HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Schwartz, B. F. Articles by Rimstidt, J. D. Search for Related Content PubMed Articles by Schwartz, B. F. Articles by Rimstidt, J. D. GeoRef GeoRef Citation Agricola Articles by Schwartz, B. F. Articles by Rimstidt, J. D. Related Collections Soil Methods/Instrumentation Water Content Field-Scale Studies Time Domain Reflectometry, TDR Field evaluation techniques Data acquisition and assimilation

SOIL PHYSICS

Calibrating Access-tube Time Domain Reflectometry Soil Water Measurements in Deep Heterogeneous Soils

^a Dep. of Geosciences, 4044 Derring Hall, Virginia Polytechnic and State Univ., Blacksburg, VA 24060
^b Currently at: Dep. of Biology, Texas State University, San Marcos, TX 78666

^* Corresponding author (bs37{at}txstate.edu).

Hydrologic characterization of the vadose zone requires accurate measurements of soil water in a variety of soil textures. Time domain reflectometry (TDR) instruments are commonly used to obtain soil moisture. Although there are advantages to using TDR, certain types of instruments pose challenges, including proper installation and calibration, which must be overcome. The principal objective of this study was to develop a new method for obtaining and calibrating access-tube TDR measurements in deep heterogeneous soils. Using two regression techniques, physical and chemical property-based calibrations were developed to predict soil water and explain large differences between TDR and gravimetric soil water values. Differences between TDR soil water and gravimetric soil water were almost entirely controlled by physical and chemical soil properties; indicating that our access-tube TDR probe likely produced an accurate measurement of ‘free’ but not bound water content. The bound fraction is controlled by physical and chemical properties and is a nearly static parameter at the depths and time scales considered in this study. Changes in TDR measurements after the initial calibration represent changes in the ‘free’ water content. Our calibration equations used easily obtained parameters to predict accurate soil water values in a wide range of soil textures. Approximately 95% of the soil water values predicted using our calibration equations had residuals of less than ± 10% soil water. We also developed a cost-effective method for installing access tubes which minimized problems related to air gaps and soil structure disturbances in deep soil profiles.

Abbreviations: AIC, Akaike's information criterion • CEC, cation exchange capacity • CLR, categorical linear regression • ERT, electrical resistivity tomography • MLR, multiple linear regression • PSA, particle size analysis • TDR, time domain reflectometry • TSS, total soluble salts