Modeling desorption kinetics of the native and applied zinc in biochar-amended calcareous soils of different land uses

Abstract

Soil components including organic matter (OM) are of vital importance in sorption/desorption kinetics of potentially toxic trace elements (PTEs), e.g., zinc (Zn). Nowadays, biochars as a source of OM have received increased attention because of their potential for improving soil properties. Effect of wheat straw biochar (0, 1.5 and 3% w/w) and zinc levels (0 and 10 mg Zn kg−1 soil as ZnSO4·7H2O) on Zn desorption kinetics was evaluated in an incubation experiments with agricultural, rangeland and forest soils. There was a rapid desorption rate during the first 2 h, followed by a slower rate during the next 14 h in all soil types. High rates of Zn desorption were observed in Zn-treated soils. In all soil types, biochar reduced Zn desorption, whereas, Zn increased it. The highest amounts of Zn desorption in both no Zn-treated and Zn-treated soils corresponded to the forest soil followed by the rangeland and agricultural soils. The simple Elovich and two-constant rate models were the best models to describe Zn desorption from the soils. Biochar decreased the release of Zn to the soil solutions. Therefore, it may reduce the probable excessive amount of Zn uptake by plant root, transfer to food chain, Zn leaching to surface and subsurface waters and their possible risks to human health. These issues should be considered in management practices for different land uses under various Zn application strategies. Furthermore, evaluation of other levels/sources of biochar and Zn on desorption kinetics of Zn in soils of various land use types is recommended.