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Evaluation of a Root Zone TDR Sensor for Soil Water Content Measurement.

Poster Number 2405

Monday, November 4, 2013
Tampa Convention Center, East Hall, Third Floor

Xiuli Xin, Institute of Soil Science, Chinese Academy of Science, Nanjing, China, Tyson E. Ochsner, Oklahoma State University, Stillwater, OK and Steven R. Evett, USDA-ARS Conservation & Production Research Laboratory, Bushland, TX
Time domain reflectometry (TDR) is a well-established dielectric technique of measuring the soil volumetric water content (θ). However, it is expensive and difficult to determine the depth-averaged θ in the root zone using conventional TDR probes. The objectives of this study are to develop a long TDR sensor to determine the depth-averaged θ in root zone and to evaluate the performance of this sensor. We developed a root zone TDR sensor which is comprised of a pair of stainless steel rods (80 or 90 cm in length, 12.8 mm in diameter) encased with 0.5-mm thick heat shrink polyolefin coating. The probes were calibrated in water and air. The apparent permittivity (Ka) measurement of root zone TDR probes was successfully fitted to target Ka using a two-phase dielectric mixing model. Four root zone TDR probes and a set of conventional TDR probes were installed in a field and measurement of θ was taken from Oct., 2010 to Dec., 2012. The result showed that the patterns of average θ variation measured by root zone TDR probes and conventional TDR probes were synchronous. Root mean square error (RMSE) of θ was less than 0.036 cm3 cm-3 using the on-site Ka - θ calibration equations. Soil water content measured by root zone TDR probes was more sensitive to the variation of θ in top soil layer. The results suggest that a root zone TDR can be an alternative of conventional TDR probes for monitoring the depth-averaged θ of the root zone.
See more from this Division: SSSA Division: Soil Physics
See more from this Session: Advancing Measurement Technology in Soil and Environmental Physics: An Original Research Instrumentation Showcase (includes student competition)

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