Differential speciation and availability of copper in soils derived from different parent materials in Imo State, southeastern Nigeria

Abstract

Effective and efficient management of copper (Cu) in soils for optimum crop production and environmental conservation depends on proper  knowledge of the various copper forms and fractions in soils as well as
parent material. The distribution of forms of Cu in soils of different parent materials (coastal plain sands, alluvium, false-bedded sandstones and Imo clay shale) in Imo State, Southeastern Nigeria was evaluated using  sequential extraction procedure, comprising of six fractions; water soluble (WS), exchangeable (EX), specifically sorbed/CO₃ bound (SSC), Fe-Mn bound (Fe-Mn), organic matter bound (OMB) and residual bound (RE) fractions. Soil was sampled at 0-15, 15-30, 30-45, 45-60 and 60-75 cm depths from each soil. Data obtained were subjected to analysis of variance and means separation was done by the procedure of Least Significant Difference at 5% probability level. Correlation analysis of the various Cu forms and some soil properties was also carried out. Results showed that the water soluble, specifically sorbed/carbonate bound, Fe-Mn bound, organic matter bound (OMB) and residual bound (RE Cu fractions differed significantly among the soils of the different parent materials. The Fe-Mn bound copper was the dominant fraction in most of the soils, contributing 41.53-46.63% to the total Cu, being highest in the alluvial soil (6.389 mg kg^-1) and lowest in the Imo clay shale soil (2.231 mg kg^-1). Moderate concentrations of available Cu (0.694-1.456 mg kg^-1) were observed and significant differences were observed among the soils. Correlations among the different Cu forms (WS vs EX r - 0.48; EX vs Fe-Mn r −0.46) and some soil properties (OM vs Fe-Mn r −0.86; Ca vs RE r −0.59; Clay Vs Fe-Mn r −0.53) were determined.

Key words: copper fractions, copper availability, parent materials, soil properties, southeastern Nigeria