Influence of Physical-Chemical Characteristics of Soil on Zinc Distribution and Availability for Plants in Vertisols of Serbia

Sequential extraction for the determination of zinc forms in soil has been applied in order to enable clearer understanding of its mobility and availability for plants. Examinations were conducted on 20 samples of soil with different chemical and physical characteristics; plant uptake was followed on oats (Avena sativa L). A fractional scheme was applied with extraction of (I) water soluble and exchangeable adsorbed metals, (II) specifically adsorbed metals and metal bounded with carbonates, (III) reductant releasable Zn, which included Zn bonded to oxides not released in the previous step, and probably included Zn occluded in oxides, (IV) organically bonded, and (V) (residual fraction) metal structurally bonded in silicates. The majority of zinc is in residual fraction (V) (74.9% in field vertisols and 69% in meadow vertisols). Reductant releasable Zn occluded in oxides (III) is the second largest with higher values in meadows (22.2%) than in fields (17.5%). The content of zinc in organic matter (IV) is small (6.7%) in both types of soil. Specifically adsorbed zinc, and zinc bonded with carbonates (II) is low (0.1-3.1), while its' content in exchangeable fraction (I) is negligible and is about 0.2%. Exchangeable and specifically adsorbed zinc increased with the reduction of the pH of soil, CEC, clay and clay + silt, and with the increase of silt and sand. Zinc in the residual fraction increases with the pH of soil, clay, CEC, and clay + silt. The concentration of residual zinc was determined by mechanical fraction of clay.