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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVING WATER PRODUCTIVITY AND NEW WATER MANAGEMENT TECHNOLOGIES TO SUSTAIN RURAL ECONOMIES

Location: Soil and Water Management Research

Title: Evaluation of a root zone TDR sensor for soil water content measurement

Authors
item Xin, Xiuli -
item Ochsner, Tyson -
item Evett, Steven

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: August 1, 2013
Publication Date: November 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.

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.

Last Modified: 11/28/2014
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