Potassium Adsorption Characteristics of Soils under Contrasting Land-Use Systems at the University of Benin, Benin City, Nigeria

ABSTRACT Potassium (K) retention in soils is often low and varies with soil and Land-use type due to its high mobility. This study evaluated K adsorption in soils from four land-use types at University of Benin Nigeria, given widespread application of K fertilizers to address K nutrient deficiencies. Auger Soil samples were collected from 0-30 cm soil depth, in three replicates from four land-use types: Arable, Forested, Sports and Plantain-Farm, making a total of 12 samples. Potassium adsorption capacity was determined by equilibrating 1 g soil with 30 ml varying concentrations (20, 40, 60, 80 and 100 mg L⁻¹) of K prepared from potassium chloride with 0.01 M CaCl2 as background electrolyte, for 2 hours, allowed to stand for 24 hours at 25 ± 1 °C, shaken again filtered and K in filtrate was estimated using a flame photometer. The amount of K adsorbed was calculated by difference, while Freundlich and Temkin adsorption isotherm models were applied to describe K adsorption behavior. Results showed that arable land exhibited highest Freundlich K adsorption capacity (100.60 mg kg⁻¹), followed by forested (35.08 mg kg⁻¹), sports (17.43 mg kg⁻¹) and Plantain-Farm (1.78 mg kg⁻¹) land-use, suggesting reduced K fertilizer loss in arable Land-use soils compared to other Land-use. Freundlich adsorption heterogeneity parameter (1/n) ranged from 0.91 (Arable land) to 3.18 (Plantain-Farm) indicating unfavorable adsorption in all Land-use except the Arable Land-use. The Freundlich model provided the best fit (R² > 0.983) for Plantain-Farm Land-use, compared to Temkin model fit of R² = 0.883 for Plantain-Farm, indicating the suitability of Freundlich model, in describing K adsorption in the Plantain-Farm, while highlighting the influence of Land-use on K adsorption in the soils studied. Higher K adsorption in arable land soil may indicates enhanced K retention and fertilizer-use efficiency while lower K adsorption in Plantain-Farm and sports land practically implies greater K loss potential