Cadmium and Zinc Concentrations in Soils and Oil Palm Tissues as Affected by Long-Term Application of Phosphate Rock Fertilizers

The study was conducted to determine Cd and Zn concentrations in soils with three different ages of oil palm trees (<10, >15, >20 years) and plant parts as affected by long-term application of phosphate rock fertilizers. To investigate this issue on Malaysia's oil palm plantations, six soil series that undergo a scheduled fertilizer program were collected. Jawa, Selangor, and Sedu Series were selected from a plantation in the coastal area, whilst Munchong, Rengam, and Segamat Series were collected from a plantation in the inland area. Fronds and fruitlets were also collected along with the soils (paired sampling). To verify the findings of the field study, Cd and Zn adsorption isotherms were prepared. Competitive adsorption between Zn and Cd was also conducted. There was no accumulation of Cd in all the soil series but Zn accumulated in the Selangor and Segamat Series. Fruitlets (edible part) show no increase in Cd and Zn concentrations, but Jawa and Selangor Series show increasing values of Zn concentrations in the fronds. A correlation study reveals that soil pH and clay content were the soil properties that controlled Cd and Zn concentrations in soils. Cadmium in soils and soil solutions most probably contributed to the Cd concentrations in fruitlets, whereas Cd and Zn in soils may influence the uptake of these elements by the oil palm trees. The highest Cd and Zn accumulation in Segamat Series Soil had been shown in the adsorption isotherm study. Cadmium adsorption was decreased in the presence of Zn, leading to no accumulation of Cd in all the soil series.