Application of a vertically-employed electrical conductivity probe: Measurement of 3D salt distribution on saline land

Numerous studies on the reclamation of saline land have been conducted in northeastern Thailand. Despite the importance of long-term evaluations of this phenomenon, relatively few studies on this have been reported in the scientific literature. Consequently, we propose a new method for understanding the 3D salt distribution in soil. The general technique employed for evaluating salt accumulation in soil is to measure the electrical conductivity of soil samples in the laboratory. However, the collection of soil samples can be difficult when groundwater levels increase such as they do during the rainy season in northeastern Thailand. We therefore developed an instrument capable of measuring electrical conductivity in saturated soils below groundwater level. The method for determining the 3D salt distribution in soil employs an electrical conductivity probe and measurement of the geographical location of the sample site by GPS. The probe is used to measure electrical conductivity at a point perpendicular to the ground surface, and these values are then combined with the horizontal 2D coordinates for the sample site. The combination of these data can be used to determine the 3D salt distribution in soil. A field experiment was conducted in northeastern Thailand during the rainy season. By measuring the electrical conductivity at specified depths and recording the corresponding 2D location data, we were able to determine of the 3D salt distribution in soil. In addition, the outputs obtained using the electrical conductivity probe were almost equivalent to electrical conductivity measurements obtained from soil solutions (ECe) in the laboratory. We also demonstrated that it was possible to assess the 3D distribution of soil salts in a region in a day. The application of the proposed method thus makes it possible to continuously investigate the salt distribution at numerous sample sites spread across a region.