An Overview of Research, Development and Application of the Vetiver Grass System (VGS).
Paul Truong, Leader, Land Stabilisation and Rehabilitation Resource Sciences Centre, Department of Natural Resources, Brisbane, Queensland, Australia.
1.0 PAST AND PRESENT USES OF VETIVER GRASS
Since ancient times, Vetiver grass has been used for various purposes including thatching, medicinal and aromatic oil production. Its largest use at the moment is till for aromatic essential oil with plantations in Africa, Indonesia and the United States. The oil which is extracted from its roots, is used in the perfume industry and very popular in Europe and America. In addition Vetiver has been used for a long time in Asia and Africa for land stabilisation purposes; its prominent role in soil conservation started about 50 years ago in Fiji, where it was developed by the Colonial Sugar Refinery (CSR) to control soil erosion on steep canelands. This concept was later developed further by John Greenfield, one of the original members of the CSR team in Fiji, for a World Bank Watershed Management Project in India in 1989.
This massive $US100 million World Bank sponsored project, under the leadership of Dick Grimshaw adopted this concept as a low tech and low cost alternative to the more expensive traditional engineering structures. When Grimshaw returned to the World Bank Head Office in Washington he initiated the Vetiver Network to promote the use of Vetiver hedges in World Bank projects in several countries and around the world. But doubts about its effectiveness and the scarcity scientific data prompted the World Bank, US Department of Agriculture and USAID to commission the National Research Council (NRC) of the US National Academy of Sciences to "assess the state of knowledge, the promise and the possible limitations of Vetiver use, as well as research that might be needed before Vetiver can be deployed rationally and safely." The panel of review was led by the Nobel Laureate Norman Borlaug and coordinated by Noel Vietmeyer of the NRC.
After four years, a mass of information was distilled into the peer-reviewed study called Vetiver Grass: A Thin Line Against Erosion, in which the NRC panel unanimously reported the " Vetiver hedges were a cheap, safe and effective technique to slow erosion and retain soil moisture. Vetiver could be used with confidence, but much remained to be learnt. We should increase our knowledge of the system to the level known about engineered erosion control structures, and of Vetiver to the level known about other plants such as rice or wheat".
At last year international conference in Thailand, Noel Vietmeyer in his closing speech listed the following initiatives which are needed for the global acceptance of the VGS :
Basic science including CO2 absorption, C13 absorption, taxonomy, transaction of oxygen, heavy metals, disease prevention, mechanism of sterility, genetic diversity, mycorrhiza, N fixation, cold sensitivity, general tolerance, mechanism of hedge formation, dwarfing and root growth.
These initiatives show the tremendous versatility of the VGS and they include some existing knowledge and proven technologies but most importantly providing guidelines for future R& D.
Dick Grimshaw has now retired but has voluntarily devoted all his time to run the Vetiver Network which is now a truly global network with 4,000 members from over 100 countries. The Network is partly supported by the World Bank but mostly by grants and donations from such diverse sources as the King of Thailand, governments and recently the Network won the John Franz Award ($US100,000) for World Environment and Economic Sustainability from Monsanto. Recently regional networks have been established in Latin America, Europe, China, the Philippines and shortly the Pacific and Oceania, and west Africa.
In the last five years, three international conferences and workshops have been held on the application of VGS, one in Malaysia in 1992, one in Nigeria in 1994 and in February 1996 in Thailand. The latest conference attracted delegates from over 40 countries who contributed about 150 papers covering a wide range of topics.
2. 0 WHAT DOES VGS DO?
VGS is a very simple, practical, inexpensive, low maintenance and very effective means of soil and water conservation, sediment control, land stabilisation and rehabilitation. Being vegetative it is also environmentally friendly.
3.0 HOW DOES VGS WORK?
When planted in rows Vetiver plant will form a hedge, a living porous barrier which slows and spreads runoff water and traps sediment. As water flow is slowed down, its erosive power is reduced and at the same time allows more time for water to infiltrate to the soil, and any eroded material is trapped by the hedges. Therefore an effective hedge will reduce soil erosion, conserve soil moisture and trap sediment on site.
This is in sharp contrast with the contour terrace/waterway system which runoff water is collected by the terraces and diverted as quickly as possible from the field to reduce its erosive potential. All this runoff water is collected and concentrated in the waterways where most erosion occurs particularly on the vertisols of the Darling Downs. This water is lost from the field. With the VGS, not only this water is conserved but no land is wasted on the troublesome waterways.
Although any hedges can do that, Vetiver grass, due to its extraordinary and unique morphological and physiological characteristics can do it better than all other systems tested.
3.1 Morphological Characteristics
Vetiver is an erect grass with stiff stem, it has neither stolons nor rhizomes and a massive finely structured root system, reaching down to 3-4m in the first year. This extraordinary thick root system is probably resulting from centuries of selection for aromatic oil production. This massive root system bind the soil and at the same time makes it very difficult to be dislodged.
This very deep root system has also made Vetiver very tolerant to drought, it did not only survive but continued to grow through the worst drought in Australia early in the 1990's, in the western Darling Downs, Queensland.
In addition Vetiver has the following desirable characteristics:
3.2 Physiological Characteristics
Tolerance of extreme climatic variation such as prolonged drought, flood, submergence and extreme temperature from - 14oC to 48oC (Queensland) and higher in India and Africa.
Ability to regrow very quickly after being affected by drought, frost, salt and other adverse soil conditions when the adverse effects are removed.
Wide range of soil pH (3.0 to 10.5)
A wide range of toxicities including heavy metals in the soils. My research in Australia in the last 8 years has established that when adequately supplied with N, P nutrients and soil moisture, Vetiver can tolerate a wide range of adverse soil conditions:
Table 1: Levels of Heavy Metal Toxic to Vetiver and other Species.
|Heavy Metals||Soil levels (mg/kg)||Soil levels (mg/kg)|
|Chromium||18||0.02 - 0.2|
|Nickel||347||10 - 30|
|Arsenic||72||1 - 10|
4.0 Research and Development on Vetiver Cultivars, Seed Sterility and Weed Potential
In general there are two Vetiveria zizanioides L. genotypes being used for soil and water conservation purposes, the wild and seeded north Indian variety and the sterile or very low fertility south Indian variety which is the main cultivar for essential oil production therefore widely spread around the world. Recently, preliminary results of the Vetiver Identification Program (by DNA analysis) coordinated by Mark Dafforn of the NRC for the Vetiver Network have identified 25 identical DNA samples from around the world: north and south America, Asia, Oceania and Africa (Malawi and South Africa). Most interestingly, among these cultivars are Monto (Australia), Sunshine (US) and Vallonia (RSA) from Maxime Robert's sugar estate in Umhlali Natal. The implication is that, as all Vetiver researches conducted in Australia have been based on Monto Vetiver, all the Australian results presented in this paper can be applied with confidence here in South Africa when the Vallonia cultivar is used.
It is very important that any plants used for soil and water conservation will not become a weed in the local environment, particularly in a new country where its weed potential is greatest due to the lack of its natural enemies. Therefore, only sterile cultivars should be used. From the three Vetiver cultivars present in Australia, a sterile line is selected and rigorously tested for its sterility. For the last eight years, it has consistently produced no caryopses when grown in both glasshouse and field conditions under dryland, irrigated and wetland habitats and from semi arid areas of central Australia, to the wet tropics of north Queensland, to the temperate region of south east Australia. This cultivar was registered in Queensland as Monto Vetiver to commemorate the Monto district where the first field trial was conducted.
Monto Vetiver is a non aggressive plant, it produces neither stolons nor rhizomes and has to be established vegetatively by root (crown) divisions or slips. Monto Vetiver is readily grazed by cattle, dairy cows, sheep and horses as well as some native animals once they are familiar with the plant and Monto Vetiver has been used in all research, development and application works conducted in four states: Queensland, New South Wales, Victoria and Western Australia.
In Fiji where Vetiver grass was introduced to the country for more than 100 years and it has been widely used for soil and water conservation purposes for more than 50 years, it has not shown any weed potential.
5.0 APPLICATIONS OF THE VETIVER GRASS SYSTEM:
At the last International Conference early in 1996, almost 150 papers were presented, ranging from basic research on Vetiver physiology, ecology and adaptation to socio-economic impacts of VGS applications. The followings are highlights of some of the works known to date and papers presented at the conference.
5.1.1 Soil Erosion Control, Water Conservation and Crop Production
In India, the effects of Vetiver hedges, Leucaena hedges, graded contour banks and contour cultivation on runoff, soil loss and crop yield were compared on a range of soils on relative flat land (0.7-2.0% slope). Results over the four year period 1988-1991 show that in comparison with contour cultivation, surface runoff and soil loss from Vetiver plots were significantly lower and sorghum yield was much improved (Table 2). The yield increase was attributed mainly to uniform in situ soil and moisture conservation over the entire toposequence under the Vetiver hedge system.
In Venezuela under field simulation rain conditions it was shown that both soil loss and runoff were substantially reduced by Vetiver hedges as compared with control treatments and other vegetative barriers (Table 3).
Research at ICRISAT (International Crops Research Institute for the Semi-Arid Tropics) showed that under small plot conditions Vetiver was more effective at runoff and soil loss control than lemon grass or stone bunds. The runoff from the Vetiver plots was only 44% of that of the control plots on 2.8% slope and 16% on 0.6% slope. Relative to control plots, average reduction of 69% of runoff and 76% of soil loss were recorded from Vetiver plots.
In Australia, field data have shown that under drought or low rainfall conditions, mature Vetiver hedges could compete for soil moisture with the adjacent crop rows, up to 1.5m for sorghum, resulting in poor establishment and reduced yield. However, when soil moisture is not limited or under irrigation, crop establishment and yield were not affected. This small yield reduction in dry years would be a small premium to pay for the insurance against severe erosion when the drought broke.
Table 2: Effects of conservation measures on arable crop land (1.7% slope) 1988-1991.
|Surface runoff as % of rainfall||23.3||19.2||15.5||21.1|
|Infiltration as % of rainfall||76.7||80.8||84.5||78.9|
|Soil loss (t/ha)||14.4||7.5||3.9||11.3|
|(% reduction over T1)||4.75||72.9||21.6|
|(% reduction over T4)||33.1||65.5|
|Grain Yield (q/ha)||25.2||27.4||28.8||25.8|
|(% increase over T1)||8.9||14.5||3.3|
T1 Contour cultivation and sowing
T2 Leucaena hedge system
T3 Vetiver hedge system
T4 Graded bank system
Table 3: Soil loss and runoff under various hedgerow treatments on two slope gradients.
|Hedge Row||Soil Loss (t/ha)||Soil Loss (t/ha)||Runoff|
|Treatment||15% slope||26% slope||% Rainfall|
|Control (no Hedges)||16.81||35.52||88|
In South Africa, Maxime Robert has fully incorporated the VGS into the management of his farm in Natal. Vetiver has been used successfully for steep slope stabilisation, farm road and stream bank stabilisation, and contour terrace replacement at his Vallonia Sugar Estate.
In Thailand, for soil moisture conservation in orchard, planting Vetiver grass in semi circle of 2m radius downslope from the tree gave best results, this follows by semi circle of 4m radius and 4m in straight row conserved the least moisture for the trees.
5.1.2 Flood Erosion Control on the Floodplain
In Australia, VGS has is being assessed on floodplain of the Darling Downs, Queensland, as a supplement to or an alternative to strip cropping which at times provides little protection from erosion. This is particularly so during drought or when low stubble-producing crops such as sunflower and cotton are grown in alternate strips. Eight rows of Vetiver totalling almost 6,000m, were planted at 90m intervals down a strip cropped slope. Flume tests conducted at the University of Southern Queensland, found that when fully established, the Vetiver hedges should provide adequate protection from floodwater over the 90m spacing on 0.2 - 0.35% land slope which is equivalent to five existing strips at this particular site.
The incorporation of Vetiver hedges as an alternative to strip cropping on floodplains should result in more flexibility, more easily managed land and more effective spreading of flood flows in drought years and with low stubble producing crops An added benefit is that the area cropped at any one time could be increased by up to 30%.
Results to date have been very encouraging, the hedges were successful in reducing flood velocity and limiting soil movement, resulting in very little erosion and a young sorghum crop was completely protected from flood damage. The hedge spacings predicted by the hydraulic model were not excessive.
5.2.1 Hedge Hydraulics and Sediment Trapping
The hydraulic characteristics of Vetiver hedges under deep flows were determined in the above ground flume at the Agricultural Engineering Department of the University of Southern Queensland. These hydraulic parameters were needed for the design and incorporation of Vetiver hedges into strip cropping layout to control flood erosion on the floodplain mentioned above. Figure 1 shows the physical model of floodplain flow.
Fig.1: Hydraulic model of flood flow through Vetiver hedges. (Dalton et al, 1996, Agric.Water Manag. 31: 91-104)
In his paper "The Hydraulics and Sediment Trapping of Vetiver Hedges on Steep Slopes" presented at the recent Workshop on Vetiver R&D and Application in Queensland, Rod Smith (Professor of Agricultural Engineering at the University of Southern Queensland) concluded that in hydraulic terms, on slopes higher than 5%, apart from slowing the flow in the zone immediately upstream of each hedge, it is reasonable to assume that the hedges do not affect the flow, that is, the hedges will not materially affect the volume or rate of flow. On the sediment trapping of Vetiver hedges, he considered that the most important factors are hedge spacing and the thickness (density) of the hedge. Closely spaced hedges will minimise the quantity of sediment entrained by the flow. Dense hedges will maximise the depth upstream, the length of the back water and the settling time for particles and hence proportion of the sediment trapped. As terraces form the length of the backwater will increase and the sediment trapping efficiency will also increase - provided the hedge grows out of the sediment layer, remains dense and upright and is not overtopped by the flow.
5.2.2 Steep Slope Stabilisation
In their paper "An assessment of strength properties of Vetiver grass roots in relation to slope stabilisation" Diti Hengchaovanich and Nimal Nilaweera of Erocon Malaysia, outlined their innovative and tedious methods of determining root tensile strength and subsequently shear strength increase of Vetiver roots in soil blocks. They reported that the tensile strength of Vetiver roots increases with the reduction in root diameter, this phenomenon implies that stronger fine roots provide higher resistance than larger roots. The tensile strength of Vetiver roots vary between 40-180 Mpa for the range of root diameter between 0.2-2.2mm. The mean tensile strength is about 75 Mpa (equivalent to approximately one third of mild steel) at 0.7-0.8mm root diameter which is the most common size for Vetiver roots. This indicates that Vetiver roots are as strong as, or even stronger than that of many hardwood species which have been proven positive for root reinforcement in steep slopes. In the shear test, they found that root penetration of an 2 year old Vetiver hedge with 15cm plant spacing can increase the shear strength of soil in adjacent 50 cm wide strip by 90% at 0.25m depth. The increase was 39% at 0.50m depth and gradually reduced to 12.5% at 1m depth. Moreover, because of its dense and massive root system it offer better shear strength increase per unit fibre concentration (6-10 kPa/kg of root per cubic metre of soil) compared to 3.2-3.7 for tree roots.
In the paper "Use of Vetiver grass for engineering purposes in Malaysia with particular reference to slope stabilisation and erosion control" presented at the recent Vetiver Workshop in Queensland, Diti Hengchaovanich, General Manager of Terratech Consultants, a leading consultant firm in highway design and construction in Malaysia, pointed out that Vetiver can grow vertically on slope steeper than 150%, faster growing and imparts more reinforcement to the make it a better candidate for slope stabilisation than other plants. Another less well known characteristics which sets it apart from other tree roots is it power of penetration. Its 'innate' strength and vigour enable it to penetrate through difficult soil, hard pan or rocky layer with weak spots. It even manage to punch through asphaltic concrete pavement. He added that, indeed one can say that Vetiver roots basically behave like living soil nails or dowels of 2-3m depth commonly use in 'hard approach' slope stabilisation work. However, due to the high rainfall of Malaysia (1 750 to 3 500mm/year depending on the region) the effectiveness of the mechanical mechanism mentioned above may be reduced by the negative effect of the hydrological mechanism (increased infiltration and permeability which can induce mass movement). Although Malaysia is probably leading the world in the application of Vetiver for erosion and slope stabilisation in highway engineering, the author conceded that the design is still somewhat conservative, treating Vetiver as 'a bonus' or added assurance. Once more design parameters, especially the evapotranspiration and hydraulic aspects, and track records come to light, bolder and more innovative designs maximising the full potential of Vetiver grass should be adopted.
The US Corps of Engineers, Construction Engineering Research Laboratory (USACERL) over the past five years has incorporated Vetiver into various experimental designs to measure its effectiveness as a biotechnological tool in the stabilisation and reclamation of soil with different structures and textures. Experimental sites include borrow pits, abandoned strip mines, stream banks, military training areas, gully heads, steep embankments. The evaluation report concluded that Vetiver displays characteristics which are well suited for this purpose and the addition of Vetiver to land reclamation and rehabilitation programs has proven to be very effective.
5.3.1 Bio-remedial Applications
Research in Queensland showed that Vetiver is highly tolerant to toxic levels of Arsenic, Cadmium, Chromium and Nickel in the soil (Table 1).
Landfill sites (rubbish dump) and industrial wastes are usually contaminated with heavy metals such as Arsenic, Cadmium, Chromium, Nickel, Copper, Lead and Mercury which are highly toxic to both plants and human. As these old sites are often adjacent to residential and recreational areas, the movement of these contaminated materials from the sites must be adequately controlled. As Vetiver is highly tolerant to toxic levels of most of these heavy metals, it is most suitable for use in the rehabilitation of these sites. Works conducted with the Redland Shire Council have conclusively shown that Vetiver can stabilise the highly erodible slopes and drainage lines and also very effective in reducing leachate from an old dump near Cleveland (see poster).
In Thailand, Vetiver was reported to accumulate Cadmium, Lead and Mercury in both stem and roots. In addition it was reported that Vetiver hedgerows played an important role in the retention and decontamination of agro-chemicals especially pesticides, preventing them from contaminating and accumulating in crops, streams and other ecosystems.
In the US, researchers have recently reported that Vertical Flow Wetland (VFW) and Horizontal Flow Wetland (HFW) cells planted with Vetiver, respectively, removed 98% and 96% total suspended solids (TSS), 91 and 72% total chemical oxygen demand (COD) and 81 and 30% dissolved COD from sludge derived from a trout farm. Both wetland types removed most, 82-93%, of the dissolved phosphate, total Kjeldahl nitrogen and total phosphate.
When established across drainage lines and water courses, Vetiver hedges filter and trap both coarse and fine sediment resulting in cleaner runoff water. At an working quarry, Vetiver was used to stabilise steep slopes of overburden and waterways. When planted across a long (500m) and steep (20%) waterway, Vetiver hedges stopped the erosion on the waterway floor and trapped both coarse and fine sediment in runoff water from this working quarry. On another waterway leading to a dam, Vetiver hedges trapped most fine sediment resulting in less polluted water in the dam. Following the success of these trials, Vetiver is now being used as a standard method of trapping sediment and land stabilisation at the quarry.
The combination of Vetiver and African star grass have filtered out both bed and suspended load of runoff water on a pineapple farm in Queensland. Sediment load was reduced from 3.94g/L to 2.33g/L after passing through the hedge, and similarly, electrical conductivity was reduced to half (263uSm/cm to 128uSm/cm) and the high dose of weedicides used did not affect Vetiver growth..
In Thailand it is a common practice to plant Vetiver around farm dams and ponds to trap sediment in runoff water and also to stabilise the walls from erosive runoff. Short rows of Vetiver are also commonly established across all waterways leading to water storage areas.
In India, Vetiver was used to reclaim highly sodic land with pH between 9 and 10.6 throughout the soil profile.
With its wide range of tolerance to adverse soil and climatic conditions mentioned above, Vetiver would be highly suitable for the rehabilitation of mine wastes. In South Africa, Tony Tantum of Specialised Soil Stabilisation of Howick have successfully used Vetiver in the rehabilitation of highly acidic gold mine tailings and highly sodic diamond mine tailings, under extremely harsh conditions, low rainfall and extreme temperatures.
In Australia Vetiver have been successfully used to stabilise overburden and highly saline and alkaline tailings of coal mines in central Queensland and highly acidic (pH 3.5) tailings of a gold mine in north Queensland. Vetiver has also been used to rehabilitate salt affected lands due to both dryland salinity and irrigation.
In northern Australia, vetiver has been successfully used in the stabilisation and rehabilitation of 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. Vetiver was successfully established on this soil without any fertiliser and reached a height of 80cm after 8 months. Much more vigorous growth occurred when DAP ( 300kg/ha) was applied at planting.
5.4 Economic Returns
Results of cost benefit analysis conducted on the Maheswaran watershed in India where both engineering structures and vegetative barrier with Vetiver grass were used, showed that Vetiver systems are more profitable even during the initial stages due to their efficiency and
low cost. Therefore the vegetative measures are expected to be used in large areas in the future by virtue of their replicability, efficiency and profitability.
5.5 Applications of the VGS in Queensland and Australia
Queensland has very similar climate to Natal, its capital city Brisbane is on approximately the same southern latitude as Durban. The climate is subtropical in the south and tropical in the north, temperature is moderate on the coast but can be extreme inland, ranging from more than 45oC in summer to -15oC (ground) in winter. Rainfall varies between 1500mm/year in the south to over 3 500mm in the north along the coastal fringe and between 300-800mm/year inland in the agricultural zone. But this rainfall is highly variable and prolonged drought is a common feature of Queensland and Australian climate. Soil types range from the highly fertile black earth (minority) to poorly structured and infertile solodics (majority), except for the well structured red earth, all Queensland soils are highly erodible. Therefore erosion and sediment control in both agricultural and urban lands is imperative, particularly with the recent concerns about environmental degradation caused by soil erosion.
I first started conducting R&D works on Vetiver in 1988, most basic researches were conducted under glasshouse conditions but field works were established in all regions of Queensland and in cooperation with others throughout mainland Australia. Some of these works have been mentioned above, the followings are some other works of interest.
5.5.1 Substitution of Contour Banks in Steep Canelands
In steep canelands the traditional method of soil conservation using contour banks can present some problem for machinery operation as the channels and banks can be dangerous for harvesters and haul out machinery. Replacements of contour banks with rows of vegetation such as Vetiver grass could offer a solution to the problem. In addition space saved from the conventional banks can be used to plant another row of cane next to the Vetiver hedge.
Two rows of Vetiver totalling 800m were planted on contour line on a property on the wet tropical coast near Innisfail. Results to date are very encouraging, however the full results cannot be assessed until the next new planting when the old crop will be ploughed out and fallowed. Vetiver hedges are in place to protect the steepland from early season storms.
.5.2 Steep Slope Stabilisation
Embankment of both cut and fill slopes can be effectively stabilised by establishing Vetiver on contour lines. The deep root system stabilises the slope while the hedges reduce runoff, increase infiltration and trap sediment providing a very favourable environment for the colonisation by local volunteer species. This is well illustrated in the following two examples.
A very steep (1:1) and highly erodible sodic soil on a railway embankment near Cairns collapsed and needed to be rebuilt after almost every wet season. Obviously, the solution to this problem is a very costly engineering structure. As a trial, six rows of Vetiver were established on mini benches (0.25m wide) on the slope at 1m VI (Vertical Interval). A total of approximately 250m embankment was stabilised with Vetiver in June 1992. The Vetiver established and grew well despite the dry season and by December 1992, the slope was reasonably stabilised by the young Vetiver plants and local species began to establish between the Vetiver rows. In March 1993, nine months later, the slope was completely covered with local vegetation between the Vetiver hedges. Fifteen months later the embankment was completely stabilised with a mixture of Vetiver and mature local grass species. This embankment has withstood up to the last three wet seasons.
On another site, an old quarry at Henley Hill in Cairns where the old rubble surface has remained bare of vegetation since the quarry operation stopped five years earlier. Four rows of Vetiver, established on an 80% slope at 1m VI. Despite the extremely poor and hostile conditions of the coarse gravelly ground, Vetiver established well (with NPK fertiliser) and started trapping debris from upslope. The stiff stems of Vetiver provided a very effective barrier trapping debris and rocks up to 70mm in diameter. Twelve months later the old gravelly slope was 75% covered with local vegetation between the rows of Vetiver hedges which had grown to 1.2m tall. Eighteen months later the slope was completely stabilised and revegetated with Vetiver and other local species including a pasture legume (Stylosanthes).
5.5.3 Gully Stabilisation
Vetiver hedges are very effective in stabilising gully erosion. When planted on contour line above gully head, Vetiver hedges will spread and slow down runoff water and stop the advancement of gully heads. This is well illustrated at a number of gullies in both cropping and grazing lands. Following the control of active erosion at the gully heads, gully floors are normally revegetated naturally with native species.
On large and long gullies where active erosion occurs both on gully floors and walls, Vetiver hedges established on gully floor will reduce flow velocity, trap sediment and reduce further erosion on the floor. At Ashall Creek, a very large gully system in the black earth on the Darling Downs, more than 0.3m of sediment was trapped by a series of 17 hedges over an area more than 400m long and 50m wide during the 1994 summer.
5.5.4 Stabilisation of Structures in Flooded River
A large water cascade was built by South Johnstone sugar mill near Innisfail on the bed of the flood prone South Johnstone River to cool off wastewater from the mill. One side of the cascade is a large bund of about 200m long and 4m high at the top end lowering down to river floor level at the bottom end with 2:1 slide slope. This bund was built mostly from the highly erodible sand and gravel material from the river bed. Vetiver was used to stabilise the steep side slope, protecting it from high velocity flow during the wet season. This bund was completely stabilised and Vetiver has successfully protected this bank from several flood flows during the last two wet seasons.
In addition, Vetiver was also planted across the cascade floor to reduce flow velocity. Parts of these rows were completely submerged in hot running water during week days. Although still very young (3-4 weeks old) these Vetiver plants survived under these conditions for a few months, with water temperature reaching 45oC most of the time, but they were eventually washed away.
As a result of this success Vetiver is now being used by the Johnstone River Improvement Trust for several similar projects in the Johnstone catchment area.
5.5.5 Wave Erosion Control
Being able to establish and thrive under waterlogged conditions, Vetiver has proved to be very effective in reducing erosion caused by wave action on big farm dam walls. The erosion caused by wave action on the inside wall of a very big farm dam near Cloncurry was effectively controlled by establishing a Vetiver hedge along the high water mark.5.5.6 Applications in Forest Plantation
Vetiver has been used successfully to stabilise shoulders of driving tracks on very steep slopes as well as gullies in a forest plantation at Imbil. It is also very effective in stabilising and trapping sediment in waterways on very poor sandy soil at the Toolara forest.
5.5.7 Applications in Pineapple Farms
Farm chemicals and nutrients from pineapple plots were effectively trapped by Vetiver rows planted across drainage lines which were also successfully stabilised by these rows.
5.5.8 Lowering Water Table in Saline Lands
With its salt tolerant ability and deep rooting characteristics, Vetiver has been successfully used to control soil erosion and at the same time lower the saline water level in a trial in temperate southern Australia. It is now being trialled on a large scale for the same purposes in Western Australia.
5.5.9 Providing Shade for Sheep.
(Extract from Toni Somes' article in Queensland Country Life, 10 November 1994).
"An Asian grass, already used extensively to control soil erosion, may soon prove instrumental in boosting lambing percentages in western Queensland. The Vetiver grass (Vetiveria zizanioides) is being grown as part of shade plot trials at Toorak, a QDPI research station, south of Julia Creek.
Research has already found artificial shade plots on Mitchell grass country can boost lambing percentages by 15 percent. According to Toorak Manager, Tony Barnes, the Vetiver grass has considerable advantages over native trees and its predecessors, particularly Prickly Acacia and Parkinsonia. "Introducing thorny trees and shrubs like Prickly Acacia and Parkinsonia, for animal welfare reasons, has seriously threatened the viability of Mitchell grass pastures", Mr Barnes said. "But research shows Vetiver doesn't spread - it can only be propagated by root division or slips - and therefore will not compete with natural grasses like Mitchell and Flinders". "It also grows rapidly and is capable of providing adequate shade for adult sheep after at least 12 months".
Although the Toorak trial is in early stages, research officer, Greg Bortolussi said he was confident of finding favourable results. "We planted the grass in February last year and now it stands about 1.7m high and provides quite adequate shade for sheep". Mr Bortolussi said: "Heat stress is currently blamed for approximately 20 percent reduction in the birth weight of lambs and up to 30 percent increases in lamb mortality".
6.0 WHERE FROM HERE?
At the recent International Conference in Thailand, I was asked to lead the discussion on future applications of Vetiver grass. From the results of our research in Queensland and outcomes of the discussion panel, I concluded that we now have enough evidence that Vetiver is ready to move out of the farm gate, beyond the soil and water conservation applications in agricultural lands to the protection of the environment in general, with particular emphases on engineering applications, rehabilitation of contaminated lands, mining wastes and bio-remedial applications including wetlands and aquaculture.
From the above it can be concluded that:
With its wide ranging tolerance of adverse climatic and edaphic conditions the Vetiver Grass System offers a simple and low cost alternative to constructed soil erosion and sediment control measures.
On disturbed lands, where conventional methods of stabilisation and reclamation are limited and costly, the Vetiver system offers a unique means of rehabilitation of these highly erodible lands.
More specifically with its high level of tolerance to extreme soil pH, soil salinity, Al and Mn toxicities, Monto Vetiver has great potential for reclamation work in mining and other industrial waste and contaminated lands.
Future application in bio-remedial works.
On engineering applications, although results to date have been very impressive, application of the VGS in engineering designs is till somewhat limited due to the lack of knowledge and design parameters which now start to emerge from recent researches. More researches are needed in this area so that bolder and more innovative applications, utilising its full potential, can be adopted with confidence.
8.0 Publications on Works Associated with the Vetiver Program Australia
Truong, P.N.V., and Scattini, W. (1990). Vetiver - the hedge against soil erosion? Australian Journal of Soil and Water Conservation: 3: 16-18.
Truong P.N.V. and Roberts H.M (1992). Salt tolerance of some tropical and subtropical grass species grown in Queensland - Proceedings, National Workshop in Productive Use of Saline Land. Adelaide September 1992.
Truong, P. (1993). Report on the international Vetiver grass field workshop, Kuala Lumpur. Australian Journal of Soil and Water Conservation : 6: 23-26.
Truong, P.N.V. (1994). Vetiver grass, its potential in the stabilisation and rehabilitation of degraded and Saline lands. Ed. V.R. Squire and A.T. Ayoub: Halophytes a resource for livestock and for rehabilitation of degraded land, Kluwer Academics Publisher, Netherlands., 293-296.
Truong, P. and Creighton, C. (1994). Report on the potential weed problem of Vetiver grass and its effectiveness in soil erosion control in Fiji. Division of Land Management, Queensland Department of Primary Industries, Brisbane, Australia.
Truong, P., McDowell, M. and Christiansen, I. (1995). Stiffgrass barrier with Vetiver grass - A new approach to erosion and sediment control. Proceedings, Downstream Effects of Land Use Conference, Rockhampton, Australia. (in press).
Truong, P., Baker, D. And Christiansen, (1995). Stiffgrass barrier with Vetiver grass - A new approach to erosion and sediment control. Proceedings, Third Annual Conference on Soil and Water Management for Urban Development, Sydney, Australia, pp 214-222.
Freebairn, D., Truong, P., Miles, R., Ciesiolka, C., Titmarsh, G., and Norrish, S. (1995). Practical measures to counter soil erosion. Proceedings, Downstream Effects of Land Use Conference, Rockhampton, Australia. (in press).
Truong, P.N.V., Dalton, P.A., Knowles - Jackson, C., and Evans, D.S. (1996). Vegetative Barrier with Vetiver grass: An alternative to conventional soil and water conservation systems. Proceedings 8th Australian Agronomy Conference. Toowoomba (1996): 550-553.
Truong, P.N.V., Baker, D. and Christiansen, I.H. (1996). Effectiveness of Vetiver hedges in soil erosion and sediment control in Queensland. ASTAG World Bank, Vetiver Network Newsletter No.15 pp.32.
Truong, P.N.V. and Claridge, J.(1996). Effects of heavy metal toxicities on Vetiver growth. Proceedings, First International Vetiver Conference. Chiang Rai, Thailand (in press).
Truong, P. and Gawander, J. (1996). Back from the future: Do's and don'ts after 50 years of vetiver utilisation in Fiji. Proceedings, First International Vetiver Conference. Chiang Rai, Thailand (in press).
Truong, P., Gordon, I. and Baker, D. (1996). Tolerance of vetiver grass to some adverse soil conditions. Proceedings, First International Vetiver Conference. Chiang Rai, Thailand (in press).
Dalton, P. and Truong, P. (1996). Soil moisture competition between Vetiver hedges and sorghum under irrigated and dryland conditions. Proceedings, First International Vetiver Conference. Chiang Rai, Thailand (in press).
Dalton, P.A., Smith, R.J. and Truong, P.N.V. (1996). Hydraulic characteristics of Vetiver hedges: An engineering design approach to flood mitigation on a cropped floodplain. Proceedings, First International Vetiver Conference. Chiang Rai, Thailand (in press).
West, L., Sterling, G. and Truong, P. (1996). Resistance of Vetiver grass to infection by root-knot nematodes (Meloidogyne spp). Proceedings, First International Vetiver Conference. Chiang Rai, Thailand (in press).
Truong, P. and Baker, D. (1996). Vetiver grass for the stabilisation and rehabilitation of acid sulfate soils. Proc. Second National Conference on Acid Sulfate Soils, Coffs Harbour, pp. 196-8.
Truong, P., Baker, D. and Stone, R. (1996). The use of Vetiver grass in the stabilisation and rehabilitation of an old landfill site at Judy Holt Park, Cleveland (ex council dump site) (Poster presentation).
Truong, P.N.V. (1990-1996). Numerous contributions to ASTAG World Bank, Vetiver Network Newsletters.
Dalton, P.A., Smith R.J. and Truong, P.N.V. (1996). Vetiver grass hedges for erosion control on a cropped floodplain, hedge hydraulics. Agric. Water Management : 31 (1,2) pp. 91-104.