EFFECTS OF TOPO POSITION ON PHYSICO-CHEMICAL PROPERTIES OF THE SOIL AT EZEAGU AREA OF ENUGU STATE, SOUTHEASTERN NIGERIA.

Abstract

Topographic position is a key landscape control on soil redistribution and the spatial organization of soil physicochemical properties along hillslopes. This study examined the influence of topo-position (upper, middle, and bottom slopes) on selected soil physico-chemical properties in Olo, Ezeagu Local Government Area, Enugu State, Southeastern Nigeria. A stratified transect sampling design was applied across three representative topo positions. Transects extended from crest to foot slope and soil samples were collected at a uniform depth of 0 – 20 cm using a stainless steel, soil auger and core samplers at 20 m intervals. A total of 27 disturbed and undisturbed soil samples were collected at Nine sampling points on each topo position. The samples were subjected to laboratory analyses using standard procedures, and data were evaluated using Analysis of Variance and correlation analysis with spatial variability discussed using Coefficients of Variation (CV). Results showed systematic topo position controls on soil physico-chemical properties. Particle Size Distribution showed low variability (CV < 15%) with sand content decreasing downslope (24.70–20.40%) and clay content increasing (39.90–44.80%). Bulk Density and total porosity also exhibited low variability (CV < 2%), declining downslope from 1.35 to 1.31 g cm⁻³ and increasing from 48.93 to 50.52%, respectively reflecting relatively uniform soil structural conditions across the topo positions. Soil pH showed low variability (CV = 5.27%) and increased downslope from moderately to slightly acidic conditions (5.77–6.40). Organic Carbon displayed moderate variability (CV ≈ 21%), which was highest at the middle slope (1.09%), suggesting partial deposition and stabilization zones. In contrast, total nitrogen (CV = 51.70%) and Available Phosphorus (CV = 82.65%) exhibited high variability with pronounced downslope declines from 0.18% to 0.07% and from 11.20 to 2.80 mg kg⁻¹ respectively. This shows strong sensitivity of nutrient pools to slope-driven redistribution. Cation exchange capacity showed low variability (CV < 10%) and was highest at the middle slope (5.60 cmol kg⁻¹). These findings emphasize that topo-position exerts strong control over both physical redistribution and chemical differentiation along the hillslope.