Characteristics, classification and genesis of vertisols under seasonally contrasted climate in the Lake Chad Basin, Central Africa
Publication date: Available online 13 November 2018
Source: Journal of African Earth Sciences
Author(s): Temga Jean Pierre, Azinwi Tamfuh Primus, Basga Djakba Simon, Zo'o Zame Philemon, Gouban Hamadjida, Abossolo Monique, Nguetnkam Jean Pierre, Bitom Dieudonné Lucien
General properties of Vertisols are known world-wide, but these properties vary in different areas due to specific environmental conditions. The mastery of the specific characteristics of each Vertisols in a given area requires detailed site-scale investigation. This work aims to study the properties of the Lake Chad Basin Vertisols, attempt to highlight their genetic processes and classification. These Vertisols are dark, clayey and massive, very compact, with deep wide-opened cracks and gilgaï micro-relief. They show neutral to slightly alkaline pH, low organic matter content (0.7–2.73%) and high C/N ratio values (7.34–39.64). Ca2+ and Mg2+ are the most represented exchangeable cations (5.92–30.72% and 1.28–5.44%, respectively) on the absorption complex. Smectite is the main clay mineral species, but small contents of kaolinite, illite, quartz and feldspars are also present. The most concentrated elements in the profile are silica (61.07–77.78 wt.% SiO2), aluminium (7.08–15.54 wt.% Al2O3) and iron (1.78–6.92 wt.% Fe2O3). The Si/Al ratio (>2) and chemical index of alteration (CIA) are moderate to high (56.76–88.39) and indicate a moderate to intense weathering. Such properties reflect the pedogenic influence of the environmental factors like contrasting climate, low topographic position and the alluvial parent material. The accumulation of basic cations favours the neosynthesis of smectite minerals typical of a dominant bisiallitisation process. The Vertisols profiles, due to the presence of a perched water table, enable to classify these soils as Epiaquerts and Endoaquerts Vertisols (USDA soil taxonomy) and Gleyics and Fulvics Vertisols (WRB). Their physical characteristics and notably their difficult water management constitute a limitation to agricultural activities.