Vetiver Grass: The Hedge against Erosion
By John Greenfield
Download file: vetiver grass-the hedge againts erosion
Sumber Foto: John C Greefield
Sheet erosion is initially the most damaging form of erosion, mainly because it often is not recognized and therefore is seldom treated. Triggered by rainfall, sheet erosion accounts for the loss of billions of tons of soil every year. As raindrops pound the ground, particles of soil are knocked loose and then carried away by the runoff. This runoff further strips unprotected areas of their valuable topsoil and becomes the muddy water that ends up in drains, streams, and rivers. Sheet erosion leads to more striking forms of erosion—rills and gullies, for example, the focus of most conservation efforts to date.
Figure 7-1a. Sheet erosion leaves visible marks Figure 7-1b. The land shows signs of sheet erosion Although not as spectacular as rills and gullies, sheet erosion does leave visible marks, as shown in Figure 7-1a: soil collecting behind obstructions on a slope (such as the brick in example A), stones left behind by the runoff because they were too heavy to be carried away (B), or molded
mounds of soil and other debris trapped under branches, twigs, or even clumps of straw (C). The reality of sheet erosion’s marks appears in the photo, Figure 7-1b.
The effects of sheet erosion are more readily apparent in forest areas that are devoid of ground cover, and in fields or wastelands with a few standing trees, where the loss of soil exposes the roots of the trees. (See Figure 7-2a and the photo in Figure 7-2b.) Water can then easily pass beneath the trunks of the trees and among their roots. After all the soil that supported them and gave them life is washed away, the trees will be washed out of the ground as well.
Trees by themselves do not prevent soil loss caused by sheet erosion; forests do, with their thick litter and low-growing vegetation. In areas where forest cover is not possible or practicable, vegetative barriers can be used to stop the loss of soil. Fibrous-rooted shrubs and grasses planted as hedges along the contour of the land slow the runoff, spread the water about, weaken its erosive power, and cause it to deposit its load of valuable soil behind the hedgerows. As a result, the runoff proceeds gently down the slope, and if the hedges have been planted at the correct vertical interval (discussed later and illustrated in Figure 7-23), it proceeds without further erosive effect.
The amount of soil lost through sheet erosion is alarming. Figure 7-3a, which depicts two surviving plants whose roots prevent sheet erosion, shows how the amount can be measured. In this case a layer of soil 50 centimeters deep—as measured by the distance between the top of the plant mounds and the present soil surface—has been lost across the entire area of the field since the plants became established. The photo in Figure 7-3b shows the vulnerability of the exposed roots after the soil has washed away.
The traditional way of farming in rainfed areas, no matter how flat the land may seem, is along the slope, or up and down the hill. (See Figure 7-4a and the photo in Figure 7-4b.) This system encourages runoff and soil loss and thus makes sheet erosion worse. Often more than 50 percent of the rainfall is lost as runoff and thereby is denied to the crops; and the steeper the slope, the faster and more erosive the runoff. Rainfall is less effective because the water is not given a chance to soak in. By plowing along the slope, the farmer in Figure 7-4a is unknowingly encouraging the rainfall to leave his field.
Figure 7-5a and the photo in Figure 7-5 b illustrate the method advocated in this handbook—the use of vegetative contour hedges to prevent erosion and conserve natural moisture in the soil. Once established, such hedges need no maintenance and will protect the land from erosion for years as they build up natural terraces. In contrast to the planting furrows in Figure 7-4a, those at A in Figure 7-5a follow the contour of the land as laid out by the vegetative hedges at B in the illustration. Constructed earthen embankments, or contour bunds, have slowed erosion throughout the world since the 1930s. But this constructed method of soil conservation creates an unnatural system of drainage and, from my experience in the field, I no longer consider it appropriate for smallholders.
The embankment in Figure 7-6a was constructed with topsoil taken from point A, which was thereby transformed into a channel to convey the runoff sideways.
But the bank is made of the same soil it is supposed to protect, and because its construction makes the slope steeper, over time the bank will erode and “melt” away. Then it will have to be replaced—at great cost to the farmer. Moreover, to collect ufficient soil to make the bank and channel shown in Figure 7-6a, a 5-meter-wide strip of land must be taken out of production over the entire length of the bank. This represents a loss of 1 hectare of productive farmland for every 20 hectares of land treated with embankments or bunds. The photo in Figure 7-6b clearly shows a typical failure of the constructed system of conservation in self-mulching vertisols in India.
Figure 7-7 shows the unnatural way the land is drained by the constructed system. All of the runoff is channeled sideways and dumped into a constructed but unproductive waterway that no smallholder would want running through his or her farm. This system makes the areas below the banks too dry and the channel areas too wet for optimum crop production.
In contrast, the vegetative method of soil and moisture conservation uses nature to protect itself. In the system demonstrated in this handbook with vetiver grass, only a 50-centimeter strip—or one-tenth of the land occupied by earthen embankments or bunds— is taken out of production. (See Figure 7-8a.) Because the grass root divisions, or slips as they are called, are planted in a single plowed furrow, little soil is disturbed. And whereas earth banks have to be made with bulldozers or by hired labor, the vegetative system requires no special tools or labor beyond that which a farmer would already have.
The bottom illustration in Figure 7-8a shows what happens over time in the vegetative system: the runoff drops its load of soil behind the vetiver hedge, the grass tillers up through this silt, and a natural terrace is created. The terrace becomes a permanent feature of the landscape, a protective barrier that will remain effective for decades, even centuries. The photo in Figure 7-8b shows how the terrace builds up over time.
The photo in Figure 7-9a shows not only the failure of a constructed bank in India but also the failure of the cotton crop the bank was designed to protect. Before this bank’s failure, the entire area was flooded by the constructed system’s trapping of too much water. Because cotton cannot tolerate poor drainage, the crop failed completely.
The photo in Figure 7-9b was taken on the same day in a different location of the same field as in Figure 7-9a. In this situation the cotton crop thrived, protected by a single vetiver hedge that spread the runoff out and gave the water a chance to soak into the ground over the whole area protected by the hedge, thus producing an excellent crop of cotton.
With the vegetative system, when the runoff reaches the hedges, it slows down, spreads out, drops its silt load, and oozes through the hedgerows, a large portion of the water soaking into the land along the way. (See Figure 7-10.) No soil is lost, and there is no loss of water through the concentration of runoff in particular areas. The system requires no engineering—the farmers can do the whole job themselves.
Near Mysore in the southern Indian state of Karnataka (in the villages and hamlets of Gundalpet and Nanjangud, for example), farmers have been maintaining vetiver hedges as boundary markers around their farms for more than 100 years. To keep the hedges narrow, the farmers simply plow around the edges of the hedgerows whenever they plow the rest of the field for cropping. The hedges are in perfect condition and provide permanent protection against erosion.
Vegetative Contour Hedges
Figure 7-11a presents a cross-sectional view of a vetiver contour hedge at work. The leaves and stems of the vetiver plant slow the silt-loaded runoff at A and cause it to deposit the silt behind the plant at B while the water continues down the slope at C at a much slower pace. The plant’s spongy root system, pictured at D, binds the soil beneath the plant to a depth of up to 3 meters. By forming a dense underground curtain that follows the contour of the land, the roots prevent rilling, gullying, and tunneling. The photo in Figure 7-11b shows how the soil from the runoff has been trapped above the original topsoil behind the vetiver hedge.
The strong aromatic oil contained in vetiver makes the grass unpalatable to rodents and other pests, and many Indian farmers report that it also keeps rats from nesting in the area. Because the dense root system repels rhizomes of grasses such as Cynodon dactylon, the hedgerows prevent such grasses from entering the farm field and becoming a weed. Another benefit of planting the hedgerows, according to the farmers near Mysore, is that the plant’s sharp, stiff leaves keep away snakes.
To be effective as a method of soil conservation, the vegetative system must form a hedge, as shown in Figure 7-12a and in the photos in Figures 7-12b and 7-12c. Although under certain circumstances thick hedges can be formed in one year, it generally takes two to three growing seasons to establish a hedge dense enough to withstand torrential rains and protect the soil. During the first two seasons, and sometimes the third, the vetiver plants need protection, and any gaps in their line have to be filled. (During the first two seasons it should also be easy to see the silt being trapped behind the plants as they are establishing, a phenomenon that extension workers should try to point out when explaining the system to farmers.) Although the earth banks used in the constructed method of soil conservation are effective immediately, they break down over time and frequently burst open in heavy rainstorms. Once a vegetative hedge has been established, it will neither wear out nor require further maintenance, other than periodic trimming. The photos in Figures 7-12b and 7-12c provide a good example of this use of the Vetiver System.
Trimming the hedges to a height of 30 to 50 centimeters prevents them from seeding and makes them thicken up, thereby increasing their effectiveness in filtering runoff. In several villages and hamlets near Mysore, the farmers trim their hedges every 2 weeks throughout the year and feed the young palatable leaves (which are out of reach to the rodents) to their livestock, often chopping them up and mixing them with other fodder. They are thus ensured a year-round supply of stock fodder regardless of rainfall.
Following the Contour
Many fieldworkers—and even research workers—lack a clear understanding of what is
meant by the contour. Figure 7-13a illustrates a common misconception: that a furrow
plowed along the main slope follows the contour. This is incorrect.
A true contour embraces all slopes, major or minor; it is a line of equal elevation around a hill. The furrows in Figure 7-13a, which starting from point A, follow the main slope straight down to point C, instead of curving around the hill; they are not on the contour and therefore will neither conserve moisture nor prevent erosion. The true contour, pictured in Figure 7-13b, runs from A to B to D and continues around the hill, maintaining equal elevation all the way.
Because constructed earth banks that conventionally are used to control erosion must convey the runoff to a waterway off to the side of the field, they have to be constructed on the exact contour As shown in Figure 7-13c, such a line (marked with pegs at A) can be difficult for the farmer to follow when plowing.
The vetiver hedges, however, do not have to be exactly on the contour to provide effective soil and moisture conservation since their purpose is to reduce the velocity of the water as it passes through them and not to channel the water elsewhere. After the contour line has been pegged in (see Figure 7-18a), the extension worker can smooth it out to make it easier for the farmer to follow. In Figure 7-13c hedges and plow furrows (crop lines) need only follow line B. The silt filtered from the runoff will build up behind the hedges and eventually form a natural terrace. Because the hedges run across the slope, the ends of each hedgerow should be turned up the slope to prevent runoff from spilling around the sides; this will encourage natural terraces to form more readily and prevent erosion at the ends of the hedgerows, especially in steep lands.
In Figures 7-14a and 7-14b we see two farmers, A and B. Both are good farmers, but farmer A in Figure 7-14a is a wise farmer; he has protected his land against soil loss by planting vetiver hedges on the contour, and he is using the hedgerows as guidelines to plow and plant on the contour.
The furrows created in this fashion will hold rainfall and store extra moisture in the soil, thus allowing crops to withstand long periods of dry weather. What farmer A is doing costs no more than what farmer B in Figure 7-14b is doing. All that is involved is a change in land management.
Farmer B is a good farmer, but he is not farming wisely; he is not thinking. By plowing just straight up and down the slope, even a very gentle slope, he is encouraging the rainfall to run off his farm, taking his farmyard manure (FYM) and an irreplaceable layer of topsoil along for the ride. The rainwater runs off so quickly it does not have a chance to soak into the soil, and thus his crops have no protection against dry spells.
Figures 7-15a and 7-15b illustrate what happens when the two farming systems are exposed to heavy rainfall. Farmer A’s field is protected by the vegetative hedges, and there is no loss of soil (Figure 7-15a). The contour furrows store all the rainwater they
can hold. Any surplus rainfall runs off, but the vetiver hedges control the flow—slowing it down, spreading the water about—and cause the silt to be deposited. As a result, the runoff is conducted down the slope in a safe, nonerosive manner.
On Farmer B’s unprotected land, the rainfall runs off at great speed, taking along his fertilizers and topsoil. The uncontrolled ride down the slope causes unnecessary and damaging erosion (Figure 7-15b). Because the runoff races by so quickly, no moisture is stored. Rainfall is only 40 to 50 percent effective, and farmer B is always complaining about droughts. Ultimately he will have to abandon his farm because there will be no soil left in which to grow crops. Farmer A will never have this problem; his yields will increase over the years.
The photos in Figures 7-15c and 7-15d show the importance of land management for moisture conservation in rainfed areas. Unlike irrigated farming, in which farmers have complete control over their crops’ water needs, rainfed farming is totally limited by the amount of rain that falls in the area for the success or failure of the crops. By plowing and planting on the average contour, rainfed farmers have a better chance of holding the rain that falls in the field and in the actual crop rows, which means that the whole field benefits. In heavy storms, when the crop rows cannot hold the rainfall, the vetiver hedges prevent any damage from erosion by spreading the runoff out and giving it time to soak into the ground.
Thanks to his vetiver contour hedges, farmer A obtains an excellent crop. (See Figure 7- 16a.) Because the soil has retained ample moisture from earlier rains, his crop is benefiting from the warm sunshine, all the grains are filling, and the crop stand shows even growth. Farmer A will reap a high yield.
In contrast, farmer B has a disappointing harvest. (See Figure 7-16b.) His crop has all but failed, and what little remains—growing in pockets where some moisture was trapped— is being dried out by the sun. Only a small percentage of the grain will fill, and the resulting crop is uneven. Farmer B can expect a low yield. Yet he planted the same crop as farmer A, used the same fertilizer, planted at the same time, and received the same amounts of rainfall and sunshine. Unlike his neighbor, however, farmer B lost most of his fertilizer, 60 percent of his rainfall, and a layer of soil, possibly a centimeter thick, from his farm—all because he did not plow on the contour and use vegetative hedges to protect against erosion and help his cropland retain moisture from the rain. If he had taken the advice of his extension service and plowed and planted on the contour, farmer B could have obtained the same high yields as farmer A. The photos in Figures 7-17a and 7-17b attest to the success of crops that are protected by vetiver hedges.
Having learned his lesson, farmer B contacts his extension worker, and together they mark, or peg out, contour lines across the old furrows. (See Figure 7-18a.) This simple process requires virtually no engineering skills—only the use of a small hand-held level. The extension worker stands at the edge of the field and, sighting through the level, has farmer B move up or down the slope until the two people are standing level, at which point the farmer marks the spot with a peg. In Figure 7-18a, the contour line (X) has already been pegged out, and the farmer has but to follow the line of pegs with his plow (as shown in Figure 7-18b) to create the furrow in which to plant the slips of vetiver grass that will eventually form a contour hedge. This is all that has to be done to establish the vegetative system of soil and moisture conservation. The photo in Figure 7-18c shows an extension worker and farmers working together to peg out vetiver hedges on the contour.
Like any long-lived plant, however, the vetiver hedge system normally takes two to three seasons to become fully effective. You cannot plant a mango tree today and expect to pick mangoes next month, but it is possible to get some immediate effect from the system by using dead furrows as a preliminary step until such time as the vetiver grass can be established.
The preliminary stage of establishing the vegetative system is depicted in Figure 7-19a. While waiting for vetiver planting material to be produced in the nursery, the farmer laid out the contours, prepared seedbeds following the contour furrows, and every 5 or 6 meters double plowed a dead furrow. The two dead furrows in the figure have been planted on the contour to pigeon peas and intercropped with six rows of groundnuts. The shape of each seedbed is show beneath the crop illustration: DF marks the deeper dead furrow, PP the row of pigeon peas it supports. Eventually, vetiver grass will be planted in some of the dead furrows, but in the interim these furrows themselves will provide a bit of protection against runoff. Planting the vetiver grass will stabilize the whole system, as shown in Figure 7-19b, where a vetiver hedge has taken the place of one of the dead furrows.
Establishing Vetiver Hedges
To establish a vetiver hedge, follow the step-by-step instructions that appear on the next few pages, along with tips on handling the planting material, advice about the best time to plant, and information about what to expect after the grass is planted.
The first step for establishing a vetiver hedge is obtaining the planting material, usually from a vetiver nursery. If vetiver grass is unknown in your area, check with the nearby botanical gardens. Ask them to look up Vetiveria zizanioides. If it has been collected, the herbarium sheet will show what the plant looks like, note where the specimen was found, and provide the local name of the plant. Vetiver is found throughout the tropics and has been grown successfully as far north as 42° latitude. Vetiver nurseries are easy to establish. Inlets to small dams or water holding tanks make the best nursery sites, because water en route to the dam or tank irrigates the vetiver grass, which in turn removes silt from the water.
Large gullies protected with vetiver grass also make good informal nurseries. For best results in establishing a vetiver nursery, the vetiver root divisions, or slips, should be planted in a double or triple line to form parallel hedges across the streambed. The hedgerows should be about 30 to 40 centimeters apart.
To remove a clump of vetiver grass from the nursery, as shown in illustration A, Figure 7-20a, dig it out with a spade or fork. The root system is too massive and strong for the grass to be pulled out by hand. Next, tear a handful of the grass, roots and all, from the clump (B). The resulting piece, the slip, is what will be planted in the field (C). In the photo in Figure 7-20b, women in India prepare vetiver clumps for transport to the fields by separating them into planting slips, trimming the slips, and bundling them. Before transporting the slips from the nursery to the field, cut the tops off about 15 to 20 centimeters above the base, and the roots 10 centimeters below the base. Cutting will improve the slips’ chances of survival after planting by reducing the transpiration level and thereby preventing them from drying out. As shown in Figure 7-21a, all that is needed to prepare the slips for planting is a block of wood and a knife—a cane knife, machete, cutlass, or panga will do. The finished planting piece is shown in Figure 7-21b.
Although vetiver grass can be planted from single tillers (when planting material is scarce), this practice is not recommended for grass to be planted in the field, because it takes too long to form a hedge. Fertilizing the slips with di-ammonium phosphate (DAP) encourages fast tillering and is helpful both in the nursery and in the field. To do this in the field, simply dibble DAP into the planting furrow before planting the slips.
Always plant the slips at the beginning of the wet season to ensure that they get full benefit of the rains. Planting vetiver slips is similar to planting rice seedlings. Make a hole in the furrow that was plowed to mark the contour. Push the slip into the hole, taking care not to bend the roots upward. Then firm the slip in the soil. Then 10 to 15 centimeters from the slip, along the same contour furrow, plant the next slip, and so on. (See Figure 7-21c and the photo in Figure 7-21d.)
Only a single row of slips need be planted. If planted correctly, the slips can withstand up to one month of dry weather. Some slips may die, however, and leave gaps in the hedge line. If possible, fill these gaps by planting new slips. In some instances it may be possible to use the live flower stems, or culms, of neighboring plants—simply bend the culms over to the gap and bury them. The live stems will produce roots and leaves at the nodes.
Of course for this or any vegetative system to work, the plant must form a hedge; otherwise, the system cannot act as a barrier against soil loss. Planting the slips too far apart (see Figure 7-22a) would render the system almost useless because it would take too long for the slips to grow together to form a hedge. The photo in Figure 7-22b shows a hedge in China that was planted in the wrong way. Even though the farmer had the extension workers’ handbook showing the correct method for achieving a hedge with vetiver and had advice in the field, he planted the slips too far apart. This method of planting will never work as a method of soil conservation, and the farmer will eventually abandon the system—not because the system does not work, but because the farmer did not lay it out according the instructions.
Moreover, without the extra support of a hedge to hold the soil, fertilizer, and moisture against the vetiver grass, the plants would not be able to survive the worst droughts. Even in arid areas that receive less than 200 millimeters of rain a year, an effective vetiver contour hedge could ensure its own viability. The combined effect of contour cultivation and the hedge’s performance in slowing and spreading the runoff is to increase infiltration of water into the soil. Thus the hedge can help itself to what might be the equivalent of half again as much rainfall.
For the system to provide maximum protection against erosion, the hedgerows should be spaced apart at the proper vertical interval (VI). The VI is the vertical distance from one hedgerow to the next one down the slope. The actual distance measured along the ground, called the surface run, depends on the steepness of the slope. With a vertical interval of 2 meters, for example, the hedges on a 5 percent slope would be about 40 meters apart, whereas those on a 2 percent slope would be about 100 meters apart. As shown in Figure 7-23, the surface run between hedgerows planted on a 57 percent slope with a VI of 2 meters is about 4 meters. For a more comprehensive look at the relationships among slope, surface run, and vertical interval, see Table 7-2 at the end of this chapter. In practice, a VI of 2 meters has generally been found to be adequate.
After the hedges have been established in the farm field, the only care they will need is annual trimming to a height of about 30 to 50 centimeters to encourage tillering and prevent shading of the food crops. When plowing for cropping, plowing along the edges of the hedgerows will remove any tillers that encroach upon the field and will thus prevent the hedges from getting too wide.
Although measures to retain natural moisture in the soil are essential to all rainfedfarming systems, the art of in situ moisture conservation, as it is called, is rarely practiced and not widely understood. There is no such thing as flat land; water runs off all land. No matter how flat it may seem, all land must be contoured if it is rainfed. Earth shaping, land leveling, and similar techniques are required in irrigated areas only; rainfed areas must be contoured. Figure 7-24 shows what happens when land is planted on the “flat” without the benefit of contour furrows.
In view A, the rain runs straight off the field. View B shows the results: because no moisture has been stored, the plants wilt and die in the sun. View C shows the same area planted to contour furrows, with a pair of dead furrows taking up the surplus runoff until the vetiver can be planted. Rain caught and held in each furrow’s micro-catchment has the chance to soak in. Each furrow can hold 50 millimeters of rainfall, so in most storms there is no runoff. Thanks to this natural system of water storage, the plants can benefit from the sunshine, as shown in view D. In view E, one of the dead furrows has been planted to vetiver grass to stabilize the system.
A vetiver grass hedge is the key to the in situ moisture conservation system. Once established, it serves as a guideline for plowing and planting on the contour, and in times of heavy storms it prevents erosion from destroying the farmer’s field. The beauty of the plant is that, once it has established, the hedge is permanent.
Figure 7-25a is a diagrammatic representation of what a vetiver grass system would look like in a smallholder farming area. The Vetiver System fits perfectly into the individual farm system, where no waterways or earthworks exist. Most farmers have one line of vetiver roughly in the middle of their fields, no matter what the shape; long fields may need two lines to stabilize them. Although each field has its own line or lines of vetiver, the entire hillside is protected against erosion because each line protects the ones farther down the slope. Under this system, once the hedges are established, no further protective work is needed, and maintenance is minimal. The farmers each have their own supply of vetiver planting material. Should a gully start to form anywhere, the farmer obtains cuts slips of vetiver from an existing hedge and plants it across the incipient gully to prevent its spread—permanently and at no cost except for the farmer’s own labor.
The photo in Figure 7-25b shows vetiver hedges planted over a large area. Unlike a constructed system, the Vetiver System requires no waterways, and runoff does not have to spill into any drainage network. Because they do not convey runoff, the hedges can be as long as any given farmer’s field. The hedges spread out the runoff, providing moisture conservation over the entire area. At the same time, the hedges filter out the silt, enabling the excess runoff to flow harmlessly down the slope.
Why Vetiver Grass Is the Ideal Plant for the Vegetative System of Soil and Moisture Conservation
Although many grasses and trees have been tried over the years as measures to prevent erosion, to date only vetiver grass has stood the test of time. As made clear by the following list of its characteristics—derived from observations of V. zizanioides throughout the world—this truly remarkable plant is ideally suited for the vegetative system of soil and moisture conservation. No other grass is known to rival its hardiness or diversity.
- When planted correctly, will quickly form a dense, permanent hedge.
- Has a strong fibrous root system that penetrates and binds the soil to a depth of up to 3 meters and can withstand the effects of tunneling and cracking.
- Is perennial and requires minimal maintenance.
- Is practically sterile; because it produces no stolons or rhizomes, it will not become a weed.
- Has a crown that is below the surface, which protects the plant against fire and overgrazing.
- Has sharp leaves and aromatic roots that repel rodents, snakes, and similar pests.
- Has leaves and roots that have demonstrated a resistance to most diseases.
- Once established, is generally unpalatable to livestock. The young leaves, however, are palatable and can be used for fodder. (In Karnataka, India, a cultivar of V. zizanioides selected by farmers has softer leaves and is more palatable to livestock. This cultivar is also denser, less woody, and more resistant to drought than some of the other available cultivars.)
- Is both a xerophyte and a hydrophyte, and once established, vetiver grass can withstand drought, flood, and long periods of waterlogging.
- Will not compete with the crop plants it is used to protect, and in fact, vetiver grass hedges have been shown to have no negative effect on—and may in fact boost—the yield of neighboring food crops.
- Is suspected to have associated nitrogen-fixing mycorrhiza, which would explain its green growth throughout the year.
- Is cheap and easy to establish as a hedge and to maintain—as well as to remove if it is no longer wanted.
- Will grow in all types of soil, regardless of fertility, pH, or salinity, including sands, shales, gravels, and even soils with aluminum toxicity.
- Will grow in a wide range of climates and is known to grow in areas with average annual rainfall between 200 and 6,000 millimeters and with temperatures ranging from -9º to +50º Centigrade.
- Is a climax plant; therefore, even when drought, flood, pests, disease, fire, or other adversity destroy all surrounding plants, the vetiver will remain to protect the ground from the onslaught of the next rains.
Other Practical Uses for Vetiver Grass
Apart from its success as a system of soil and moisture conservation, vetiver grass has
proved effective for a variety of other purposes.
Stabilizing terrain and structures. One of the most important uses of vetiver grass is stabilizing the terrain and structures such as dams, canals, and roadways. Figure 7-26, for example, shows how vetiver can be used to stabilize a typical paddy field that relies on earth banks to keep irrigation water at the correct level. These banks (top illustration) can be worn down by the action of wind-churned water (lap erosion) and the activities of rats, crabs, and other hole-burrowing pests. The subsequent large-scale erosion, not to mention the loss of expensive and in some cases irreplaceable irrigation water, could lead to loss of the crop.
Vetiver can be planted on top of the paddy banks to stabilize them (bottom illustration). Vetiver grows well under these conditions and does not suffer from the occasional inundation of water. In addition, vetiver roots contain an essential oil that repels rodents. Furthermore, because its roots grow straight down and not out into the crop, the grass has no negative effect on the rice or its yield. Each year the vetiver can be cut back to ground level to prevent shading of the crop.
In another example, vetiver can be used to maintain river levees by preventing them from being eroded back into the fields. (See Figure 7-27a and the photo in Figure 7-27b.) It can also be used on river flats to prevent silt from entering the watercourse from the runoff of surrounding fields.
Establishing tree crops. Vetiver’s stabilizing influence is especially useful in steep and rolling country, where the distribution of moisture cannot be controlled. Unsuitable for the cultivation of cereal or other annual crops, such areas, when stabilized by vetiver grass, can be successfully planted to perennial tree crops on the contour. Most attempts to grow tree crops on steep hillsides are abandoned because the resulting poor, uneven stands are not worth the cost of maintenance.
Figures 7-28a and 7-29a show a method of establishing tree crops on such hills using contour vetiver hedges. First the contours of the hill are pegged out. Next, by hand or with a bulldozer and ripper unit, the farmer digs shallow V ditches along the contour lines. A row of trees is planted close to the edge of each ditch, and vetiver grass is planted in the ditches.
Under this arrangement of planting, the runoff between one row of trees and the next one down the slope collects in the vetiver-lined ditches (there is usually sufficient drainage on the slopes to preclude the possibility of waterlogging). Thanks to the effects of such water harvesting, the rows of trees do not have to be planted as close together as the trees within a row. Initially, the V ditch will provide a measure of runoff control, thereby increasing the soil’s moisture content, and both the vetiver and the planted trees will benefit. By the time the ditch “melts” away after a couple of years, the vetiver hedge will be established and performing its function of increasing the infiltration of runoff, halting the loss of soil and soil nutrients, and creating a natural terrace.
Because the collection of runoff in the contour ditches has the effect of doubling or tripling the amount of effective rainfall, fruit trees planted by this method need no irrigation in the first three years of establishment. The vetiver grass lines stabilize the whole system. The photos in Figures 7-28b and 7-29b show the success of such systems.
Mulching. After the vetiver hedges are properly established, the farmer can cut down the vetiver grass to ground level when the dry season sets in and use its leaves as mulch at the base of the fruit trees to help retain stored moisture. (See Figure 7-30a and the photo in Figure 7-30b.) The advantage of using vetiver for this purpose is that its leaves harbor few insects and last well as mulch. Vetiver hedges also protect the young trees in the hot summer months by providing some indirect shade; in the colder winter months the hedges act as windbreaks.
Establishing forests. Forest trees should be planted by the same method as when establishing tree crops—on the contour and, if possible, in V ditches bordered by vetiver hedges to stabilize them. Where this has been done, the results have been spectacular: more than 90 percent of the seedlings planted by this method survived the 1987 drought in Andhra Pradesh, India, whereas 70 percent of the other seedlings died.
Stabilizing masonry walls for hill farming. In the Indian Himalayan highlands, where farming is carried out on terraces, vetiver grass is now being used to stabilize the masonry risers that have been erected over the centuries. The walls pictured in the photo in Figure 7-31a need all the support they can get to withstand the seas whipped up by typhoons, and during tropical storms, to withstand the massive damage caused by runoff from associated torrential rain pouring over the walls, and even through the walls, from the catchment above. The hedges in the photograph have withstood the rigors of a typhoon that destroyed other walls in the area that were not protected by vetiver hedges.
Without some form of vegetative support, these ancient structures require continual maintenance. If one riser washes out during a heavy storm, other terraces farther down the slope often suffer considerable damage because of the domino effect. Figure 7-31b, which depicts a typical terrace system in the hills, shows the type of damage frequently sustained. To allow for drainage between the stones, the masonry risers are not bound together with mortar. If the walls were solid, instead of just a small section falling out, the whole wall might collapse and trigger a landslide that could destroy the entire farm. Although these terraces have done an excellent job through the years, they do exact a toll in the form of crop losses, and they require a lot of hard work in repairs.
When we explained the Vetiver System of stabilization to the hill farmers, they wanted to plant as many areas as possible. In a World Bank project begun in 1986, vetiver grass was planted along the edge of the terraces during the rainy season in the hope that its strong root system would reinforce the masonry risers. It worked perfectly.
Figure 7-31c shows what the vetiver grass-protected terraces should look like once established. The grass is planted only at the extreme edge of each terrace so the hedges do not impede the essential drainage between the stones. According to the farmers, what causes most of the damage during heavy storms is the cascading of water down the slopes and over the top of the masonry terraces, especially if the water has a chance to concentrate into a stream. Once established, the vetiver hedges should take most of the erosive power out of this runoff as well as protect the edge of the terrace.
As shown in the close-up in Figure 7-31d, the masonry risers are vulnerable because they are simply stones stacked on top of each other and are usually 2 to 3 meters high. Because its strong root system can easily penetrate to the bottom of the risers, vetiver grass can be used to protect the entire rock face.
In another project in the Himalayan highlands, in areas with no masonry terraces to halt massive sheet erosion, vetiver grass contour lines are being established to determine whether the natural terraces that build up behind the hedges will form a base of stable land for the production of fuel wood and fodder crops. In China, in the provinces of Jiangxi and Fujian, vetiver grass hedges are now being used to protect the edges of citrus and tea terraces.
Protecting roads. Vetiver grass is also used to protect road cuttings, as shown in Figure 7-32a. People in St. Vincent in the Caribbean use it to line the outer edge of the tracks to their houses. The grass has exhibited a remarkable ability to grow in practically any soil. In Andhra Pradesh, India, for example, it was observed growing at the Medicinal and Aromatic Research Station at the top of a bare hill. Even though the soils on that hill are skeletal—granite boulders had to be In the West Indies, the plant has been used extensively for stabilizing roadsides and has completely prevented erosion for years bulldozed to make a plot for the grass—and are deprived of most of the benefits from rainfall (since they are located at the very top of the hill), and at the time supported no other form of growth, the vetiver grass showed no signs of stress. A plant that can thrive under these extreme conditions should be able to do an excellent job of stabilization almost anywhere.
The photos in Figures 7-32b and 7-32c show how vetiver grasses have been used in Malaysia to protect roads. In Figure 7-32b, the hedgerows stabilize the slopes of country roads. Once the hedges are established, the roads are fully stabilized and do not slip. The cost to establish the hedges is minimal, and the maintenance is even less. The same Vetiver System is used to stabilize high-cost highways, as shown in Figure 7-32c.
Stabilizing wasteland development. The use of vetiver grass in wasteland development has recently been tested, and vetiver has proved effective as the initial stabilizing plant. In the Sahel region of Africa (in the state of Kano, Nigeria) and in Bharatpur in central India, under the extreme conditions of constant fire and drought, V. nigritana and V. zizanioides, respectively, have survived as the climax vegetation for hundreds of years. When planted as contour hedges in wasteland areas—the first stage in stabilizing such areas—V. zizanioides reaps the benefits of any surplus runoff and harvests organic matter as it filters the runoff water through its hedges. Because the foothills of the Indian Himalayas are very young geologically, they are highly erodible; planting vetiver contour hedges around these slopes and then across the short erosion valleys will stabilize these areas. A masonry plug at the end of the system allows silt to build up and give the grass a basis of establishment. (See Figure 7-33.)
The same would apply to normal gullies as shown in Figure 7-34a. Once established, the grass would fill and terrace the gullies with silt. In an upland area of Fiji, as shown in Figure 7-34b, a gully was stabilized with vetiver grass some 30 years before the photo was taken. In the photo, the gully is fully stable and the hedges remain where they were originally planted.
Stabilizing riverbanks and canal walls. Using vetiver grass to stabilize riverbanks and canal walls is another recommended practice. In an experiment in Tanzania, on the road to Dodoma, a road engineer used vetiver grass to protect the wing wall of a bridge on one side of the river and constructed the usual concrete wing wall on the other side. Some30 to 40 years later, the concrete wall had already collapsed into the river, and the bank it was protecting was eroded. On the other side, the vetiver grass was still holding the bank in perfect shape. Figure 7-35a shows how vetiver grass can be used to protect the river approaches to a bridge. The success of the Vetiver System is evident in the photo in Figure 7-35b, where newly planted vetiver hedges protect the approaches to a small bridge in El Salvador. During the floods of Hurricane Mitch in 1998, this bridge did not wash out.
Figure 7-36a shows how vetiver grass can be used to protect the banks of a major irrigation canal. In Bangladesh, as seen in the photo in Figure 7-36b, the canal has been stabilized with vetiver hedgerows for decades, and the plants do not invade the river or the fields behind the rows.
The contour irrigation aqueducts that lead back from the main canal around the foothills to the upper reaches of a command area suffer from siltation and erosion as they wind their way around the slopes. The typical problem is depicted in the top illustration in Figure 7-37a: the concrete conduit is undercut by erosion at point A and fills with silt at point B. To overcome this problem, vetiver grass should be planted parallel to the upper and lower sides of the concrete conduit. As shown in the bottom illustration, the upper hedge will prevent silt from entering the canal, while the lower two hedges will prevent erosion and thereby keep the concrete structure from being undermined by rills or gullies.
On a sugarcane farm in Zimbabwe, as seen in the photo in Figure 7-37b, the left side top vetiver hedge is protecting an irrigation channel from silting up behind the hedge, while the other rows protect the drain from erosion and silting and help maintain its shape.
Protecting dams. A similar approach can be taken to protect dams. Small dams are silting up at an alarming rate throughout the world. Once they become filled with silt, they are of no further use—and in many cases there is no other site suitable for a new dam. If vetiver grass is planted around the sides of the dam, as shown in the top illustration in Figure 7-38a, the silt carried by runoff from the surrounding hills will be trapped before it reaches the dam. Vetiver hedges planted across the inlets (A) of small dams on intermittent streams will protect the dams from siltation. In time, these hedges will form stable terraces that can be used for cropping or tree planting. In the bottom illustration, vetiver has been planted on the walls of a dam to protect them from being worn down by rill erosion, a problem afflicting many unprotected earth dams around the world. To make it easier to spot seepage along the toe, or very bottom of dam walls and canal banks, vetiver should not be planted in those areas.
The photo in Figure 7-38b shows a small farm reservoir in India around which the farmer planted vetiver grass to protect the reservoir from wave action (lap erosion). The photo in Figure 7-38c shows a dam wall in Zimbabwe on which vetiver provides complete protection and stabilization.
Common applications. The versatile vetiver plant has numerous common applications as well. It makes good bedding for livestock, because it soaks up the urine and stays dry longer. Ultimately, it makes good compost. In countries with strong winds, vetiver grass hedges make good windbreaks to protect young fruit and timber trees. The grass when green also serves as a firebreak. Vetiver is used as mulch for tree crops and as thatch for roofs of houses, sheds, and shelters. (See the photo in Figure 7-39.) The grass is woven into baskets, and the leaf midribs and flower stems make excellent brooms.
In the preface of the first edition of the handbook, we asked users to give us their views and share their experiences. Below are some of the responses we received.
- Well-grown vetiver hedges result in less runoff and improved groundwater supplies. Dry-season stream flow improves under the hedge system of in situ moisture conservation.
- In most instances on slopes of up to 5 percent, about 10 centimeters of silt is deposited behind the hedges annually.
- In addition to its use for soil and moisture conservation, vetiver is being used for fodder, thatch, mulch, livestock bedding, windbreaks, roadside protection, and brooms.
- Where hillside crop drainage is required—as in the case of tobacco ridges on a graded slope—vetiver hedges act as an excellent buffer against erosion if placed on the contour at fixed intervals on the hillside.
- Most vetiver plant roots grow straight down for at least 3 meters. Other roots will grow out into the field for up to 50 centimeters, but they do not significantly affect crop growth—probably because of the high moisture content of the soil associated with the hedge.
- Vetiver hedges take about three years to be fully effective under low rainfall conditions. If vetiver slips are planted 10 to 15 centimeters apart, the hedge will form more quickly. Even where gaps exist, interplant erosion does not seem to be a problem because the roots join together in the first year to form a subsurface barrier.
- Where vetiver is planted along the edge of terraces, forward-sloping terraces are better than backward-sloping terraces because less runoff is removed by the terrace back channels. Also because one can dispense with the back channel—and also in some instances the front channel, where constructed—more land will be available for cropping. The ultimate objective should be to dispense with terracing, where possible, through the use of vetiver hedges, so that the topsoil can remain relatively undisturbed.
- Vetiver has been observed growing under conditions ranging from 200 to 6,000 millimeters of rainfall annually and at 2,600 meters above sea level. It survives snow and frost (in tropical mountain areas) and grows on most types of soil. It
obviously grows better where the soil is moist and fertile, but even under adverse conditions it grows extremely well compared with other grasses.
- In many countries vetiver has been infected with brown spot. The disease does not seem to have an adverse effect on its growth, however. A few instances of black rust have been observed but are not significant. In India the rust seems to be vetiver-specific and does not cross-infect other plants. In China stem borers have attacked vetiver, but in most cases the borer dies once it gets in the stem. Farmers generally are unconcerned and tend to respond by selecting plants that are more pest and disease resistant.
- Some early results from India, on both alfisols and vertisols, indicate that rainfall runoff was reduced from 40 percent to 15 percent (compared with the control), and silt loss was reduced from 25 tons per hectare to 6 tons per hectare (all for 2- year-old hedges on 2 percent slopes). The time to wilting in one demonstration on alfisols increased from 7 days to 20 when in situ moisture conservation measures were applied.
- An interesting technique observed in China was the plaiting, or interlacing, of vetiver leaves and stems from separate, neighboring plants to create a temporary barrier until the full hedge could be established.
- The cost of vetiver hedges depends on the availability and cost of planting material. In India the initial cost of hedge establishment is estimated at US$8 per 100 meters of hedge, US$6 of which goes for planting materials and other inputs. Once the live material, in the form of a hedge, is on the farm, the cost to produce new hedges is relatively low—it may be as little as US$2 per 100 meters. Under such conditions the economic rate of return is more than 100 percent. Where the slopes are less than 5 percent and the hedges are spaced about 40 meters apart, 250 meters of hedge is required per hectare at a cost of between US$5 and US$20. (See Table 7-3 at the end of this chapter.)
Selecting planting material
- In Karnataka, India, to date six cultivars have been identified. One cultivar selected over the years by farmers exhibits superior characteristics for hedge formation; fodder; and insect, disease, and drought resistance.
- When selecting material, choose plants that exhibit resistance to pests and diseases and that tiller well.
- Where winters are cold, select material that is more tolerant of cold temperatures.
- Vetiver planted densely in large gullies can be used for replanting elsewhere. Gullies make good informal nurseries because often they are permanently moist and have conditions good for growth.
- Stem and root cuttings grown under plastic may be a cheap way of vegetative propagation.
- For optimum tillering, nurseries should be fertilized (150 kilograms per hectare of nitrogen) and irrigated (especially in very dry areas).
- Nursery plants should be cut back to about 30 to 50 centimeters to encourage tillering.
- The best nurseries seem to be in loamy sands to sandy-clay soils where the drainage is good and where it is easy to dig up the plants for transplanting. We have seen excellent nurseries (when well watered) in sandy areas near perennial
- As long as the vetiver is planted when the ground is wet, it can survive a long period of drought after planting.
- On very small farms and fields where land is scarce and where farmers are reluctant to plant across their fields, vetiver should be planted on the field boundaries.
- On non-arable lands that are heavily eroded, vetiver should be planted first in the gullies and around the gully heads. The material from the gullies can then be used
for planting across the slopes in subsequent years.
- Gap filling is essential and should be done at the beginning of the wet season. The possibility of “layering” live stems across the gaps should be tried as a gap-filling measure.
- To encourage tillering and hedge thickening, the grass should be cut back to 30 to 50 centimeters after the first year. Cutting in the first year does not seem to have any incremental impact on tillering.
- Termite infestation (attacking dead material) can be controlled by applying 1 kilogram of benzene hexachloride (BHC) for every 150 meters of hedge line.
- Once the vetiver has established (one month after planting), plowing a small furrow immediately behind the vetiver hedge line helps to capture runoff and results in better growth of the plant.