An Overview of Research, Development and Application of the Vetiver Grass System (VGS) Overseas and in Queensland


Paul Truong, Resource Sciences Centre,

Department of Natural Resources, Indooroopilly

(Paper presented at the Vetiver Workshop, Toowoomba Nov.6-7, Qld, 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 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.

This massive $US100 million World Bank sponsored project, under the leadership of Dick Grimshaw adopted this concept as a low tech and low cost alternative to the more expensive traditional engineering structures. When Grimshaw returned to the World Bank Head Office in Washington he initiated the Vetiver Network, which is now a truly global network with 4,000 members from over 100 countries. Grimshaw has now retired but has voluntarily devoted all his time to run the Vetiver Network which is partly supported by the World Bank and mostly by grants and donations from such diverse sources as the King of Thailand, governments and recently the Network won the John Franz Award from Monsanto ($US100,000) for World Environment and Economic Sustainability from Monsanto. Recently regional networks have been established in Latin America, Europe, China and shortly the Pacific Rim and Oceania.

In the last five years, three international conferences have been held on the application of VGS, one in Malaysia in 1992, one in Nigeria in 1994 and in February this year in Thailand. The latest conference attracted delegates from over 40 countries who contributed about 150 papers covering a wide range of topics.

Early this year a Memorandum of Understanding was established between the Royal Project Foundation of Thailand, Department of Natural Resources ( then DPI )and the University of Southern Queensland. This Memorandum provides the three organisations opportunities to work and share Research, Development and Application knowledge and experience on the VGS in both countries.

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 bank/waterway system which runoff water is collected by the banks 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 black earth 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 no above or underground runners and a massive root system, reaching down to 3-4m in the first year. This extraordinary thick root system is probably a result of centuries selection for aromatic oil production. This massive root system bind the soil and at the same time makes it very difficult to dislodge.

This very deep root system has also made Vetiver very tolerant to drought, it did not only survive but continued to grow through our worst drought in the last few years in the Western Downs.

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 - 12 C to 48 C (Queensland) and 75 C (South Africa).

Ability to regrow very quickly after being affected by drought, frost, salt and other adverse soil conditions when the adverse effects are removed.

When adequately supplied with N and P nutrient Vetiver can tolerate:

Wide range of soil pH (3.0 to 10.5)

High levels of Aluminium, Manganese, Arsenic, Cadmium, Chromium, Nickel, Lead and Mercury in the soil.

4.0 OVERSEAS RESULTS ON THE APPLICATION OF VGS

As mentioned above almost 150 papers were presented at the last International Conference in Thailand early this year, ranging from basic research on Vetiver physiology, ecology and adaptation to socio-economic impact of VGS applications. The following are highlights of some more important topics:

4.1 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 1). The yield increase was attributed mainly to uniform in situ soil and moisture conservation over the entire toposequence under the Vetiver hedge system.


Table 1: Effects of conservation measures on arable crop land (1.7% slope) 1988-1991.

T1 Contour cultivation and sowing

T2 Leucaena hedge system

T3 Vetiver hedge system

T4 Graded bank 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 2).


Table 2: Soil loss and runoff under various hedgerow treatments on two slope gradients.

Hedgerow

Soil loss (t/ha)

Runoff

Treatment

15% Slope

26% Slope

(% Rainfall)

Control (no hedges) 16.81 35.52 88
 Lily  11.98  16.06  76
 Lemon Grass  7.58  7.62  81
 Fern  4.22  1.55  66
 Vetiver  1.13  4.91  72
LSD (5%) 1.87 2.68 5.0


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.


4.2 Rehabilitation

In India, Vetiver was used to reclaim highly sodic land with pH between 9 and 10.6 throughout the soil profile.

In South Africa, Vetiver is instrumental in the rehabilitation of highly acidic gold mine tailings and highly sodic diamond mine tailings, under extremely harsh conditions, low rainfall and temperature ranging from sub zero to 75oC.

4.3 Stabilising Engineering Structures

In Malaysia shear tests on Vetiver roots showed that tensile strength of Vetiver roots at 75 MPa ( one third of the strength of mild steel reinforcement ) is as strong as, or even stronger than that of many hardwood species which have been proven positive for root reinforcement in steep slopes.

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.

4.4 Flood Mitigation

The pioneering works on hydraulic characteristics of Vetiver hedges under high flow conditions conducted at the University of South Queensland, have been successfully incorporated into the strip cropping layout on the floodplains of the Darling Downs.

4.5 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 3).

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.

4.6 Economics

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.

5.0 RESEARCH AND DEVELOPMENT OF THE VGS IN QUEENSLAND

The author first heard of Vetiver grass from an article in the Economist, reporting on the World Bank Vetiver program in India, and after a two year search Vetiver was found in the Herb and Fragrance section of the Mount Cootha Botanic Gardens in 1988. Over the last eight years, works in Queensland has been concentrated on three areas:

Research and development of Vetiver cultivar suitable for soil and water conservation in Queensland

Establishment of conditions and tolerance levels where Vetiver can be established

Evaluation of the effectiveness of the VGS in soil erosion and sediment control under Queensland conditions


5.1 Research and Development on Vetiver Sterility and Weed Potential

To overcome the weed potential of an introduced species, only sterile cultivars should be used in soil and water conservation. There are several Vetiveria zizanioides cultivars in Australia, and a sterile cultivar has been selected from this group. This sterile cultivar is registered in Queensland as Monto Vetiver, which for the last eight years, has consistently produced no caryopses when grown in both glasshouse and field conditions under dryland, irrigated and wetland habitat and from north and west to south Queensland. Monto Vetiver was readily grazed by cattle, dairy cows, sheep and horses as well as native animals.

Monto Vetiver is a non aggressive plant, it produces neither stolons nor rhizomes and has to be established vegetatively by root divisions or slips. Monto Vetiver has been used in all research, development and application works conducted in Queensland, New South Wales, Victoria and Western Australia.

In Fiji where Vetiver grass has been widely used for soil and water conservation purposes for more than 50 years, it has not shown any weed potential.

5.2 Tolerance Levels

Soil Acidity. Most tropical soils are acid or highly acid (low pH) which often affects plant growth through the release of highly toxic elements such as Al, Mn, Zn etc. Research has shown that Vetiver can tolerate a wide range of soil pH (3.0-9.5) provided N, P and soil moisture are available.

Aluminium Toxicity. Vetiver can withstand very high level of soil Al, higher than 68% (Al saturation % of CEC) . This is an extremely high level of Al tolerance as the critical Al toxic level for rice plant, the most Al tolerant crop is 45%.


Manganese Toxicity. Vetiver tolerates very high levels of Mn in a tropical soil. Mn toxicity in Vetiver could not be induced when soil exchangeable Mn was as high as 578 mgKg-1 and Mn concentration in plant top was 890 mgKg-1 ..

High Salinity. Both glasshouse and field trials have established that Monto Vetiver is highly tolerant to saline conditions, it has a critical salt toxicity level at Ece = 8 dSm-1 and 50% yield reduction at 17.5 dSm-1. It can tolerate chloride concentration higher than 3,500 mgKg-1. These levels establish Monto Vetiver as one of the most salt tolerant plant among tropical and sub tropical crop and pasture species .

High Sodicity. Vetiver can tolerate highly sodic conditions. Again with adequate supply of N and P, growth of Monto Vetiver was not affected when ESP (Exchange Sodium Percentage) was as high as 33% . Soil with ESP higher than 15% is considered sodic .

Acid Sulfate Soils. Vetiver has been used successfully to rehabilitate and stabilise a highly erodible acid sulfate soil near Babinda. This site has initial soil pH = 3.5, oxidised pH = 2.8 and Total Potential Acidity (TPA) of 535 mole H+/T.

Heavy Metal Toxicities. Vetiver can tolerate very high levels of heavy metals often found at landfill sites such as Arsenic, Cadmium, Chromium, Nickel (Table 3).

Table 3: Levels of Heavy Metal Toxic to Vetiver and other Species.


Heavy Metals

Soil Levels (mg/kg)

 

Vetiver

Other Species

Chromium

Nickel

Arsenic

Cadmium

Copper

18


347

72

48

15

0.02 - 0.2


10 - 30


1 - 10


5 - 20


15 - 25


5.3 Hydraulic Characteristics.

The hydraulic characteristics of Vetiver hedges are needed for the design and incorporation of Vetiver hedges into strip cropping layout. These characteristics were determined under flume conditions by the Agricultural Engineering Group at the University of Southern Queensland.

6.0 APPLICATION OF THE VGS IN QUEENSLAND

A large number of field trials were carried out to verify the effectiveness of Monto Vetiver in soil erosion and sediment control in Queensland. The followings are some case studies typifying the effectiveness of the VGS in a wide range of land use and climatic conditions over a wide geographic distribution.

6.1 Substitution and/or Supplementation of the Strip Cropping Layout on the Floodplain

Vetiver suitability has been assessed on floodplains 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.

A major project, incorporated Vetiver hedges into an existing strip cropping layout, was carried out on Mark Hensel property in the Linthorpe Creek catchment in Jondaryan. Eight rows of Vetiver totalling almost 6,000m, were planted at 90m intervals down a strip cropped slope. Flume test 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, which is equivalent to five existing strips at this particular site.

If proven successful, 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 are very encouraging, very little erosion occurs and a young sorghum crop was completely protected from flood damage.

6.2 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 Alex Gatera property 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.

6.3 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).

6.4 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.

6.5 Filter Strips

When established across drainage lines and water courses, Vetiver hedges filter and trap both coarse and fine sediment resulting in cleaner runoff water. At Excel Quarries north of Brisbane, 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.

6.6 Stabilisation of Structures in Flooded River

South Johnstone sugar mill near Innisfail built a large water cascade 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 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 considered by the Johnstone River Improvement Trust for similar projects in the Johnstone catchment area.

6.7 Rehabilitation, Erosion and Leachate Control of Contaminated Land

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).

6.8 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.

6.9 Rehabilitation of Mining Wastes

With its wide range of tolerance to adverse soil and climatic conditions mentioned above, Vetiver would be highly suitable for the rehabilitation of mine waste. Results to date indicate that it can be successfully established on overburden and highly saline and alkaline tailings of coal mines in central Queensland and highly acidic tailings of a gold mine in north Queensland.

6.10 Applications in Forest Plantation

Vetiver has been used successfully to stabilise shoulders of driving tracks on very steep slopes in a forest plantation at Imbil. It is also very effective in stabilising and trapping sediment in waterways on wallum soil at the Toolara forest.

6.11 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.

6.12 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".

7.0 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, we 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 the rehabilitation of contaminated lands, mining wastes and bio-remedial applications including wet land and aquaculture.

8.0 CONCLUSION

From the above it can be concluded that:

With its wide ranging tolerance of adverse climatic and edaphic conditions the Vetiver hedge 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.


Publications on Works Associated with the Vetiver Program :

1. Truong, P.N.V., and Scattini, W. (1990). Vetiver - the hedge against soil erosion? Australian Journal of Soil and Water Conservation: 3: 16-18.

2. 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.

3. Truong, P.(1993). Report on the international vetiver grass field workshop, Kuala Lumpur. Australian Journal of Soil and Water Conservation : 6: 23-26.

4. 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.

5. 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.

6. 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 ).

7. 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.

8. 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 ).

9. 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.

10. 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.

11. 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).

12. 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).

13. 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).

14. 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).

15. 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).

16. 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).

17. 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, Coff Harbour, pp. 196-8.

18. 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 ).

19. Truong, P.N.V. ( 1990-1996 ). Numerous contributions to ASTAG World Bank, Vetiver Network Newsletters.

20. 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