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Effects of Liquid‐phase Electrical Conductivity, Water Content, and Surface Conductivity on Bulk Soil Electrical Conductivity
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1976
Year
Geotechnical EngineeringSoil CharacterizationLow Salinity Water FloodingSurface ConductivityEngineeringSoil PropertyEnvironmental EngineeringLiquid PhaseCivil EngineeringSoil SalinityLiquid‐phase Electrical ConductivityElectrophysiologyEc WSoil PropertiesCalibration CurvesSoil PhysicWater ContentElectrochemistry
Field soil salinity can be inferred from four‑electrode soil electrical conductivity (ECa) when the profile is near field capacity and calibration curves based on saturation extract salinity (ECe) are available. The study aimed to extend this field method to arbitrary water contents by measuring ECa in the laboratory as a function of water content (θ) and in‑situ soil water conductivity (ECw) using undisturbed cores of four soil types. Laboratory cells were equilibrated with waters of specified ECw and adjusted to desired θ using a pressure‑membrane apparatus, and ECa was calculated from four‑electrode resistances with an appropriate cell constant, with the relationship derived from a simple capillary model treating liquid‑phase and surface conductivities as parallel resistors. Results showed that over the practical θ range, ECa equals a transmission coefficient times θ times ECw plus surface conductivity.
Abstract Recent research has demonstrated that field soil salinity can be inferred from four‐electrode soil electrical conductivity (EC a ), if the soil profile is near “field capacity” and calibration curves, based on saturation extract salinity (EC e ), 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 (EC w ). 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 EC w and, using a pressure membrane apparatus, adjusted to a desired θ. Values of EC a were calculated for each EC w − θ equilibration from measured four‐electrode resistances and an appropriate cell constant. Our results indicated that over the θ‐range of practical concern, EC a = (transmission coefficient) × θ × EC w + 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.