Effects and limitations of elemental sulphur applications for enhanced phytoextraction

The application of elemental sulphur (S) to heavy metal contaminated soils is a strategy to increase metal extraction by plants. Here, we examined to which degree the efficiency of phytoextraction could be enhanced by increasing the S application rate on afield where S had already been applied for 6 years. For this purpose, the field experiment was continued for another two years doubling the S application rate on half of the S treatment plots, while continuing application at the previous rate on the other half. Doubling the application rate significantly accelerated the dissolution of calcite and the decrease in soil pH and also increased cadmium (Cd) and zinc (Zn) uptake by sunflower and tobacco. But even in a best-case-scenario remediation of the site would still take more than a century. The results indicate that we reached the maximum potential of S application to enhance metal phytoextraction on the study site. Further decrease in pH by additional S applications would bear an excessive risk of decreasing yields and increasing metal leaching out of the root zone.