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Simulation of a Potential Error in Determining Soil Salinity from Measured Apparent Electrical Conductivity

Institute of Soil, Water, and Environmental Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel

*Corresponding author (vwsfried{at}volcani.agri.gov.il).

ABSTRACT

A common method for estimating soil salinity is by in situ measurements of the apparent electrical conductivity, EC_a, usually by a four-electrode probe. It is assumed that the EC_a can be regarded as taking place in parallel mode by two conductors on a bulk scale: the dissolved (EC_b) and the adsorbed (EC_s) ions. Therefore, the contribution to the EC_a by the soil solution electrolytes, EC_b, which serves to assess its salinity, can be deduced by subtracting the estimated EC_s from the measured EC_a. This assumption is wrong and leads to an evaluation of EC_b higher than its real value. This study was conducted to characterize the error in estimating soil solution electrical conductivity, EC_w. A simplified model of a randomly diluted and pore-size-distribution-decorated simple cubic lattice serves to describe the pore network of a saturated soil. It is assumed that only within each pore can the electrical conductance be represented by a sum of two conductors: the dissolved and the adsorbed ions, acting in parallel. Using Monte Carlo lattice simulations, it was shown that the error due to the assumption of parallel mode on a bulk scale increases with increasing broadness of the pore-size distribution, decreasing connectivities, and increasing cation-exchange capacity. An illustrative example of real soils, typical of irrigated soils, indicated errors of up to 25% for electrolyte concentrations.

Received for publication February 20, 1995.

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