Effect of forest enchroachment on some soil properties in Khlong Yan Watershed
1997
Sophon Chaiwong
In order to prove plausibility of forest enchroachment for agricultural uses in humid mountainous area on deterioration of some soil properties and ecosystem, Khlong Yan Watershed was investigated. This watershed area has rugged and complicated mountain range of Granite and Limestone and heavy rainfall which have high potential factors affecting severe soil erosion. Whenever mature forest, because of its close system even in the strong acid and low fertility old forest soils, is destroyed, secondary particle of the surface soil will be directly detached by raindrop into primary particles; the detached clay particle and some silt will be rapidly and strongly transported out of the area by runoff water. If the storm is heavy stronger sand particle should also be transported. The study results showed that forest enchroachment for agricultural uses significantly increased sand fraction over the reference site particularly in Limestone soils but not very clear in Granite soils. Naturally higher quartz composition of the selected Granite reference site than that of the enchroachment areas overwhelmed the result. Influence on chemical properties and fertility characteristics of the forest enchroachment over the reference sites were not clear. Organic matter of the reference sites only slightly higher than that of the enchroachment areas. Unlike forest soils of other regions, abundance of low activity clay mainly sesquioxides and Kaolinite in this study area might decrease humus adsorption. Complexicity of the extruded Granite surrounded by Limestone naturally affected water quality of seapage which will partly and/or locally stabilized soil pH and contamination of Calcium and Magnesium. Fertilization in some enchroachment areas brought about contamination of Potassium and Phosphorus. Wischmeier Universal soil loss equation using parameters reported by Land Development Department, clearly showed severe to very severe soil loss in enchroachment areas, but very slight in the reference sites.
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