Application of Vetiveria zizanioides Assisted by Different Species of Earthworm in Chromium-Contaminated Soil Remediation

An earthworm-assisted phytoremediation of Cr contaminated soil was conducted to study the performance of different earthworm species in Cr accumulation of Vetiver Grass (vetiveria Zizanioides VG). Two species of earthworm (Eisenia Foelide and Pheretima guillemi Michaelsen) were added in trial. The result showed Vetiveria Zizanioides can absorb great amounts of chromium in soil. The decline rate of Cr was up to 87% and 78% respectively in the tiral of Eisenia Foelide (EF) and Pheretima guillemi Michaelsen(PGM) at 60th day. As the concentration of Cr gradually increased within 3.3-120mg/kg, the accumulation activity of two groups presented first increase and then decrease and reached maximum 976.7mg/kg and 943.1 mg/kg in root. It began to decrease when the Cr concentration was above 120mg/kg.Vetiveria Zizanioides's accumulation ability differs in root and shoot. It presented root>shoot. With a comparative analysis, PGM has higher accumulation and resistance to Cr at any designed treatments. In the analysis of relation between plants and soils, it was found that there was significant correlation in Cr contents between plants and soils (P<0.05). There was a high retention rate of Vetiveria Zizanioides root to Cr. Retention rate of any treatments adding earthworm were all greater than 87.91%. The biggest value was up to 96.23%. There was no obvious difference between EG and PGM in retention rate.