Polymer tensiometers with ceramic cones: direct observations of matric pressures in drying soils

Abstract. Measuring soil water potentials is crucial to characterize vadose zone processes. Conventional tensiometers only measure until approximately −0.09 MPa, and indirect methods may suffer from the non-uniqueness in the relationship between matric potential and measured properties. Recently developed polymer tensiometers (POTs) are able to directly measure soil matric potentials until the theoretical wilting point (−1.6 MPa). By minimizing the volume of polymer solution inside the POT while maximizing the ceramic area in contact with that polymer solution, response times drop to acceptable ranges for laboratory and field conditions. Contact with the soil is drastically improved with the use of cone-shaped solid ceramics instead of flat ceramics. The comparison between measured potentials by polymer tensiometers and indirectly obtained potentials with time domain reflectometry highlights the risk of using the latter method at low water contents. By combining POT and time domain reflectometry readings in situ moisture retention curves can be measured over the range permitted by the measurement range of both POT and time domain reflectometry.

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Polymer tensiometers with ceramic cones: performance in drying soils and comparison with water-filled tensiometers and time domain reflectometry

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-6-4349-2009 ◽

2009 ◽

Vol 6 (3) ◽

pp. 4349-4377 ◽

Cited By ~ 1

Author(s):

M. J. van der Ploeg ◽

H. P. A. Gooren ◽

G. Bakker ◽

C. W. Hoogendam ◽

C. Huiskes ◽

...

Keyword(s):

Polymer Solution ◽

Time Domain ◽

Response Times ◽

Time Domain Reflectometry ◽

Matric Potential ◽

Indirect Methods ◽

The Relationship ◽

Wilting Point ◽

Water Contents

Abstract. Measuring soil water potentials is crucial to characterize vadose zone processes. Water-filled tensiometers only measure until approximately −0.085 MPa, and indirect methods may suffer from the non-uniqueness in the relationship between matric potential and measured properties. Recently developed polymer tensiometers (POTs) are able to directly measure soil matric potentials until the theoretical wilting point (−1.6 MPa). By minimizing the volume of polymer solution inside the POT while maximizing the ceramic area in contact with that polymer solution, response times drop to acceptable ranges for laboratory and field conditions. Contact with the soil is drastically improved with the use of a cone-shaped solid ceramics instead of flat ceramics. The comparison between measured potentials by polymer tensiometers and indirectly obtained potentials with time domain reflectometry highlights the risk of using the latter method at low water contents. By combining POT and time domain reflectometry readings in situ moisture retention curves can be measured over the range permitted by time domain reflectometry.

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Measuring transient solute transport through the vadoze zone using time domain reflectometry

Soil Research ◽

10.1071/sr00100 ◽

2001 ◽

Vol 39 (6) ◽

pp. 1359 ◽

Cited By ~ 10

Author(s):

I. Vogeler ◽

S. Green ◽

A. Nadler ◽

C. Duwig

Keyword(s):

Electrical Conductivity ◽

Solute Transport ◽

Time Domain ◽

Deterministic Model ◽

Soil Surface ◽

Time Domain Reflectometry ◽

Richards Equation ◽

Electrical Conductivities ◽

Destructive Measurement

Time domain reflectometry (TDR) was used to monitor the transport of conservative tracers in the field under transient water flow in a controlled experiment under a kiwifruit vine. A mixed pulse of chloride and bromide was applied to the soil surface of a 16 m2 plot that had been isolated from the surrounding orchard soil. The movement of this solute pulse was monitored by TDR. A total of 63 TDR probes were installed into the plot for daily measurements of both the volumetric water content (θ) and the bulk soil electrical conductivity (σa). These TDR-measured σa were converted into pore water electrical conductivities (σw) and solute concentrations using various θ–σa–σw relationships that were established in the laboratory on repacked soil. The depth-wise field TDR measurements were compared with destructive measurement of the solute concentrations at the end of the experiment. These results were also compared with predictions using a deterministic model of water and solute transport based on Richards’ equation, and the convection–dispersion equation. TDR was found to give a good indication of the shape of the solute profile with depth, but the concentration of solute was under- or over-estimated by up to 50%, depending on the θ–σa–σw relationships used. Thus TDR can be used to monitor in situ transport of contaminants. However, only rough estimates of the electrical conductivity of the soil solution can so far be obtained by TDR.

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An Innovative Use of TDR Probes: First Numerical Validations with a Coaxial Cable

Journal of Environmental and Engineering Geophysics ◽

10.2113/jeeg23.4.437 ◽

2018 ◽

Vol 23 (4) ◽

pp. 437-442

Author(s):

Raffaele Persico ◽

Iman Farhat ◽

Lourdes Farrugia ◽

Sebastiano D'Amico ◽

Charles Sammut

Keyword(s):

Magnetic Properties ◽

Transmission Line ◽

Time Domain ◽

Numerical Data ◽

Time Domain Reflectometry ◽

Coaxial Cable ◽

Transmission Line Model ◽

Properties Of Materials

In this paper we propose a study regarding some possibilities that can be offered by a time domain reflectometry (TDR) probe in retrieving both dielectric and magnetic properties of materials. This technique can be of interest for several applications, among which the characterization of soil in some situations. In particular, here we propose an extension of the paper “Retrieving electric and magnetic propetries of the soil in situ: New possibilities”, presented at the IWAGPR, held in Edinburgh in 2017, and as a new contribution we will validate a transmission line model with numerical data simulated by the CST code.

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