Abstract
This paper describes a technique for in situ-measurement of soil electrical conductivity using a four-electrode EC-probe. The study has been conducted in the field on a loam soil having a wide rang of salinily levels and a calibration curve has been prepared showing relationship between soil electrical conductivity (EC ) and bulk soil electrical conductivity ( ECb ) In addition a calibration curve showing relationship between apparent solution conductivity (ECu ) and actual EC of synthetic 'aline solutions has been repor. tcd. The correlation found in both the above cases are hroly significant and results arc reproducible.
INTRODUCTION
The electrical conductivity of saturation soil extract (Fee ) is a conven-tional measure of soil salinity, though the ideal method of appraising the salinity consists of measuring the salt concentration of an extract obtained at field water content (Bower & it ox, 1965). In the later method, the difficulty of obtaining soil extract limits its routine use. The standard laboratory technique in which soil samples are wetted to a saturated paste has some demerits (McNeal et ai., 1970; Oster & McNeal, 1971; Ulrich. & Khanna 1972). The MOSE important may be the effect of dilution upon the EC of the extract, a disruption of gaseous equilibria notably COrcarbonate system occurs which exerts a significant effect on the EC (`rear& Johnston,1929). Moreover, the increased solubility of some ions, like bicarbonate or borate, may cause an over-estimation of their concentration in soil.
To overcome these problems, the immiscible displacement (1D) technique was developed by Mubarak & Olsen (1977). With this method soil samples are centrifuged in the presence of a suitable organic solvent which displaces the soil solution. However, this method is also lengthy. In addition, these meth-
