ekS - Instytut Agrofizyki im. Bohdana DobrzaÅskiego PAN w Lublinie ...
ekS - Instytut Agrofizyki im. Bohdana DobrzaÅskiego PAN w Lublinie ...
ekS - Instytut Agrofizyki im. Bohdana DobrzaÅskiego PAN w Lublinie ...
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Notice that at C s = 0, ie when distilled water was used to moisten the soil, the<br />
salinity index possesses a certain baseline magnitude, X si , which is assumed to<br />
result from initial salinity, C si , of water, coming from residual soluble salts<br />
present in the soil. Even if distilled water, having practically zero conductivity, is<br />
used as the input solution, X s remains greater than zero. This seems to be because<br />
the matrix of any soil possesses some soluble components, such as residual salts,<br />
carbonates, silica, etc., which can contribute to the initial conductivity of the soil<br />
water extract (ie distilled water as the input solution). Therefore electrical<br />
conductivity of soil water defined as the soil salinity, EC w , is always greater than<br />
zero.<br />
3.3.3. Summary<br />
Direct calculation of bulk electrical conductivity of the soil from attenuation<br />
of the electromagnetic pulse leads to significant error.<br />
The TDR attenuation-based method for the determination of the soil bulk<br />
electrical conductivity can be applied after fitting an appropriate correction to the<br />
EC a-4p (EC a-TDR ) relationship according to the polynomial from Fig. 5.<br />
Salinity index, defined as the derivative of bulk electrical conductivity to bulk<br />
electrical permittivity, which can be determined s<strong>im</strong>ultaneously by TDR<br />
measurements, can be applied as a moisture-independent electrical variable to<br />
express relative changes in the soil salinity without entailing any calibration.<br />
3.4. Choice of frequency of the electric field in dielectric measurement of<br />
soil water content in saline soils<br />
Water concentration in soil (soil water content) and soil temperature are the<br />
quantities of strong temporal and spatial variability, while the concentration of<br />
solid phase (soil density) as well as the density of its elements (particle density) is<br />
practically stable.<br />
Changes of electrical capacity of a capacitor with soil as the dielectric are<br />
attributed to the soil water content changes because the dielectric constant of<br />
water (equal to 81 at 18 ºC) dominates the dielectric constant of soil solid phase<br />
(equal to 4 ÷ 5) and air (equal to 1). Considering above, the electric measurement<br />
of soil water content is done on the base of the correlated dielectric constant<br />
(Gardner et al. [32], Malicki [51], Malicki and Skierucha [59], White et al. [101]).<br />
Such a solution to the problem is not ideal. The presence of ions in the “soil<br />
water” causes the conduction electric current. Therefore soil has dual nature.<br />
S<strong>im</strong>ultaneously it possesses the properties of an insulator characterized by the<br />
dielectric constant of water, soil solid phase elements and air, as well as a<br />
conductor characterized by the electrical conductivity of an electrolyte (it is<br />
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