|Vetiver Grass: A Thin Green Line against Erosion (BOSTID, 1993, 157 p.)|
In light of the massive environmental destruction now caused by erosion, any system that retards soil loss would seem to be a candidate for instant and widespread use. Indeed, if the power of the vetiver system is as great as now appears, in a few decades the world could see thousands of kilometers of vetiver hedges in a hundred different countries, in climates from lush to harsh, and in sites from verdant to sparse.
But the experiences so far are limited, and many uncertainties
remain. It is time, therefore, for a wide-ranging exploration of this new, and
seemingly revolutionary, technique.
In this chapter we identify some of the important, as well as some of the interesting and challenging, actions that could be taken to help vetiver progress in an orderly, responsible, and yet rapid manner.
CONTINUATION OF WORLD BANK EFFORTS
As discussed earlier, it has been World Bank agriculturists who have reintroduced the vetiver method of erosion control. Their enthusiasm and energy have stimulated people all over the world and it will be of inestimable value to the testing and adoption of vetiver if these activities continue.
The World Bank staff also created the Vetiver Network-a service that collects and disseminates vetiver information and maintains an address list of more than 2,000 vetiver specialists and aficionados. With interest in this grass rising rapidly, continued support for this activity is essential. Such a service prevents duplication of effort and ensures that interested people receive constant updates of information on experiences with vetiver in other parts of the world.
The fostering of a new technology like this is not, however, a normal World Bank operation, and it would be prudent for other organizations to initiate a complementary operation to take over should the abandonment of this project occur.
It is clear that vetiver could become a vital component of land use throughout the warmer parts of the world. It might be a low-cost way to protect billions of dollars of investment already made in agriculture and forestry, not to mention roads, dams, and other public works throughout Africa, Asia, and Latin America. It also could become a backstop built into future projects as a way to help protect the environment from many soil disturbances.
At present, however, that is all speculation. It is critical for countries to establish vetiver trials quickly, which would serve to show local decision makers what this grass has to offer their programs and projects.
To expedite, motivate, and assure success in such a massive number of trials, we suggest consideration of what could be called a "vetiver SWAT team." This might involve a small number of vetiver specialists, brought in on short-term assignment to show local authorities how and where to put in small vetiver demonstration trials.
These trials might be incorporated into specific projects dealing with topics such as those discussed below.
In farming areas, trials could be particularly effective. With vetiver hedges reducing rainfall runoff, farmers should encounter more moisture in their soils so that crops produce higher yields and tolerate drought better. Given a successful demonstration, the word is likely to spread rapidly from farmer to farmer. Thus, not only the environmental stability of an area but also its productivity may increase.
Foresters are likely to be impressed as well. By holding soil and moisture on site and by providing windbreaks, vetiver strips would be particularly valuable in the early stages of tree growth. At present, a huge proportion of tree-planting projects are failing because of dismal rates of establishment and survival. Vetiver might also act as a barrier against ground fires and creeping grasses, both of which often devastate young tree plantings.
At least initially, engineers are likely to be apathetic (if not apoplectic) toward the idea of using a grass for erosion control. The past 50 years or so have seen the rise in popularity of erosion controls based on bulldozers, land surveys, and engineered systems such as terraces, berms, bunds, and contour drains. By contrast, a strip of grass seems puny and insignificant.
However, demonstrations are likely to persuade everyone that vetiver hedges can protect and enhance the performance, as well as extend the useful lifetimes, of many structures made of steel, concrete, or asphalt. For instance, vetiver could help protect footpaths, railroads, and road cuts from washouts and slips. In addition, it has potential benefits for wastewater treatment and flood-control facilities. Further, because it can withstand lengthy submergence (more than 2 months has been reported), it can be planted along the edges of dikes, irrigation canals, bridges, and dams to prevent scouring.
Most observers have despaired of the possibility of radically reducing the vast amounts of silt washing every day into ditches, canals, reservoirs, rivers, harbors, estuaries, and other waterways worldwide. This would be a massive, perhaps impossible, task for any erosion-control technique. Vetiver, though, just might work. Rows of this grass across critical watersheds should reduce silt buildup downstream. Indeed, although huge plantings would be required, government authorities might find the expense and effort far outweighed by the financial benefits of extending the useful life of multimillion-dollar water projects, not to mention the protection of wetlands, coral reefs, and other vital economic environments.
The advantage of the vetiver system is the fact that it is applicable on a wide scale with little equipment, planning, or logistics. Further, it is likely to appeal to those actually occupying the land. This is vital: farmers and foresters may well protect their land with little or no urging-not for soil conservation per se, but for the increased yields fostered by the moisture held back by the vetiver hedges, not to mention the by-products of vetiver-fire control, forage, mulch, thatch, and so on.
Wherever in the tropics localized flash flooding is a problem, vetiver could be part of the solution-especially when the flooding is caused by denuded watersheds that can no longer soak up and hold back the rainfall and runoff.
Although rain falls infrequently in arid lands, it often adds up to considerable amounts. Moreover, desert rains are often intense deluges and the water rushes away uselessly down wadis and washes. Paradoxically, the water the desert needs so desperately is lost by flooding.
Vetiver barriers across those wadis and washes would likely capture the floodwater to recharge the thirsty aquifers beneath. Walls of vetiver would also hold back silt in which crops might grow vigorously.
In addition, vetiver hedges might prove excellent as windbreaks in decertifying areas. Already, palm fronds are used for wind protection in the Sahel, for example (see Appendix A). These palm-frond fences look somewhat like rows of dead vetiver, but it is likely that the living, growing, real thing would be far better-especially given vetiver's ability to withstand undermining and to "rise up" as sand or soil collects around it.
There is currently a great interest in keeping agriculture productive and self-sustaining. Although vetiver has seldom been considered in the many parleys, papers, projects, and predictions, keeping the soil on the site is the most fundamental part of the process. Vetiver, therefore, could be a key to success in many of the different sustainable agriculture systems under development for Third World conditions.
This and other vegetative systems of erosion control should provide long-term stability and, if combined with good crop-rotation practices, such as the use of green manures and organic mulches, could lead to stable sustainable farming that might even render slash-and-burn cultivation obsolete in many places.
Trials are urgently needed throughout the tropics.
Despite general opinion, vetiver hedges can provide a number of products that are especially useful to farmers in the tropics. These products can be harvested without sacrificing erosion control. They will provide farmers with extra income, and this should enhance everyone's interest in establishing vetiver hedges on their lands.
These products include:
· Mattress stuffing;
· Animal bedding; and
· Mats, baskets, and screens.
Setting up markets for local vetiver products may be one of the best incentives for inducing the mass planting of vetiver hedges throughout any neighborhood.
Although vetiver has been grown in scores of countries for decades or even centuries, not a lot is known about the plant itself. Studies should be undertaken of topics such as plant morphology, physiology, ecology, and cold tolerance.
Despite the general impression that vetiver is a single clone, it contains much variation. In one project in India, for example, six different botanical collections grown side by side were strikingly different in color, rigidity, flowering, and other features. Each type could easily be distinguished, for example, by the length and strength of the culms and by the barbs on the leaf margins .
Everyone interested in vetiver should now search through the germplasm for "super vetiver" cultivars for erosion control. Attributes to look for include the following:
· Method of forming clumps;
· Persistence of clump integrity;
· Structural strength;
· Root form; and
· Level of sterility.
Much valuable research could also be accomplished by studying details of the plant's physiology. Researchers experienced in the study of maize, sorghum, or sugarcane could provide useful insight here. More information is required on the following subjects:
· Seeding variability within and among genotypes.
· Flowering. Some cultivars have flowering heads; most have none.
· Structural unity. Why don't the stems rot and fall off?
· Nitrogen fixation. Does vetiver by any chance benefit from associated nitrogen-fixing bacteria as does Bahia grass and some other tropical grasses? Most C4 grasses have associated nitrogen fixation by Azospirillum that live in the rhizosphere.
· Allelopathy. Does vetiver adversely affect neighboring plants?
· Silica content of leaves. Is a high silica content what repels insects?
· Mycorrhizae. Are vetiver roots colonized by the beneficial fungi called "mycorrhizae"? Can mycorrhiza inoculations benefit the plant's growth?
· Water relations. What gives the plant its ability to withstand waterlogging and even submergence on the one hand and severe drought on the other?
· Mineral nutrition.
To understand more completely the potential for problems as this plant goes global, we need to understand its gynecology (the structure, development, and distribution of vetiver communities in relation to their environments). For example:
· What is the plant's best ecological niche?
· What other plants grow with it under normal conditions?
· Which animals, microorganisms, and insects associate with it?
· What are its soil interactions?
· What are its shade and water tolerances? Growth chamber studies could be useful here.
· Is the oil in vetiver roots fungicidal? Bactericidal?
Vetiver's gravest limitation is that it is currently restricted to the warmer parts of the world. Wherever cold occurs, even infrequently, the plant cannot be relied on to hold back soil down the years. Breaking through this cold barrier would open the possibilities of using vetiver with confidence in the frost-prone parts of the planet. This might best be done by an organized search for winter hardiness among the various genotypes.
In most cases vetiver can merely be planted and left alone. Nonetheless, a detailed knowledge of the conditions for its optimum performance would be extremely beneficial. Research on this might include subjects such as:
· The best spacing between the hedges down the
· The best spacing between the plants within the hedges;
· The nutrients that, at the time of planting, ensure optimal survival and growth; and
· Relations between pruning and regrowth.
Other features of hedge establishment and maintenance worthy of investigation include:
· Mass planting techniques. The machines used to plant
tobacco, beach grasses, trees, and vegetables should be tested.
· Herbicide sensitivity tests.
· Assessment of weediness.
· Potential as host for pests and diseases.
Effects on nearby crops also deserve detailed investigation. These include checking for the following:
· Nitrogen deficiency in the soil next to the
· Competition for other nutrients;
· Root interactions with neighboring plants; and
· Moisture deficiencies in the soil beside the hedges.
The integration of vetiver into various farming systems also deserves study. For example, how might vetiver hedges be fitted into alley cropping, slash-and-burn, terrace farming, horticulture, rice paddies, large-scale mechanized agriculture, and other types of farming?
RESTORING DEGRADED SITES
Degraded lands are so prevalent and so vast in the tropics and subtropics that to restore even a fraction of them may seem impossible. In this regard, vetiver unaided can do little, but it offers a starting point, or at least a ray of hope. To finally have a way to preserve whatever meager soil remains is a first step. From this, techniques for integrating various crops, trees, or wild plants that will help to rebuild the capacity of the land can then be envisaged.
Something of this sort has been pioneered in northern New Zealand where earlier this century huge barren coastal dunes were slowly rolling over valuable farmland. Nothing would grow in the sand- nothing, that is, until marram grass, Ammophila arenaria, was tried. This salt-tolerant European species put down deep roots, collected wind-borne sand, and stabilized the giant sandy juggernaut in just a few years. That was a feat, but the true payoff occurred after foresters planted a shrubby legume (Lupinus arboreus) amongst the grass. The sand then began to build up fertility (notably nitrogen) and organic matter. Within another year or two, the site was fertile enough for pine seedlings to thrive among the shrubs. The eventual result: the giant dunes were tamed; for decades the forest there has provided much of the timber used in Auckland, the country's largest city.
Marram grass is not like vetiver, but it acted as a rugged pioneer that enabled the restoration of this highly degraded site. Vetiver, with its even broader adaptability and greater potential, seems likely to do the same for many barren lands in the tropics and subtropics. This possibility should be evaluated.
An idea as revolutionary as this one opens several possibilities for innovations, a few of which are discussed below.
These days everybody thinks of farms in terms of hectares or acres. But John Greenfield suggests that in extremely arid or thin-soiled areas "a one-dimensional farm" might be run along the back of a vetiver hedge. It would be only one row wide, but might run for many kilometers. The crops would grow in the narrow band of soil trapped behind the hedge and would also be watered by the concentrated runoff. This is an unconventional notion, of course, but it just might be a way to get productive farming into areas so arid that people now consider the production of any food or tree crops impossible.
Warding Off Weeds
As mentioned earlier, vetiver is reputed to be a barrier to grassy stoloniferous weeds. This should be investigated. If it proves true, vetiver hedges would likely be planted in many places not to stop erosion but to stop the invasions of Bahia, St. Augustine, couch, kikuyu, or other pestilential grasses that constantly creep into farmers' crops on silent stolons.
Blocking Crabs and Rats
Creeping grasses are not the only pests that might be held at bay. Vetiver's dense network of oil-filled roots may block burrowing creatures of various kinds. Examples of such subterranean pests are the crabs that attack paddy bunds; and moles, mole rats, and other burrowing animals.
This, too, is an unorthodox idea, but not an idiotic one Trials at Kericho in Kenya have already shown that mole rats cannot abide a vetiver root in their burrows. They cast it out or tunnel around it and block it off, apparently to keep the smell from their living quarters (Information from C.O. Othieno).
As earlier noted, insects avoid vetiver oil and vetiver roots. This might have some modern utility. Would solid bands of vetiver block termites, fire ants, or other insidious underground insects? Might the oil or the smoke from burning roots be used against household pests and vectors of disease?
Vetiver burns in a lively fashion when the tops of the plant are dry. But in many places its roots, tapping into reserves of deep moisture, keep the plants lush and green long into the dry season. Bands of these succulent plants across hill slopes are said to make good firebreaks. This may not be a wholly reliable method of fire prevention, but many fires in rural Third World areas creep along the ground through the dry grasses. It seems possible, therefore, that stout, unbroken lines of vetiver might be a godsend to foresters and farmers who, only too often, see years of effort and millions of investment dollars go up in smoke in a single afternoon.
One small plant is a big constraint to cereal production in Africa and India. Usually called striga or witchweed, it is a parasite that spends its first few weeks of life living off the juices of other species. Its roots bore into neighboring roots and suck out the fluids. The vegetative victims are left dried out and drained of life.
Unfortunately, striga thrives in maize, sorghum, millet, cowpeas, and other valuable crops. Millions of hectares of farmland are constantly threatened; hundreds of thousands are infested each year. And today, nothing can be done. When striga breaks out, farmers abandon their land. Some of the most productive sites now lie idle-victims of this abominable sapsucker.
Vetiver is a member of the same subtribe of grasses as sorghum and maize, and it may prove to be a sacrificial barrier to the spread of striga. Alternately, the oils in its roots may suppress this powerful parasite that does its dirty work underground. Sucking in a dose of vetiver oil may be enough to do it in.
In Zimbabwe, wildlife researchers have found that blocks of napier grass, strategically placed, can attract nightly flocks of weaverbirds. These grain-devouring pests (usually called quelea) like to roost together in the tall grass after a day in the fields. The simple concept of providing a man-made haven for the night offers a means for capturing them in quantity. On moonless nights they can be approached and either caught for food or otherwise destroyed.
Despite the promise inherent in this approach to one of the world's worst pest problems, there are at present several operational difficulties. One may well be overcome using vetiver, which would likely be an ideal grass for creating the trap roosts. Compared with napier grass, vetiver would be permanent, nonspreading, and safe from wandering wildlife or loose livestock. Given further innovation, perhaps blocks of vetiver will eventually be used as "lenses" to focus flocks of pestiferous small birds wherever they are a farm problem (More information on the pioneering work in Zimbabwe can be found in the companion report on Africa's promising native cereals, Lost Crops of Africa Volume 1: Grains. For information on BOSTID publications, see page 162. Napier grass is mentioned in Appendix B).
Vetiver represents a whole new approach to erosion control. The hedge concept is a point of departure for future elaborations. We have included a section on the idea of searching for more species to use where (or if) vetiver fails. For details see Appendix B.