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RESEARCH ARTICLE
Contents Vol 45(3)

Field calibration of ThetaProbe (ML2x) and ECHO probe (EC-20) soil water sensors in a Black Vertosol

J. L. Foley A C and E. Harris B
+ Author Affiliations
- Author Affiliations

A Agricultural Production Systems Research Unit, Queensland Department of Natural Resources and Water, PO Box 318 Toowoomba, Qld 4350, Australia.

B Ecole Supérieure d’Agriculture de Purpan, 75, voie du T.O.E.C BP 57611, 31076 Toulouse, Cedex 3, France.

C Corresponding author. Email: Jenny.Foley@nrw.qld.gov.au

Australian Journal of Soil Research 45(3) 233-236 https://doi.org/10.1071/SR06156
Submitted: 7 November 2006  Accepted: 16 April 2007   Published: 18 May 2007

Abstract

Past studies have shown that soil-specific calibrations are required to attain a higher level of accuracy when measuring soil water content with ThetaProbe and ECHO probe soil water sensors, particularly in swelling clay soils. Both probes were assessed for their capacity to accurately monitor soil water in a deep drainage study on a Black Vertosol. Probes were trialled in situ and calibrated against hand-sampled volumetric measurements. The generic calibrations given by the manufacturers resulted in significant errors in water content estimates for both probes. Using the generic calibration, ECHO probes under-estimated water content by 0.10–0.2 m3/m3, whereas ThetaProbes under-estimated by 0.04 m3/m3 at the wet end and over-estimated by 0.08 m3/m3 at the dry end. The soil-specific calibrations significantly improved the accuracy of both probes. ThetaProbes were chosen for the drainage study. The calibration allowed for accuracy across the full wet–dry range to within 0.001–0.004 m3/m3 of volumetric measurements. ECHO probes were less accurate at the wet end, but still determined soil water content to within 0.02–0.05 m3/m3 of volumetric measurements.

Additional keywords: frequency domain reflectometry, dielectric sensor, soil water content, cracking clay, swelling clay.


Acknowledgments

This project was funded by GRDC project DNR3 and Department of Natural Resources and Water. Our thanks go to Department of Primary Industries & Fisheries for the use of the Kingsthorpe Research Station. We especially thank Dr Bryan Bridge for the loan of equipment, for invaluable technical assistance and for reviewing the manuscript. Additional thanks go to Don Pegler, Ralph DeVoil, and Denis Orange for technical and field assistance. We would also like to thank Dr Mark Silburn for his comments and review.


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