Phytoextraction of cadmium contaminated agricultural soil by tobacco and swiss chard rotation systems

Phytoremediation of heavy metal contaminated soil has the advantages of environmental friendliness, moderate cost and in situ restoration. The farmland soil with medium and high risk of heavy metal pollution were selected for pot experiments to explore the remediation potential of tobacco (Nicotiana tobaccum L.) and swiss chard (Beta vulgaris var. cicla L.) rotation model for the heavy metals Pb, Zn, Cu and Cd in the contaminated soil of two kinds of farmland. The results showed that, on the tested soils, tobacco and swiss chard had certain enrichment capacity for Pb, Zn, Cu and Cd, especially for Cd. In the soil with high heavy metal pollution risk, the concentration of Cd in the lower leaves of tobacco at the mature stage was the highest, which reached 41.63 mg/kg, and the enrichment coefficient and transport coefficient of Cd with lower leaves of tobacco was 17.06 and 17.42, respectively; the Cd concentration in the roots of swiss chard at the mature stage was 7.55 mg/kg, and the enrichment coefficient was 3.85, significantly higher than that in the above ground part. According to the pot experiment with soil of medium heavy metal pollution risk, the concentration of Cd in the lower leaves of tobacco at the mature stage reached 34.59 mg/kg, and the enrichment coefficient and the transport coefficient was 40.69 and 13.67, respectively; the Cd concentration in the roots of swiss chard at the mature stage was 4.33 mg/kg, and the enrichment coefficient was 7.69. After the tobacco-swiss chard rotation pot experiment, the total amount of Pb, Zn, Cu and Cd in the two kinds of soils decreased by 2.99%, 3.55%, 12.41%, 57.64%, and 3.32%, 1.63%, 9.45%, 24.59%, respectively. At the same time, the effective concentrations of heavy metals Pb, Cu and Cd in soils were significantly reduced. In conclusion, the tobacco-swiss chard rotation model could provide good application potential in remediation of farmland polluted by heavy metals with medium and high pollution risk.