Evaluation of Time Domain Reflectrometry Device in Saline Clay and Sandy Soils

Document Type : Research Paper

Authors

Abstract

Measuring the precision quantity of soil moisture in agricultural science is very important.
Therefore, it is important to have accurate and fast measurement of soil water content, especially to
achieve soil characteristics by a non-invasiveness way. In recent years, application of time domain
reflectometry (TDR) as a well-known for measuring soil water and electrical conductivity in short
time has been common. The objective of this study was to evaluate the accuracy of the TDR probe
under laboratory conditions in clay and sandy soils at four soil salinity levels of 2, 6, 12 and 18 dS
m-1 which were packed in a PVC cylinder with 27 cm in diameter and 300 cm in length. The TDR
underestimated dielectric coefficient and volumetric moisture in heavy soil due to the effect of bound
water in heavy soil which reduced the time delay. Also soil dielectric coefficient increased with
increasing soil salinity, resulting in overestimation of the soil moisture. The result of soil salinity and
texture interaction showed that under high soil salinity levels (12 and 18 dS m-1) the estimated
moisture by the device was less than the volumetric method, whereas under low soil salinity it was
vice versa. This indicated that in high salinity level, the effect of clay caused the low estimation of
soil water content but in the low soil salinity level, electric conductivity would lead to over estimating
moisture content.

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Main Subjects


منابع مورد استفاده
  سالاری ا، 1384. بررسی اثر شوری بر واسنجی دستگاه TDR در مکش­های مختلف خاک. پایان­نامه کارشناسی ارشد در رشته آبیاری و زهکشی، دانشکده  مهندسی علوم آب، دانشگاه شهید چمران اهواز.
سلطانی محمدی ا، 1384. تأثیر بافت خاک روی کالیبراسیون TDR برای اندازه­گیری رطوبت در شرایط خاک­های خوزستان. پایان­نامه کارشناسی ارشد آبیاری و زهکشی، دانشکده مهندسی علوم آب، دانشگاه شهید چمران اهواز.
نامدارخجسته د، شرفا م، اسکندری ذ و فاضلی سنگانی م،1390.  تأثیر میزان رس و شوری خاک در رطوبت حجمی اندازه­گیری شده با انعکاس سنج زمانی. مجله پژوهش­های خاک، جلد25، شماره 2، صفحه­های 103تا 112.
Baumhardt RL, Lascano RJ and Evett SR, 2000. Soil material, temperature, and salinity effects on calibration of multisensor capacitance probes. Soil Science Society of America 64:1940-1946.
Cosh MH,Thomas J, Bindlish R, Famiglietti JS, Ryu D, 2005. Calibration of an impedance probe for estimation of surface soil water content over large regions. Journal of Hydrology 311: 49–58.
Gong YQ, sun Z, 2003. The effects of soil bulk density, clay content and temperature on soil water content measurement using time-domain reflectometry. Hydrological Processes 17: 3601–3614.
Hilhorst MA, Dirksen C, Kampers FW and Feddes RA, 2001. Dielectric relaxation of bound water versus soil matric pressure. Soil Science Society of America Journal 65: 311–314.
Hook WR and Livingston NJ, 1996. Errors in converting time domain reflectometry measurements of propagation velocity to estimates of soil water content. Soil Science Society of America Journal 60: 35-41.
Huang Q, Akinremi OO, Sri Rajan R and Bullock P, 2004. Laboratory and field evaluation of five soil water sensors. Canadian Journal of Soil Science 84: 431-438.
Jacobsen OH, Schjonning P, 1993. A laboratory calibration of time domain reflectometry for soil water measurement including effects of bulk density and texture. Journal of Hydrology 151: 147–157.
Pumpanen L and vesniemi H, 2005. Calibration of time domain reflectometry for forest soil humus layers. Boreal Environment Resource Journal 10: 589-595.
Rhoades JD, Manteghi NA, Shouse PJ and Alves WJ, 1989. Soil electrical conductivity and salinity: new formulations and calibrations. Soil Science Society of America Journal 53: 433–439.
Roth K, Schulin R, Fluhler H and Attinger W, 1990. Calibration of time domain reflectometry for water content measurement using a composite dielectric approach. Water Resource Research 26:2267-2273.
Sarani N, Afrasiab P, 2012. Effect of soil texture on moisture measurement accuracy with Theta probe ML2 in Sistan region. International Conference on Chemical, Ecology and Environmental Sciences (ICEES'2012) march 17-18, 2012 Bangkok.
Sun ZJ, Young GD, McFarlane R and Chambers BM, 2000. The effect of soil electrical conductivity on moisture determination using time domain- reflectometry in sandy soil. Canadian Journal of Soil Science 80: 1: 13–22.
Topp GC, Davis JL and Annan AP, 1980. Electromagnetic determination of soil water content: measurements in coaxial transmission lines. Water Resources Research 16: 574–582.
Topp GC, Zeglin S and White I, 2000. Impacts of real and imaginary components of relative permittivity on time domain reflectometry measurements in soil. Soil Science Society of America Journal 64: 1244–1252.