Time-Domain Reflectometry: Simultaneous Measurement of Soil Water Content and Electrical Conductivity with a Single Probe

Dalton, F. N.; Herkelrath, W. N.; Rawlins, D. S.; Rhoades, J. D.

doi:10.1126/science.224.4652.989

Cited by 348 publications

(179 citation statements)

References 4 publications

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“…Observa-se que a CEw varia linearmente com a CEa. Essa linearidade também foi observada em outras pesquisas (RHOADES et al, 1976;DALTON et al, 1984;VOGELER et al, 1997;NADLER, 1997;MMOLAWA & OR, 2000;MUÑOZ-CARPENA et al, 2001). Verifica-se que, para um mesmo valor de CEa, a CEw é tanto menor quanto maior for o teor de água no solo, o que se deve à maior diluição dos sais presentes na solução do solo.…”

Section: Resultsunclassified

“…Uma alternativa para o monitoramento do estado iônico do solo, visando ao correto manejo da fertirrigação, é a técnica da TDR que, além de possibilitar, com o uso de uma única sonda, a determinação simultânea do teor de água (θ) e da condutividade elétrica aparente do solo (CEa), em tempo real, de formas contínua, automática e rápida, e com o mínimo distúrbio da estrutura do solo, viabiliza, de forma indireta, o conhecimento da condutividade elétrica da solução do solo (CEw) (DALTON et al, 1984;WRAITH & DAS, 1998;NOBORIO, 2001;MUÑOZ-CARPENA et al, 2001).…”

Section: Introductionunclassified

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Estimativa da condutividade elétrica da solução do solo a partir do teor de água e da condutividade elétrica aparente do solo

Santana¹,

Coelho

Silva³

et al. 2006

Eng. Agríc.

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RESUMO:O crescente uso da técnica de fertirrigação não tem sido acompanhado com pesquisas para disponibilizar informações capazes de proporcionar o correto manejo dessa técnica. A reflectometria no domínio do tempo (TDR) possibilita o monitoramento simultâneo e contínuo do teor de água (θ) e da condutividade elétrica aparente do solo (CEa). A literatura apresenta diversos modelos que relacionam θ e CEa com a condutividade elétrica da solução do solo (CEw), com vistas à predição da CEw a partir de dados de θ e CEa obtidos por meio da técnica da TDR. Porém, muitas pesquisas demonstram a necessidade de avaliação e calibração desses modelos para solos de diferentes classes texturais. Neste trabalho, foram avaliados seis modelos com o objetivo de conhecer a capacidade dos mesmos em relacionar θ, CEa e CEw. Experimentos de laboratório foram feitos, com solo de classes texturais franca e franco-arenosa, aplicando-se soluções com cinco condutividades elétricas combinadas com cinco teores de água no solo, resultando em 25 colunas de solo. Os modelos demonstraram capacidade para relacionar θ, CEa e CEw. PALAVRAS-CHAVE:TDR, modelos matemáticos, manejo de fertirrigação. ESTIMATIVE OF SOIL SOLUTION ELECTRICAL CONDUCTIVITY FROM SOIL WATER CONTENT AND SOIL BULK ELECTRICAL CONDUCTIVITY ABSTRACT:The increase of fertigation techniques has not been followed by researches that generate available information to guide a correct fertigation management. The time-domain reflectometry allows the simultaneously monitoring of soil water content (θ) and bulk electrical conductivity (CEa). Literature presents various models which relate TDR readings of θ and CEa to soil solution electrical conductivity (CEw). Nevertheless, many researches demonstrate the need for evaluation and calibration of these models under different soil conditions. In this work, six mathematical models were evaluated in order to establish the relationship among θ, CEa e CEw. Laboratory experiments were carried out using two soil materials, by means of applying five electrical conductivities combined with five soil water contents in PVC columns. The models allowed a reasonable relationship among θ, CEa e CEw with better performance of de RHOADES et al. (1976) e de VOGELER et al. (1996 models for the soils 1 and 2, respectively.

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Section: Resultsunclassified

Section: Introductionunclassified

Estimativa da condutividade elétrica da solução do solo a partir do teor de água e da condutividade elétrica aparente do solo

Santana¹,

Coelho

Silva³

et al. 2006

Eng. Agríc.

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“…8 to obtain correct moisture readings in saline soil requires the information of soil electrical conductivity. This can be achieved either by a direct measurement using salinity sensors or estimated from a TDR wave trace (Dalton et al 1984;Topp et al 1988). Nevertheless, Figs.…”

Section: The Logarithm Calibrationmentioning

confidence: 99%

The effect of soil electrical conductivity on moisture determination using time-domain reflectometry in sandy soil

Sun¹,

Young²,

McFarlane³

et al. 2000

Can. J. Soil. Sci.

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The effect of soil electrical conductivity on moisture determination using time-domain reflectometry in sandy soil. Can. J. Soil Sci. 80: [13][14][15][16][17][18][19][20][21][22]. A series of laboratory experiments was conducted, in order to systematically explore the effect of soil electrical conductivity on soil moisture determination using time domain reflectometry (TDR). A Moisture Point MP-917 soil moisture instrument (E.S.I. Environmental Sensors Inc., Victoria, BC, Canada) was used to measure propagation time (time delay) of a step function along a probe imbedded in fine sand with different moisture and salinity. The volumetric soil water content was independently determined using a balance. With the help of the diode-switching technique, MP-917 could detect the reflection from the end of the probe as the electrical conductivity of saturated soil extract (EC e ) increased to 15.29 dS m -1 . However, the relationship between volumetric soil water content and propagation time expressed as T/T air (the ratio of propagation time in soil to that in air over the same distance) deviated from a linear relationship as the conductivity exceeded 3.72 dS m -1 . At the same water content, the time delay in a saline soil was longer than that in a non-saline soil. This leads to an over-estimation of volumetric soil water content when the linear calibration was applied. A logarithmic relationship between volumetric soil water content and T/T air has been developed and this relation includes soil electrical conductivity as a parameter. With this new calibration, it is possible to precisely determine the volumetric water content of highly saline soil using TDR. A l'aide de la technique brevetée MoisturePoint utilisant des rupteurs à diodes, MP-917 pouvait détecter la réflexion à la fin de la sonde, jusqu'à un niveau de conductivité électrique de 15.29 dS m -1 . Cependant, la relation entre humidité volumétrique et temps de propagation (exprimé sous la forme de T/T air : le rapport du temps de propagation dans le sol sur le temps de propagation dans l'air, pour la même distance et le même signal) s'écartait d'une relation linéaire pour les valeurs de conductivité supérieures à 3.72 dS m -1 . A teneur en humidité égale, le temps de propagation dans une eau saline était plus long que dans une eau non saline. En conséquence, l'humidité volumétrique était sur-estimée quand l'équation linéaire habituelle était appliquée. Une relation logarithmique entre teneur en eau et T/Tair a été établie, et cette relation varie avec la conductivité électrique. Avec cette nouvelle calibration, il est possible de déterminer avec précision l'humidité volumétrique de sols relativement salins par la méthode de TDR. Mots clés:Refléctométrie en Domaine Temporel, temps de propagation, conductivité electrique apparente (σ), humidité volumétrique (θ), permittivité relative ou constante, diélectrique (ε r ), vitesse de propagation V p Time-domain reflectometry has been used to measure volumetric water content of soil and other porous materials since 19...

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“…Time domain reflectometry (TDR) measures both the water content and the EC in approximately the same volume of porous medium [Dalton et al, 1984;Toppet al, 1988]. Standard TDR probes comprise two or three parallel metal rods.…”

Section: Introductionmentioning

confidence: 99%

The dependence of the electrical conductivity measured by time domain reflectometry on the water content of a sand

Ferré¹,

Redman²,

Rudolph³

et al. 1998

Water Resources Research

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Abstract. We present paired measurements of the water content and electrical conductivity collected in a laboratory column packed with a homogeneous, clean sand over a wide range of water content and pore water electrical conductivity (EC) conditions. The EC was determined using the method of Nadler et al. [1991] from waveforms collected with two-rod time domain reflectometry (TDR) probes with and without baluns and with three-rod probes without baluns. Following Heimovaara et al. [1995], we calibrated the probes in saline solutions to account for the series resistance of the cable and connectors. The calibrated EC shows a nonlinear dependence on the water content that is well described by a simple power relationship [Archie, 1942]. Recognizing that calibration in saline solutions is impractical for some TDR probes, we demonstrate that the EC response can be calibrated directly using the results of drainage events, incorporating only a separate calibration of the cable resistance. None of the probe designs shows any clear advantage for EC measurement.

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Time-Domain Reflectometry: Simultaneous Measurement of Soil Water Content and Electrical Conductivity with a Single Probe

Cited by 348 publications

References 4 publications

Estimativa da condutividade elétrica da solução do solo a partir do teor de água e da condutividade elétrica aparente do solo

Estimativa da condutividade elétrica da solução do solo a partir do teor de água e da condutividade elétrica aparente do solo

The effect of soil electrical conductivity on moisture determination using time-domain reflectometry in sandy soil

The dependence of the electrical conductivity measured by time domain reflectometry on the water content of a sand

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