Effect of mineral amendment on the gypsum and salinity distributions in soil from a South Tunisian oasis

The Tunisian oases are almost the only arboreal agricultural resource in the southern desert of Tunisia. These oases suffer from soil salinization due to a rising saline water table. To compensate for this issue, farmers add sand to the oasis soil. To determine the most effective soil treatment to suppress the salinization and reduce the excessive gypsum content of the oasis soil, the present work investigated the effects of adding three types of sand to oasis soil: gypsum sand (S1), quartz sand (S2), and siliceous sand (S3), as these types of sand are commonly added to oasis soil by farmers. The properties of the treated soils were compared with those of untreated soil (U). For each treated soil, it was found that the electrical conductivity (which is indicative of the salinity) and the gypsum concentration decreased with increasing depth compared to the corresponding values for untreated soil. The greatest reduction in soil gypsum content was obtained with treatment S2, which yielded a gypsum content in the surface layer (0-20 cm) of 30.14 +/- 0.22%, followed by S3 and S1, which yielded surface gypsum contents of 39.14 +/- 0.88% and 40.40 +/- 0.07%, respectively. This traditional and ancestral practice was therefore shown to be a valuable method of sustaining the oasis system and maintaining land productivity.