The arrangement of soil particles, particle size, mineralogy, solute concentration, and bulk density affects electrical (σ) and thermal (λ) conductivities, which are key properties for estimating soil physical states, subsurface water and energy balances, and land-atmosphere interactions. The purpose of this study was to compare how σ and λ change as a function of water content for soils under different vegetation and with different properties. Soil samples were collected from selected field sites in Idaho, Texas, Colorado, Iowa, and Ohio and packed into cylinders at a density of 1.2 Mg m−3 and then wetted to predetermined water contents (θ) between 0.10 and 0.45 m3 m−3. A thermo-time domain reflectometer was used to determine σ and λ at each θ at room temperature. Soil and vegetation-influenced differences within a state were only occasionally statistically significant; however, differences between states were highly significant for both σ and λ. The λ decreased as the amount of sorbed water (related to soil-specific surface area) increased. The λ increased more rapidly at low water contents than did σ, but σ increased more rapidly at high water contents. Changes in σ and λ with water content are related to the changing tortuosity of the solid plus liquid phases versus only the liquid phase (including sorbed water). This study contributes toward improved understanding of soil thermal and electrical conductivities over a range of soils.
1National Laboratory for Agriculture and the Environment, 2110 University Blvd., Ames, IA 50011. Dr. Logsdon is corresponding author. E-mail: email@example.com
2USDA-ARS, Ag. Syst. Res. Unit, Ft. Collins, CO.
3USDA-ARS, North Appalachian Exp. Watershed, Coshocton, OH.
4USDA-ARS, NW Watershed Res. Ctr, Boise, ID.
5USDA-ARS, Soil and Water Res., Bushland, TX.
Received July 8, 2010.
Accepted for publication September 14, 2010.