The nexus of soil fertility, bioconcentration and soil pollution load in the tropical land use systems of western Ghana

Meryem El Mellouki^1*Ali Boularbah²Fassil Kebede¹

• ¹Universite Mohammed VI Polytechnique, Ben Guerir, Morocco
• ²Universite Cadi Ayyad, Marrakesh, Morocco

Tropical agricultural soils are influenced by diverse management practices affecting soil fertility and trace metal accumulation. This study evaluated soil fertility, trace metal bioaccumulation, and pollution load across four land use systems,cacao (Theobroma cacao), oil palm (Elaeis guineensis), cocoyam (Xanthosoma sagittifolium), and maize (Zea mays),cultivated on Ferralsols and Acrisols in western Ghana. Soil chemical properties, including total organic carbon , total nitrogen , exchangeable potassium , available phosphorus , pH, and cation exchange capacity , were determined to compute the Soil Fertility Index (SFI). Bioconcentration factors (BCFs) for Al, Cd, Cu, Mn, Ni, Zn, Sr, and Ti were calculated from plant and soil concentrations, while contamination factors (CFs) and the Soil Pollution Load Index (PLI) assessed soil contamination.SFI values ranged from 0.41 ± 0.13 (low fertility) in Ferralsols under maize to 0.78 ± 0.26 (high fertility) in Acrisols under cacao. BCFs varied significantly, with cacao on Ferralsols showing the highest uptake for Mn (1.98×10⁻⁴ ±1.15×10⁻⁴), Cu (1.70×10⁻³ ±1.21×10⁻³), and Sr (2.32×10⁻³ ±1.53×10⁻³), whereas maize and oil palm had minimal accumulation. These differences likely reflect selective ion uptake, root exclusion barriers, and sequestration strategies that limit potentially toxic element assimilation. PLI values were low across all systems (1.56×10⁻⁵–8.08×10⁻⁵), indicating generally uncontaminated soils.Correlation analyses revealed a strong positive relationship between SFI and BCF Ni (r = 0.93), while Cd, Cu, and Zn accumulation depended more on soil properties, such as pH and organic carbon, than overall fertility. BCFs of Cd and Cu were highly correlated (r = 0.96), suggesting shared uptake pathways. The low PLI values contrasted with high cacao–Ferralsol bioconcentration, indicating soil pollution alone does not explain plant metal uptake. PCA distinguished crop,soil elemental patterns, with Cu, Ni, Mn, Cd, and Ti prevalent in cacao on Acrisols, whereas Sr and Zn dominated in oil palm on Ferralsols.The study concludes that high soil fertility does not necessarily indicate soil health, as fertile soils can harbor excessive pollutant elements in root zones. Plant behavior, particularly selective ion uptake and exclusion of toxic elements, governs PTE assimilation more than soil properties.