Soil Acidification Vulnerability and Long-term Trace Metal Depletion Under Rubber Tree Plantations in the Semi-mountainous Region of West Côte d'Ivoire

Abstract

The objective of this study was to assess the impacts of rubber cultivation on soil properties in the Tonkpi region, western Côte d’Ivoire. The study proceeded by comparing soils under rubber tree cultivation of different ages to those under other crops or fallow. The soils were sampled from a depth of 0 to 25 cm. The samples were dried and then sent to the central laboratory of the University of Man for physical and chemical analyses. Soil pH was measured with the multiparameter HANNA HI9829. Soil potentially toxic elements like As, Zn, Cu, Ni, Co, Cr, Mo, Fe, Se, Ca, Pb, K, Mn and V were analyzed, at the geological laboratory of the University Felix Houphouet-Boigny with a handheld NITON XL3t X-ray fluorescence analyzer. The results showed that soils from rubber-cultivated areas had a sandy loamy-clay texture, while those from the control area had a sandy-loamy texture. The soil pH was strongly to slightly acidic, with pH varying from 4.86 to 6.34, while the bulk densities varied from 0.51/g cm3 to 0.62 g/cm3. The redox potential of the soils was inferior to 400 mV (Eh ˂ 400 mV). This study also revealed a general decrease in the potentially toxic element content of soils under rubber cultivation. The soil contents of Cr, Co and Cu were inferior to the limit of detection. The Pb, Mn and Ca concentrations were 4.81, 194.2 and 2140 µg g-1, respectively, and these were significantly different from those of the other soils. This study provided a major insight into the effect of rubber cultivation in western Côte d'Ivoire.