Lixiviation and Extraction of Zinc in a Calcareous Soil Treated with Zinc-Chelated Fertilizers

When Zn is added to calcareous soils to avoid Zn deficiencies, it can be fixed, if the source is a soluble inorganic salt, and leached, if it is a stable complex. Relative mobilities of Zn−EDTA and Zn−lignosulfonate (LS) chelates added to calcareous soil columns as coated and uncoated fertilizers were determined. Zn−EDTA migrated and distributed throughout the columns. About 51% of the Zn was leached with uncoated fertilizers but only about 10% when coated fertilizers were used. Zn−LS migrated very little, especially with coated fertilizers; the Zn remained mostly in the upper zone of the column and was not leached. The distribution of the added Zn between different fractions of soil was determined by a sequential extraction procedure. When Zn−EDTA was added, the percentage of the most labile fractions increased slightly with respect to the control soil throughout the entire profile of the column. Zn−LS displayed higher increases in the most labile fractions but only in the top layer of the column. Correlations between the extracted fractions (P < 0.001%) showed that in general a dynamic equilibrium existed between them. DTPA-extractable Zn correlated (P < 0.001%) with the two most labile fractions and to a lesser extent with the nonbioavailable forms. Comparisons between coated and uncoated fertilizers show that the presence of coatings benefits Zn−EDTA fertilizers, decreasing the leaching and increasing the amount of biavailable Zn, but had no beneficial effect for Zn−LS fertilizers. Keywords: Zn chelates; controlled-release; calcareous soil columns; speciation; leaching