Soil texture and salinity effects on calibration of TDR300 dielectric moisture sensor
George Kargas A C , Nikolaos Ntoulas B and Panayiotis A. Nektarios BA Laboratory of Agricultural Hydraulic, Department of Natural Resources Management and Agricultural Engineering, Division of Water Resources Management, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece.
B Laboratory of Floriculture and Landscape Architecture, Department of Crop Science, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece.
C Corresponding author. Email: kargas@aua.gr
Soil Research 51(4) 330-340 https://doi.org/10.1071/SR13009
Submitted: 8 January 2013 Accepted: 11 June 2013 Published: 15 August 2013
Abstract
Newly developed sensors have simplified real-time determination of soil water content (θm). Although the TDR300 is one of the most recent dielectric sensors, little is known with regard to the accuracy and dependency of its measurements of soil type and other environmental factors. In this study, the performance of TDR300 was investigated using liquids of known dielectric properties and a set of porous media with textures ranging from sandy to clayey. The experiments were conducted in the laboratory by mixing different amounts of water with each soil to obtain a sufficient range of soil water contents. For sand, the calculated permittivity values (εr) correlated adequately with Topp’s equation derived for time domain reflectometry. However, for the remaining inorganic porous media, εr values were overestimated compared with those resulting from Topp’s equation, especially for water contents exceeding 0.2 cm3/cm3. The results suggested that the relationship between θm and √εr was strongly linear (0.953< r2 <0.998). The most accurate results were provided by soil-specific calibration equations, which were obtained by the multi-point calibration equation. However, two-point calibration equations determined water content in all tested soils reasonably well, except for clay soil. A linear regression equation was developed that correlated the slope of the relationship θm–√εr with bulk soil electrical conductivity (EC). The regression slope was influenced more by soil EC than by soil texture. Also, TDR300 response was investigated in bi-layered systems (liquid–air and saturated porous media–air). In a bi-layered sensing volume characterised by strongly contrasting dielectric values, the appropriate bulk permittivity values for water and loam soil were determined by arithmetic rather than refractive index averaging, while for butanol and sand these values remained somewhere between the two averaging schemes, indicating that the upward infiltration calibration technique is inappropriate for the TDR300 sensor. Soil solute EC, as determined by measurements conducted in liquids and sand, significantly affected permittivity values at much lower levels than the limit of EC <2 dS/m, as suggested by the manufacturer. However, the relationship θm–√εr remained linear up to EC 2 dS/m, which corresponded to a bulk soil EC value of 0.6 dS/m. By contrast, for EC values >2 dS/m, the relationship θm–√εr was not linear, and, thus the TDR300 device calibration became increasingly difficult. Therefore, rather than operating as a time domain device, TDR300 operates as a water content reflectometer type device.
Additional keywords: electrical conductivity, dielectric sensors, permittivity.
References
Anisko T, NeSmith DS, Lindstrom OM (1994) Time domain reflectometry for measuring water content of organic growing media in containers. HortScience 29, 1511–1513.Campbell Scientific Inc. (1996) ‘CS615 water content reflectometer instruction manual.’ Campbell Scientific Inc.: Logan, UT)
Chan CY, Knight RJ (1999) Determining water content and saturation from dielectric measurements in layered materials. Water Resources Research 35, 85–93.
| Determining water content and saturation from dielectric measurements in layered materials.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1MXit1Wntrk%3D&md5=879bc32cc9f1f6c9f64bf797a34a6ffbCAS |
Chan CY, Knight RJ (2001) Laboratory measurements of electromagnetic wave velocity in layered sands. Water Resources Research 37, 1099–1105.
| Laboratory measurements of electromagnetic wave velocity in layered sands.Crossref | GoogleScholarGoogle Scholar |
Da Silva FF, Wallach R, Polak A, Chen Y (1998) Measuring water content of soil substitutes with time domain reflectometry (TDR). Journal of the American Society for Horticultural Science 123, 734–737.
Delta-T Devices Ltd (1999) ‘ThetaProbe ML2x User manual.’. (Delta-T Devices Ltd: Cambridge, UK)
Delta-T Devices Ltd (2005) ‘User manual for the WET sensor (type WET-2).’ (Delta-T Devices Ltd: Cambridge, UK) Available at: www.delta-t.co.uk
Evett SR, Parkin GW (2005) Advances in soil water sensing: The continuing maturation of technology and theory. Vadose Zone Journal 4, 986–991.
| Advances in soil water sensing: The continuing maturation of technology and theory.Crossref | GoogleScholarGoogle Scholar |
Evett SR, Tolk JA, Howell TA (2005) Time domain reflectometry laboratory calibration in travel time, bulk electrical conductivity, and effective frequency. Vadose Zone Journal 4, 1020–1029.
| Time domain reflectometry laboratory calibration in travel time, bulk electrical conductivity, and effective frequency.Crossref | GoogleScholarGoogle Scholar |
Evett SR, Tolk JA, Howell TA (2006) Soil profile water content determination: Sensor accuracy, axial response, calibration, temperature dependence, and precision. Vadose Zone Journal 5, 894–907.
| Soil profile water content determination: Sensor accuracy, axial response, calibration, temperature dependence, and precision.Crossref | GoogleScholarGoogle Scholar |
Ferre A, Topp GC (2002) ‘Methods of soil analysis. Part 4. Physical methods.’ Soil Science Society of America Book Series, Vol. 5. pp. 434–446. (Soil Science Society of America Inc.: Madison, WI)
Heimovaara TJ (1994) Frequency domain analysis of ttime domain reflectometry waveforms: 1. Measurement of the complex dielectric permittivity of soils. Water Resources Research 30, 189–199.
| Frequency domain analysis of ttime domain reflectometry waveforms: 1. Measurement of the complex dielectric permittivity of soils.Crossref | GoogleScholarGoogle Scholar |
IMKO (2000) ‘Operating manual TRIME-FM.’ (IMKO Micromodultechnik GmbH: Ettlingen, Germany)
Jones SB, Blonquist JM, Robinson DA, Rasmussen VP, Or D (2005) Standardizing characterization of electromagnetic water content sensors: Part 1. Methodology. Vadose Zone Journal 4, 1048–1058.
| Standardizing characterization of electromagnetic water content sensors: Part 1. Methodology.Crossref | GoogleScholarGoogle Scholar |
Kargas G, Kerkides P (2008) Water content determination in mineral and organic porous media by ML2 theta probe. Irrigation and Drainage 57, 435–449.
| Water content determination in mineral and organic porous media by ML2 theta probe.Crossref | GoogleScholarGoogle Scholar |
Kargas G, Kerkides P (2009) Performance of the THETA PROBE ML2 in the presence of nonuniform soil water profiles. Soil & Tillage Research 103, 425–432.
| Performance of the THETA PROBE ML2 in the presence of nonuniform soil water profiles.Crossref | GoogleScholarGoogle Scholar |
Kargas G, Soulis K (2012) Performance analysis and calibration of a new low-cost capacitance soil moisture sensor. Journal of Irrigation and Drainage Engineering 138, 632–641.
| Performance analysis and calibration of a new low-cost capacitance soil moisture sensor.Crossref | GoogleScholarGoogle Scholar |
Kargas G, Kerkides P, Seyfried M, Sgoumbopoulou A (2011) WET sensor performance in organic and inorganic media with heterogeneous moisture distribution. Soil Science Society of America Journal 75, 1244–1252.
| WET sensor performance in organic and inorganic media with heterogeneous moisture distribution.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXhtVeisrnM&md5=24209e3b465f32fb731f0fecad3a77deCAS |
Kelleners T, Seyfried M, Blonquist J, Bilskie J, Chandler D (2005) Improved interpretation of water content reflectometer measurements in soils. Soil Science Society of America Journal 69, 1684–1690.
| Improved interpretation of water content reflectometer measurements in soils.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXht1WrurvK&md5=57e5870744909f53fc41c9c6084ac93cCAS |
Kelleners T, Paige GB, Gray ST (2009) Measurement of the dielectric properties of Wyoming soils using electromagnetic sensors. Soil Science Society of America Journal 73, 1626–1637.
| Measurement of the dielectric properties of Wyoming soils using electromagnetic sensors.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXhtFSqu7rO&md5=7ee5aceee9f27f2bfca93bac8a2bb92cCAS |
Kizito F, Campbell CS, Campbell GS, Cobos DR, Teare BL, Carter B, Hopmans JW (2008) Frequency, electrical conductivity and temperature analysis of a low-cost capactitance soil moisture sensor. Journal of Hydrology 352, 367–378.
| Frequency, electrical conductivity and temperature analysis of a low-cost capactitance soil moisture sensor.Crossref | GoogleScholarGoogle Scholar |
Ledieu J, de Ridder P, de Clerck P, Dautrebande S (1986) A method of measuring soil moisture by time-domain reflectometry. Journal of Hydrology 88, 319–328.
| A method of measuring soil moisture by time-domain reflectometry.Crossref | GoogleScholarGoogle Scholar |
Logsdon SD (2009) CS616 calibration: field versus laboratory. Soil Science Society of America Journal 73, 1–6.
| CS616 calibration: field versus laboratory.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXitVarsr8%3D&md5=4f7339ad0e0c35bf1848a8d17a6632b7CAS |
Regalado C, Ritter A, Rodriguez-Gonzalez RM (2007) Performance of the commercial WET capacitance sensor as compared with time domain reflectometry in volcanic soils. Vadose Zone Journal 6, 244–254.
| Performance of the commercial WET capacitance sensor as compared with time domain reflectometry in volcanic soils.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXltVygu7s%3D&md5=93c71192b61270999bc7ff923d8e56b4CAS |
Robinson DA (2001) Comments on “Field calibration of a capacitance water content probe in fine sand soils”. Soil Science Society of America Journal 65, 1570
| Comments on “Field calibration of a capacitance water content probe in fine sand soils”.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD38Xptlal&md5=774bb4f0c893330049b68945f789695fCAS |
Robinson DA, Jones SB, Blonquist JM, Friedman SP (2005) A physical derived water content/permittivity calibration model for coarse—textured layered soils. Soil Science Society of America Journal 69, 1372–1378.
| A physical derived water content/permittivity calibration model for coarse—textured layered soils.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXhtVWis7vJ&md5=fdcc4db7268f493da6d778e3af631293CAS |
Roth C, Malicki M, Plagge R (1992) Empirical evaluation of the relationship between soil dielectric constant and volumetric water content as the basis for calibrating soil moisture measurements by TDR. European Journal of Soil Science 43, 1–13.
| Empirical evaluation of the relationship between soil dielectric constant and volumetric water content as the basis for calibrating soil moisture measurements by TDR.Crossref | GoogleScholarGoogle Scholar |
Saarenketo T (1998) Electrical properties of water in clay and silty soils. Journal of Applied Geophysics 40, 73–88.
| Electrical properties of water in clay and silty soils.Crossref | GoogleScholarGoogle Scholar |
Schaap MG, Robinson DA, Friedman SP, Lazar A (2003) Measurement and modeling of the TDR signal propagation through layered dielectric media. Soil Science Society of America Journal 67, 1113–1121.
| Measurement and modeling of the TDR signal propagation through layered dielectric media.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXlslCqtLg%3D&md5=d9429d909fcb3e1834b991d33d28b20dCAS |
Seyfried MS, Murdock MD (2001) Response of a new soil water sensor to variable soil, water content and temperature. Soil Science Society of America Journal 65, 28–34.
| Response of a new soil water sensor to variable soil, water content and temperature.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXhvFSlt7g%3D&md5=433e0702e8933eab9ea7f389c27be283CAS |
Seyfried MS, Murdock MD (2004) Measurement of soil water content with a 50-MHz soil dielectric sensor. Soil Science Society of America Journal 68, 394–403.
| Measurement of soil water content with a 50-MHz soil dielectric sensor.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2cXitV2ntrc%3D&md5=d750bdba8d135d6d2cda79311ceed11fCAS |
Seyfried MS, Grant LE, Du E, Humes K (2005) Dielectric loss and calibration of the hydra probe soil water sensor. Vadose Zone Journal 4, 1070–1079.
| Dielectric loss and calibration of the hydra probe soil water sensor.Crossref | GoogleScholarGoogle Scholar |
Spectrum Technologies, Inc. (2009) ‘Field Scout TDR300, Product manual.’ (Spectrum Technologies Inc.: Plainfield, IL)
Topp GC, Reynolds WD (1998) Time domain reflectometry: a seminal technique for measuring mass and energy in soil. Soil & Tillage Research 47, 125–132.
| Time domain reflectometry: a seminal technique for measuring mass and energy in soil.Crossref | GoogleScholarGoogle Scholar |
Topp GC, Davis JL, Annan AP (1980) Electromagnetic determination of soil water content: Measurements in coaxial transmission lines. Water Resources Research 16, 574–582.
| Electromagnetic determination of soil water content: Measurements in coaxial transmission lines.Crossref | GoogleScholarGoogle Scholar |
Topp GC, Davis JL, Annan AP (1982) Electromagnetic determination of soil water content using TDR: I. Applications of wetting fronts and steep gradients. Soil Science Society of America Journal 46, 672–678.
| Electromagnetic determination of soil water content using TDR: I. Applications of wetting fronts and steep gradients.Crossref | GoogleScholarGoogle Scholar |
Young MH, Fleming JB, Wierenga PJ, Warrick AW (1997) Rabid laboratory calibration of time domain reflectometry using upward infiltration. Soil Science Society of America Journal 61, 707–712.
| Rabid laboratory calibration of time domain reflectometry using upward infiltration.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2sXjvVOqsr4%3D&md5=5676edc13d55429694e9d00fad84ebdaCAS |
