MICROMORPHOLOGICAL AND MINERALOGICAL EVALUATION OF ULTISOLS DEVELOPED OVER DIFFERENT PARENT MATERIALS IN NORTHERN GUINEA SAVANNAH, NIGERIA

MICROMORPHOLOGICAL AND MINERALOGICAL EVALUATION OF ULTISOLS DEVELOPED OVER DIFFERENT PARENT MATERIALS IN NORTHERN GUINEA SAVANNAH, NIGERIA

Abstract:

Micromorphological and mineralogical properties can provide insights and aid interpretation of soil classification. Field and laboratory studies were conducted on soil formed in two different parent materials in Plateau State. With a view to characterize physical, chemical and morphological properties of selected soils, investigating the micromorphological and mineralogical properties of Ultisols derived from basalts and granite-gneisses, and determining if differences in properties could be used in the classification of Ultisols at the lower levels of Soil Taxonomy and World Reference Base (WRB). Based on the geological map sheet used to identify different parent materials, eight (8) profiles were dung and described. Results obtained revealed that micromorphology of surface horizon in basaltic derived soils shows a porous (compound packing) and crumb microstructure. The groundmass consists mainly of fine iron hydroxides in crystallitic micromass. In the subsoil horizons, the microstructure varied between vughs and channels with subangular shapes. Compound coatings of radial distributed and isotropic (“amorphous”) iron hydroxides line the pores. In many cases, several coatings of isotropic iron hydroxides, differing in colour intensity, fill the pores. In granitic soils, surface horizon was mainly crumb with vughs and channels microstructure. Complete infillings coating clay, orthic typic nodules and subhedral crystals, red and yellow mineral colour indicate finely dispersed hematite/some amorphous Fe gels and goethite respectively. The subsurface horizons were mainly vughy microstructure. Anhedral to euhedral crystal mineral grains with interference colour, strongly impregnated groundmass iron hydroxides nodules (anorthic and orthic) with black dotted micromass. On the whole, granitic derived parent material compares in terms of pedofeatures characteristics, speckled groundmass and vughy microstructures. Micromophologically, old parent materials have porphyric c/f related distribution pattern, low c/f 2u ratios, poor sorting and common infilling and coatings of voids as compared to enaulic c/f related distribution, high c/f 2u ratio in young parent materials. Similarly, self-mulching as a pedofeatures was observed in basaltic soils as opposed to granite parent material. The micromorphological properties of all soils are affected by their parent materials and genesis. The coarser textured soils have compact grain structure while the finer-textured soils have an apedal microstructure. Mineralogical composition of the soils were similar (kaolinite, micavermiculite, chlorite, rutile, quartz, goethite, hematite and gibbsite) between parent materials but different in proportions, except for gibbsite and chlorite which was absent in granitic derived soils and quartz, rutile and halloysite were absent in basaltic soils. According to the USDA system of classification, profiles BST01 and BST02 (basaltic PM) and GNT03 and GNT04 (granite PM) were classified as Typic Haplustults while GNT02 was Typic Plinthaquults. The evidence of pedofeatures such as porphyric c/f and typic orthic nodules confirms highly weathered soils. Profiles BST03 and BST04 are classified as Andic Haplustepts and GNT01 as Oxic Haplustepts. In the FAO/WRB system, profiles BST01 and BST02 are classified as Ferralic Acrisols, BST03 and BST04 as Andic Cambisols. While profiles GNT02, GNT03 and GNT04 are classified as Haplic Acrisols, GNT01 as Arenic Cambisols. Therefore, the distinct differences in micromorphological features among these soils might be employed as diagnostic horizons to differentiate soils while the quantifiable micromorphological features might potentially be selected as diagnostic indices for soil taxonomic classification

MICROMORPHOLOGICAL AND MINERALOGICAL EVALUATION OF ULTISOLS DEVELOPED OVER DIFFERENT PARENT MATERIALS IN NORTHERN GUINEA SAVANNAH, NIGERIA

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