Calibration and modification of impedance probe for near surface soil moisture measurements

Abstract

A reliable and low cost sensor that can measure soil moisture at or near the soil surface is currently not available. The objectives of this study were: (i) to evaluate the possibility of modifying an impedance probe (IP) to measure soil moisture content at a very shallow depth (2–5 cm); and (ii) to compare the soil moisture values obtained using the IP to the values obtained using the traditional gravimetric method. The research was conducted at the Winfred A. Thomas Agricultural Research Station (WTARS) Hazel Green, Alabama. The standard IP that is capable of measuring soil moisture content at 6-cm soil depth was modified to measure soil moisture at 2-, 3-, and 5-cm depths. Using a site and depth-specific calibration technique it provided results that were comparable to the values that were obtained following the traditional gravimetric water content determination protocol. We found that the instrument was very sensitive to changes in soil moisture content and has great potential as a replacement for the gravimetric technique. It allows repetitive measurements of soil moisture content at a very shallow depth with minimal soil disturbance. Fur thermore, the instrument is particularly valuable for providing ground- truth soil moisture contents to validate remotely sensed data. Key words: Soil moisture, remote sensing, impedance probe, ground-truth, validation