Journal of Global Ecology and Environment

The accurate evaluation of available nutrients remains challenging due to problems associated with nutrient fixation, variable parent materials, and anthropogenic inputs resulting from agricultural and industrial activities. This work evaluated the effectiveness of two universal extractants, 0.01 M calcium chloride (CaCl₂) and Agro-Services International (ASI) multi-nutrient extracting solution, employed for the extraction of available phosphorus, potassium, iron, and manganese within effluent-impacted soils in a highly weathered tropical region. These extractants were employed on soils underlying palm oil mill effluent and cassava mill effluents within coastal plain sands, beach ridge sands, and sandstone-shale parent materials in the study area in Southern Nigeria. Soil samples acquired at depths of 0-20 and 20-40 cm were analyzed using standard laboratory procedures. Results indicated that ASI extractants consistently extracted higher nutrient concentrations than CaCl₂ across all parent materials, treatments, and depths. Phosphorus was the dominant nutrient extracted, followed by manganese, iron, and then potassium, with greater nutrient accumulation observed within the 0–20 cm depths. Effluent-impacted soils recorded higher nutrient concentrations in comparison to control soils, indicating nutrient contributions from the palm oil and cassava mill effluents.  Correlation analysis revealed significant relationships between extractable nutrients and soil properties, illustrating the strong influence of soil physicochemical characteristics on nutrient dynamics and extractant performance. This study demonstrates that extractant choice impacts nutrient evaluation in effluent-amended tropical soils. It also establishes ASI extractants as a more efficient universal extractant for evaluating potentially available nutrient levels in highly weathered acidic soils.