Topographic Influence on Soil Physicochemical Properties along the Volcanic Slopes of Mount Cameroon

Abstract

Understanding how topography shapes soil properties is critical for sustainable land management in mountainous agro-ecosystems. This study examined the influence of slope position on soil physicochemical properties along the southeastern slope of Mount Cameroon. A stratified sampling approach was adopted, and twelve composite soil samples were collected from three slope positions: lowland, mid-slope, and upper slope. Samples were obtained from major crop farms cultivating maize, plantain, and vegetables, while an undisturbed agro-forest served as a control. Each composite sample consisted of six sub-samples collected from a depth of 0–15 cm. Standard laboratory procedures were used to determine soil texture (hydrometer method), organic matter (Walkley–Black oxidation), total nitrogen (Kjeldahl digestion), available phosphorus (Bray-1 extraction), exchangeable potassium (flame photometry), bulk density (core method), and moisture content. One-way ANOVA results indicated that seven of the eight measured soil properties varied significantly with slope position (p < 0.05). Total nitrogen, available phosphorus, bulk density, moisture content, and particle size fractions showed particularly strong differences, with F-values ranging from 4.52 to 3286.47, confirming a strong topographic influence. Lower slopes contained higher nutrient concentrations (0.160% nitrogen and 14.5 mg/kg phosphorus), finer soil fractions (45.2%), and higher moisture content (27.5%). In contrast, upper slopes exhibited greater soil compaction (1.38 g/cm³ bulk density), coarser textures (71.9% coarse fraction), and lower fertility levels (0.090% nitrogen and 12.0 mg/kg phosphorus). Pearson correlation analysis revealed strong relationships among soil properties, particularly between moisture and nitrogen (r = 0.85), fine fraction (r = 0.78), and bulk density (r = −0.80). Exchangeable potassium showed no significant variation across slope positions (p = 0.420), likely due to continuous weathering of volcanic parent materials. These findings highlight the need for slope-specific soil management strategies in volcanic mountain landscapes.