Impact of Secondary Salinization of Irrigated Perimeters on the Physico-Chemical Parameters of the Soil

Around the world, arid and semi-arid regions are almost permanently marked by water deficit. This water deficit associated with extreme ETP evapotranspiration makes the use of land irrigation inevitable. The latter is often done using brackish water, which exposes the land to the risk of secondary salinization, especially when irrigation techniques are unsuitable and drainage is deficient. In Tunisia, soils affected by salts occupy an area of 1.5 million hectares, this area represents a proportion of 10% of the total area of the country. This study aims to characterize and monitor soil characteristics and physico-chemical parameters of soil (Electrical Conductivity EC, pH, Organic Matter OM, Organic Carbon Stock OCS, calcium bicarbonate, phosphorus, and major elements) and to determine the effect of salinization on these parameters also on the organic carbon stock, in two irrigated agricultural perimeters, located in Laaroussa (2723 ha) and Gaafour (1642 ha), belonging to the governorate of Siliana in the northwest of Tunisia, these two perimeters are irrigated by dam water and pumped water. Understanding the dynamics of secondary salinization required a pedological and physico-chemical study of the 0–30 cm layer of the soil, of which 20 samples were taken at Laaroussa and 11 samples at Gaafour. The results of the analyses show that the irrigation waters belong to a class of high salinity and an average risk of alkalinization with high sodium contents. The soils are very salty to extremely salty with an electrical conductivity of 8.46 mS/cm at Laaroussa perimeter and 17.57 mS/cm at Gaafour perimeter, the pH of the two soils is around 8.32, which has a significant influence on the soil organic matter (SOM) which controls, in a major part, the physical properties of soil (stabilization of soil structure), chemical properties (buffering and pH changes) and biological properties (microbial activity).