Assessment of Physio-Chemical Properties and Potassium Forms in Soils of Southeastern Nigeria

Abstract

This study was conducted to explore the intricate relationship between soil physio-chemical properties and potassium (K) forms in tropical soil of southeastern Nigeria. Soils of the region are characterized by diverse geological parent materials, including coastal plain sand, alluvium, shale, sandstone, and basement complex. A systematic sampling approach was employed, involving soil collection at three depths (0–20 cm, 20–40 cm, and 40–60 cm) across 45 sites, based on detailed geological maps. Laboratory analyses of collected samples were carried out for soil pH, texture, organic carbon, cation exchange capacity (CEC), and potassium fractions; (total, water-soluble, exchangeable, non-exchangeable, and mineral K), using standardized protocols. Key findings indicated that soil pH predominantly ranged from 4.37 to 5.47, with basement complex soils exhibiting the highest acidity (pH 4.5–4.7), and sandstone derived soils showing relatively higher pH (5.3–5.4). Textural analysis revealed high sand content (>81%) in sandstone and coastal plain sands, influencing drainage and nutrient retention. Organic carbon and CEC varied significantly among parent materials, with volcanic soils (sandstone and alluvium) displaying higher organic matter and potassium availability. Correlation analyses showed significant positive relationships (p < 0.05) between soil pH, organic carbon, CEC, and potassium forms, especially water-soluble and exchangeable K. Notably, soils derived from sandstone and alluvium parent materials had higher potassium concentrations, suggesting better nutrient availability, whereas acidic, low-CEC soils like shale and basement complex exhibited lower potassium mobility and fixation. These results underscore the critical influence of soil physio-chemical attributes particularly pH, organic matter, and texture on potassium dynamics, which directly impact soil fertility and crop productivity. The findings highlight the need for tailored nutrient management strategies that consider geological and soil property variability to optimize potassium use efficiency and sustain soil health in southeastern Nigeria’s diverse agro-ecological zones.