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ARS Home » Plains Area » Bushland, Texas » Conservation and Production Research Laboratory » Soil and Water Management Research » Research » Publications at this Location » Publication #300884
Title: Evaluation of a root zone TDR sensor for soil water content measurement

Author
item XIN, XIULI - Chinese Academy Of Sciences
item OCHSNER, TYSON - Oklahoma State University
item Evett, Steven - Steve

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/2013
Publication Date: 11/3/2013
Citation: Xin, X., Ochsner, T., Evett, S.R. 2013. Evaluation of a root zone TDR sensor for soil water content measurement [abstract]. ASA-CSSA-SSSA Annual Meeting Abstracts. Session, 143-3, p.107.

Interpretive Summary:

Technical Abstract: Time domain reflectometry (TDR) is a well-established dielectric technique of measuring the soil volumetric water content (VWC). However, it is expensive and difficult to determine the depth-averaged VWC 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 VWC 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 VWC was taken from Oct., 2010 to Dec., 2012. The result showed that the patterns of average VWC variation measured by root zone TDR probes and conventional TDR probes were synchronous. Root mean square error (RMSE) of VWC was less than 0.036 m**3 m**-3 using the on-site Ka - VWC calibration equations. Soil water content measured by root zone TDR probes was more sensitive to the variation of VWC 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 VWC of the root zone.