Soils, landforms and landuse in the agroecosystems of Rataphum watershed area, and the risk of chemical pollution

摘要

Analysis of the physical and chemical characteristics of the top one metre of soil was carried out at six sites representing the major soil units under the different landforms and landuses in the Rataphum watershed. The results show that in low areas, poorly-drained hydromorphic gley and low humic gley soils have low leaching potential due to low hydraulic conductivity throughout the profile. Due to the combination of high organic matter and medium clay content, transportation of chemicals to the groundwater was retarded. However, the heavy input of chemicals may induce higher contamination at local spots. In the lowland coastal plain, groundwater podsolic soils are widely used for vegetable production. This well drained sandy-loam to loamy sand has medium hydraulic conductivity in the top 25 cm and low conductivity below this point. The tow hydraulic conductivity and lower input of chemicals may decrease the risk of contamination to groundwater. Low humic gley soil in low terraces derived from old alluvium has higher hydraulic conductivity and lower clay content than soils derived from recent riverine deposits. The former are used for rubber plantations, where contamination from chemical fertilisers and herbicides may occur at higher rates. In the foothills, red-yellow podsolic soils contain a higher percentage of gravel at the top, while the clay content increases with depth. Due to the higher hydraulic conductivity in the top 50 cm and low organic matter, the risk of leaching of chemicals is higher.