Transformation of zinc in soil as affected by different levels and sources of zinc application

Abstract

In order to study the bioavailability of zinc (Zn) and the distribution of zinc fractions in soil, a laboratory incubation study was conducted with different levels and sources of Zn. The experiment comprised of three different sources with each five levels of Zn. The experimental soil was sandy clay loam and was incubated for a period of 60 days and destructive sampling was done at 15, 30, 45 and 60 days after incubation. Sequential extraction of Zn was done to analyse water soluble plus exchangeable (WS-Ex.Zn), organically complexed (Org.Zn), carbonate bound (Car.Zn), iron- manganese oxide bound (Fe-Mn Ox.Zn) and residual Zn besides analysing soil available Zn. The results revealed that irrespective of the sources of Zn applied, all the Zn fractions increased with increasing levels of Zn. With the advancement of incubation, WS-Ex.Zn and Org.Zn decreased whereas Car.Zn, Fe-Mn Ox. Zn and residual Zn increased. The distribution of Zn fractions followed the order WS-Ex.Zn < Car.Zn < Org.Zn < Fe-Mn Ox.Zn < Residual Zn. Available Zn increased with increasing levels of Zn application but decreased with advancement of incubation. The labile fractions comprised of WS-Ex. Zn and Org. Zn which contributed the lowest amount of about 0.24% and 2.63% of total Zn. Residual Zn fraction which is held within the silicate minerals and unavailable to plants contributed the highest amount of 81.43% of total Zn. The highest Zn recovery in labile pools was found in Zn-EDTA followed by Zn citrate and ZnSO4.