Abstract

Time domain reflectometry (TDR) has capability of distinguishing the dielectric property of solid, air and liquid phases of the soils and has become increasingly popular for determining the soil water content (SWC). The purpose of this study was to find a relationship between soil bulk density (BD), clay content, clay mineralogy with dielectric constant. The latter is a function of SWC. For this purpose 10 soil samples were taken from five areas with different textures and depths (from topsoil, 0 to 0.3 m and subsoil, 0.3 to 0.6 m), The BDs were varied from 1.18 to 1.65 Mg m^-3. Soil physical and chemical properties such as organic matter, clay, silt, and sand percentages as well as clay minerals were measured. Results showed that high clay contents underestimated the SWC in the low moisture range and overestimated the SWC in the high moisture range. Results also showed that soils with similar clay content but different minerals had different impact on dielectric constant. Soils with high BD, or low porosity, had higher dielectric constant value than soils with low BD and high porosity.

Key words: Clay mineralogy, dielectric constant, bulk density, soil water content, time domain reflectometry.