Soil salinity related to physical soil characteristics and irrigation management in four Mediterranean irrigation districts

▶ EMI surveys and the EC a–EC e calibration equations satisfactorily appraised irrigation–district soil salinity. ▶ The calibration equations were site-specific, and must be developed for the particular soils of interest. ▶ The EC a profiles were generally normal or uniform, showing that the soils were subject to salt leaching. ▶ Soil salinity, preponderantly affected by irrigation water salinity and irrigation efficiency, was low to moderate in the four irrigation districts. ▶ Drainage water salinity varied between 9.0 and 1.4 dS m −1 and was related to soil salinity and irrigation efficiency. ▶ The control of off-site salt loads requires the reduction of actual high drainage volumes in two of the studied districts. Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the Mediterranean basin. The objective of this work was to quantify soil salinity through electromagnetic induction (EMI) techniques and relate it to the physical characteristics and irrigation management of four Mediterranean irrigation districts located in Morocco, Spain, Tunisia and Turkey. The volume and salinity of the main water inputs (irrigation and precipitation) and outputs (crop evapotranspiration and drainage) were measured or estimated in each district. Soil salinity (EC e) maps were obtained through electromagnetic induction surveys (EC a readings) and district-specific EC a–EC e calibrations. Gravimetric soil water content (WC) and soil saturation percentage (SP) were also measured in the soil calibration samples. The EC a–EC e calibration equations were highly significant ( P < 0.001) in all districts. EC a was not significantly correlated ( P > 0.1) with WC, and was only significantly correlated ( P < 0.1) with soil texture (estimated by SP) in Spain. Hence, EC a mainly depended upon EC e, so that the maps developed could be used effectively to assess soil salinity and its spatial variability. The surface-weighted average EC e values were low to moderate, and ranked the districts in the order: Tunisia (3.4 dS m −1) > Morocco (2.2 dS m −1) > Spain (1.4 dS m −1) > Turkey (0.45 dS m −1). Soil salinity was mainly affected by irrigation water salinity and irrigation efficiency. Drainage water salinity at the exit of each district was mostly affected by soil salinity and irrigation efficiency, with values very high in Tunisia (9.0 dS m −1), high in Spain (4.6 dS m −1), moderate in Morocco (estimated at 2.6 dS m −1), and low in Turkey (1.4 dS