ARS | Publication request: The Dielectric Permittivity of Calcitic and Arid Zone Soils with Carbonate Minerals

Submitted to: Soil Science Society Of America Journal
Publication Acceptance Date: May 26, 2004
Publication Date: September 1, 2004
Citation: Lebron, I., Robinson, D.A., Goldberg, S.R., Lesch, S.M. 2004. The Dielectric Permittivity Of Calcitic And Arid Zone Soils With Carbonate Minerals. Soil Science Society Of America Journal. 68:1549-1559.

Interpretive Summary: The determination of soil water content from the measurement of soil dielectric permittivity has become a widely accepted method. Understanding the dielectric properties of soils is also required for the improved interpretation of data from methods such as ground penetrating radar and microwave remote sensing. In order to model a complex material such as soil it is required that the dielectric permittivity of all phases (gas, solid and liquid) be known. The permittivity of air and water are well documented, however, the permittivity of soil minerals is often estimated and their permittivity essentially remains a fitting parameter in many models. In this work we measure the dielectric permittivity of 4 illitic soils using a method developed for granular materials. For the first time we directly measured the solid permittivity of our soils and found that for arid soils the permittivity is at least one unit higher than the traditional value used for water content estimations. Our findings will improve our capability to estimate water content in soils.

Technical Abstract: Measurement of water content in soils is needed for management purposes. Irrigation schedules and fertigation can be planned more efficiently if we have knowledge of the soil water content. Soil dielectric permittivity is widely used to estimate water content in soils from remote sensing data and from in situ soil sensors such as time domain reflectometry. Dielectric permittivity of the soil mineral phase, for modeling purposes, is assumed in most cases to be 5, a value based on a further assumption that soils are predominantly quartz. However, micaceous clays have been found to have permittivity values around 6, and calcite, a major constituent of some arid zone soils, is known to have a permittivity nearly twice that of quartz. This study was conducted to measure the solid permittivity of 4 illitic soils to determine whether or not the assumption of 5 for the dielectric permittivity of arid zone soils is correct. From these 4 soils two contained 35 and 41% calcite, the other two had similar mineralogy but without calcite. We also measured the permittivity of Iceland Spar calcite and a microcrystalline calcite. We found dielectric permittivities for our soils to be in the range of 5.8 to 6.6, the more calcite content the higher the permittivity value.