A NEW METHOD TO MEASURE BULK ELECTRICAL CONDUCTIVITY IN SOILS WITH TIME DOMAIN REFLECTOMETRY

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Abstract
The bulk electrical conductivity of a porous medium can be determined by measuring the reflection of an electromagnetic pulse in transmission lines which are installed in this medium (the method is known as Time Domain Reflectometry (TDR)). The reflection is not only influenced by the medium, but also by the measuring system. A new method is described which corrects for influences of the measuring system by comparing a reflection measurement with a reference measurement performed in air. Calibration measurements were made in water and in water-saturated sand and loam soils. Columns with different, well-determined solute concentrations were prepared. Linear regression analyses were performed between the electrical conductivity determined with TDR and the electrical conductivity of the solutions. All slopes were close to one and the correlation coefficients were high: 0.993, 0.993 and 0.968 for water, sand and loam, respectively. For the two soils significant intercepts were found. These might be related to the surface charge of the soil particles. Key words: Dielectric constant, soil water, electrical conductivity, solutes

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