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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property is their ionic nature. The ability to conduct electrical charge by ions<br />
present in the soil water is the reason that the soil conducts current. Therefore, the<br />
electrical measurement of soil salinity should be based on the measurement of its<br />
electrical conductivity.<br />
Soil salinity is expressed by a total concentration of salts in the soil, and<br />
practically their ions in the “soil water”. Due to technical reasons connected with<br />
the determination of such a defined salinity, its measure by indirect quantity –<br />
electrical conductivity of the soil extract, named as a soil electrolyte, which is<br />
taken from the soil after its saturation by distilled water (Marshall and Holmes<br />
[63]). This procedure proposed by US Salinity Laboratory [94], has been<br />
recognized as standard. However this method cannot be used in in situ<br />
measurements and also in automatic monitoring systems of soil salinity.<br />
The in situ and non-distructive alternative is the measurement of the soil<br />
apparent electrical conductivity, EC a , as the basis for determination of the<br />
electrical conductivity of the soil electrolyte, EC w (Rhoades et al. [76], Nadler<br />
[70]). For this purpose a four-electrode method is often used (Kirkham and Taylor<br />
[46]; Gupta and Hanks [35]). It consists in the measurement of the voltage drop<br />
along the current, which is forced by other, in relation to measured, pair of supply<br />
electrodes. Such a solution enables to avoid disturbances caused by<br />
electrochemical polarization of at the interface electrode-electrolyte. However the<br />
EC a depends also on soil water content, θ, and to determine EC w it is necessary to<br />
measure EC a and θ, s<strong>im</strong>ultaneously. Rhoades et al. [76] presented a model<br />
relating EC a , EC w and θ as follows:<br />
( a + a ) <strong>ekS</strong><br />
ekG = ekEθ 0θ 1 +<br />
(1)<br />
where: a 0 and a 1 are empirical indexes different for various soils and profile<br />
layers of the given soil, EC s , is the electrical conductivity of the soil solid phase<br />
dependent on the concentration of cations adsorbed on the surface of clay<br />
minerals and the presence of ferrite minerals.<br />
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