Zinc fractionation of soils of different parent materials and their relationships with some soil properties

Understanding the distribution of various fractions of micronutrients in soils is important for effective and efficient management of soils for optimum crop production and environmental conservation. Distribution of various Zn fractions in soils of different parent materials (coastal plain sands, alluvium, false bedded sandstones and Imo clay shale) in Imo State, South-eastern Nigeria was evaluated using sequential extraction procedure, comprising six fractions: water soluble, exchangeable, specifically sorbed/CO3 bound, Fe-Mn bound, organic matter (OM) bound and residual bound. Soil samples were sequentially extracted and the various Zn fractions determined using atomic absorption spectrophotometer. Also, various Zn fractions were correlated to selected soil properties. On average value basis, zinc fractions in mg/kg decreased in the order of residual bound (0.695) > FeMn oxide bound (0.598) > specifically sorbed/CO3 bound (0.454) > exchangeable (0.241) > water soluble (0.209) > OM bound (0.143) in soils of Coastal Plain Sands; specifically sorbed/CO3 (0.408)> water soluble (0.378) > exchangeable (0.375) > residual bound (0.250) > OM bound (0.217) > Fe-Mn oxide bound (0.121) in soils of alluvium; specifically sorbed/CO3 bound (0.581)> residual bound (0.560) > Fe-Mn oxide bound (0.464) > OM bound (0.402) > exchangeable (0.283) > water soluble (0.182) in soils of false bedded sandstones; and residual (1.163) > specifically sorbed/CO3 bound (1.086)> exchangeable (0.587) > Fe-Mn oxide bound (0.389) > OM bound (0.364) > water soluble (0.154) in soils of Imo clay shale. Available zinc concentrations were low and varied among the soils of different parent materials in a decreasing order of alluvium (0.753 mg kg-1) > Imo clay shale (0.741 mg kg-1) > false bedded sandstones (0.464 mg kg-1) > coastal plain sands (0.449 mg kg-1) while total zinc concentrations were in decreasing order of Imo clay shale (3.742 mg kg-1) > falsebedded sandstones (2.471 mg kg1 ) > coastal plain sands (2.340 mg kg-1) > alluvium (1.749 mg/kg). Zn fractions correlated among each other and with pH, OM, ECEC, available P, Ca and clay.