Abstract
A greenhouse experiment aimed to assess the effects of poultry manure, sorghum, and clover residues (0 and 15gkg-1) on the zinc (Zn) bioavailable fraction in contaminated calcareous soil using two chemical assays, including diffusion gradient in thin-films (DGT) and diethylene triamine pentaacetic acid-triethanolamine (DTPA-TEA), and a bioassay with corn (Zea mase L.). The results showed that poultry manure, clover, and sorghum residues application increased dissolved organic carbon (DOC) by 53.6 and 36.1, and 9.2%, respectively, and decreased soil pH by 0.42, 0.26, and 0.06 units, respectively compared to unamended soil. These changes resulted in increases of Zn effective concentration (CE) and DTPA-Zn, and plant Zn concentration as observed by the increase in exchangeable form of Zn. In the sorghum residues-amended soils, CE-Zn decreased by 29.5% compared to other treatments. The best correlations between corn metal concentrations and soil metal bioavailability were obtained for CE-Zn using the DGT technique, which also provided the best Zn bioavailability estimate. It is concluded that sorghum residues could be used to reduce the phytotoxicity risk of Zn in calcareous contaminated soil, and the DTPA method is the less robust indicator of Zn bioavailability than the DGT technique.
Highlights
Metals present in different concentrations in all soils, most play a major role at relatively low levels for biological life such as Zinc (Zn)
The findings of organic amendments characteristics used in this study revealed that the highest of Zn concentration was in poultry manure, clover, and sorghum residues, respectively
The addition of poultry manure and clover residue significantly increased, and sorghum residues decreased the effective concentration of Zn (CE-Zn) measured by diffusion gradient in thin films (DGT) method
Summary
Metals present in different concentrations in all soils, most play a major role at relatively low levels for biological life such as Zinc (Zn). Organic amendments have widely been used as a remediation method to reduce the metals phytotoxicity and bioavailability in contaminated soils (Palansooriya et al 2020). Organic amendments affects the distribution of chemical forms of metals by modifying some soil properties (Ashraf et al 2019). The use of organic matter as a soil amendment is based on the hypothesis that metal precipitation and sorption reactions induced by organic matter may result in an increase in metal retention on the solid phase, and a decrease in the metal availability (Nwachukwu and Pulford 2009), while it is not always the case. This study indicated that organic amendment increased soil absorption phases and reduce the metals availability. The organic amendment efficacy at reducing the heavy metals bioavailability is mostly dependent on the type of organic amendment and metal, as well as the potential measures of heavy metals
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