STUDIES OF THE DISTRIBUTION AND BIOAVAILABILITY OF SOIL ZINC FRACTIONS

This investigation was undertaken to study the distribution and availability of Zn in different soil fractions. The proportions of total Zn present in the soils in exchangeable, organically bound, complexed or adsorbed and residual fractions were determined by sequential extraction with CaCl2, H2O2, EDTA and HCl/HNO3 respectively. Most of the total Zn was, on average, present in the EDTA-Zn (15.5%) and HCl/HNO3-Zn (78%) forms. The CaCl2-Zn and H2O2-Zn fractions averaged 5.0 and 1.5% of the total Zn respectively. Zinc present in exchangeable (CaCl2-Zn), organically bound (H2O2-Zn) and complexed (EDTA-Zn) forms was closely related to the bioavailability of Zn to maize plants grown on these soils. The residual Zn (HCl/HNO3-Zn) was not readily available.