VETIVER GRASS SYSTEM FOR ENVIRONMENTAL PROTECTION
Dr. Paul Truong and Dennis Baker
Resource Sciences Centre
Indooroopilly, Brisbane, Australia .
( Bulletin no.98/1, Pacific Rim Vetiver Network )
Although Vetiver grass (Vetiveria zizanioides) has been used for land protection purposes for about 50 years, its real impact on soil and water conservation world wide was only started in the late 1980s following its promotion by the World Bank through The Vetiver Network which was established by Dick Grimshaw.
The Vetiver Grass System (VGS) was first developed to protect farmlands from soil erosion and to conserve water. While this application still has a vital role in agricultural lands, its tolerance to highly adverse soil and climatic conditions has emerged as the most exciting natural tool in the increasingly concerned field of environmental protection. This was recognised by His Majesty, King Bhumibhol Adulyadej of Thailand as early as 1991 and was reconfirmed by research works conducted by the authors in Queensland in the last 6 years and also at the First International Vetiver Conference in Thailand in 1996.
2. Environmental Degradation
There has been a world wide concern, about the contamination of the environment by urban wastes and by-products of rural, industrial and mining industries particularly in the rapidly developed economies of developing countries. The majority of these contaminants are high levels of chemicals by products and heavy metals which can affect flora, fauna and humans living in the areas, in the vicinity or downstream of the contaminated sites. Table 1 shows the maximum levels of heavy metals tolerated by environmental and health authorities in Australia and New Zealand .
Concerns about the spreading of these contaminants have resulted in strict guidelines being set to prevent the increasing concentrations of heavy metal pollutants. In some cases industrial and mining projects have ceased until appropriate methods of decontamination or rehabilitation have been implemented at the source.
Methods used in these situations have been to treat the contaminants chemically, burying or to remove them from the site. These methods are expensive and at times impossible to carry out as the volume of contaminated material is very large, examples are gold and coal mine tailings.
If these wastes cannot be economically treated or removed, off-site contamination must be prevented. Wind and water erosion and leaching are often the causes of off-site contamination. An effective erosion and sediment control program can be used to rehabilitate such sites. Vegetative methods are the most practical and economical, however, revegetation of these sites is often difficult and slow due to the hostile growing conditions present which include toxic levels of heavy metals.
Vetiver grass (Vetiveria zizanioides) which has been widely known for its effectiveness in erosion and sediment control (9), has also been found to be highly tolerant to extreme soil conditions including high metal concentrations (10,11,12,13). Research and field applications in Queensland have shown that vetiver grass is suitable for the rehabilitation of contaminated lands.
Table 1: Investigation threshold concentrations for potential contaminants of soils, as set by the ANZECC/NHMRC (1992) and the then Chemical Hazards and Emergency Management (CHEM) Unit (1991) ( Reference 2)
All the research and applications conducted in Australia have been based on the genotype Monto
( registered in Australia as Monto vetiver ), which is genetically similar to the majority of non-fertile genotypes such as Thailand, India, Malaysia, Philippines, Fiji ,Sunshine (USA), Vallonia (South Africa ) and Guiyang (China) (1). Therefore the Australian results can be applied with confidence elsewhere when the cultivar is us used.
3. Some Special Attributes of Vetiver Grass
3.1 Morphological characteristics
Vetiver grass has neither stolons nor rhizomes and a massive finely structured root system. In some applications rooting depth has reached 3-4m in the first year. This massively thick root system binds the soil and at the same time makes it very difficult to be dislodged under high velocity flows. In addition this very deep root system has also made vetiver very drought tolerant, as an example vetiver did not only survive but continued to grow through the worst drought in Australia early in the 1990s. Further advantages include :
3.3 Genetic Characteristics
There are three Vetiver species being used for soil conservation purposes: V.zizanioides, V. nigritana and V. nemoralis.
V.nigritana is native to Southern Africa and its application is mainly restricted to the sub continent.
There are two V.zizanioides genotypes being used in Asia for soil and water conservation purposes:
The South Indian genotype is the main cultivar used for essential oil production and this is the genotype that being used around the world for soil and water conservation purposes because of its unique and desirable characteristics already mentioned. Recent results of the Vetiver Identification Program, by DNA typing, conducted by Adams and Dafforn (1) have shown that of the 60 samples submitted from 29 countries outside South Asia, 53 (88%) were a single clone of V.zizanioides.(1)
The 53 samples tested came from North and South America, Asia, Oceania and Africa. Most interestingly among these cultivars are: Monto (Australia), Sunshine (USA), Vallonia (South Africa) and Guiyang (China). The implications are that, once the genotype is identified, all our R, D and A (Application) can be shared around the world. For example, as all vetiver research conducted in Australia have been based on Monto vetiver, all the Australian results presented at this publication can be applied with confidence in Thailand when the south Indian cultivars are used and likewise the Guiyang cultivar in China, Vallonia cultivar in Southern Africa.
3.4 Ecological Characteristics
Although vetiver is very tolerant to some extreme soil and climatic conditions, it is highly intolerant to shading. Shading will reduce its growth and in extreme cases, may even eliminate vetiver in the long term. Therefore vetiver produces best growth in the open and weed control may be needed during establishment phase.
Also because of this characteristics vetiver can be considered as a pioneer plant on disturbed lands. Vetiver first stabilises the erodible ground ( particularly steep slopes), then improves its micro environment so other volunteered or sown plants can establish later. If the planted or invaded local native species, such as trees and shrubs, were taller than vetiver, these plants would shade the vetiver out, reducing its growth and in the long term (if desirable) can replace vetiver as the main stabilising agent. Australian and overseas results have shown that within two years local species can reduce vetiver growth substantially. Therefore vetiver is highly suitable for land rehabilitation in combination with native plants.
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3.4 Weed potential
It is very important any plants that are used for soil and water conservation do not become a weed in the local environment. It is therefore imperative that only sterile cultivars be used. From the three vetiver cultivars present in Australia, a sterile line was selected and rigorously tested for its sterility. From 1989 this cultivar has consistently produced no caryopses when grown under glasshouse and field conditions and in dryland, irrigated and wetland habitats. This cultivar was registered as Monto vetiver as the Monto district was the site of first field trial in Queensland. Establishment of Monto vetiver is by vegetative means by subdivisions of the plant base or slips.
Monto vetiver is readily grazed by cattle, dairy cows, sheep and horses as well as some native animals..
A field study conducted in Fiji where vetiver has been widely used for soil conservation purpose for more than 50 years, showed that vetiver has not become a weed under a wide range of habitats (8).
4.1 Sediment trapping /Filtering
The barrier formed from the thick growth of vetiver hedges is also a very effective filter of both coarse and fine sediment in run-off water. These sediment need to be trapped on site or they will pollute and silt up streams, roads and other infrastructure. Chemical pollutants also often adsorbed by these sediments which when trapped by vetiver hedges will lessen off-site pollution.
In Thailand Vetiver hedges are used extensively in the stabilisation of earth banks and also to filter run-off water of farm dams and fish ponds.
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In Australia: Vetiver filter strips are being used extensively in Queensland to trap sediment in both agricultural and industrial lands. At a working quarry, vetiver hedges planted across waterways and drainage lines reduced erosion and trapped both coarse and fine sediment resulting in less sediment in the dam water.
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In Thailand, research conducted in cabbage crops grown on steep slope (60%) indicated that Vetiver hedges had an important role in the process of captivity and decontamination of agrochemicals especially pesticides such as carbofuran, monocrotophos and anachlor preventing them from contaminating and accumulating in crops (4). Other research found that vetiver grass can absorb substantial quantity of Pb, Hg, Cd in waste water (6). Methanol extracts of ground stem and root was found to be very effective in preventing the germination of a number of both monocot and dicot weed species. These results indicate the potential of vetiver extract as a natural pre-emergent weedicide. (7).
4.3 Water purification
In China research showed that vetiver can reduce soluble P up to 99% after 3 weeks and 74% of soluble N after 5 weeks and the potential of removing up to 102t of N and 54t of P per year per hectare of vetiver, VGS is highly suited for the removal of these two elements in the polluted environment.
In addition works conducted in Thailand showed that VGS could absorb substantial amount of Cd, Hg and Pb in waste water. Therefore can be effectively used for the following applications:
As soluble N and particularly P are usually considered to be key elements for water eutrophication which normally leads to blue green algal growth in inland waterways and lakes, the removal of these elements by vegetation is a most cost effective and environmental friendly method of controlling algal growth.
Chinese works indicated that Vetiver could remove dissolved nutrients and reduced algal growth within two days under experimental conditions(15,16). Therefore VGS can be used very effectively to control algal growth in water infested with blue-green algae. This can be achieved by both planting vetiver on the edges of the streams or in the shallow parts of the lakes where usually high concentrations of soluble N and P occurred and by growing Vetiver hydroponically on floating platforms which could be moved to the worse affected parts of the lake or pond. The advantages of the platform method is that vetiver tops can be harvested easily for stock feed or mulch and Vetiver roots can also be removed for essential oil production ( vetiver oil is a high priced essential oil used by the perfumed industry).
4.4 Effluent Disposal
With the potential of removing up to 102t of N and 54t of P per year per hectare of Vetiver planting. Vetiver grass is a species highly suitable for the removal of P and N from effluent from sewage, abattoirs, feedlots, piggeries and other intensive livestock industries.
It has also been successfully used to stabilise and rehabilitate a highly erodible acid sulfate soil on the coastal plain where actual soil pH is around 3.5 and oxidised pH is as low as 2.8 (12).
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In Australia Landfill and industrial waste sites are usually contaminated with heavy metals such as As, Cd, Cr, Ni, Cu, Pb and Hg which are highly toxic to both plants and humans. The movement of these contaminated materials from these sites needs to be adequately controlled.
The very high level of tolerance to heavy metals such as As, Cd, Cr, Ni, Ca, Pb, Zn, Se and Hg and agro-chemicals reported above indicate vetiver grass is most suitable for use in the rehabilitation of such contaminated sites. Works conducted in Queensland have conclusively shown that vetiver can be used to rehabilitate the highly erodible slopes and drainage lines and in reducing leachate from these contaminated sites (10,15).
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In China studies on the effects of Vetiver in purifying urban garbage leachate indicated that of the seven parameters measured in the study, ammoniac nitrogen was the best cleansed, and its purification rate was between 83%-92%, indicating that vetiver has strong absorption abilities to ammoniac N dissolved in water. In addition, Vetiver showed a quite high purification rate for phosphorus (more than 74%). Results also indicated that vetiver was the best among the four species of plants tested in term of their purifying effects and their tolerance to high leachate concentrations (16).
In Australia vetiver is highly successful in the rehabilitation of both old and working quarries where very few species can be established due to the hostile environment. Vetiver is able to stabilise the lose surface first so other species can colonise the areas between hedges later. After two years the site was completely revegetated with vetiver and local species.
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In Australia vetiver has been successfully used to stabilise mining overburden and highly saline, sodic and alkaline (pH 9.5) tailings of coal mines and highly acidic (pH 3.5) tailings of a gold mine.(5)
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In South Africa vetiver has been very effectively used to stabilise/rehabilitate "slimes dams" (tailings). Works at de Beers diamond mine slimes dams at Premier (800 mm annual rainfall) and Koffiefonteine (300 mm) mines confirms that vetiver can survive in very harsh environments where surface temperatures of the slimes dam materials, that are black in colour, reach over 550C. At this temperature most seeds are unable to germinate. Vetiver hedges at 2 m VI (Vertical Interval) provides shade that cools the surface thus allowing germination of other grass seeds. Wastes and slime dams from platinum and gold mines have also been successfully stabilised with vetiver (3)
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