Mineralogical compositions of soils under three geological formations in some parts of Ogun state, Nigeria and their agricultural potentials

Understanding soil mineralogical composition provides insight into the agricultural behaviour of soils, pedogenesis and their response to environmental conditions and management. Examination of the mineral compositions and diversities of soils developed over the Basement complex rock, Coastal plain sands and Ewekoro formations were carried out. Using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and Petrography, the mineral contents and their relative abundance, elemental compositions and morphologies of the fine sand, coarse silt and clay fractions of the soils at different topographic positions were identified, described and compared. Results obtained from XRD and SEM analyses exhibited similarities. The presence of mixed-layer illite, mica, kaolinite, quartz, hematite, anatase, goethite, and chlorite at varying degrees was observed in the pedons developed on these geological formations, although kaolinite and quartz dominated the soil matrix. The mineralogical complexity of the pedons followed the order of basement complex > coastal plain sand > Ewekoro formation. Profiles developed on the Ewekoro formation exhibited the highest degree of weathering, as evidenced by their chemical properties and mineralogical compositions. The petrographic evaluation of the three geological formations revealed that all pedons were rich in quartz and exhibited varying degrees of mineral complexity and maturation. The overlapping and distinct characteristics among the geologies indicated different stages of weathering. The petrographic analysis further confirmed that profiles from the Ewekoro formation were the most weathered. The use of such soils for agriculture would necessitate significant investments in agro-inputs and sound principles of soil management through integrated soil fertility management.