Prof. E.R. Orhue

Heavy metals are naturally occurring metallic elements with high atomic weights and densities at least five times greater than water which due to their persistence, toxicity, and bio-accumulative nature, they pose significant environmental and health risks (Ali et al., 2020). Lead (Pb), cadmium (Cd), mercury (Hg), and arsenic (As) are toxic even at low concentrations (Tchounwou
et al., 2020). Heavy metal bioaccumulation refers to the progressive increase in concentration of toxic metals (e.g., Pb, Cd, Hg, As) in living organisms over time, primarily through uptake from contaminated water, soil, or food, exceeding environmental levels due to slow excretion rates (Ali et al., 2023). This process involves the absorption and retention of heavy metals in tissues of organisms, leading to higher internal concentrations than their surroundings, with potential transfer across food chains (biomagnification) (Javed et al., 2022).

Phosphorus (P) is one of the essential macronutrients needed for plant growth but its use efficiency is reduced due to adsorption sometimes caused by influence of pH. The study aimed at
determining the chemical and physical properties of the sampled soil as well as P sorption capacity at different pH in kulfo soil series of Nigeria Institute for Oil Palm Research (NIFOR), Benin city, Edo state. The study was conducted on twelve (12) samples collected from four (4) soil depths (0-30, 30-60, 60-90, and 90-120 cm) in four (4) replicates from the Kulfo soil series. Physical and chemical properties were determined following standard procedures while the P sorption capacity were determined by equilibrating 5 g soil for 24 hours in 25 ml of P retention solution containing 1000 mg P/L as KH2PO4. The P in the soil P retention suspension was read using the Nitric vanadomolybdate yellow method. The amounts of P adsorbed were calculated by plotting a graph of absorbency against % p retention (100, 80, 60, 40, 20 and 0%) of the standard serial solution. Afterward, P retention of the samples were determined from the regression equation of the curve. The data obtained were subjected to statistical analysis using Genstat statistical package. The means were separated at 5% level of probability using Duncan multiple range test. The physical properties indicated that the soil's textural class was predominantly sandy loam for all depths, except at 0-30 cm, where it was Loamy Sand. The chemical properties of the soils revealed that they were acidic, with a mean pH value of 4.71. Other soil properties such as K, Ca, Mg and Na were within the normal range of crop production. The % p sorption varied with soil depths at all pH level, the % P retention at pH (3.0, 4.6, 7.0 and 8.6) had a mean value of (23.5, 19.0, 13.85 and 14.15) respectively. The influence of pH on P sorption calls for a compressive P management approach for the soil, designing the best P management practice to reduce P sorption in soil.