Effects of Irrigating with Saline Water on Soil Salinization (Eastern Tunisia)

This study was conducted in the irrigation zone of ‘Zelba’, located in the Region of Mahdia (Eastern Tunisia). The main objective of the study is to investigate the effect of irrigating with saline water on soil properties. Soil sampling was carried out to a depth of 150 cm, with samples being collected from 20 plots. Two soil profiles were drilled in each plot. The first profile was taken from an irrigated area, where water salinity is around 7 mS/cm. The second profile was taken from a non-irrigated area. Salinity maps were developed using a kriging method. Soil characterization revealed that the soil is of a deep isohumic type with silty to silty-clay texture. The analysis results showed the presence of a high sodicity level. In fact, soil adsorption ratio and exchangeable sodium percentage exceeded the acceptable thresholds, being 10 and 15%, respectively. Salinity mapping of five soil layers showed little change of soil salinity for all the examined 20 plots. Nevertheless, the highest salinity levels occurred in the deepest layers of the southwestern part of the studied irrigation zone. For instance, the electric conductivity was shown to vary between 1.5 and 1.7 mS/cm, in the irrigated profile, while it varied between 1.5 and 2.6 mS/cm, in the non-irrigated profile. The low salinity observed in the north of the study area could be explained by the fact that this part is closer to the water well. Moreover, compared to irrigated zones, the non-irrigated areas are characterized by a higher level of salinity. Irrigation lowered the salinity of the irrigated area through salts leaching. Monitoring of soil salinity and sodicity over time proved an enrichment of soil by salts and exchangeable Na + content. This trend is attributed to the application of saline irrigation water.