In the present study, two topomorphic vertisols profiles used for sorghum production were described and characterized. After macroscopic characterization, physicochemical, mineralogical and geochemical analyses were made. Physicochemical analyses were made by standard methods while mineralogy was determined on clay fraction (˂2µm) by X-ray diffraction coupled to Fourier transform infrared spectroscopy. Geochemical analysis was determined on 180µm fraction by inductively coupled plasma-Atomic Emission Spectroscopy (ICP-AES) and mass spectrometry (ICP-MS). Results revealed that studied vertisols were average deep, less differentiated with desiccations cracks and gilgai micro relief. The angular blocky structure and clayey texture were observed. They were alkaline (7.3 ≤ pHwater ≤ 8.4) and recorded a low to moderate organic matter and nitrogen contents. Cation exchange capacity was high reaching 52.24 meq 100g-1 and exchangeable cations were moderates with Ca 2+ (3.69-29.6 meq 100g-1) the most represented cation. Vertisols were made of smectites associated to kaolinite and a lesser content of quartz. Illites and calcite were also identified in some horizons. On the geochemical point of view, Si02 (55.87-83.64%), Al2O3 (6.08-20.25%), Fe2O3 (2.09-6.39%) and K2O (1.43-2.24 %) were the dominant oxides. Traces elements were represented essentially by Ba (518-1202 mg kg-1), Zr (334-685 mg kg-1) and Sr (71-190 mg kg-1). The overall features are suitable to dry season sorghum production. The amount of smectites seemed to be an important factor affecting their water holding capacity on which dry season sorghum production depends. Improved cropping systems have to be developed to sustain productivity in vertisols with low smectites and where annual rainfall is lesser.
The study of the soils from Mbé and Wack is carried out in the framework of the knowledge of soils from the Adamawa Region of Cameroon and their erodibility was investigated using erodibility indices obtained through physico-chemical data. Eleven topsoils (0 -20 cm) samples were collected on different land use and their susceptibility to erosion was assessed. The water dispersible clay (34.92 -121.75 g•kg −1 ), the clay dispersion ratio (0.45 -0.84) and the dispersion ratio (0.75 -0.89) were high in the studied soils while the clay aggregation (13.16 -42.27g•kg −1 ) and the clay flocculation index (0.16 -0.55) were low to moderate indicating their high erodibility. The soils under natural vegetation, more clayey, displayed the highest amount of water dispersible clay while cropped soils recorded the smaller ones. Globally, in cropped soils, those under cereals displayed the highest clay dispersion indices than those under tubers. This suggests that tubers cropping practices in studied soils enhance their erodibility. Statistical analyses revealed that amorphous Al and Fe are elements which limit soils erodibility while K + and 4 NH + promote soils particles dispersion. Sustainable management of these soils will consist on limiting runoff through agricultural practices such as direct seedling and orienting tillage perpendicularly to slope gradient.
Due to the increasing demand resulting from the use of REE in many fields of human life, a weathering profile developed on granites in the semi-arid region of Biou area (North-Cameroon) has been characterized for rare-earth elements (REE) exploration. The mineralogical compositions of weathered materials were revealed by X-ray diffraction (XRD). X-ray Fluorescence (XRF) and Inductively Coupled Plasmas-Mass Spectrometry (ICP-MS) have been used to determine the geochemical composition of granites and the overlying weathered materials. The S-type and peraluminous granites are constituted by quartz, orthoclase, microcline, plagioclase, biotite, muscovite, pyroxene and opaque minerals. Accessory minerals are probably responsible for the interesting contents in REE + Y and some trace elements (e.g., Zr, Zn, Ba, Rb). The weathering profile show from the bottom to the top: (i) saprolitic horizons; (ii) lower loose clayey horizon; (iii) iron duricrust horizon; (iv) upper loose clayey horizon; (v) and organo-mineral horizon. Some weathered rock fragments remain in the loose clayey and organo-mineral horizons. The mineralogical composition of the weathering materials is dominated by illite, muscovite and feldspar. The low weathering degree of the materials is justified by the climatic and reducing conditions. The large ion lithophiles and ferromagnesian elements (Mg, Fe, V, Cu, Co, Cs Cr, Ni, Sc and Li) which are supposed to be mobile are so much accumulated in the weathering materials. REE show very low degree of fractionation in weathering profile due probably to the lack of good drainage. The whole weathering materials shows high REE + Y contents as its parent rock. Geochemical mass balance and enrichment factor reveal that REE, especially light REE, are so much enriched in the iron duricrust horizon (ion-adsorption REE deposit type). Some heavy REE are also enriched in the lower loose clayey horizon. This first survey has revealed that the weathering materials developed on granites in Biou area are favorable for further REE exploration.
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