Fig. 5. Illustration of soil-type-dependent behavior of gas diffusivity in undisturbed soils. Data for two soils with different soil-water characteristic (SWC) behavior (different Campbell b values). Also shown are predictions by two SWC-independent gas diffusivity models (Eq. [2] and [4]), and the Troeh et al. (1982) model (Eq. [10]) fitted to the measured data. = soil air content; D_P/D₀ = relative soil-gas diffusion coefficient.