Effects of Irrigation Water Quality on Soil Physico-chemical Proprieties: Case Study in North-West of Tunisia

Poor-quality water containing a high concentration of soluble salts is used to irrigate cropland worldwide, especially in arid and semi-arid regions, the limited rainfall is insufficient to wash away salts from the root zone, which builds up salt in the soil and affects soil properties, causing secondary soil salinization. This risk makes it necessary to monitor the variation of salinization in the irrigated perimeters through physico-chemical analyses. In Tunisia, soils affected by salts occupy an area of 1.5 million hectares, about 10% of the country’s total area. Our study aims to make a diagnosis of irrigation water quality, investigate its effect on the physicochemical properties of soil, and determine the soil salinity states of two irrigated agricultural perimeters. The two study areas located in Laaroussa (2723ha) and Gaafour (1642 ha), belonging to the governorate of Siliana in the northwest of Tunisia, Laaroussa perimeter is irrigated by groundwater pumped from “Krib” aquifer and Gaafour area irrigated from Siliana river. Understanding the Dynamics of secondary salinization required a pedological and physico-chemical study of the 0–30 cm layer of the soil, which 20 samples were taken from Laaroussa perimeter and 11 samples from Gaafour perimeter. The soils of two study areas are very salty to extremely salty with an electrical conductivity (EC) equal to 8.46 mS/cm at Laaroussa perimeter and 17.57 mS/cm at Gaafour perimeter, the pH of the two soils is alkaline with a value equal to 8.32, having an impact on the soil organic matter (SOM), which plays an important role in the physical (stabilization of soil structure), chemical (buffering and pH changes) and biological (microbial activity) regulation of soil properties. The chemical analysis results of irrigation water show that groundwater (Krib aquifer) used for irrigation belongs to a class of very high salinity and low risk of alkalinization with high sodium contents and surface water (Siliana river) belongs to a class of high salinity and low risk of alkalinization. The expansion of irrigated agriculture is of enormous importance to feeding the world's burgeoning population. However, without appropriate management, this expansion can lead to environmental problems of soil salinization induced by irrigation, which is the case in our study area and in any country with an arid and semi-arid climate, so appropriate management of Soil salinization is imperative to achieve most sustainable developmen