Vetiver Grass: A Thin Green Line Against Erosion (1993)

This chapter presents 22 of the concerns most commonly raised about vetiver, together with what seem to be the best available answers. These pages reflect the general state of knowledge in the early 1990s. They result from reviews and comments collected from a dozen experienced vetiver specialists and a dozen vetiver skeptics.

The accumulation of experiences worldwide is convincing: vetiver hedges can indeed block the passage of soil. They may not stop a hillside from slumping, but they can keep topsoil on site and, over time, retard most surface erosion. In many cases they can also help fill up gullies.

With the experiences of India, Fiji, China, Malaysia, St. Lucia, St. Vincent, South Africa, Malawi, the United States, Haiti, and other nations, it can be said with confidence that hedges of this deeply rooted perennial are indeed capable of catching eroded soil and helping to build up terraces that stabilize the site. Moreover, they seem capable of doing so under many conditions except where freezing occurs. The actual amount of erosion controlled on any given site cannot now be predicted with confidence, but, at least in some cases, the reductions can be dramatic.

It should be understood that, in a strict sense, vetiver doesn't stop erosion. The soil between the hedges is still free to move. However, the hedges block its further progress and prevent it from leaving the site.

Although it has the power to hold back soil, there are undoubtedly sites where vetiver will fail: climates may be too dry or too cold, slopes may be too steep or too boulder-strewn, or soils too toxic or too shallow, for example.

Vetiver is already so well known in so many countries that any serious threat from its use for erosion control would by now be obvious and widely reported. However, there are fertile types in India that could become hazardous if they are distributed.

A major reason for confidence in vetiver's safety is that the plant will seldom have to be introduced anywhere. It is already found throughout the tropics and has been there for at least a century. Apparently it has never spread in an uncontrolled manner or become a major nuisance. Possibly, such difficulties may be found as people investigate this plant more thoroughly, but, by and large, vetiver has not become a problem.

It is important, however, that only the right kind of vetiver be used. The types of South Indian origin apparently produce nonviable seeds and must be maintained by vegetative methods. Luckily, this is the fragrant-root type that has been spread throughout the tropics. In areas where it has been planted for decades, or in some cases for more than a century, it has seldom (if ever) spread from seed. In a few areas vetiver is reported as an escape, but even there it neither spreads rapidly nor is considered a nuisance.

On the other hand, types of vetiver grown from seeds introduced from northern India into the United States in 1989 have formed seeds and have germinated in areas adjacent to small plots in Georgia. This fertile type should not be introduced to new areas. It has long been used to protect canal banks in irrigated agriculture in northern India and the neighboring Terai of Nepal without becoming a pest or spreading uncontrollably from seed. Nonetheless, at this time, because of its potential hazard, only vegetative materials should ever be planted. Vetiver must never be propagated from seed.

Yes, although by how much will depend on local conditions and is not now known.

A key claim for the vetiver system is that contour hedges of this grass can slow down and hold back moisture that would otherwise rush off and be lost to the slopes. This claim appears to be valid. For example, in Karnataka, India, farmers who plant vetiver can dig behind their hedges and find moist soil when their neighbor's land is parched. Similar observations have been made elsewhere. In many areas, this ability to hold moisture on the slopes, and thus increase infiltration,

will likely boost crop yields and appeal to farmers, foresters, and civil authorities.

On the other hand, vetiver is not a barrier in the sense of being like a wall. Its hedges are more like tight filters laid across the land: they slow down runoff and retard its progress, but do not physically dam it up. Shallow runoff seeps through the lower part of the hedge; deeper runoff pours through (or even over) the upper parts. In this way, runoff is neither ponded nor concentrated but stays spread across the slope as it fell. The vetiver method contrasts with rock walls, dirt barriers, and other mechanical methods that hold, concentrate, or divert water off site.

Vetiver supporters see this ability to keep the water spread out across the slopes as a major advantage. They are probably right, at least for most locations. Much of today's most dramatic erosion is caused when runoff concentrates and scours out the land in "gully washers."

In most places, yes—but not everywhere.

This simple, cheap, and easily understood way to control soil losses should be highly acceptable to farmers, foresters, and other potential users throughout the warm parts of the world.

For one thing, vetiver is not demanding. Its hedges are seldom more than 1 m wide and therefore take up little land. It generally requires relatively few plants to establish the hedges. It can be installed by farmers using their own labor and materials. It requires little or no maintenance once established, and the hedges can last for years.

For another, there are incentives for farmers to use vetiver. In most cases, the hedges will guide the bullock, the tractor, or the hoe along the contour. The resulting contour farming alone will likely conserve soil and improve moisture, and thereby give better yields, healthier plants, quicker growth, and more resistance to droughts and other hazards.

The appeal to self-interest could be powerful, obvious, and rapid; however, it is likely that certain farmers will resist the vetiver technique. Some will have farms so small that they cannot afford even the tiny strips occupied by vetiver hedges. Some will have narrow farms running up and down the slope (a common way of subdividing land among family members in some locations) so that hedges across the slopes would make plowing and other operations impractical or inconvenient. And some will care little for the land or its future (they may, for example, be tenant farmers, resentful of the landowner).

Not often.

One criticism leveled against vetiver relates to the fact that its roots are worth money. Farmers, the critics charge, will dig up their hedges whenever cash becomes more important to them than erosion, which is to say almost always.

Reportedly, farmers have already dug up vetiver erosion hedges at least once in both Indonesia and Haiti. However, although such experiences will inevitably occur again, they will undoubtedly be few, far between, and seldom repeated. There are three major reasons for this:

• Difficult harvesting. Vetiver roots are threadlike strands that form lacy networks throughout a large volume of soil. To obtain the roots in quantity, therefore, vast amounts of dirt must be dug. Except in loose, light soils, the workload is enormous, especially considering the small amount of root obtained. Even in volcanic ash and sandy bottomlands, the task of digging vetiver roots is so difficult that it is often hard to find people willing to do it.

  Also, separating the soil from the intricate roots involves extreme drudgery. Commercial production is usually done only near waterways where the soil can be washed off.

• Lack of markets. The total world demand for vetiver oil is only about 250 metric tons per year (see sidebar, page 78). Moreover, there is little or no "elasticity" in the market, and the prospects for anyone to sell larger supplies are poor. Indeed, demand has been declining in recent years, and existing producers are more than capable of meeting any likely rebound. Currently, organized production is found in only three countries: Haiti, Indonesia (actually, only Java), and the tiny Indian Ocean island of Réunion. It is unlikely that they can be undercut because production costs in Indonesia and Haiti are probably as low as could be achieved anywhere. Further, the world's vetiver oil buyers have contracts and relations with the traditional producing nations; they are therefore unlikely to turn to a new supplier without extraordinary financial or oil-quality inducements.

• Lack of facilities. To extract the oil from the roots is not easy or cheap—it demands a steam-distillation facility. Such a relatively expensive factory is unlikely to be an attractive investment in areas that don't already have one.

The answer is not clear. Depending on the crop and the level of stress at the site, some edge effects will undoubtedly be noted. However, neither vetiver nor its roots are inherently spreading, and in most cases, the effects should be minimal.

In theory, vetiver should compete with immediately adjacent plants for the use of water and nutrients, but in practice it doesn't seem to. Some yield reduction has been observed in the rows nearest the hedges in certain crops at certain sites (maize in India, for example). However, whether this results in an overall decrease in yield is as yet unclear—gains from the improved moisture levels across the whole field may well offset the losses at the upper and lower edges.

Certainly in some cases (cotton fields laced by vetiver hedges in South India, for example), no obvious edge effects are seen; the plants beside the hedges are as tall and productive as those elsewhere across the field. Perhaps this is because topsoil and organic debris washing off the fields accumulate behind the hedges and overcome any competition from the grass.

No, but certain diseases and one potentially serious pest are known. In future these or other organisms might restrict the plant's usefulness to certain locations or climatic zones. Also, they might increase the need for the care and maintenance of the hedges.

Although vetiver plants are usually remarkably free of disease, several fungi have been identified in a few locations. For example, two smuts and a leaf blight (Curvularia trifolii) have been identified on vetiver plants in Bangalore, India. In Malaysia, three fungal diseases (tentatively identified as species of Nigrospora, Curvularia, and Helminthosporium) have been observed, but they do not appear to be virulent.

As for pests, a potentially nasty stem borer has been found in China. A severe but localized infestation of Eupladia grubs has been found in Africa. And termites are known to attack the dead stems, a particular problem in dry areas. None of these insects, however, seems to be a devastating threat to the plant's worldwide use.

Vetiver's edaphic limits are unknown, and there are undoubtedly sites in which it will not grow. Nonetheless, the plant seems to tolerate a remarkable array of soil types.

There are well-documented examples where vetiver is growing in very adverse soils. For example:

• Coastal sand dunes in South Africa.

• Extremely acid soils (with pH as low as 4.0) in Louisiana.

• Highly alkaline soils (pH up to 11) at Lucknow, India.

• Black cotton clays (which heave and split and eject most plants) in Central India.

• Barren soils with little fertility or organic matter in South China and other places.

• Waterlogged soils in the black cotton clays, and even swamps, of India.

• Parched land. In the arid state of Rajasthan, India, vetiver is common.

• Saline soils in Australia.

Although vetiver can survive on many hostile sites, it should not be expected to grow there with its full vigor. On many poor soils the plant will probably be difficult to establish, its growth will be retarded, and its ability to form a hedge to catch erosion will be long delayed. Some fertilization will often be required on such sites to create and maintain fully functioning hedges.

Details are unknown, but vetiver's climatic limits seem to be remarkably broad. The plant, however, cannot reliably withstand freezing conditions.

Heat seems to be no barrier. Vetiver is reported to grow vigorously under some of the most torrid conditions faced by farmers anywhere.

On the other hand, vetiver is definitely limited by cold. It can take a mild freeze, but even this may be misleading. An erosion-control barrier must be able to function for years to be reliable; should a hedge die with even infrequent cold snaps, all the soil accumulated behind it would be left vulnerable.

From experiences in New Zealand and southern England, it appears that vetiver will succeed only where the sun is hot and bright. Maritime temperate locations may prove too cool and cloudy for the hedges to form up quickly.

So far, no other plant with all of vetiver's major qualities has been found. However, some have certain of its qualities.

It would be most desirable to have additional species to use in narrow vegetative barriers. They could extend the geographic range of hedgerow erosion control, give farmers more options, and provide substitutes for vetiver should it ever get struck down by epidemic disease.

Effectiveness of other species is also a management question. Napier grass might be as efficient as vetiver if kept as a much wider hedge, but it would require significantly more care, expense, and labor—as well as replanting every few years.

Yes. At present, however, there seems to be no alternative for use in narrow hedgerow barriers against erosion.

The job vetiver can do is so important that it would be absurd not to take advantage of it just because some unknown disease may possibly break out in future. Research should be maintained on alternatives (see Appendix B), but vetiver is currently the only practical species for low-maintenance, single-plant hedgerow erosion barriers.

Although the vetiver found almost everywhere in the tropics is the same species, it has been scattered in myriad locations for a long time, and it is possible that the germplasm is not as genetically uniform as might appear.

Perhaps, but there is no evidence for it at present.

Vetiver belongs to the same subtribe of the grass family as maize, sorghum, lemongrass, and citronella. It is therefore not unexpected that it will be susceptible to some of the same maladies. A more serious fear, however, is that bands of this perennial across the fields might act as sources of infections that damage the crops.

To date, no one has reported that vetiver hedges can act this way. They of course take up only a small area and are unlikely to produce massive populations of pests even in the worst of cases. Thus, although they may provide cozy places for pests to overwinter, the probability of serious problems seems slight. It is likely, also, that management practices (such as periodically burning and topping the hedges) will further minimize any threats.

Certain types appear to be sterile in that they do not spread under normal circumstances. However, whether they produce truly sterile seed or whether they germinate only under special and unusual conditions is not clear.

It is legitimate to fear that any grass belonging to vetiver's subtribe could become a weed. Others have become so: shattercane and Johnson grass are just two examples. But the South India form of vetiver is not considered a weed in the dozens of places where it has been planted around the world. Also, the weedy members of the subtribe tend to be annuals. The perennials, such as vetiver, show a marked tendency toward low seed-set and an absence of female flowers. This makes them less aggressive.

It is important, however, that any vetiver planted be of the South India type. This is the type now spread widely through the tropics. As previously noted, a second type growing wild in North India is flowering and fertile and produces seedlings under conditions of high humidity and high soil moisture.

Although in one or two cases even the "sterile" vetiver has been declared a weed, it was a mild nuisance rather than a spreading terror. In hundreds of locations, the plant is considered benign at worst and highly beneficial at best. Indian farmers, for example, do not see it as a weed, even where it has been on their farms for centuries.

Generally, vetiver grows only where people plant it.

Vetiver is a perennial and, at least in some locations, hedges formed from it seem capable of surviving for decades.

This grass is remarkably persistent. On the island of St. Vincent in the Caribbean, vetiver barriers have been used for 50 years and some are still active even without maintenance. On an experiment station in northern Zambia, vetiver is reportedly still in the same lines that were planted 60 years ago. Some boundary strips in vetiver's native region of India are purported to be at least 200 years old.

There are mixed reports on this, but probably a rough trimming every year or two will be needed to keep most hedges in the best operating condition.

Although vetiver stays in place without requiring attention, it tends to break up into clumps if not trimmed. This usually takes a long time, however. Fiji's sugarcane fields offer an example where hedges given little or no maintenance produced excellent results for more than 30 years.

On the other hand, it is reported in St. Lucia that the hedges get rough and ragged unless they are periodically trimmed. One hedge in St. Lucia showed some gullying where gaps had formed, but it had been abandoned for probably more than 30 years. In addition, the flat surface of the terrace showed signs of sheet erosion (rocks on top of the soil) because water had drained too fast through the thinned hedge.

Trimming the hedges is usually not difficult. Generally, farmers merely run a plow along the edge to cut off any spreading tillers and cut back the tops with a machete. The effort can provide at least small amounts of forage, mulch, animal bedding, or thatch.

The vetiver method is inherently low cost.

Compared to terracing, bunding, or land leveling, vetiver is very inexpensive. In the red soils area of China, for example, the mechanical techniques cost, on average, $900 per hectare; vetiver, by contrast, costs less than $200. A similar ratio has been measured in India, where the cost for bunds was $60 per hectare and for vetiver less than $20 per hectare.

These figures were for initiating a vetiver program. They include costs for nurseries, the production of planting materials, the planting process itself, and perhaps some early maintenance (watering, fertilizing) to give a hedge a head start. As the critical mass of hedge builds up, the farmers obtain planting material from their own plots at no cost.

Once established, the hedge requires little or no expense. Constructed soil-conservation measures, on the other hand, require constant, and sometimes extremely costly, maintenance.

When the whole system is taken into account, vetiver in many places may more than pay for itself in improved crop yields. Yield increases of 25–60 percent have been recorded for contour cultivation of cotton, sorghum, and other crops in India.

In most places in the tropics it should be easy to establish vetiver hedges. In some, however, careful tending and perhaps years of delay will be required before the hedges are fully serviceable.

Vetiver is easily planted by hand, but machines (tobacco-or vegetable-or tree-seedling planters, perhaps) could also be used. The main work is to break up sprigs and to set them in the soil.

Any shortage of planting materials will, in most cases, be temporary. Over the years, a little patch of nursery can produce planting materials that can cover vast areas. Under irrigation and fertilization, a single hectare of nursery can, within a few months, provide enough slips to plant about 150 km of hedgerows, which, depending on slope, could protect up to 450 hectares.

Although vetiver establishes amazingly well where conditions are at least moderately favorable, delays and disappointing results can occur where conditions are difficult. For example, it requires good management to get vetiver established in very dry areas. Here, several years may pass before the plants have grown together to form tight hedges.

No.

Whereas a gap in an earth bund is catastrophic because the impounded body of water pours through, a vetiver hedge is not a solid barrier and it need not be perfect to work. Because the hedge filters water and doesn't dam it or divert it, it is tolerant of an odd gap. Nonetheless, a continuous hedge is desirable, and there are some reports of "gappy" hedges exacerbating erosion by channelling the water.

It is tolerant of other imperfections as well. For example, the hedge need not be exactly on the contour nor have perfectly even growth. Any low points will tend to gather more soil and trash and therefore will respond with more sediment accumulation, eventually forming a level terrace. Bunds and berms, on the other hand, must be on the exact contour because they function by damming or diverting the runoff water.

Maybe, in some situations.

Some have said that to be acceptable to farmers, any erosion-blocking plant should be more palatable to animals. That way, they say, people will put in the hedges to feed their livestock. Without some such incentive, they claim, farmers won't respond.

We are not convinced of this argument. Indeed, if a grass barrier is too palatable to livestock, it may lose its effectiveness. Animals are found almost everywhere in Third World countries, and wildlife or livestock will reduce an edible erosion barrier to ground level, especially in the dry season when feeds are in short supply. The advantage of vetiver, however, is that once it is established, livestock do not affect its usefulness.

Actually, though, vetiver yields several products that can be sold without damaging its effectiveness; for example, its stems and leaves can be used for making ropes, hats, brushes, thatch, mats, and fuel. They also make excellent mulch and animal bedding. In some places, vetiver is an important medicinal plant and, although the whole plants are shunned by animals, young vetiver leaves are palatable to livestock and can be used as feed.

No.

It may seem ironic, but it is nonetheless true that vetiver cultivation is barred from certain parts of Indonesia solely because it "causes soil erosion." This had led several people to denounce all efforts to promote the wider use of vetiver. After all, they point out, more vetiver is grown for oil in Indonesia than anywhere else except Haiti; surely Indonesians must know the plant and its performance.

Closer inspection, however, shows that the culprit is not vetiver itself but the specific way farmers grow and harvest it there. It is so difficult to dig up the roots that the plants are grown in special sites where the soil is extremely light. Only there can the farmers obtain the roots with a reasonable effort. When the time comes, they rip the plants out, leaving behind trenches of loose dirt that could hardly be more erodible if designed for the purpose. Some farmers even place their rows up and down (rather than across) the slopes. This allows the rain to scour the land in an even more disastrous manner.

When vetiver hedges are established on the contour and left in place, there is no evidence that they cause erosion.

No.

Vetiver is easily killed by slicing off the crown with a shovel or other implement. It is also easily eradicated by systemic herbicides. It is so easy to remove that in some places it is used in crop rotations as a fallow crop.

We don't know why.

Over the past 50 years, the main approach to worldwide erosion control has been oriented toward engineered systems, such as terraces, bunds, or contour drains. The use of vegetative systems is generally not attractive to conservation specialists trained in engineering techniques.

Another major approach worldwide is the use of cultural systems such as crop rotations, contour planting, ridge planting, and mulches. Erosion-control hedge technology has been lying dormant.