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Air Permeability in Undisturbed Volcanic Ash Soils

Predictive Model Test and Soil Structure Fingerprint

^a Dep. of Environ. Engineering, Aalborg Univ., Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark
^b Osozawa), Dep. of Regional Crops Science, Natl. Agric. Res. Center for Western Region, Senyu 1-3-1, Zentsuji, Kagawa, 765-8508 Japan
^c Yamaguchi), Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okub, Saitama, 338-8570 Japan
^d Soils and Biogeochemistry, Dep. of Land, Air, and Water Resources, Univ. of California, Davis, CA 95616

View larger version (32K): [in a new window]   Fig. 1. The Campbell (1974) soil-water characteristic model (solid lines) fitted to measured data for four Andisols. The pF equals Log(- in cm H2O). Data from Moldrup et al. (2003).

View larger version (28K): [in a new window]   Fig. 2. Air permeability (closed symbols; data from this study) and gas diffusivity (open symbols; data from Moldrup et al. (2003) as functions of volumetric soil-water content for Miura 3 Andisol. DP and D0 are the gas diffusivities in soil and free air, respectively. Measurements on three closely spaced 100-cm3 undisturbed soil cores are shown.

View larger version (50K): [in a new window]   Fig. 3. Test of air permeability models, Eq. [2] with = 2 and = 1 + 0.05b, against measured data for 12 undisturbed Andisols. Values of Campbell b and total porosity () are given for each soil. Soil macroporosity (100) is marked for each soil. Measurements are mean of three closely spaced soil cores. Note that three different y-scales are used (60, 120, and 300 µm2).

View larger version (24K): [in a new window]   Fig. 4. Comparison of air permeability (ka) and relative gas diffusivity (DP/D0) as a function of soil-air content () for the Tsumagoi 6 Andisol. Measurements on three closely spaced soil cores. The solid line is a predictive model with reference-point at -100 cm H2O of matric potential and with = 2.

View larger version (19K): [in a new window]   Fig. 5. Scatter plot comparison of predicted and measured air permeabilities in 16 undisturbed Andisols. Test of (a) Eq. [2] with = 2, (b) Eq. [2] with = 1 + 0.05b, and (c) Eq. [2] with = 1 + 0.25b.

View larger version (27K): [in a new window]   Fig. 6. Air permeability at -100 cm H2O of soil matric potential (ka,100) as a function of soil macroporosity (100). Solid line is best-fit line to measured data for the Tsumagoi soils.

View larger version (18K): [in a new window]   Fig. 7. Soil structure fingerprint (SSF) for 6 Andisols from (a) Tsumagoi, (b) Miura, and (c) Kyushu. The equivalent pore diameter, d, is calculated from measured air permeabilities and gas diffusivities (Eq. [4]).