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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #151902

Title: Field calibration of water content reflectometers

item Seyfried, Mark
item Murdock, Mark

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/2003
Publication Date: 6/20/2004
Citation: Chandler, D.G., Seyfried, M., Murdock, M., and McNamara, J.P., Soil Science Society of America Journal, 2004. Field Calibration of water content reflectometers, abstract, vol.68, pp 1501-1507.

Interpretive Summary: Recent advances in electronics technology have been applied to the problem of soil water content measurement. This is of interest for practical applications, such as irrigation scheduling, and well as research of soil water processes. In general, these new instruments have not been will characterized in terms of accuracy and precision. Specifically, more information concerning calibration accuracy is needed to make these instruments practical. We tested a method of field calibration which can be performed with minimal disturbance on one such new soil water sensor, the Water Content Reflectometer. We found that the field calibration technique resulting in improved measurement accuracy and that, even in coarse textured soils where the instrument should work best, on-site calibration is desirable.

Technical Abstract: Soil volumetric water content (VMC) is regularly monitored through measurement soil dielectric properties with techniques similar to time domain reflectometry (TDR). The accuracy of these techniques relies on both the sensor uniformity and accuracy of the calibration equation. An in situ technique for calibrating one such instrument, the Campbell Scientific Water Content Reflectometer (WCR), with TDR is presented. The field calibration reduced the error estimate to near ± 1% VWC, from the factory calibration error estimate of ± 3% VWC. The improved accuracy from the in situ calibration resolved some apparent problems in the soil moisture profiles, as represented by the standard calibrations for the WCRs, at soil pits of two different textures.