficient and gas concentrations (qcal) and the average of qmes is 1.5 times as large as that of qcal. The correlation coefficient between qmes and qcal is small (0.43). The coefficient of variance of qmes, qcal and the gradient of gas concentration is similar (0.48, 0.50 and 0.47, respectively), while that of gas diffusion coefficient is small (0.21). This result indicates that the spatial variability of the soil gas flux is mainly result from the variability of gas concentration and the gas diffusion coefficient is more uniform than soil gas flux.
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