R.M. Shelton. CARE, Australia, Simbu Agroforestry and land Use Project, PNG
Vetiver grass was introduced to PNG in the late 1980's and established on a Department of Agriculture and Livestock (DAL) Research Station in the coastal lowlands. All the planting material used in the PNG Highlands originated from this plot. Nursery blocks were established on Government Stations in a number of rural areas of Simbu Province by Extension Officers of the Provincial Department of Primary Industries (DPI). To date, the only on-farm plantings of vetiver grass in the highlands have been in about 40 gardens in Simbu Province.
Vetiver grass extension in Simbu Province prior to 1994.
There was little information available on the culture of vetiver grass to the DAL Extension Officers who made the first on-farm plantings of vetiver grass n Simbu in l993/94. The slips were planted at 30 to 50 cm centers in straight lines across the gardens, most of which have slopes over 40% The lines were not planted on the contour. Slips that died were not replaced. Few of the clumps of grass in these plantings have formed complete hedges and many gaps still remain. Their effectiveness in preventing soil loss has been minimal. The growth rate of the grass was satisfactory on fertile soils, but slow on shallow soils. Little follow up extension was given to farmers to encourage them to persist with the grass or manage it in any way as DAL Extension Officers were provided with few resources for this purpose.
CARE Australia's program with vetiver grass extension since June 1994.
The Simbu Agroforestry and Land Use Project, is managed by CARE Australia on behalf of the Australian Government Aid Agency, Aus Aid. One of it's components is to investigate ways to use vetiver in gardens in the Province. After a review of the literature, observation of the plots already established, and discussions with officers of the DAL and village farmers, a vetiver grass extension program was commenced. On-farm plots were established and follow-up extension visits are made on a regular basis.
The extension message is constantly reviewed in the light of the increasing practical experience. Texts in Tok Pigin, a commonly spoken language throughout PNG, are being prepared to provide farmers with information about all aspects of vetiver grass culture and management.
The extension methods used.
· The extension effort emphasizes the grass's likely benefits to the farmer and to the gardening system. No funding is allocated by Government or SALUP to provide incentives for farmers to plant the grass.
· Few farmers have access to capital for the purchase of inputs such as fertilizer, or labor. Establishment and management methods that need no cash and little extra labor are emphasized.
· Farmers are taken to visit already established plots, on-farm field days and discussions are held, radio programs on vetiver grass are broadcasts, and follow up farm visits are made so that farmers have all the information they need to incorporate the grass into their garden system successfully.
· Farmers are supplied with limited amounts of free planting material and encouraged to establish their own nurseries as existing nursery areas are small.
· Papua New Guineans are very innovative gardeners and will adapt and adopt worthwhile new technologies to suit their situation, if they have all the information they need.
· Women have a major role in garden management. and all extension effort must include them.
Recommendations for establishment and management of the grass.
Preparations prior to planting.
Diversion drain: If there is a long slope without tree cover above it diversion drains should be dug to protect the garden from large flows of surface runoff that may run across it while the grass is establishing itself. Serious loss of soil and landslides occurred in a number of gardens which had no protection from this type of surface runoff. The hedges were still in the establishment phase. It is likely that less damage would have occurred to the garden if diversion drains had been dug above them. Care must be taken to ensure that the diversion drain itself does not cause erosion at its outlet.
Contouring: The vetiver grass slips should be planted on the contour if possible. Some washing of soil has been noticed from high points to low points along terraces about 1 m wide, formed behind hedges that were not planted on the contour. As the hedges are likely to last for many years and form sizable terraces, the extra trouble taken to mark out contours during the initial establishment is considered worthwhile and does not need to be repeated in later years as the hedges are permanent. Lines of crop plants will also be planted parallel to the hedges, on the contour and will contribute to erosion control. The contour can be marked out using a simple "A" Frame. It is a technology that can be mastered by local gardeners, with minimum of training.
Soil retention barriers
Soil retention barriers are a useful tool when establishing vetiver grass, particularly in very steep gardens. These barriers are built after the initial clearing of the garden and before planting of the crop. They are temporary structures that rot within 6 to 9 months of their construction, when soil accumulated on their up-slope side is normally lost down the slope. Vetiver grass slips are provided with an ideal seed bed for their establishment when they are planted in this accumulated soil and their roots prevent it's loss when the barrier rots. Some gardeners, against recommendations by SALUP, planted the vetiver grass hedges on the lower side of the soil retention barriers. Grass growth was satisfactory, but when the barrier rotted, soil held by the barrier fell on top of the grass and some was lost down the slope. It is too early yet to determine if the grass will survive this treatment. They are most effective if they are established on the contour at 2 m vertical intervals.
Vertical interval between hedges
The ideal is to plant the lines of vetiver grass at no more than 2 m vertical interval. If the vertical interval between hedges is more than 2 m, the velocity of runoff water on steep slopes during heavy rain is likely to cause heavy rilling and scouring which can lead to land slides in extreme cases. A 2 m. vertical interval on a 45% slope allows a surface distance of only 2.8 m between hedges. Most gardeners consider this is too narrow a space to crop and a compromise must be made between the ideal and the practical. On the steeper plots farmers have accepted vertical intervals of up to 3 m.
Planting of vetiver grass should take place early in the wet season, if possible. Vetiver grass hedges have been planted throughout the year. While most slips survive when planted during periods of drought (usually less than 3 weeks in PNG), their growth is minimal and some deaths occur. Slips planted when there is regular rain establish much faster.
Timing in the gardening cycle
Planting of the vetiver grass in a garden should take place just before the crop is planted. At this time conditions are ideal for quick establishment of the grass as competition from weeds is at a minimum, and the farmer can observe the grass regularly when caring for the crop. By the time the garden is fallowed the grass should be well established so that it can compete successfully with invading volunteer species and still be present when the garden is re cultivated.
Vetiver grass can be planted into stands of Kunai (Imperata cylindrica) (the most common local grass) by cultivating a narrow strip where the slips are to be planted. Kunai is an aggressive species and while most of the vetiver grass survives, its growth is very slow unless the kunai is regularly cut. Few farmers are prepared to invest the time and effort required. It is also difficult to separate the kunai from the vetiver grass when the garden is cultivated later. As very little erosion occurs in established stands of kunai, there appears to be no advantage in planting vetiver grass into such swards. Established hedges should be able to compete successfully with kunai that grows during the fallow period.
The effectiveness of vetiver grass in controlling erosion depends largely on it's ability to form a complete hedge without gaps, across the slope. If the gaps between the clumps of vetiver grass are to close quickly, under conditions in Simbu, the slips must be planted at no more than 10 cm centers. Given reasonable growing conditions, most of the gaps will close within 12 months. Slips planted at 30 to 50 cm centers still have gaps after 2.5 years of growth.
A mulch of leaves, dead grass, etc. should be placed around the slips when they are planted, particularly in dry weather. The mulch prevents the soil from drying out, keeps the surface cool, retains some soil, and generally improves conditions for the establishment of the grass.
Use of leguminous coppices
A line of Leucaena spp. trees, which will be coppiced when they have grown, planted parallel to the vetiver grass hedge, will help to improve soil fertility in the garden. The trees which have been planted at 50 cm centers in a line 50 cm to 1 m from the hedge, have a threefold benefit. They contribute nitrogen directly to the soil from their roots and indirectly through the coppiced material which is used as a mulch, their roots help to hold the soil on steep slopes, and the trunks and larger branches of the plants can be used for firewood or construction timber. The traditional nitrogen fixing tree used in PNG is Casuarina oligodon. It cannot survive coppicing, though it can be pollarded. Its use is generally as a tree cover/soil improver during longer fallow periods. Coppicing is a new technique in the Highlands and more research needs to be done into the best species and methods to use. An extension program will be needed if it is to gain widespread acceptance as a worthwhile practice.
Replacement of slips that die
Any slips in the hedge that die should be replaced as soon as possible. The gaps left in the hedge take a long time close up as replacement slips suffer from heavy competition from already established clumps if replanting is not done quickly. Trimming existing clumps will help. Ensuring that the original planting material is of good quality will reduce the number of dead slips. To date, no culms over 20 cm long, that could be used layered in these gaps, have been observed on any clumps.
Occasional trimming of the hedge will increase the number of tillers in the clumps of grass. A simple experiment to test the effect of trimming the leaves of clumps at 10 cm above the ground was conducted. It indicated that tillering increased significantly as a result of cutting. The trimmed leaves can be used as mulch or as thatch. The large majority of houses in rural areas still have thatched roofs.
After prolonged periods of rain in steep gardens some vetiver grass hedges have been lost through land slips. Experience in Simbu is too recent to know how effective the grass will be in preventing landslides once it has a fully developed root system. The soil in many gardens overlays rock or clay, conditions that restrict root growth and are highly conducive to land slides, particularly when the soil is saturated.
The future for vetiver grass.
Much has been learnt in the last three and a half years but more experience must be gained before a definitive answer about the place of vetiver grass in the traditional garden system can be given. Villagers from one of the areas where the vetiver grass has been planted said, when they were interviewed recently, that they needed to observe the grass for a longer period before they were prepared to form a definite opinion about it's usefulness. However, requests for vetiver grass planting material continue to be received from other farmers in this area, and most seem confident that it will be a useful tool in making sure that their children will inherit land suitable for growing their future food needs.
Vetiver grass has a place within the gardening system, but will only be one of a number of technologies that must be mobilized to ensure that crops will continue to be produced given the extreme terrain encountered in this region of the world. Miracles are needed, vetiver could well be one of them.
Bourke, R. M. (May 1990). Subsistence Agriculture In North Simbu, Papua New Guinea . Paper prepared for: Simbu Provincial Government; Australian International Development Assistance Bureau, Canberra: International Fund for Agricultural Development, Rome. Tropical Agricultural Consultants Pty. Ltd., Canberra, Australia.
Scott, R. M., Healey, P. A., and Humphreys, G. S. (1985). Land Units of Chimbu Province Papua New Guinea. Natural Resources Series No.5. Division of Water and Land Resources. Institute of Biological Resources, Commonwealth Scientific and Industrial Organisation, Australia.
Wohlt, P. B., and Goie, A (1986). North Simbu Land Use. Research Report of the Simbu Land Use Project, Volume V. Institute of Applied Social and Economic Research, Port Moresby.