EVALUATION OF A DIELECTRIC-BASED MOISTURE AND SALINITY SENSOR FOR IN-SITU APPLICATIONS

Abstract

A low resonant frequency, dielectric based soil moisture sensor developed by Retrokool Inc. wastested in a Rincon loam, Yolo loam, and a Capay clay soil over a range of volumetric moisture contents. Theresponse of this sensor was insensitive to changes in soil texture. However, the response of the sensor wasinfluenced greatly by temperature changes and changes in salinity. A two factor factorial test was conducted todetermine the effect of changes in dielectric constant and conductivity on the output voltage and frequency ofthis moisture sensor. The results indicated that as soil moisture content changed the output voltage, which isrelated to variations in conductance, changed much more than the output frequency, which is related todielectric changes. When the terminals were coated with an insulating material, we were able to minimize theeffect of changes in soil conductance and the sensor responded primarily to changes in soil moisture content.