Elemental sulfur effects on Pb and Zn uptake by Indian mustard and winter wheat

A pot experiment was conducted to investigate the influence of elemental sulfur to contaminated soil on plant uptake by a heavy metal hyperaccumulator, Indian mustard (Brassica juncea) and a field crop, winter wheat (Triticum. aestivum). Elemental sulfur (S) with different rates was carried out, they were 0 (S0), 20 (S20), 40 (S40), 80 (S80), and 160 (S160) mmol/kg respectively. Extra pots with the same rates of S but without plants were used for soil sampling to monitor pH and CaCl2-extractable heavy metal changes. The results showed that S enhanced phytoextraction of Pb and Zn from contaminated soil. Application S effectively decreased soil pH down to 1.1 as the most at the rate of S160. The concentrations of CaCl2-extractable Pb and Zn in soil and uptake of Pb and Zn by the plants were increased with soil pH decreased. A good correlation between CaCl2-extractable Pb/Zn and soil pH was found (R2Pb = 0.847 and R2Zn = 0.991, n = 25). With S application, soil CaCl2-extractable Pb and Zn concentrations, concentration of Pb and Zn in plants and the amount of removal by plant uptake were significantly higher than those without S. Under the treatment of S160, the highest CaCl2-extractable Pb and Zn were observed, they were 4.23 mg/kg and 0.40 mg/kg, 2.7 and 2.0 times as that of the control (S0) respectively. At the highest rates of S (S160), both Indian mustard and winter wheat reached the highest uptake of Pb and Zn. The highest Pb concentrations in wheat and Indian mustard were 32.8 mg/kg and 537.0 mg/kg, all 1.8 times as that of the control, and the highest Zn concentrations in wheat and Indian mustard were 215.5 mg/kg and 404.0 mg/kg, 2.4 and 2.0 times as that of the control respectively. The highest removals of Pb and Zn from the contaminated soil were 0.41 mg/pot and 0.31 mg/pot by Indian mustard in the treatment of S160 through 50 days growth.