TDR pressure cell for monitoring water content retention and bulk electrical conductivity curves in undisturbed soil samples

Hydrological Processes - Tập 26 Số 2 - Trang 246-254 - 2012
David Moret‐Fernández1, José Vicente2, Borja Latorre1, F. Lera3, Carmen Castañeda1, M.V. López, J. Herrero1
1Departamento de Suelo y Agua, Estación Experimental de Aula Dei, (CSIC), PO Box 13034, 50080 Zaragoza, Spain
2Departamento de Ingeniería Electrónica y Comunicaciones, Universidad de Zaragoza, I3A—Edificio I + D, C/Mariano Esquillor S/N, Despacho 4.0.05, 50018 Zaragoza, Spain
3Departamento de Ingeniería Electrónica y Comunicaciones, (ICMA-CSIC), Universidad de Zaragoza, C/María de Luna 1, 50018 Zaragoza, Spain

Tóm tắt

AbstractThe water retention curve (θ(ψ)), which defines the relationship between soil volumetric water content (θ) and matric potential (ψ), is of paramount importance in characterizing the hydraulic behaviour of soils. However, few methods are so far available for estimating θ(ψ) in undisturbed soil samples. We present a new design of TDR‐pressure cell (TDR‐Cell) for estimating θ(ψ) in undisturbed soil samples. The TDR‐Cell consists of a 50‐mm‐long and 50‐mm internal diameter stainless steel cylinder (which constitutes the outer frame of a coaxial line) attached to a porous ceramic disc and closed at the ends with two aluminium lids. A 49‐mm‐long and 3‐mm‐diameter stainless steel rod, which runs longitudinally through the centre of the cylinder, constitutes the inner rod of a coaxial TDR probe. The TDR‐Cell was used to determine the θ(ψ) curves of a packed sand and seven undisturbed soil samples from three profiles of agricultural soils. These θ(ψ) curves were subsequently compared to those obtained from the corresponding 2‐mm sieved soils using the pressure plate method. Measurements of bulk electrical conductivity, σa, as a function of the water content, σa(θ), of the undisturbed soil samples were also performed. An excellent correlation (R2 = 0·988) was found between the θ values measured by TDR on the different undisturbed soils and the corresponding θ obtained from the soil gravimetric water content. A typical bimodal θ(ψ) function was found for most of the undisturbed soil samples. Comparison between the θ(ψ) curves measured with the TDR‐Cell and those obtained from the 2‐mm sieved soils showed that the pressure plate method overestimates θ at low ψ values. The σa(θ) relationship was well described by a simple power expression (R2 > 0·95), in which the power factor, defined as tortuosity, ranged between 1·18 and 3·75. Copyright © 2011 John Wiley & Sons, Ltd.

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Hydrological Processes

Tập 26 Số 2

246-254

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