Manure Application and Cannabis Cultivation Influence on Speciation of Lead and Cadmium by Selective Sequential Extraction

Abstract

The contamination of agricultural soils by heavy metals is a worldwide problem. Degradation of organic matter (OM) from organic amendments used in the remediation of metal-contaminated soils leads to changes in soil chemical properties shortly after their addition, which may affect the soil metal distribution. The effects of four differing organic amendments on chemical forms of Pb and Cd in a contaminated soil were investigated in a pot experiment of control unamended soil and soils amended with dry cow and poultry manures (20 g CM or PM kg⁻¹ soil), and cow and poultry manure extracts (2 g CME or PME kg⁻¹ soil) cultured with cannabis sativa. After eight weeks, a sequential extraction scheme was used to fractionate soil Pb and Cd into soluble-exchangeable (Sol-Exch), organic matter associated (AOM), and carbonates associated (ACar) forms. The addition of animal manures and their extracts increased the DTPA-extractable Pb and Cd in soil significantly. Soil Pb and Cd in Sol-Exch fraction were increased by manure applications. Both Pb and Cd in AOM fraction were increased by application of manures and their extracts. This increase was more obvious for Pb in application of cow and poultry manure extracts. The ACar chemical forms of Pb and Cd were also increased by application of manures and their extracts. The increases of Pb and Cd in Acar fraction was noticeable in soils treated with cow manure. Soil cultivation with cannabis sativa increased available, Sol-Exch, and AOM chemical forms of Pb in soil significantly compared to control soil. However, soil Pb and Cd in ACar fraction were decreased significantly by cannabis cultivation. The effect of cannabis cultivation on all of the Cd chemical forms (except on Sol-Exch) was similar to the results of Pb chemical forms. Plant cultivation had no significant effect on Cd in Sol-Exch chemical form.

Keywords:

• heavy metals
• fractionation
• cannabis cultivation
• calcareous soil

Acknowledgments

This study was supported by funds allocated by the Vice President for Research of the Bu-Ali Sina University. We acknowledge the assistance of N. Nikbakht for some help in laboratory analysis.