ABSTRACT

Two models, the Universal Soil Loss Equation (USLE) and the Soil Loss Estimation Model of the Southern Africa Model (SLEMSA), were adopted to assess soil losses and identify the most effective land use for mitigating erosion. The land use systems considered were forest (FF), cassava plot (CP), grassland fallowed (GF), and oil palm plantation (OP).The experimental design was a Balanced Replicated Fixed Design (BRFD) under a two-factor factorial experiment where land use and soil depth were the factors involved. Four spots within a land use were randomly selected for sample collection. Within a spot, disturbed (auger) and undisturbed samples were randomly collected from four different points at two depths (0-15 and 15-30 cm) and replicated in four different locations for a good spread across the state.  A total of 256 sampling units were collected and taken to the laboratory. Standard procedures were followed for sample analysis, including rainfall, topography, erosion control measures, and vegetation data generation. Data obtained were inputted into the USLE and SLEMSA models for soil loss determination with analysis of variance for the BRFD used for data analysis. Least significant difference at a 5% probability level detected mean differences, while correlations, regressions, and Python programming established relationships between soil properties and soil loss. A T-test compared the two models, and principal component analysis (PCA) identified key soil properties influencing land use-specific soil loss. Soil under GF had the highest sand content (830.894 g/kg) but the lowest silt (66.792 g/kg) and clay (103.542 g/kg) contents whereas FF soil had the lowest sand content (743.683 g/kg) but the highest silt (86.075 g/kg) and clay (173.398 g/kg) contents. Textural classes of the area varied ranging from loamy sand to sandy loam. Soil organic matter (SOM) content in the area was generally high with the soil of the FF land use containing the highest. Consequently, other properties such as soil bulk density, total porosity, moisture characteristics and aggregate stability also varied. The USLE prediction ranged from 0.610 to 14.943 t/ha/yr while SLEMSA prediction was from 3.031 to 23.928 t/ha/yr. The two models indicated FF as the most effective in soil loss mitigation while PP was the least, with rankings as FF > GF > CP > OP. Soils higher in colloidal materials and with good vegetation cover had better stability and thus resulted to lower soil loss as seen in FF.  The USLE model predicted lower soil loss with higher precision and consistency than SLEMSA and thus more suited for the CPS soils of Akwa Ibom State. PCA indicated that sand, silt, coarse sand, SOM, available water content, field capacity, saturated hydraulic conductivity, pH, bulk density, and total porosity were the important components influencing soil losses. The study showed that FF and GF soils were the most effective in erosion control of the CPS soil, indicating the impact of land use on soil loss. Land use practices such as afforestation, plantation cropping and fallowing are recommended for enhancing soil stability and regeneration of CP, GF and OP soils.