Determination of the salinity of an irrigated soil by electromagnetic conductvity.

A prerequisite for the control of salinity in soils is the determination of the salinity of the upper first metre of the soil with the greatest accuracy. This is commonly done from saturated paste extracts but on too small a volume and too restricted a number of samples. This must be done without modification of the soil structure and on a sufficiently narrow grid. Electromagnetic conductivity meters of Slingram type are convenient to indirectly determine the salinity by measurement of electrical conductivity. However the depth of investigation commonly exceeds the first metre and the saturated salted zone beneath significantly influences the results. A theoretical study together with a complete calibration test on the border of Chott El Guettar (Tunisia) confirms that short coil separation (60 cm) increases the sensitivity of the apparatus to conductivity variations in the first metre of soil.