Assessing Spatial Variability of Soil Physical and Chemical Quality as Affected by Slope Curvature and Aspect of Acid Soils in Akwa Ibom State, Nigeria

The study was conducted to evaluate the spatial variability of soil physical quality affected by slope aspect and curvature in acid soils of Akwa Ibom state, Nigeria. Twenty-four soil samples were collected from three locations in three slope positions on two slope characteristics in the study area. The soil samples were air-dried and sieved through 2mm sieve for the determination of the physical and chemical properties of the soil. Indices of soil quality (modified clay ratio, silt clay ratio, sodium absorption ratio, weight of organic matter) were calculated. The data generated were summarized using descriptive statistics and correlation analysis was used to determine the relationship between slope curvature and aspect with physical properties of the soil. The results show that in physical properties, south facing slope recorded higher sand, Bulk density and Total porosity (922.33 %, 27.83 %, 1.61 Mgm-3and 0.76 m3m-3) respectively, while north-facing had high clay and low hydraulic conductivity (59 % and 4.10 cmhr-1) respectively. In slope curvature, concave slope recorded high mean content of silt, Bulk density and Total porosity (26 %, 2.45 Mgm-3 and 0.81 m3m-3) respectively, the convex slope had a high content of silt, clay and saturated hydraulic conductivity (919 %, 58.83 % and 4.14 cmhr-1) respectively. The results of soil chemical properties in comparing the slope aspect indicated that north-facing slope recorded a high mean value in pH (6.04) and base saturation (51.73 %), while south facing slope recorded high mean value in organic matter (3.90 %), available phosphorus (5.81 mgkg-1), calcium (17.77 cmolkg-1), magnesium (1.17 cmolkg-1), potassium (0.30 cmolkg-1), sodium (0.38 cmolkg-1), exchangeable acidity (5.04 cmolkg-1), and effective cation exchange capacity (9.50 cmolkg-1). Results on indices of soil physical properties in north facing slope had mean value of (19.59, 0.18, 673 and 17.65) for Silt Clay Ratio (SCR), Sodium Adsorption Ratio (SAR), Weight of Organic Matter (WOM) and Modified Clay Ratio (MCR), respectively, while south facing slope had 20.34, 0.46, 780 and 30.78, for SCR, SAR, WOM and MCR respectively. Concave slope had mean values of 18.02, 0.20, 739 and 15.94 for SCR, SAR, WOM and MCR respectively. Convex slope indicated mean values of 18.55, 1.20, 67 and 17.70 for SCR, SAR, WOM and MCR respectively.