R.G.Grimshaw. The Vetiver Network
Regions of Western Panama have been identified as sites for soil and water conservation programs that will involve erosion reduction measures using biological systems. These include the use of grass hedge rows - primarily vetiver grass; on farm cultivation practices - primarily contour cultivation, and soil fertility and insitu conservation measures that focus on green manuring and leguminous cover crops - particularly applicable to the maize crop. This note will focus primarily on the use of vetiver grass as a hedgerow barrier.
Existing uses of Vetiver in western Panama
In all the regions (Chiriqui, Veraguas, Herrea, Los Santos, Coclé and western Panama), see attached map, visited there was evidence of the existence of Vetiver grass (Vetiveria zizanioides). In most instances it can be found on household plots as single clumps of grass used for medicinal purposes. In fact it is apparent that in the past few years a large number of households have heard of the grass and have acquired it for this purpose. The local name is "Secate Valeriana". It was probably introduced from neighboring Costa Rica or Honduras. Some folk have had the grass for fifteen years or more. It should be noted that in no instance was vetiver reported as invasive, it was certainly not considered a weed, and no one had ever seen it flower. Many farmers showed very good powers of observation as to the grass's growing habits.
At Cerro Punta, in Chiriqui Region, the NGO group, AMISCONDE, was introducing vetiver grass for soil and water conservation. AMISCONDE had brought the planting material in from a coffee farm in nearby Costa Rica, and had established a small demonstration plot near its office. The Cerro Punta area is characterized by very steep hills., intensively cultivated with vegetable crops. Much of the cultivation is down the slope, and erosion studies indicate soil losses of more than 200 tons per annum. Much of this soil loss could be reduced if vetiver hedges were established on the contour across the slope. Photo 1 shows one such hedge on a 100% slope located on the opposite side of the valley from the site shown on photo 2. In this instance the farmer with the help of AMISCONDE technicians established a hedge on the lip of a small terrace. The hedge, about one year old is well established and the farmer reports significant soil loss reduction, and much reduced rainfall runoff. The scene also shows how the farmer has developed vegetable beds on the contour. The farmer also cuts the hedge from time to time and use the cuttings as a mulch. These farmers are very much aware of potential soil loss as some of them dig small pits to trap sediment which they then dig and spread on their fields. The farmer is extending his hedge row plantings by using material from existing hedges and from additional material from Costa Rica.
Vetiver has been used to protect an irrigation pipes on steep hills. Many of these pipes, if unprotected, end up hanging in the air due to the erosion of the soil on which they originally rested. The hedge will also stop the pathways from eroding. Another use of the hedge rows on steep slopes is that they make a strong and stable pathway for farmers to get to their crops.
At Rio Sereno y Caizán a coffee farmer was using vetiver for stabilizing the edge of the coffee fields and the plantation roadsides. The growth of vetiver at these sites was extraordinarily good. It was all less than two years old, and had very good growth rates, probably due to the trapping of excess fertilizer from the adjacent coffee fields. The altitude was about 1,000 meters and rainfall about 1500 mm over a period of about 7 months. The coffee plantation owner was agreeable to set up a nursery for the up coming project. All the farmers and users of vetiver were information starved!! They were happy to be given copies of the Spanish edition of "Vetiver Grass - A Hedge Against Erosion" This booklet should be widely distributed in Panama as part of the soil and water conservation program.
On one occasion in Chiriqui vetiver had been damaged by a very large rodent (the size of a cane rat). The rodent had burrowed along side a row of vetiver in an effort to find a weak spot to traverse the vetiver line. In doing so it cut many of the vetiver roots. It is surmised that when fully mature hedge rows have been established it will be very difficult for the rat to penetrate the hedges, and therefore that latter might turn out to be an effective barrier against in field crop damage.
Proposed uses of Vetiver
On farm soil and water conservation. There are abundant opportunities to extend the practices just started in Cerro Punt to conserve the steeply cultivated lands that support high value vegetable and beverage crops. A 3 hectare site near Boquete that has slopes over 100%. Some large banks have been built across the slope to remove excess water, but these eventually fail with devastating results. This could be prevented if slopes were protected with vetiver. The vetiver lines would be planted about 10 meters apart, on the contour, starting from the top of the slope. These hedges, if planted 15 cm apart within the line, would be effective within a year, and would result in a slow down of runoff, and the retention of sediment and nutrients. Erosion would be further reduced by improved in field practices including mulching and across the slope cultivation. Water would no longer be concentrated and would be dispersed gradually across the slope.
In other areas such as Los Santos and Herrea soil slips are frequent due to shallow soils on a rather impermeable subsoil. These lands will erode rapidly and will slip. Vetiver grass hedge rows planted on the contour will prevent these problems. The predominant crop is maize. If the a leguminous cover crop of beans were planted with the maize then it would be possible to improve soil fertility substantially - as demonstrated in Honduras. The combination of vetiver hedgerows and leguminous cover crops would probably result in complete stabilization and soil fertility maintenance. Erosion would be reduced to less than 3 tons per ha, and run off would also be reduced. The result would be that current labor intensive slash and burn farming systems would be minimized, farms would be stabilized, land slips would no longer occur, and sediment loads in the streams and rivers would be very much reduced. Crop yields and incomes would improve substantially.
Waste land stabilization
Vetiver has a good chance of growing on the hostile salt degraded soils near Chitré. These flat tidal areas have become totally denuded and are effected by wind and rainfall erosion. Vetiver should be test planted. If it grows, then vetiver hedges could be planted 50 meters apart. The effect would be to slow down runoff, improve infiltration and probably improve the washing out of salts. Grasses and other species are expected to establish naturally between the hedges. Trees such as Cassurina, and shrubs such as Atriplex (salt bush) should also be test planted to determine survival and growth rates.
Land slippage Most areas suffer from land slippage. Some are massive others are slight but could get very much worse. Some large slips have produced a massive amount of sediment directly into the rivers, and have been caused by deforestation for coffee, and further aggravated, in some cases by an unprotected road cuts. These slips could have been prevented if the land had not been deforested. Further soil losses could be prevented by planting vetiver hedges to stabilize the slip. A slip in Los Santos was probably caused by cultivation. This massive slip landed up in a nearby stream -- just another example of "point source erosion" The slipped area has naturally re vegetated, but could have been done quicker with the aid of vetiver grass hedgerows. In this case these slips were due to over grazing and the slip started probably along a cattle path. If these slips are not checked, massive sliding can occur at a later date. Vetiver grass hedges might stop this slippage, as the hedge roots could pin the shallow overlying top soil to the underlying parent material. Research needs to be carried out to determine hedgerow effectiveness and hedgerow architecture under different circumstances.
Stabilization of roads and river banks
Vetiver grass has been used for years in the Caribbean, Guatemala, Brazil, Bangladesh and Natal (South Africa) to stabilize road sides, drains, and river banks. In western Panama much of the sediment flow in rivers can be traced back to point source erosion sites. The collapse of a river bank or the fill area of a road will add tons of sediment to nearby streams and waterways. This has been identified in foregoing paragraphs in relation to land slips. A road side near Boquete that had collapsed and rebuilt could have been stabilized with vetiver to prevent slippage at a later date. A typical road site in the Chiriqui area has eroding side drains and rock debris fill from above. Much of this could be prevented if vetiver hedge rows were planted along the up side edge of the drain. The hedge would trap falling debris, and would keep the drain clean. Road drains erode because existing miter drains either don't exist or don't work. Often where they do exist they create gullying in the land adjacent to the road. This can be prevented by cutting a miter drain in the correct place, placing a vetiver hedge on the down side of the drain and extending it across the road side lateral drain (to act as a diversion), and protect the exit of the miter drain with vetiver hedges to prevent erosion.
River bank erosion can cause damage to property and structures. A property owner at the picturesque tourist town of El Valle had attempted to protect the garden from river damage using oil drums and concrete -- not a very pleasing sight! and probably not a long lasting solution. Using containerized plants vetiver grass would probably provide a long lasting solution, and would look much nicer. River flow can also do great damage to road structures and can easily wash away gabbions. For long term stabilization river banks should be "graded" and planted to vetiver hedgerows using containerized plants. The gabbions and concrete should also be protected with vetiver. On the down stream side of the bridge there was a real mess caused by uncontrolled stream flow. Stream flow could be harnessed over a period of time by placing vetiver hedge rows (containerized plants) along what should be the stream bank. Over time sediment deposits would build up in front of the vetiver, and the vetiver would grow up through the sediment to form a new bank. Note planting of containerized plants should be at the end of the wet season when no further flooding is expected.