POTASSIUM ADSORPTION CHARACTERISTICS OF SOILS DERIVED FROM DIFFERENT PARENT MATERIALS IN SOUTHEASTERN NIGERIA.

ABSTRACT This study investigated potassium (K) adsorption characteristics of soils derived from five contrasting parent materials (alluvium, basement complex, coastal plain sand, sandstone, and shale) at three soil depths (0-20, 20-40, and 40-60 cm) in Southeastern Nigeria. Soil samples were collected from multiple locations across Abia, Imo, Anambra, Ebonyi, Enugu, and Cross-River States. Three adsorption models (Langmuir, Freundlich, and Temkin) were employed to characterize K adsorption behavior. Results showed that K adsorption rates varied significantly among parent materials, ranging from 1537 mg/kg (coastal plain sand) to 1694 mg/kg (sandstone), with significant depth-related variations. The Freundlich model provided the best fit (R² = 0.56-0.99, mean = 0.88) compared to Langmuir (R² = 0.58-0.89, mean = 0.72) and Temkin (R² = 0.21-0.88, mean = 0.45) models. Sandstone-derived soils exhibited the highest mean K adsorption rate (1694 mg/kg), while coastal plain sand showed the lowest (1537 mg/kg). Adsorption parameters varied considerably among parent materials, with alluvium showing positive adsorption maximum in the Langmuir model, indicating favorable K retention. These findings provide crucial insights for developing parent material-specific K fertilization strategies in Southeastern Nigerian soils.