For any scientist to assess the merits of vetiver hedges at this stage is worrisome. Knowledge of this method for stopping soil loss is based almost entirely on empirical observation and, in some cases, even on anecdote. Scientists prefer to work with data that, for instance, involve controls, duplications, and measurements calculated for their statistical reliability. With vetiver, few such figures or factual comparisons are available.
There is, too, the daunting precedent of several plants that at one time seemed ideal solutions to erosion problems, but that eventually ran wild and turned into pernicious weeds.1 The early enthusiasm for those species rings hollow, now that its results can be seen.
Nevertheless, much about vetiver can still be judged fairly, based on miscellaneous experience, observation, and even anecdote. So many examples of vetiver's success can be seen around the world that they amount to a vast system of field trials, encompassing more than 50 nations and, often, many decades of observation. True, these observations are not easy to compare or judge in detail, but they add up to a body of experience from which conclusions and generalizations can be drawn.
Further, it is important also to place this in context. In global terms, erosion is continually increasing. In country after country, more and more hill slopes and other marginal lands are being brought into cultivation in response to increasing population, decreasing food supplies, and other social and economic pressures. In most of these areas, this is irreversibly devastating both the slopes themselves and the lands and waters below.
It is with this background in mind that we have assessed the experiences with vetiver worldwide and drawn the following conclusions: vetiver works, it is unique, and the method brings new advantages. Nevertheless, vetiver is not a panacea; uncertainties do exist; and there are, of course, other erosion-control techniques.
Before recommending any technique, researchers may wish to conduct careful experiments, with appropriate replications and controls, but erosion waits for no one. Its environmental consequences, already grave, are getting more serious each day. Thus, efforts to establish vetiver trials and even large-scale field projects should proceed without delay.
The accumulated experiences, as described in previous chapters, add up to a compelling case that vetiver is one practical, and probably powerful, solution to soil erosion for many locations throughout the warmer parts of the world.
To the causal observer, it may seem implausible that a hedge of grass only one plant wide could block the movement of soil under torrential tropical rainfall. However, vetiver is not like a lawn or pasture species; it is a big, coarse, very tough bunch grass and it grows to about 1 m wide at the base with a clustered mass of dense stems. Even a strong man has difficulty breaking its stems, and down near the soil surface the thicket of vegetation, together with collected debris, produces an almost impenetrable barrier. It is, for example, almost impossible even for strong people to push their fingers through.
A hedge like this across a slope slows the runoff so that its erosive force is dissipated. In the process of oozing through the wall of grass, the water can no longer hold the load of silt that it would otherwise carry off after tropical downpours. Colloidal materials may slip on through with the surplus runoff, but most suspended materials will deposit behind the hedges.
Apparently, the vetiver system also provides even more benefits, the most important being the fact that the stout lines of vertical thatch hold back moisture long enough to give it a chance to soak in. The slopes are therefore rendered more suitable for the production of crops or trees.
Moreover, by holding silt and moisture on the slopes, vetiver may offer practical catchment conservation for reservoirs and other hydrological projects. In many places this will undoubtedly prove impractical, but it could nonetheless be invaluable to certain projects involving canals, rivers, reservoirs, flood-control facilities, and other
waterways to even out the flow of runoff throughout the year. Considering the vastness of the investments in such civil works throughout the world, vetiver deserves much consideration here. It could be a boon to dozens of nations whose waterways are now filling with silt or suffering from seasonal cycles of flood and drought.
VETIVER IS UNIQUE
Although other grasses and trees have been used as vegetative barriers for soil conservation, vetiver seems to combine several characteristics that make it special:
It reduces erosion when in a hedge just one plant wide. (Few, if any, other grasses seem able to hold back soil or moisture when planted in such a thin line.)
Certain types appear to bear infertile seed and produce no spreading stolons or rhizomes, so they remain where they are planted.
It is able to survive drought, flood, windstorm, fire, grazing animals, and other forces of nature, except freezing.
It has a deep-penetrating root system.
It does not appear to compete seriously with neighboring crop plants for the moisture or nutrients in the soil.
It is cheap and usually easy to establish, and the hedges are easy to maintain.
It is not difficult to remove if no longer wanted.
It is (at least so far) largely free of insects and diseases and does not appear to be a host for any serious pests or pathogens that attack crops.
It can survive on many soil types, almost regardless of fertility, acidity, alkalinity, or salinity. (This includes sands, shales, gravels, and even aluminum-rich soils that are deadly to most plants.)
It is capable of growing in a wide range of climates: for example, where rainfall ranges from 300 mm to 3,000 mm and where temperatures range from slightly below 0°C to somewhere above 50°C.
VETIVER BRINGS NEW ADVANTAGES
If erosion is to be controlled across the globe, it is vital that it be done in ways that appeal directly, and obviously, to the farmers' immediate self-interests. Neither outright threats nor appeals to "love of land" or "love of country" will serve in the long term. Ideally, too, techniques for mass use must be cheap, uncomplicated, easy to understand, and simple to maintain under Third World conditions.
Vetiver can be all of these things.
Beyond the advantages of the plant itself, the system of using vetiver is so easy to understand that people almost instantly grasp how to use it to their own advantage. Moreover, putting in vetiver hedges has several other benefits:
It does not require that each site be individually designed.
It does not require foreign exchange or expensive equipment.
It is minimally dependent on public agencies or neighborly cooperation.
It does not need laborious maintenance.
It does not require careful layouts or high-quality control.
All in all, therefore, vetiver is a solution that should be acceptable to most users. It seems promising as a way for local people to involve
themselves naturally in erosion-control activities—something that national planners have long dreamed of.
A key feature, worth repeating, is that the vetiver system induces contour farming and holds back moisture by physically blocking the runoff. Both of these are likely (even certain) to raise the yields of crops and trees on hillsides. Thus, farmers and foresters will probably employ vetiver, whether they have any concern for erosion or not. Self-interest should drive them.
VETIVER IS NOT A PANACEA
Vetiver is not a panacea; it cannot solve all the problems. Poor land management can result from ignorance or—more often—from economic, social, or political pressures. For example, rents may be too high, fertilizers unavailable, or crop prices too low—all of which
can force farmers to overexploit their land in their attempts to grow more.
Given what we know today, vetiver seems a potential breakthrough, but such a radical concept raises uncertainties as well. Some difficulties, however, can already be foreseen.
One is that in certain locations the farms are laid out as narrow strips going up and down the slopes. In practical terms, such farms can be plowed only vertically. Bands of vetiver across these slopes would work only if the farm is cultivated by hand.
Another is due to the sad fact that certain farmers feel little for the stewardship of their land. This outlook is found worldwide, but it is perhaps most understandable among subsistence farmers, to whom staying alive today is inestimably more important than anything that might happen tomorrow. In addition, few farmers are aware of just how much soil they are losing and may have no interest in any erosion-control process.
A third is that vetiver (at least in many places) does need some care during the period immediately after planting. Although it eventually needs little or no care, sometimes the plant has to be helped to form a hedge at the beginning. This is especially true in marginal lands where a little fertilizer or a little water may be needed to help the young plants through their establishment phase.
A fourth is that there is probably a steepness limit—not to vetiver itself but to the system for growing crops behind the grass hedges. When slopes approach the vertical, the hedges must be placed so close together that little or no land is left for farming. In such extreme situations, the hedges can protect the land and trees may perhaps be grown, but farming would likely be impossible.
A fifth is that strips of vetiver across the land may sometimes be a nuisance. (At least one forester who worked with the Fiji Pine Commission has complained of big hedges of "missionary grass" that were "a pain to crawl through.") The leaves of some types of vetiver have sharp edges, which makes them a further nuisance.
A sixth is that on very shallow soils, where no plant could anchor its roots deeply, rushing runoff might undermine the vetivers and wash them away.
Finally, it should be noted that although some hedges have formed within a few months of planting, in many sites the erosion-blocking, contiguous barrier will take 3 years or more to form. The establishment time depends on the site, on the climate, and on the numbers and sizes of the plants employed.
Vetiver may fail to form functional hedges on sites with only moderate temperatures and sunlight. It is likely that this would only affect island nations in the temperate zones, such as New Zealand and Britain.
Why Conservation Schemes Fail
There is a school of thought that says that technology for controlling erosion is not the missing ingredient at all. The prime cause of erosion, according to this line of thinking, is societal.
"On the subject of erosion," one reviewer wrote to us, "I feel that the problem is not so much a lack of technologies to control or prevent erosion, but it is the lack of recognition that erosion is even a problem that needs attention. Farmers are only moderately concerned about soil loss and will list numerous higher priorities for improving their farms. Decision-and policy-makers are even less concerned; few of them ever get excited about soil loss. Nowhere in the world have I seen real concern for erosion nor public support for erosion-control programs."
Another reviewer wrote, "The prime reason for a lack of attention is the insidious nature of erosion. One rainstorm can remove a millimeter of soil from one hectare. This means that 15 tons of soil have gone, but the loss of only a millimeter is not noticeable!"
Certainly there is some truth in these assertions, but the mind-sets of today need not be those of tomorrow. Changes can be made. Piers Blaikie,* for instance, claims that governments can create the right policy environment for attacking the causes of soil erosion by stimulating such actions as:
In a related vein, a few years back, an FAO publication** highlighted what its authors considered the reasons why large-scale centralized soil-conservation schemes failed. It identified the following reasons:
To every thoughtful observer, it is obvious that government policies, farming practices, excessive pressures on the land and its vegetation—not to mention foolishness, ignorance, and even a malevolent self-interest that sometimes verges on "eco-vandalism"—all lead to soil erosion. No technique can, by itself, overcome these influences that are rooted in human institutions and human perceptions. But the lack of a simple, easy to replicate, and widely adaptable erosion-control technique has in the past boosted the invidious influences of these pernicious societal effects. Vetiver, therefore, might help. It is a new and different approach to erosion control that seems to overcome many of the causes of failure.
Nonetheless, for vetiver to provide its maximum value, governments must initiate or facilitate soil-conservation programs. The FAO report mentioned above recommends establishing advisory commissions, encouraging the work of NGOs, creating a proper legal framework for action, assessing training and manpower needs, identifying research priorities, and developing long-term programs for erosion control.
VETIVER IS COMPATIBLE
Vetiver isn't the only erosion-control technique, of course. Others include the following:
Engineered systems, such as terraces, rock walls, and earthen berms and bunds;
Plants that spread over the land;
Broad (as opposed to narrow) strips of grass;
Contour cultivation, mulches, crop rotations, strip-cropping, and no-till farming; and
Forestry, agroforestry, and living fences.
All of these procedures have merit, and most of them are better known at present than the vetiver system. Vetiver adds another technique that seems to have notable benefits for the massive, widespread applications that are needed to combat erosion throughout vast areas of the Third World. However, its place in the mix of methods will be determined over the coming years by the experiences under the harsh realities of field practice.
Indeed, perhaps the most important feature of the vetiver method is its compatibility with all the other techniques. Vetiver is already being planted in several countries to reinforce and improve the stability of terraces, berms, and bunds. It has outstanding promise as a "safety line" to anchor broad strips of other grasses, such as napier grass. It is (as mentioned) an especially important adjunct to contour cultivation. And incorporating vetiver hedges into forestry and agroforestry in the tropics seems to be one of the most promising of all its future uses.