Fig. 3. Test of the Buckingham-Burdine-Campbell (BBC), Eq. [5], and the macroporosity-dependent (₁₀₀), Eq. [7], gas diffusivity models against measured data for 15 undisturbed Andisols. Values of Campbell b and total porosity (, m³ m^-3) for each soil are given. Except for Kyushu 4, the measured value at the smallest and highest soil-air contents correspond to -10 cm H₂O (pF 1) and -15000 cm H₂O (pF 4.2) of matric potential, respectively, as illustrated in Fig. 3a,f,k. = soil air content; D_P/D₀ = relative soil-gas diffusion coefficient, with D_P as the gas diffusion coefficient in soil, m³ soil air m^-1 soil s^-1; pF = Log(- in cm H₂O).