Caractérisation, typologie et monitoring des sols de la région des Ziban- Biskra

Abstract

In this thesis, the soil characterization, monitoring, and typology of the Ziban region (Biskra) were approached in a way that allows a comparison between the 1991 diagnostic of the soil status in the Western Zab (OZ) of this region (Ain Ben Noui, El Hadjeb, and Oumache) with results obtained in 2016 and 2021 on the agroecosystems (AES) of the oases. The study approach was based on field investigation (detailed description of site physiography and sampling of soil and water) and laboratory work (physicochemical characterization). Remote sensing techniques were used to complement the conventional approach in the monitoring aspect. The AES under study are fragile, dynamic environments with various constraints (dry and evaporative climate, salinity, poor soil organic matter, wind erosion, etc.) and are highly valued for date palm cultivation and vegetable farming. The soil typology of eight soil typological units (UTS) from 1991 was updated according to WRB (2015) and ST (2014). Various types of Gypsisols and Solonchaks were identified, corresponding to the Gypsids and Salids suborders in the ST system; gypsum accumulation and salinity are the main features. Their state of degradation, studied in Tolga in 2016, revealed that secondary salinization and waterlogging are issues that could worsen due to defective or absent drainage systems. In the oasis of Bordj Ben Azouz (BBA), Tolga, the salinity of a forming lake was 67 dS.m-1, seven times higher than that of the drainage water. Statistical analysis (Tukey‘s HSD test, 0.05) confirmed differences between the oases in drainage water management. The dynamics and functioning of AES after 30 years were studied through 10 profiles distributed across two toposequences, revealing an exacerbation of secondary salinization in depression zones (pedons 2, 4, and 5). Gypsum content varied (4–87% in P7); gypsum crusts and encrustation were common. Water accumulation was occasionally observed in the Bordj Ben Azouz oasis, Tolga, along with aeolian deposits in the southern foothills of Boughezal Mountain. Soil pH was alkaline, and CaCO3 levels were generally moderate. The chemical facies of the soil solution was either hyper- chloride-calcium or hyper-sulfate-calcium. Analysis of vegetation index changes using Landsat 5 and Landsat 8 satellite images showed significant AES dynamics; changes in vegetation index reflected a notable evolution in land occupation and usage changes in the region. Cultivated areas expanded in El Hadjeb, east of M'lili, north Tolga, and south Lichana, while vegetation cover regressed in Oumache, south Tolga, and M'lili, likely due to palm grove aging and decline caused by salinization.