Evaluation of the SoilVUE10 Time Domain Reflectometry for soil water
measurements in testbed field conditions
Abstract
The U.S. Climate Reference Network (USCRN) has been engaged in
ground-based soil water and soil temperature measurements since 2009. As
a nationwide climate network, the network stations are distributed
across vast complex terrains. Due to the expansive distribution of the
network and the related variability in soil properties, obtaining
site-specific calibrations for sensors is a significant and costly
endeavor. Presented here are three commercial-grade electromagnetic
sensors, with built-in thermistors to measure both soil water and soil
temperature, including the SoilVUE10 Time Domain Reflectometry (TDR)
probe (hereafter called SP, for SoilVUE Probe) (Campbell Scientific,
Inc., Logan, UT), the 50 MHz coaxial impedance dielectric sensor (model
HydraProbe (hereafter called HP), Stevens Water Monitoring Systems,
Inc., Portland, OR), and the TDR-315L Acclima Probe (hereafter called
AP) sensor (model TDR-315L, Acclima, Inc., Meridian, ID), which were
evaluated in a nonconductive loam soil in Oak Ridge, Tennessee, USA from
2021 to 2022. The manufacturer-supplied calibration equation for loam
soils was successfully used in this study. Measurements of volumetric
water content by SP were much lower than gravimetric measurements in the
top 20-cm soil horizon, where soil water showed relatively large spatial
variability. Study results highlight that the SP may be an important
alternative to reduce soil disturbances that usually ensue when HP and
AP sensors are installed; however, in-situ calibrations are essential
for the SP for xeric soil water conditions.