Jornal de Geologia e Geofísica
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Analysis of Soil and Sub-Soil Properties around Veritas University, Obehie, Southeastern Nigeria

Youdeowei PO and Nwankwoala HO

This study is aimed at assessing the soil and sub-soil characteristics around Veritas University, Obehie, Abia State, Nigeria. The study revealed that the soils are loose, coarse texture with 78 – 80% sandy fractions having single grain structure from unconsolidated materials of recent alluvial deposits, with soil pH values between 4.8 and 5.8 which could be attributed to leaching of the basic cations to lower depth. Organic carbon content ranged from moderately low 1.50% to high 2.38% due probably to high surface litter and vegetation cover. The low levels of total nitrogen could be attributed to the heavy losses through leaching and responsible for the very low levels of available phosphorus (0.96 - 2.81 μg/g). Nitrate levels are very low (4.33 - 7.80 μg/g) due to the combined effects of intensive cultivations, poor nitrification as well as high leaching processes which occurred in the soils as evidenced in the moderate/high carbon-nitrogen ratio (15 - 43) indicating slow mineralization and humidification process. The three boreholes reveal an overburden brown, medium grained, stiff consistency silty clay soil with thickness of 6-8 meters and underlain by 1 to 2 m depth of brown, medium grained clayey sand. Below this stratum is the aquiferous brown, coarse-grained, gravelly sand to the bored depth of 10 m. Results obtained from the grain size analysis of samples from the boreholes show that the fine to medium grained soils of silty clay and clayey sand have moderate to high fines passing sieve No. 200 (22 to 75%) while the coarse grained gravelly sands have much less silty/clay fractions (10 to 15%). The results show a low plasticity range (6 to 8.7%) for the cohesive soils, while the gravelly sands are non-plastic. The low values of plasticity indices of the plastic soils are an indication of their low water retaining capacity. The soils were classified under the unified soil classification system as SW, SC and CL implying well-graded gravelly sand, clayey sands and low plasticity clays. The permeability test results reveal low values of 1.65 x 10-8 to 1.60 x 10-5 cm/sec. for the clayey soils. The gravelly sand shows a high coefficient of permeability of 1.36 x10-2 cm/sec.