Vetiver Grass For Phytostabilization Of Metalliferous Ecosystems

The vetiver grass (Vetiveria zizanioides L.) has rather unique morphological and physiological characteristics. It has the ability to control erosion and sedimentation, to withstand extreme soil and climatic variations, and to tolerate elevated heavy metal concentrations in water and soil [107,108]. Vetiver is sterile and noninvasive; it does not compete with native vegetation and, as a nurse plant, it fosters the voluntary return of native plants. Most importantly, however, vetiver is proven technology: its effectiveness as an environmental protection tool has been demonstrated around the world and in some parts of the U.S. [109]. Due to its unique character, vetiver grass has been widely known for its effectiveness in erosion and sediment control [110,111].

The most conspicuous characteristics of vetiver grass include its fast growth, large biomass, strong root system, and high level of metal tolerance; therefore, it is an important candidate for stabilization of metal-contaminated soils. Results from glasshouse studies show that, when adequately supplied with nitrogen and phosphorus fertilizers, vetiver can grow in soils with very high levels of acidity, aluminum, and manganese. Vetiver growth was not affected and no obvious symptoms were observed when soil pH was as low as 3.3 and the extractable manganese reached 578 mg kg-1, and plant manganese was as high as 890 mg kg-1. Bermuda grass (Cynodon dactylon), which has been recommended as a suitable species for acid mine rehabilitation, has 314 mg kg-1 of manganese in plant tops when growing in mine wastes containing 106 mg kg-1 of manganese [112]. Vetiver also produced excellent growth at a very high level of soil aluminum saturation percentage (68%), but it did not survive an aluminum saturation level of 90% at soil pH of 2.0. The toxic level of aluminum for vetiver would be between 68 and 90% [113]. It also has been observed that vetiver thrives well on highly acidic soil with aluminum saturation percentage as high as 87%.

In Australia, V. zizanioides has been successfully used to stabilize mining overburden and highly saline, sodic, magnesic, and alkaline (pH 9.5) tailings of coal mines, as well as highly acidic (pH 2.7) arsenic tailings of gold mines [114]. In China, it has been demonstrated that V. zizanioides is one of the best choices for revegetation of Pb/Zn mine tailings due to its high metal tolerance [115,116]; furthermore, this grass can also be used for phytoextraction because of its large biomass.

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