SOIL-EROSION AND ENVIRONMENTAL-IMPACT OF VEGETABLE PRODUCTION IN THE CAMERON-HIGHLANDS, MALAYSIA

Vegetable production in the Cameron Highlands of Malaysia has expanded over the past 25 years and has been implicated in the increase in sed imentation in reservoirs in the region. The present study was executed to evaluate current methods, patterns and profitability of vegetable production; study the causes, environmental impact and externality cos t of soil erosion; assess the effectiveness and adoption of soil conse rvation and management practices; determine the extent of adoption of integrated pest management methods; and elicit farmers' perceptions re garding the main constraints in vegetable cultivation. Recent changes in land use within the area are quantified by a geographical informati on system, Landsat imagery, a digital elevation model and a 1992 farm survey of 10% of the farmers. Farmers modify the natural environment b y mechanical excavations and other earthworks, and compensate for the negative effects of soil erosion on productivity by extensive use of i rrigation, chicken manure, lime, and inorganic fertilizers. The prepar ation of broad platform terraces, cut out of the natural slope, is a m ajor source of soil erosion which is estimated at 24 t ha(-1) year(-1) on average. However, on a per event basis, soil loss may be as high a s 155 t ha(-1) per event. Terraces are resurfaced periodically because of impoverished soil and reducing yields. Bench terraces, while reduc ing erosion, are rare owing to labor shortages. With the exception of polyethylene rain shelters, other agronomic practices do not substanti ally reduce soil erosion. Recommendations are made regarding the timin g of land clearing and resurfacing of terraces, and suggestions for in terventions that may improve catchment management are offered. The val ue of the negative externalities imposed on the Electricity Board as a result of sedimentation in waterways and reservoirs is estimated at M $ 2 X 10(6) per year, or less than 4% of the total annual gross value of vegetable production in the CH. However, soil erosion resulting fro m vegetable cultivation in the CH is likely to cause other negative of f-site effects that cannot easily be quantified, including adverse eff ects on public health as a result of run-off of chemicals, loss of wil dlife habitat, and potential loss of tourism.