Forms of Zinc, Cobalt, and Chromium in Soils Cultivated to Oil Palm and Rubber in the Rainforest

The study aimed to determine the status of six forms of Zinc (Zn), Cobalt (Co), and Chromium (Cr) in soils cultivated for Oil palm and Rubber in the rainforest belt of Nigeria. Soils were collected from 2 (Oil palm and Rubber) plantations using a Randomized complete block design from 4 depths in 3 replications to make a total of 24 soil samples. A Laboratory experiment was conducted in the soil and land management division of the Nigerian Institute for Oil palm Research (NIFOR) between February and September 2018. Some soil properties and forms of Zn, Co, and Cr were determined by 6 steps of sequential fractionation following highspeed centrifugation and decantation at each step. Zn, Co, and Cr in the soil extracts were read using an Atomic adsorption spectrophotometer. Correlation analysis was used to determine the relationship between some soil properties and Zn, Co, and Cr forms. Results showed acidic soil reaction (< 4.91) with Oil palm plantation slightly higher in organic carbon (32.60 g/kg) and available P (18.00 mg/kg) when compared to Rubber plantation. The results also indicated variations in the Zn, Co, and Cr fractions in both plantations. The influence of some soil properties on forms and speciation of Co and Zn was indicated by significant correlation results. The present study indicated that the soils can be continuously used for citrus and teak production since the various forms of Co, Zn and Cr were within permissible levels and thus poses no health risk to the food chain.