Three-Dimensional Numerical Modeling of a Capacitance Probe

Bolvin, Hervé; Chambarel, André; Chanzy, André

doi:10.2136/sssaj2004.0440

Cited by 8 publications

(8 citation statements)

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“…Classical methods include gravimetric measurement, neutron scattering (Gardner and Kirkham 1952;Bavel et al 1956) or dielectric methods such as Time Domain Reflectometry (TDR) or capacitance probes (Topp and Davis 1980;Bolvin et al 2004). However, these methods are invasive, may disturb the soil structure and give local measurements at the profile scale.…”

Section: Introductionmentioning

confidence: 99%

Estimation of the spatial variability of root water uptake of maize and sorghum at the field scale by electrical resistivity tomography

2009

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Saving water for crop production is an old, but ongoing, challenge which requires a better understanding of the in situ functioning of root systems. In particular, this requires a better quantification and understanding of the spatial and temporal variability of the root water uptake at the field scale. Electrical Resistivity Tomography (ERT) is a nondestructive soil imaging technique, related to water content, which could help in spatializing active zones of water uptake. In this article, we evaluate ERT as an alternative method for quantifying and spatializing root water uptake at the field scale. To this aim, an experimental field study with maize and sorghum submitted to different water supply levels (Fully, Moderately or Poorly Irrigated treatments-FI, MI, PI zones) was conducted for 3 months with concomitant conventional, local, water balance measurements and 2D ERT imaging. ERT images showed an heterogeneous depletion of soil water by the crops, particularly, in the MI and PI zones with patches of high/low electrical resistivity (and thus water content) variations. This heterogeneity was greatest in the MI zone and points to spatial variations in rooting pattern and/or root efficiency. The 5-days difference in electrical resistivity could be quantitatively related to root uptake in the surface layer (down to 60 cm) but the relationship depends on the mean soil water content. At greater soil depth, in the water stressed zones, the water extraction front progressing downwards could not be assessed with the ERT surface setting used in this study. As a conclusion, ERT can be a useful, unique, technique for monitoring and estimating field water uptake by plant roots and its variability if combined water content measurements are available for in situ calibration and if the sensitivity/resolution of the technique is improved for estimation over the whole root zone.

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Section: Introductionmentioning

confidence: 99%

Estimation of the spatial variability of root water uptake of maize and sorghum at the field scale by electrical resistivity tomography

2009

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“…The slope for a given soil material was rather variable from one sample to another (from 0.006 K −1 to 0.14 K −1 ). This variability may be explained by the variable soil structure in the probe's sphere of influence, which only covers a volume of a few cm 3 [ 30 ] and variations in soil water content and electrical conductivity. At this scale, the soil structure in the vicinity of the electrodes can change drastically from one probe to another.…”

Section: Resultsmentioning

confidence: 99%

“…One electrode is annular and has a length of 10 mm and a 22 mm diameter ( Figure 1 ). The other is a rod (20 mm long, 2 mm in diameter) located 3 mm apart the annular electrode [ 30 , 31 ]. After being calibrated in reference media, the probe gives an apparent dielectric permittivity.…”

Section: Methodsmentioning

confidence: 99%

Correcting the Temperature Influence on Soil Capacitance Sensors Using Diurnal Temperature and Water Content Cycles

Chanzy

Gaudu

Marloie

2012

Sensors

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The influence of temperature on the dielectric permittivity of soil is the result of counteracting effect that depends on the soil's composition and mineralogy. In this paper, laboratory experiments showed that for a given water content, the soil dielectric permittivity was linearly related to the temperature, with a slope (α) that varied between samples taken in the same soil. These variations are difficult to predict and therefore, a simple and straightforward algorithm was designed to estimate α based on the diurnal patterns of both the measured dielectric permittivity and the soil temperature. The underlying idea is to assume that soil water content variations can be known with a reasonable accuracy over an appropriate time window within a day. This allows determining the contribution of the soil water content to the dielectric permittivity variations and then, the difference with the observed measurements is attributed to the soil temperature. Implementation of the correction methods in a large number of experiments significantly improved the physical meaning of the temporal evolution of the soil water content as the daily cycles for probes located near the surface or the long-term variations for more deeply installed probes.

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“…Guber et al (2010) found that the largest errors in site-specific calibration of the Enviroscan sensors were at the depths where the variability of bulk densities was the highest. Modeling of the fringe fields in the media outside the access tubes, as it has been done for both homogeneous media (Schwank et al, 2006) and heterogeneous media (Bolvin et al, 2004), may help shed more light on the nature of bulk density effects on the capacitance sensor calibrations. Figure 3 provides seemingly contradictory data that the macropore sensitivity depends almost linearly on both scaled frequency and water contents, whereas the manufacturer (SENTEC, 1994) reports nonlinear dependence of SF on water content.…”

Section: Discussionmentioning

confidence: 99%

Sensitivity of a Capacitance Sensor to Artificial Macropores

Rowland¹,

Pachepsky²,

Guber³

2011

Soil Science

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The effects of large macropores, cracks, and other large heterogeneities within the capacitance sensor sensitivity volume are of concern in application of these sensors. The objective of this work was to evaluate the sensitivity of the Enviroscan sensors to the presence of macropores. The artificial macropores were manufactured from polystyrene tubes and placed in contact with the access tube and at distances of 1.5 cm and 2.5 cm in air, water, and wetted sand. Measurements were obtained during sequential filling with water eight macropores at the same distance from the access tube. The dependencies of the raw frequencies on the number of filled macropores were linear with r 2 9 0.98. The macropore sensitivity, defined as the decrease in frequency per one filled macropore, deceased exponentially with the distance from the access tube. For a given distance from the access tube, the macropore sensitivity depended linearly on the scaled frequency. The effect of the water-filled macropores on the bulk soil water content estimate decreased with the increase in soil water content. The estimated errors of measurement were approximately 0.002 cm 3 cm j3 (0.001 cm 3 cm j3 ) per 1% of soil volume near the access tube occupied by the macropore for the water content of bulk soil of 0.10 cm 3 cm j3 (0.30 cm 3 cm j3 ) and were about three times smaller at the 1.5 cm distance from the access tube. Overall, macropores near the access tube had only moderate effect on the soil water content measurements with capacitance sensors when they occupied less than 13% of soil volume near the access tube.

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Three-Dimensional Numerical Modeling of a Capacitance Probe

Cited by 8 publications

References 0 publications

Estimation of the spatial variability of root water uptake of maize and sorghum at the field scale by electrical resistivity tomography

Estimation of the spatial variability of root water uptake of maize and sorghum at the field scale by electrical resistivity tomography

Correcting the Temperature Influence on Soil Capacitance Sensors Using Diurnal Temperature and Water Content Cycles

Sensitivity of a Capacitance Sensor to Artificial Macropores

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