Electromagnetic induction prediction of soil salinity and groundwater properties in a Tunisian Saharan oasis

Electromagnetic induction measurements (EM) were taken in a saline gypsiferous soil of the Saharan-climate Fatnassa oasis (Tunisia) to predict the electrical conductivity of saturated soil extract (ECe) and shallow groundwater properties (depth, Dgw, and electrical conductivity, ECgw) using various models. The soil profile was sampled at 0.2 m depth intervals to 1.2 m for physical and chemical analysis. The best input to predict the log-transformed soil salinity (lnECe) in surface (0-0.2 m) soil was the EMh/EMv ratio. For the 0-0.6 m soil depth interval, the performance of multiple linear regression (MLR) models to predict lnECe was weaker using data collected over various seasons and years (R-a(2) = 0.66 and MSE = 0.083 dS m(-1)) as compared to those collected during the same period (R-a(2) = 0.97, MSE = 0.007 dS m(-1)). For similar seasonal conditions, for the Dgw-EMv relationship, R-2 was 0.88 and the MSE was 0.02 m for Dgw prediction. For a validation subset, the R-2 was 0.85 and the MSE was 0.03 m. Soil salinity was predicted more accurately when groundwater properties were used instead of soil moisture with EM variables as input in the MLR.