Matric Potential Sensor Using Dual Probe Heat Pulse Technique

Abstract

Soil matric potential (ψ_m) is an important property, and its measurement is necessary to determine the availability of soil water for plants. The objectives of this study are to develop a low-cost ψ_m sensor using porous media in conjunction with a dual probe heat pulse (DPHP) technique and to evaluate the performance of the developed sensor. The DPHP ψ_m sensor measures the volumetric heat capacity and thermal conductivity of the porous media and converts these thermal properties into a ψ_m value. The performance was evaluated by comparing the output of the developed DPHP ψ_m sensor with that of a commercialized ψ_m sensor, and the temperature dependence of the developed sensor was also investigated. The volumetric heat capacity and thermal conductivity of the porous media measured with the DPHP method were converted to their corresponding logarithmic value of ψ_m by means of two intersecting linear functions. The use of thermal conductivity to determine ψ_m was found to yield more accurate results than the use of volumetric heat capacity, and the accuracy of the determined ψ_m value was approximately 10%. The DPHP ψ_m sensor was found to be less sensitive to temperature than existing commercialized ψ_m sensors. Furthermore, the volumetric heat capacity showed slight temperature dependence regardless of soil water content. The developed DPHP ψ_m sensor was found to be versatile because it can use either volumetric heat capacity or thermal conductivity, depending on the magnitude of soil temperature variation and required accuracy. The DPHP ψ_m sensor is intended to contribute to expanding the use of information and communications technology (ICT) in agriculture as a low-cost ψ_m sensor.