Soil Monitoring and Pedological Typology of Oasis Agroecosystems in the Ziban Region (Algeria)

Since the 1990s, oases have undergone significant changes in the Ziban region of Algeria. These changes can be specifically related to number of factors, such as the financial assistance offered by the government to increase the production of date palms and the creation of irrigated perimeters for the cultivation of cereals and vegetable crops in greenhouses. However, Soil resources are fragile and degraded due to these anthropic perturbations, which will affect the sustainability of the oasis agroecosystem. This study was carried out in the western part of the Ziban. We used morpho-analytical and Remote Sensing (RS) techniques to assess the degree of degradation and to idetify the different types of soil resources. RS is used as part of the methodology to evaluate the risks of secondary soil salinization and the degradation of oasis ecosystems. Extraction of salt-affected areas and change detection are performed on Landsat images taken on September 2nd, 1984, and August 7th, 2015. In June 2021, a field investigation was conducted to find the representative oases. In order to characterize the soils of arid lands, we used three diagnostic criteria: soil salinization, calcareous crust, and gypsum accumulation. Then, 10 profiles were chosen, and samples were taken at various depths (0–30, 30–60, and over 60 cm). These soil samples have been characterized by measuring: EC of diluted extract 1:5, soil carbonate calcium and gypsum contents. The analytical results show that soil salinity is variable from 2 to 30 dS/cm. Gypsum is a predominant element in these oases. Its quantities vary between 10 and 85%. The CaCO3 has a limited spatial distribution and its contents do not exceed 24%. RS was useful in determining areas where secondary salinization is exacerbated. Even waterlogged soils and those with gypsum accumulation were highlighted. Due to the relative homogeneity that several profiles shown in their analytical and field characteristics (salinity, pH, CaCO3, gypsum content, form of gypsum accumulation, soil surface state), six profiles were chosen as being the most representative of the study area. Gypsisols, Solonchaks, and Arenosols were identified as the three main types of soils by using the WRB (2014) system for soil classification. Gypsisols Calcic Hypogypsic (P2, P3, and P8) and hypergypsisols (P6 and P7), which may correspond to “Deb-Deb” Crust, are found at various elevations in the landscape. The Solonchaks Hypogypsic (P1), Solonchaks Calcic Yermic (P4) and Solonchaks Hypogypsic Gypsiric (P5), are located especially in low sites. The Arenosls Gypsiric Yermic/Aridic (P9 and P10), also known as Xerosols or Yermosols in the previous classification system, are found at high points and in the piedmont of the mountain “Boughezal”. RS could be used to determine the Solonchaks and Arenosols due to the strong reflection of salts and sand-based components. And indeed, it was difficult to identify Gypsosols and soils having a waterlogging problem.