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The dependence of the dielectric constant, at frequencies between 1 MHz and 1 GHz, on the volumetric water content is determined empirically in the laboratory. The effect of varying the texture, bulk density, temperature, and soluble salt content on this relationship was also determined. Time‐domain reflectometry (TDR) was used to measure the dielectric constant of a wide range of granular specimens placed in a coaxial transmission line. The water or salt solution was cycled continuously to or from the specimen, with minimal disturbance, through porous disks placed along the sides of the coaxial tube.

Four mineral soils with a range of texture from sandy loam to clay were tested. An empirical relationship between the apparent dielectric constant K_a and the volumetric water content θ_v, which is independent of soil type, soil density, soil temperature, and soluble salt content, can be used to determine θ_v, from air dry …