ARS | Publication request: Comparison of electrical and thermal conductivities for soils from five states

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 16, 2010
Publication Date: December 9, 2010
Citation: Logsdon, S.D., Green, T.R., Bonta, J.V., Seyfried, M.S., Evett, S.R. 2010. Comparison of electrical and thermal conductivities for soils from five states. Soil Science. 175(6):573-578.

Interpretive Summary: Various soil properties affect how heat and electrical charge moves through the soil, including how dense the soil is, the temperature and water content, and how much salts, fine particles (clays), and organic matter are in the soil. This studied showed there were big differences in movement of heat and electrical charge through soils from different states. Within fields in close proximity the differences were small, though the soils were different and samples were taken from under different vegetation. Even small increases in water content can cause large increases in heat transport, but there is little further increase in heat transport at high water contents. Conversely electrical charge increases more rapidly at high water contents. This information is important for scientists who want to understand and simulate movement of heat and electrical charge through soils in different regions of the country. The movement of electrical charge and heat is important information for understanding freeze-thaw processes and proper crop seed bed conditions in the spring.

Technical Abstract: Arrangement of soil particles, particle size, mineralogy, solute concentration, and bulk density affect electrical (EC) and thermal (TC) conductivities. The purpose of this study was to compare how EC and TC change as a function of water content, for soils under different vegetation and with different properties. Soil samples were collected from Texas, Ohio, Idaho, Colorado, and Iowa and packed into cylinders at a density of 1.2 Mg m-3, and wetted to predetermined water contents (WC) between 0.10 and 0.45 m3 m-3. A thermal time domain reflectometer (thermal-TDR) was used to determine EC and TC at each WC, at room temperature. Soils from Texas and Iowa had larger amounts of high surface-area clays that sorbed water. Colorado and Texas soils had some soluble salts. Colorado and Ohio soils had lower amounts of clay. Soil and vegetation-influenced differences within a state were only occasionally statistically significant; however, differences over long range (between states) were highly significant for both EC and TC. The TC decreased as the amount of sorbed water (related to soil specific surface area) increased. The TC increased more rapidly at low water contents than did EC, but EC increased more rapidly at high water contents. Heat would be conducted through both solid and liquid phases, but electrical charge only through the liquid phase. The tortuosity of solid plus liquid phases is rapidly reduced with even a small addition of soil water, whereas larger amounts of water are needed to reduce tortuosity for the liquid phase alone.