Soil salinity assessment using electromagnetic induction method in a semi-arid environment — a case study in Tunisia

Salinization has been recognized as one of the major cause of soil degradation in Mediterranean area leading to land desertification. Globally, 25 to 30% of irrigated areas are affected by salinization. In Tunisia, secondary salinization affects more than half of irrigated land. In the current study, soil salinity was estimated and mapped based on an integrated approach that combines the ESAP software and EM38 electromagnetic inductance sensor. The method was tested in the semi-arid Draa-Tammar perimeter irrigated with treated wastewater (240 ha, in Kairouan region, Tunisia) where the soil profile was sampled at 0.2 m depth intervals and EM38 readings were collected in 2014. An appropriate calibration equation between EM38 sensor readings and soil saturated extract conductivity (ln ECe) was obtained based on a depth-specific MLR (multiple linear regression) models with an average R2 of about 0.78 (0.6 ≤ R2 ≤ 0.8) and a root mean square error (RMSE) equal to 0.13 mS m−1 (0.11 mS m−1 < RMSE < 0.18 mS m−1), for cumulative soil depth intervals (0–0.4 m, 0–0.6 m, 0–0.8 m, 0–1.0 m, and 0–1.5 m). Furthermore, soil salinity maps showed that the salinity levels ranged from high to very high for the different cumulative soil depths. In general, soil salinity increased with depth. Inefficient natural soil drainage system is the main reason for soil salinization in the study area. The new method, used in the current study for evaluating salt accumulation, presents a potential easy-to-use tool that can improve salinity management by decision-makers for water and soil protection.