Impact of soil texture on the performance of three soil moisture sensor types

Abstract

Abstract. Accurate soil moisture sensors can be an important component of precision irrigation water management. There is a large variety of commercial sensors that relate electrical output to soil water content. However, sensor electrical output is also affected by soil characteristics other than water content, such as texture, salinity, temperature, organic matter, etc. This makes it difficult to accurately measure soil moisture with most sensors without prior on-site calibration. In this study we investigated the impact of soil texture on the performance of three types of soil moisture sensors, including the EC-5 sensor (Decagon Devices, Pulman, WA), the VH400 soil moisture sensor probe (Vegetronix, Inc., Riverton, UT), and the Watermark 200ss (Irrometer Company, Inc., Riverside, CA). A replicated laboratory experiment was conducted in 2014 to evaluate the performance of these types of sensors using four major soil textural classes. We found that the three types of sensors had a significant response to changes in soil water content. The EC-5 and VH400 sensors had a linear response, while the Watermark 200ss had a curvilinear response that was explained by an exponential decay function. The response of the three sensors, however, was significantly affected by soil texture, which will significantly affect the trigger point used to initiate irrigation based on the output from these sensors. Therefore, it is suggested that guidelines on how to use these sensors for local soils need to be made available to farmers.