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.
The observed dielectric spectrum of ripe apples in the last period of shelf-life was analyzed using a multipole dielectric relaxation model, which assumes three active relaxation processes: primary α-process (water relaxation) and two secondary processes caused by solid-water-ion interactions α’ (bound water relaxations), as well as β’ (Maxwell-Wagner effect). The performance of two designs of the dielectric probe was compared: a classical coaxial open-ended probe (OE probe) and an open-ended probe with a prolonged central conductor in a form of an antenna (OE-A-probe). The OE-A probe increases the measurement volume and consequently extends the range of applications to other materials, like granulated agricultural products, soils, or liquid suspensions. However, its measurement frequency range is limited as compared to the OE probe because, above 1.5 GHz, the probe with the antenna generates higher propagation modes and the applied calibrations and calculations are not sufficient. It was shown that data from measurements using the OE-A probe gave slightly stronger correlations with apples’ quality parameters than using the typical OE probe. Additionally, we have compared twelve multipole fitting models with different combinations of poles (eight three-pole and four two-pole models). It was shown that the best fit is obtained using a two-pole model for data collected for the OE-A probe and a three-pole model for the OE probe, using only Cole-Cole poles in both cases.
A b s t r a c t. The objective of this paper is to present a method for determining diurnal distribution of the intensity of effective non rainfall water flux. It was found that the application of TDR technique for the determination of diurnal dynamics of effective non rainfall water flux requires temperature correction of sensed volumetric moisture contents. Without temperature correction the error of estimated non rainfall water flux can be as much as 26%. In addition, the effect of temperature changes on the soil surface was determined in 0.5, 1, 2, 3, 4, and 5 hours periods. It was found that the intensity of effective non rainfall water flux was determined to the greatest extent by the rate of temperature drop during the period of 3 h preceding the non rainfall water flux determination. The agreement of non rainfall water flux calculated with the method proposed and that obtained by the collector was better for dew than for hoarfrost periods.K e y w o r d s: TDR technique, effective non rainfall water flux, impermeable barrier INTRODUCTIONKnowledge of the physical processes that affect the efficiency of water infiltration into the surface horizon of soil is important in the formulation of input data for mathematical models describing the movement of water (Jacobs et al., 2002;Reinhard and Reinhard, 2005). Knowledge of the run of processes of that type is important, as water is a source of nutrients for animals and plants (Kidron, 2005;Kolev et al., 2012). In such considerations one should take into account the role of dew, hoarfrost, condenzation of water vapour contained in the soil air, and adsorption of water from the atmosphere. In regions with arid climate the effect of those processes on the water balance of the top horizon of soil may be greater than that of atmospheric precipitation (Agam and Berliner, 2006). As an example, the contribution of dew and hoarfrost in the annual water balance of the surface horizon of soil in a semi-desert area situated in Nevada, USA, amounts to 31 mm year -1 (Malek et al., 1999). With regard to the phenomena considered here, the contemporary methods for the determination of the diurnal dynamics of the intensity of water infiltration can be classified in four groups: methods consisting in measurements with the use of dew and hoarfrost collectors, lysimetric methods, models employing empirical mathematical formulae, and phenomenological models. The first group includes eg the Duvdevani dew gauge, the Cloth Plate Method and the Hiltner Dew Balance. The Duvdevani dew gauge is one of the first devices for the measurement of the dew balance (Duvdevani, 1947). The measured volume of dew deposit should be treated as an estimate and it cannot be compared with absolute values. The Cloth Plate Method is also a method in which the measurement is taken manually. The apparatus is equipped with a glass plate with dimensions of 10 x 10 x 0.2 cm, to the centre of which highly absorbing synthetic fabrics are attached, with dimensions of 6 x 6 cm (Kidron, 1998). In their study, Zangvil ...
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