Soil Aggregate Structure Effects on Dielectric Permittivity of an Andisol Measured by Time Domain Reflectometry

Miyamoto, Teruhito; Annaka, Takeyuki; Chikushi, Jiro

doi:10.2113/2.1.90

Cited by 22 publications

(35 citation statements)

References 26 publications

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“…Well‐aggregated soils have two distinct pore systems: intraaggregate and interaggregate. While the former pore system contributes to soil water retention characteristics at low matric potentials, the latter contributes at high matric potentials (Miyamoto et al, 2003). The observed soil water retention data with a dual‐porosity model fit are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Water distribution in an aggregated soil: (a) observed and predicted soil water retention curves using a dual‐porosity model for the Andisol sample used for air permeability measurements (adapted from Miyamoto et al, 2003), and (b) air permeability as a function of air content for the Andisol at 8‐kPa confined pressure.…”

Section: Resultsmentioning

confidence: 99%

“…For instance, Andisols have well‐defined intra‐ and interaggregate voids and typically have higher organic C content. Therefore, Andisols commonly have a low bulk density, high porosity, and large specific surface areas and soil air and water permeabilities (Dörner et al, 2009; Miyamoto et al, 2003). In addition, Andisols significantly shrink during drying processes due to the force of water menisci (Dörner et al, 2009).…”

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confidence: 99%

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Effects of Confining Pressure on Unsteady‐State Air Permeability Measurement Method in an Aggregated Andisol

Nakajima

Saito

Tojo

et al. 2016

Vadose Zone Journal

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Core Ideas We propose an unsteady‐state air permeability method with confined sleeve pressure. Interaggregate permeability increased slightly compared with the intraaggregate region. Air permeability is affected by air leakage through the sample–column wall space. Air permeability is also affected by soil structure and water state in an Andisol. Soil air permeability is an important parameter to characterize convective gas transport through the soil gas phases. However, current air permeability measurements have limitations, specifically in Andisols, which are highly aggregated and often shrink during drying processes. Determining the air content at different tension gradient points by drying is also time consuming because experiments have to reach several steady‐state conditions. Thus, the objective of this research was to demonstrate an unsteady‐state air permeability measurement method with confined sleeve pressure. Furthermore, the effects of confined pressure and air leakage on the measurement of air permeability were determined using an Andisol across a wide range of soil water and air contents. Under confined pressure, the air flow rates at air contents of 0.2, 0.4, and 0.6 m3 m−3 and soil bulk density of 0.75 Mg m−3 were 5.8, 2.3, and 0.8 times higher, respectively, than those under unconfined pressure. Using the unsteady‐state air permeability measurements method on the Andisol, our results show that the interaggregate region had air contents in the range from 0.13 to 0.25 m3 m−3, with air permeability ranging from 12.6 to 54.8 μm2. Conversely, the intraaggregate region had air contents ranging from 0.25 to 0.65 m3 m−3, with air permeability ranging from 54.8 to 81.5 μm2. The intraaggregate air permeability increased only slightly due to less space in the aggregate.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Effects of Confining Pressure on Unsteady‐State Air Permeability Measurement Method in an Aggregated Andisol

Nakajima

Saito

Tojo

et al. 2016

Vadose Zone Journal

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“…The response of TDR‐measured K a to increasing water content (θ) in soils with bimodal pore‐size distributions has been the subject of a significant number of studies in the soil science literature (Dirksen and Dasberg, 1993; Friedman, 1998; Jones and Or, 2003; Miyamoto et al, 2003, 2005; Blonquist et al, 2006; Robinson et al, 2009). The relationship between K a and θ in these soils, the K a (θ) function, often displays a distinct increase in slope after θ surpasses a threshold value, often called the critical water content, θ cr (Miyamoto et al, 2003). The interpretation of this change in slope has been aided by the application of dielectric mixing models.…”

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confidence: 99%

“…The estimation of ε bw ′ with mixing models is subject to considerable uncertainty because (i) it is probably a function of distance from soil particle surfaces for which there are only limited measurements available, and (ii) an average of the permittivity of all bound water layers must be calculated to represent ε bw ′ in the mixing model (Friedman, 1998; Or and Wraith, 1999; Robinson et al, 2002). Bound water phases were also included in the mixing model investigations of Friedman (1998), Or and Wraith (1999), and Miyamoto et al (2003, 2005).…”

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confidence: 99%

Bound Water, Phase Configuration, and Dielectric Damping Effects on TDR‐Measured Apparent Permittivity

Dyck

Miyamoto

Iwata

et al. 2019

Vadose Zone Journal

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Core Ideas Frequency‐dependent bound water permittivity influences TDR‐measured Ka. Predictive power of frequency‐independent dielectric mixing models is limited. TDR measurements of Ka should be paired with effective frequency measurements. The time domain reflectometry (TDR) method measures the soil apparent permittivity (Ka), which is the basis for estimation of soil volumetric water content (θ) via an empirical calibration equation or dielectric mixing model. The relationship between Ka and θ [i.e., Ka(θ)] in soils with significant volumetric fractions of bound water and with bimodal pore‐size distributions displays a distinct increase in slope after θ exceeds a threshold value. The interpretation of this change in slope has been aided with application of dielectric mixing models through the inclusion of a bound water phase and/or θ‐dependent changes in phase configuration. However, Ka measured with time‐domain reflectometry (TDR) in soils with significant volumetric fractions of bound water has been previously observed to change as a function of the effective frequency of the soil‐attenuated bandwidth. Therefore, the main objective of this work was to investigate the influence of bound water and phase configuration in four, high‐surface‐area Japanese Andisols with bimodal pore‐size distributions using dielectric mixing models alone or coupled with a dielectric damping model. Soil‐specific Ka(θ) relationships were measured in the laboratory using standard methods and were simulated with two frequency‐independent, real‐valued dielectric mixing models and a complex‐valued, frequency‐dependent model coupled with a dielectric damping model. The results of the simulations indicate that frequency‐dependent dielectric permittivity of the bound water phase significantly influences TDR‐measured Ka(θ), suggesting that soil‐ and probe‐specific calibrations may be required for soils with significant volumetric fractions of bound water.

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Vegetation effects on soil pore structure and hydraulic properties in volcanic ash soils of the high Andes

Páez‐Bimos

Villacís

Morales

et al. 2022

Hydrological Processes

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Soil hydraulic properties control the provision of hydrological services. Vegetation and topography influence these properties by altering soil structure and porosity. The underlying mechanisms are not yet fully understood for the high Andean region. In this study, we examined how vegetation and topographic attributes are related to soil hydraulic properties and soil pore structure in young volcanic ash soils, and further correlated them to soil texture, organic carbon, and root characteristics to explain these relationships. In a 0.7 km 2 study site located in the Andean páramo of northern Ecuador, we measured soil water retention, saturated hydraulic conductivity, bulk density (BD), and pore size distribution parameters on eight soil profiles with contrasting vegetation types (cushion-forming plants vs. tussock grasses) and topographic positions (summit vs. hillslope). We observed significant differences in soil hydraulic properties and soil pore structure in the uppermost horizons by vegetation type, whereas topography had a minor effect. In the A horizons, we found higher water retention at saturation and field capacity (10%-14%), higher total available water (8%-15%), and higher saturated hydraulic conductivity (4-12 times) under cushion-forming plants compared to tussock grasses. The elevated values under cushion plants were attributed to the presence of larger pores, lower soil BD, and higher soil organic carbon content as a result of coarser root systems. Total available water was generally high (0.34-0.40 cm 3 cm À3 ), and locally not associated with any soil property. The higher water retention in soils under cushion vegetation can enhance soil water storage for plants and the regulation of water flows during prolonged

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Soil Aggregate Structure Effects on Dielectric Permittivity of an Andisol Measured by Time Domain Reflectometry

Cited by 22 publications

References 26 publications

Effects of Confining Pressure on Unsteady‐State Air Permeability Measurement Method in an Aggregated Andisol

Effects of Confining Pressure on Unsteady‐State Air Permeability Measurement Method in an Aggregated Andisol

Bound Water, Phase Configuration, and Dielectric Damping Effects on TDR‐Measured Apparent Permittivity

Vegetation effects on soil pore structure and hydraulic properties in volcanic ash soils of the high Andes

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