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Determination of soil pore water salinity using an FDR sensor working at various frequencies up to 500 MHz.

Wilczek A, Szypłowska A, Skierucha W, Cieśla J, Pichler V, Janik G - Sensors (Basel) (2012)

Bottom Line: The soil salinity status was determined using the salinity index, defined as a partial derivative of the soil bulk electrical conductivity with respect to the real part of the soil complex dielectric permittivity.For the five sandy mineral soils that have been tested, the relationship between bulk electrical conductivity and the real part of dielectric permittivity is essentially linear.As a result, the salinity index method applied for FDR measurements may be adapted to field use after examination of loam and clayey soils.

View Article: PubMed Central - PubMed

Affiliation: Institute of Agrophysics, Polish Academy of Sciences, ul. Doświadczalna 4, 20-290 Lublin, Poland. a.wilczek@ipan.lublin.pl

ABSTRACT
This paper presents the application of a frequency-domain reflectometry (FDR) sensor designed for soil salinity assessment of sandy mineral soils in a wide range of soil moisture and bulk electrical conductivity, through the determination of soil complex dielectric permittivity spectra in the frequency range 10-500 MHz. The real part of dielectric permittivity was assessed from the 380-440 MHz, while the bulk electrical conductivity was calculated from the 165-325 MHz range. The FDR technique allows determination of bulk electrical conductivity from the imaginary part of the complex dielectric permittivity, without disregarding the dielectric losses. The soil salinity status was determined using the salinity index, defined as a partial derivative of the soil bulk electrical conductivity with respect to the real part of the soil complex dielectric permittivity. The salinity index method enables determining the soil water electrical conductivity value. For the five sandy mineral soils that have been tested, the relationship between bulk electrical conductivity and the real part of dielectric permittivity is essentially linear. As a result, the salinity index method applied for FDR measurements may be adapted to field use after examination of loam and clayey soils.

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Related in: MedlinePlus

On the left: bulk electrical conductivities of all measured soil samples vs. the real part of the dielectric permittivity. On the right: salinity index XS calculated as a slope of a linear Cb vs. ε′ relation, with respect to the conductivity of the moistening solutions Cs. Regression equations, R2 and standard errors of regressions are given on the plots.
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f3-sensors-12-10890: On the left: bulk electrical conductivities of all measured soil samples vs. the real part of the dielectric permittivity. On the right: salinity index XS calculated as a slope of a linear Cb vs. ε′ relation, with respect to the conductivity of the moistening solutions Cs. Regression equations, R2 and standard errors of regressions are given on the plots.

Mentions: In order to test the concept of salinity index introduced by Malicki and Walczak [7] with respect to the FDR measurements of the real and imaginary parts of the dielectric permittivity of soils, the electrical conductivity Cb of each sample versus the real part of dielectric permittivity ε′ = Re(ε*) was plotted for all moistening solutions and a straight line was fitted through each set of data points. The results are presented on the left panel of Figure 3. The regression equation, R2 and standard error of regression σ, defined as in the previous section, were presented on the graphs. For all points, error bars are present. The vertical error bars represent the standard error of determination of Cb. Taking into account these errors and high values of R2 (as presented on the graph), it transpires that for all tested samples the relations between Cb and ε′ are essentially linear. Thus, the salinity index defined as:(6)XS=∂Cb∂ɛ′is actually the slope of the fitted line in the Cb vs. ε′ graph and, for linear Cb vs. ε′ dependence, is independent of the water content. The difference between Equation (6) and Equation (1), which presents the salinity index defined for TDR measurements, is the use of the real part of the dielectric permittivity instead of the apparent dielectric permittivity. In addition, the electrical conductivity in Equation (6) was determined from the frequency spectrum of the imaginary part of the dielectric permittivity as described in Section 3.2, while in Equation (1) the quantity Cb actually denoted bulk (or apparent) electric conductivity determined from attenuation of the TDR pulse with the assumption that the dielectric loss εd = 0.


Determination of soil pore water salinity using an FDR sensor working at various frequencies up to 500 MHz.

Wilczek A, Szypłowska A, Skierucha W, Cieśla J, Pichler V, Janik G - Sensors (Basel) (2012)

On the left: bulk electrical conductivities of all measured soil samples vs. the real part of the dielectric permittivity. On the right: salinity index XS calculated as a slope of a linear Cb vs. ε′ relation, with respect to the conductivity of the moistening solutions Cs. Regression equations, R2 and standard errors of regressions are given on the plots.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472864&req=5

f3-sensors-12-10890: On the left: bulk electrical conductivities of all measured soil samples vs. the real part of the dielectric permittivity. On the right: salinity index XS calculated as a slope of a linear Cb vs. ε′ relation, with respect to the conductivity of the moistening solutions Cs. Regression equations, R2 and standard errors of regressions are given on the plots.
Mentions: In order to test the concept of salinity index introduced by Malicki and Walczak [7] with respect to the FDR measurements of the real and imaginary parts of the dielectric permittivity of soils, the electrical conductivity Cb of each sample versus the real part of dielectric permittivity ε′ = Re(ε*) was plotted for all moistening solutions and a straight line was fitted through each set of data points. The results are presented on the left panel of Figure 3. The regression equation, R2 and standard error of regression σ, defined as in the previous section, were presented on the graphs. For all points, error bars are present. The vertical error bars represent the standard error of determination of Cb. Taking into account these errors and high values of R2 (as presented on the graph), it transpires that for all tested samples the relations between Cb and ε′ are essentially linear. Thus, the salinity index defined as:(6)XS=∂Cb∂ɛ′is actually the slope of the fitted line in the Cb vs. ε′ graph and, for linear Cb vs. ε′ dependence, is independent of the water content. The difference between Equation (6) and Equation (1), which presents the salinity index defined for TDR measurements, is the use of the real part of the dielectric permittivity instead of the apparent dielectric permittivity. In addition, the electrical conductivity in Equation (6) was determined from the frequency spectrum of the imaginary part of the dielectric permittivity as described in Section 3.2, while in Equation (1) the quantity Cb actually denoted bulk (or apparent) electric conductivity determined from attenuation of the TDR pulse with the assumption that the dielectric loss εd = 0.

Bottom Line: The soil salinity status was determined using the salinity index, defined as a partial derivative of the soil bulk electrical conductivity with respect to the real part of the soil complex dielectric permittivity.For the five sandy mineral soils that have been tested, the relationship between bulk electrical conductivity and the real part of dielectric permittivity is essentially linear.As a result, the salinity index method applied for FDR measurements may be adapted to field use after examination of loam and clayey soils.

View Article: PubMed Central - PubMed

Affiliation: Institute of Agrophysics, Polish Academy of Sciences, ul. Doświadczalna 4, 20-290 Lublin, Poland. a.wilczek@ipan.lublin.pl

ABSTRACT
This paper presents the application of a frequency-domain reflectometry (FDR) sensor designed for soil salinity assessment of sandy mineral soils in a wide range of soil moisture and bulk electrical conductivity, through the determination of soil complex dielectric permittivity spectra in the frequency range 10-500 MHz. The real part of dielectric permittivity was assessed from the 380-440 MHz, while the bulk electrical conductivity was calculated from the 165-325 MHz range. The FDR technique allows determination of bulk electrical conductivity from the imaginary part of the complex dielectric permittivity, without disregarding the dielectric losses. The soil salinity status was determined using the salinity index, defined as a partial derivative of the soil bulk electrical conductivity with respect to the real part of the soil complex dielectric permittivity. The salinity index method enables determining the soil water electrical conductivity value. For the five sandy mineral soils that have been tested, the relationship between bulk electrical conductivity and the real part of dielectric permittivity is essentially linear. As a result, the salinity index method applied for FDR measurements may be adapted to field use after examination of loam and clayey soils.

Show MeSH
Related in: MedlinePlus