ARS | Publication request: Performance evaluation of TDT soil water content and watermark soil water potential sensors

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 1, 2011
Publication Date: April 26, 2011
Citation: Varble, J.L., Chavez, J.L., Andales, A.A., Butters, G.L., Trout, T.J. 2011. Performance evaluation of TDT soil water content and watermark soil water potential sensors. In Emerging Challenges and Opportunities for Irrigation Managers: Energy, Efficiency, and Infrastructure. Proceedings of the USCID Conference, Albuquerque, NM, April 26 – 29, 2011.

Technical Abstract: This study evaluated the performance of digitized Time Domain Transmissometry (TDT) soil water content sensors (Acclima, Inc., Meridian, ID) and resistance-based soil water potential sensors (Watermark 200, Irrometer Company, Inc., Riverside, CA) in two soils. The evaluation was performed by comparing volumetric water content ('v) data collected in the laboratory and in fields near Greeley, CO, with values measured by the sensors. Calibration equations of 'v were then developed based on the laboratory and field data. Statistical targets to determine accuracy of the equations were ±0.015 m3 m-3 mean bias error and a root mean square error of less than 0.020 m3 m-3. Under laboratory and field conditions, the factory-based calibrations of 'v did not consistently achieve the required accuracy for either sensor. Field tests indicated that using the calibration equation developed in the laboratory to correct data obtained by TDT and Watermark sensors in the field at Site A (sandy clay loam) was not consistently accurate. Using the laboratory equations developed for the Watermark sensors at Site B (loamy sand) accurately measured 'v. Field tests found that a linear calibration of the TDT sensors (and a logarithmic calibration for the Watermark sensors) could accurately correct the factory calibration of 'v in the range of permanent wilting point (PWP) to field capacity (FC). Furthermore, the van Genuchten (1980) equation was not significantly more accurate than the logarithmic equation, and the additional work of deriving the former equation did not seem worthwhile, within the range of soil water contents analyzed.