Performance of the Commercial WET Capacitance Sensor as Compared with Time Domain Reflectometry in Volcanic Soils

Abstract

Among different alternatives, dielectric capacitance sensors may provide simultaneous readings of the volumetric water content and the soil solution electrical conductivity in the same sample volume at low cost. Reliability of capacitive sensors may be questioned, however, due to the low signal frequency at which they work, and also because of soil electrical conductivity effects on the water content estimation. In this study we evaluated the commercial capacitive WET Sensor (Delta‐T Devices Ltd., Burwell, UK) compared with time domain reflectometry (TDR) in three volcanic soils with different textures. Although the WET Sensor uses internally the Hilhorst approach for describing the relationship between soil moisture and bulk and pore water electrical conductivity, results suggest that the Vogeler model is a better choice for the soils studied. The sensor provides good estimation of the bulk electrical conductivity, but determination of soil water content is biased. Thus, we propose an alternative empirical equation to determine the volumetric water content from the WET Sensor readings, the soil bulk density, and an estimate of the sensor's effective frequency.