Erosion control – engineering grasses

There exist different types of erosion control grass which vary distinctly based on their ability to provide vegetative erosion control cover and survive in environmental conditions that are prone erosion. We will quickly look at some of the grass varieties and their features that can be used for erosion control before we focus on the vetiver grass system as an example of choice in furthering our discussion about erosion control grass. Ryegrass quickly establishes and produces a stable turf with tolerances to sun, shade, drought, temperature and wear coupled with low maintenance requirements. Blue couch is less tolerant to changes in temperature, shade, drought relative to rye grass whilst requiring moderate maintenance. Fescue is quite tolerant to changes in temperature, wear, shade and drought with maintenance requiring limited effort. The three are favorable as cool-season erosion control grass and one of the most important considerations for their applications as either seed or sod. With such a background to some of the varieties we turn our attention to the vetiver grass system from a bioengineering and erosion control perspective with examples of applications and finally merged with the complementary technologies Global Road Technology has to offer for utilization with erosion control grass.  

Two establishment approaches

Bioengineering will be approached from a seeding vs sodding (“turfing”) perspective in order to understand the differences and similarities based on planting season, water requirements, soil preparation, weed control, uniformity, usability, erosion control and cost respectively for both of them. Seeding has its planting season during Autumn and sometime in spring whereas sod can be planted anytime. The water requirements for seeding are very high for germination and establishment whereas for sod there are low. Soil preparation for both requires tillage and fertilization amongst many other efforts whereas uniformity contrasts in that seeding varies based on weeds and washouts whereas for sodding uniformity is 99 – 100%. The usability for seeding is none for 2 months, then limited for up to 6 months whilst for sodding it is normal to high within 2 weeks. Erosion control for seeding is none until established and usually rain necessitates repair whereas with sodding it offers good erosion control after installation. The cost per m2 works on a general rule of thumb that sod costs about 20 times more than seeding, although the cost is offset by sod’s ability to be planted year-round, uniform establishment and instant erosion protection.

A grassroots movement

The Vetiver System based on the application of vetiver grass (Vetiveria zizanioides) was first developed by the World Bank for soil and water conservation in India in the mid 1980s with two genotypes namely the seeded north Indian and sterile south Indian genotypes with the latter being used for soil and water conversation and land stabilization purposes. Their extraordinary features include a massive and deep root system, tolerance to extreme climatic conditions such as prolonged drought, flood, submergence owing to stiff and erect stems, fire and frost due to the new shoots that develop from the underground crown, heat waves and extreme temperatures from -220C to 600C. Vetiver grass has been found to be also tolerant to a wide range of soil acidity, alkalinity, salinity, sodicity, agrochemicals and elevated levels of heavy metals in the soil. Its dense hedge owing to proximity of planting creates an effective sediment filter and water spreader whilst the ability for new roots to grow from nodes when buried under trapped sediment which makes it an ideal erosion control grass which can weather the extreme conditions. The erosion control grass applications of vetiver grass find its use as a bioengineering technique for steep slope stabilization and environmental protection. However, shading will reduce its growth and in worst case scenarios even go on to eliminate it completely as it thrives in the open and critically in initial establishment stages weed control is key to its proliferation. 

Application in Australia

In an Australian context, the use of vetiver grass has been regulated by strict legislation and control on introduced plants and assessment for use in environmental protection came after the assurance of it not becoming a weed at some point. The sterile vetiver cultivar was chosen in Australia after rigorous and repetitive testing for almost a decade for its sterility under various growing conditions which is now known as the Monto vetiver. On subjection to glasshouse and field conditions and in dryland, irrigated and wetland habits the Monto vetiver did not produce any grains. Monto vetiver can be used as a bioengineering tool that is a cost-effective alternative to engineered stabilization methods. It plays a crucial role in stabilizing soils and reducing the soil and water run-off that leads to the silting up of rivers and dams which can eventually lead to desertification in the forestry and agriculture steep slopes. In particular, agriculture benefits to use of erosion control grass in the form of vetiver is in soil amelioration which happens through top-soil, moisture and plant nutrients retention with mulch from vetiver used for soil betterment via facilitation for favorable growth of native plant and grass species. Rehabilitation of mine tailings in Australia varies from coal and gold overburden, coal, gold, bentonite and bauxite mine tailings and Monto vetiver has been used highly effectively for mine waste rehabilitation. The overburden of open cast coal mines in central Queensland is highly erodible and vetiver has been used to stabilize the highly sodic and erodible mine overburden. In northern Australia, vetiver has been used to stabilize a very large dam wall of a bauxite mine as a form of revegetation for the tailings.  

Complimentary technologies

Global Road Technology offers complementary technologies that can be used with erosion control grass and the incentives to use of GRT Enviro-Binder include its non-toxicity and environmentally friendly benefits to terrestrial and aquatic life. Technically, it dries and agglomerates soil preventing impact and sheet erosion on different surfaces with benefits of minimal maintenance post application. Its waterproof nature exempts it from effects associated with rainfall and other weather events which can lead to leaching and is the ultimate product to tackle erosion and sediment challenges in environmentally sensitive areas especially in the summer seasons. Combinations of bioengineering efforts through use of erosion control grass such as vetiver grass and polymeric technologies such as GRT Enviro-Binder can result in the best of both worlds in achieving erosion control. Typically in mine site rehabilitation GRT Nature Plus complements the need for revegetation in being a source of phosphorus and nitrogen for effective germination and strike rate of erosion control grass which enables stabilization to prevent soil erosion caused by rainfall and sediment loss. 

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REFERENCES 

• Cheng, L., Draper, S., and An, H. 2014. Scour and Erosion. CRC Press. Taylor & Francis Group. 
• Norris, J.E., Stokes, A., Mickovski, S.B., Cammeraat, E., van Beek, R., Nicoll, B.C., and Achim, A. 2008. Slope Stability and Erosion Control: Ecotechnological Solutions. Springer Science + Business Media B.V. 
• Oshunsanya, S., and Aliku, O. 2017. Vetiver Grass: A Tool for Sustainable Agriculture. Book chapter on Grasses – Benefits, Diversities and Functional Roles. 
• Pease, M., and Truong, P. 2000. Vetiver Grass Technology: A Tool Against Environmental Degradation in Southern Europe. 3rd International Congress of the European Society for Soil Conversation, Valencia, Spain. 
• Pitt, R., Clark, S.E., and Lake, D. 2007. Construction Site Erosion Control and Sediment Controls: Planning, Design and Performance.
• Truong, P.N.V., and Loch, R. 2004. Vetiver System for Erosion and Sediment Control. 13th International Soil Conservation Organisation Conference- Brisbane. 1-6. 
• Troung, P. 1999. Vetiver Grass Technology for Mine Rehabilitation. Resource Sciences Centre. Queensland Department of Natural Resources, Australia.