Construction and Applications of a Computer-Controlled Multiplexing TDR System

Abstract

Detailed measurements of temporal and spatial changes in water and solute contents in soil may improve knowledge of water and solute dynamics in soil. With the knowledge, more appropriate and efficient soil and water management could be explored. Recent development of time domain reflectometry (TDR) techniques enables to simultaneously and promptly measure soil water content, θ, and electrical conductivity, EC. To make automated data collection from several TDR probes, a computer-controlled and multiplexed TDR system was constructed. The system was applied to a field experiment on furrow irrigation with≈0.3 Sm^-1 NaCl solution in a bare sandy loam soil. Twenty four three-wire-type probes were horizontally inserted in a two-dimensional soil profile. Data were collected every 15 min for≈2 months. Spatial and temporal changes in two-dimensional distributions of θ and EC of soil water were successfully measured. The system was also successfully applied to estimate the hydrodynamic dispersion coefficient of loamy sand in the laboratory. This TDR system may be a useful and efficient tool to examine temporal and spatial distributions of water and solute in soil.