Theories and Tests of Electrical Conductivity in Soils

The soil's specific electrical conductivity (EC_a) is similar in principle to the EC of a pure solution, but the nonconducting soil air and solids cause complications. The EC_a measured by four-electrode Wenner arrays in laboratory and field experiments was linearly proportional to the product of the soluble salt concentration and the soil water content over a salinity range of 0 to 40 dS/m in the soil solution and 0.1 to 15 bar soil water suction. Theories of soil EC based on a conductivity cell and microscale conduction were compared to a macroscale theory and all explained the measured results equally well. Soil can be viewed as an intricate container for electrolyte solution, as a conductor having a tortuous path, or as many conduction paths of varying cross section and length. The macro model was extended to relate EC_a to soil water potential, but EC_a appears to be inherently dependent on both the soil moisture and salt contents.