A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry

Robinson, David A.; Jones, Scott B.; Wraith, Jon M.; Or, Dani; Friedman, Shmulik P.

doi:10.2113/2.4.444

Cited by 156 publications

(171 citation statements)

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“…Seedlings, which did not yet have cotyledons, were wilting, or damaged were excluded from the measurement. Complementary to this, we characterized the water retention capacity of the respective substrates bare soil, soil with inactive grass tussocks, and soil with active tussocks using time‐domain reflectometry (Ledieu, De Ridder, De Clerck, & Dautrebande, 1986; Robinson, Jones, Wraith, Or, & Friedman, 2002). Each pot was measured at 7 hr in the morning with three repeats over 10 days after a simulated rain event of 10 mm.…”

Section: Methodsmentioning

confidence: 99%

A dominance shift in arid savanna: An herbaceous legume outcompetes local C₄ grasses

Wagner

Richter

Joubert

et al. 2018

Ecology and Evolution

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The characteristic vegetation structure of arid savannas with a dominant layer of perennial grass is maintained by the putative competitive superiority of the C4 grasses. When this competitive balance is disturbed by weakening the grasses or favoring the recruitment of other species, trees, shrubs, single grass, or forb species can increase and initiate sudden dominance shifts. Such shifts involving woody species, often termed “shrub encroachment”, or the mass spreading of so‐called increaser species have been extensively researched, but studies on similar processes without obvious preceding disturbance are rare. In Namibia, the native herbaceous legume Crotalaria podocarpa has recently encroached parts of the escarpment region, seriously affecting the productivity of local fodder grasses. Here, we studied the interaction between seedlings of the legume and the dominant local fodder grass (Stipagrostis ciliata). We used a pot experiment to test seedling survival and to investigate the growth of Crotalaria in competition with Stipagrostis. Additional field observations were conducted to quantify the interactive effect. We found germination and growth of the legume seedlings to be facilitated by inactive (dead or dormant) grass tussocks and unhindered by active ones. Seedling survival was three times higher in inactive tussocks and Crotalaria grew taller. In the field, high densities of the legume had a clear negative effect on productivity of the grass. The C4 grass was unable to limit the recruitment and spread of the legume, and Crotalaria did outcompete the putative more competitive grass. Hence, the legume is able to spread and establish itself in large numbers and initiate a dominance shift in savannas, similar to shrub encroachment.

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Section: Methodsmentioning

confidence: 99%

A dominance shift in arid savanna: An herbaceous legume outcompetes local C₄ grasses

Wagner

Richter

Joubert

et al. 2018

Ecology and Evolution

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“…Despite advances in the theory [4, 13-15], the mechanisms for dielectric loss in porous multi-phase media (soils) over a broad range of frequencies are complicated [16], such that a simple correction for temperature may not be possible [5]. Kelleners et al [14] used electrical circuit theory as an analogue to describe the capacitance sensor in terms of a resistor-capacitor-inductor (RCL) circuit, where electrical conductivity of test liquids was shown to decrease the resonant frequency.…”

Section: Introductionmentioning

confidence: 99%

Simulated Effects of Soil Temperature and Salinity on Capacitance Sensor Measurements

Schwank

Green

2007

Sensors

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Dielectric measurement techniques are used widely for estimation of water content in environmental media. However, factors such as temperature and salinity affecting the readings require further quantitative investigation and explanation. Theoretical sensitivities of capacitance sensors to liquid salinity and temperature of porous media were derived and computed using a revised electrical circuit analogue model in conjunction with a dielectric mixing model and a finite element model of Maxwell's equation to compute electrical field distributions. The mixing model estimates the bulk effective complex permittivities of solidwater-air media. The real part of the permittivity values were used in electric field simulations, from which different components of capacitance were calculated via numerical integration for input to the electrical circuit analogue. Circuit resistances representing the dielectric losses were calculated from the complex permittivity of the bulk soil and from the modeled fields. Resonant frequencies from the circuit analogue were used to update frequency-dependent variables in an iterative manner. Simulated resonant frequencies of the capacitance sensor display sensitivities to both temperature and salinity. The gradients in normalized frequency with temperature ranged from negative to positive values as salinity increased from 0 to 10 g L -1 . The model development and analyses improved our understanding of processes affecting the temperature and salinity sensitivities of capacitance sensors in general. This study provides a foundation for further work on inference of soil water content under field conditions.

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“…The use of Time Domain Reflectometry (TDR) technique for permittivity measurements is based on evaluating the velocity of a step-like signal which travels along a transmission line filled with the material under test or embedded in it (for details see Ferré 2002, andRobinson et al 2003). The TDR signal has a broad band and the upper frequency, in a sample, can extend up to about 500 MHz.…”

Section: Time Domain Measurementsmentioning

confidence: 99%

Radar Signal Propagation and Detection Through Ice

Kofman¹,

Orosei

Pettinelli

2010

Space Sci Rev

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In this paper we describe the existing and planned radar measurements of the\ud planetary bodies. The dielectric properties of water ice and other potential surface and subsurface\ud materials are discussed, as well as their dependency on temperature and structure.\ud We then evaluate the performance of subsurface sounding radars using these parameters.\ud Finally we describe some laboratory technique to help interpret the radar data, presenting\ud some results obtained using dielectric spectroscopy methods

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A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry

Cited by 156 publications

References 0 publications

A dominance shift in arid savanna: An herbaceous legume outcompetes local C₄ grasses

A dominance shift in arid savanna: An herbaceous legume outcompetes local C₄ grasses

Simulated Effects of Soil Temperature and Salinity on Capacitance Sensor Measurements

Radar Signal Propagation and Detection Through Ice

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A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry

Cited by 156 publications

References 0 publications

A dominance shift in arid savanna: An herbaceous legume outcompetes local C4 grasses

A dominance shift in arid savanna: An herbaceous legume outcompetes local C4 grasses

Simulated Effects of Soil Temperature and Salinity on Capacitance Sensor Measurements

Radar Signal Propagation and Detection Through Ice

Contact Info

Product

Resources

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A dominance shift in arid savanna: An herbaceous legume outcompetes local C₄ grasses

A dominance shift in arid savanna: An herbaceous legume outcompetes local C₄ grasses