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 sedimentation 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 cost of soil erosion; assess the effectiveness and adoption of soil conservation and management practices; determine the extent of adoption of integrated pest management methods; and elicit farmers' perceptions regarding the main constraints in vegetable cultivation. Recent changes in land use within the area are quantified by a geographical information system, Landsat imagery, a digital elevation model and a 1992 farm survey of 10% of the farmers. Farmers modify the natural environment by mechanical excavations and other earthworks, and compensate for the negative effects of soil erosion on productivity by extensive use of irrigation, chicken manure, lime, and inorganic fertilizers. The preparation of broad platform terraces, cut out of the natural slope, is a major 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 as 155 t ha(-1) per event. Terraces are resurfaced periodically because of impoverished soil and reducing yields. Bench terraces, while reducing erosion, are rare owing to labor shortages. With the exception of polyethylene rain shelters, other agronomic practices do not substantially reduce soil erosion. Recommendations are made regarding the timing of land clearing and resurfacing of terraces, and suggestions for interventions that may improve catchment management are offered. The value 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 from vegetable cultivation in the CH is likely to cause other negative off-site effects that cannot easily be quantified, including adverse effects on public health as a result of run-off of chemicals, loss of wildlife habitat, and potential loss of tourism.