Recent research has demonstrated that field soil salinity can be inferred from four‐electrode soil electrical conductivity (ECa), if the soil profile is near “field capacity” and calibration curves, based on saturation extract salinity (ECe), are available. To extend the use of this field method to arbitrary water contents, we studied EC in the laboratory as a function of water content (θ) and in situ soil water conductivity (ECw). We collected undisturbed cores of four soil types (fsl, vfsl, l, cl) using Lucite column inserts, which were tapped for later insertion of electrodes. The cells were equilibrated with waters of a desired ECw and, using a pressure membrane apparatus, adjusted to a desired θ. Values of ECa were calculated for each ECw − θ equilibration from measured four‐electrode resistances and an appropriate cell constant. Our results indicated that over the θ‐range of practical concern, ECa = (transmission coefficient) × θ × ECw + surface conductivity. This relationship is derived using a simple capillary model, which assumes that liquid phase and surface conductivities (via exchangeable cations) behave as resistors in parallel.

A new model describing the relation between bulk soil electrical conductivity (ECa), volumetric content (θw) and electrical conductivity of soil water (ECw) is given along with supporting evidence for its validity. The new model distinguishes between the water and salt present in the soil in the “immobile” (fine pores) and “mobile” (large pores) phases. It provides a possible physical meaning to the transmission coefficient (T) previously used in an earlier model and eliminates a limitation of that model which existed under conditions of low salinity. New empirical relations are provided to estimate the parameters needed in the new and old models in order to utilize them for diagnosing soil salinity, in terms of the electrical conductivity of the extract of saturated soil pastes (ECe).

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The hydraulic conductivities and gradients along soil columns packed with montmorillonitic, vermiculitic, and kaolinitic soils adjusted to different levels of exchangeable sodium were determined at different salt concentrations. The data show that plugging of pores by dispersed clay particles is a major cause of reduced soil hydraulic conductivity for surface soils irrigated with sodic waters.

Two parallel metallic rods were used as a wave guide to measure the dielectric constant and electrical conductivity of soils having different electrical conductivities but the same water content. Measurements showed that the two parameters were sufficiently independent to permit simultaneous determinations of water content and bulk electrical conductivity.