| SOILS |
| Soils of the study area: |
Five main soil orders were distinguished in the study area by the LDD staff, following the USDA Soil Taxonomy (LDD, 2002). A brief description of the orders and the geographical extent of each is given below. The orders are listed according to the degree of pedogenic development (the most to the least developed): |
| Ultisols : |
| Ultisols occur in the ridges figure (6). The high temperature, together with high amounts of precipitation, combined with the stable geomorphic surface formed suitable condition (without disturbance) for the formation of these soils. Considering that the soil moisture regime is Ustic these soils were then grouped under Ustults. |
| Alfisols : |
| Alfisols were identified in sloping areas adjacent to the ridges (glacis as appears on the geopedologic map). Alfisols are considered as being pedologically less developed than the Ultisols, simply because they are associated with higher base saturation percent (meaning that they are not as leached as the Ultisols). Two suborders Ustalfs and Aqualfs were distinguished. |
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| Figure 1 : Soil map according to soil taxonomy 1999 , produced by LDD. |
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| Vertisols : |
| In a few places in the local landscape where vertisols were distinguished. The majority of the vertisols occur around rivers and channels in northern part of the study area. The occurrence of swelling clay minerals in the soils lead to the formation of vertic horizon, and consequently vertisols. According to soil moisture regime, two suborders aquerts, and usterts were distinguished. |
| Inceptisols : |
| Inceptisols occur in the lowest part of the lateral valley in between the dissected ridges. The interruption of soil forming factors because of geographical position influences the development of soil profile. A poor drainage condition is the reason that the majority of inceptisols were classified under suborder of Aquepts. |
| Entisols: |
| Entisols occur in very limited spots within the sloping areas. They all belong to sub order psamments. Entisols are formed from the materials derived from the sandstone hence residual. |
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Development of Methodologies for
Land Degradation Assessment Applied to
Land Use Planning in Thailand |
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