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Mini Tensiometer‐Time Domain Reflectometry Coil Probe for Measuring Soil Water Retention Properties
Author(s) -
Subedi Shaphal,
Kawamoto Ken,
Karunarathna Anurudda Kumara,
Moldrup Per,
Wollesen de Jonge Lis,
Komatsu Toshiko
Publication year - 2013
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2012.0106
Subject(s) - reflectometry , electromagnetic coil , tensiometer (surface tension) , calibration , soil water , materials science , water content , dielectric , calibration curve , time domain , soil science , composite material , geotechnical engineering , chemistry , environmental science , geology , electrical engineering , optoelectronics , chromatography , physics , thermodynamics , surface tension , quantum mechanics , detection limit , computer science , engineering , computer vision
Time domain reflectometry (TDR) is used widely for measuring soil‐water content. New TDR coil probe technology facilitates the development of small, nondestructive probes for simultaneous measurement of soil‐water content (θ) and soil‐water potential (ψ). In this study we developed mini tensiometer‐time domain reflectometry (T‐TDR) coil probes, 6‐mm wide and 32‐mm long. The coil probes were calibrated against a conventional three‐rod probe and were used for measuring θ for a aggregated volcanic ash soil (VAS) and a uniform sand. A commonly‐used dielectric mixing model did not accurately describe the measured relation between the dielectric constant of the T‐TDR coil probe (ε coil ) and θ, and a new calibration model for ε coil (θ) was proposed instead. The new model assumes single‐region behavior for sand and two‐region behavior for aggregated VAS, when plotting the normalized dielectric constant of the coil probe (ε coil –ε dry ; where ε dry is the dielectric constant of the T‐TDR coil probe for air‐dried material) as a function of θ. The new calibration model accurately described the (ε coil –ε dry )‐θ relations measured by 7 T‐TDR coil probes on both sand and VAS. Additionally, there was a good agreement between measured soil‐water retention curves (ψ > –100 cm H 2 O) by the new T‐TDR coil probes and independent measurements by the hanging water column method.