Fig. 7. Comparison of the three-porosity model (TPM) and the Millington and Quirk (1961) model (MQ) with measured data for field soils at Gjorslev at the (a) 0.43-m, (b) 2.15-m, and (c) 4.75-m depth. The average of soil-gas diffusivities (D_p/D₀) at each matric-potential () stage are shown in the plots. The standard deviations of both air-filled porosity and D_p/D₀ are shown in error bars. Average values of the Campbell pore-size distribution parameter b are also given.