Erosive soil is the soil which high amount of its texture, organic matter or minerals in soil surface are leached from the area by the water or the wind. In Thailand, water is an important factor for soil erosion.
       How to observe erosive soil
       1. Thickness of top soil    If the thickness of top soil is 20 cm. and its color is black, there is least soil erosion. But if the thickness of top soil is less than 10 cm., soil erosion starts to occur.
       2. Find a trail of soil erosion in the area. There are cracks different in size and depth resulted from flowing of rainwater to the soil surface. The increase of soil erosion results in the increased size and depth of the cracks.
       3. Geography of the area    In the area where it is highly sloped, the soil erosion increases. In the area where it is lowly sloped, there is little soil erosion and there is no soil erosion in plain area.
       Area where erosion soil is found
       Erosive soil is found in the upland and in the are where its slope is more than 35%.

Both of shallow and deep soils are found. Soil texture and fertility is different depending on types of stone source. There are stone pieces and rocks distributed in the area. In the upland, farm crops like corn, cassava, legumes are planted. Highland area is covered with various kinds of forest like mixed deciduous forest, dry dipterocarp forest or tropical everygreen forest. In some area, trees are cut and burned by farmer. Such area called 'Destroyed farm' is found in the highland in the North and the Northeast.
       Land reclamation and management
       Soil and plant management for soil and water conservation is as the following :
       1. Mechanical method for soil and water conservation
              1.1 Form the bench terrace by cutting the top soil of the slope and fill the below area with the soil until it becomes terrace wide 1-3 m. Do it with the machine or labourer. This method is suitable for slope in the highland.
              1.2 Build the ditch around the mountain by cutting the top soil of the slope and fill the below area with the soil. Make it as the ditch around the mountain with 1.5-2 m. width. The ditch space is 6-10 m. This method is suitable for slope in the highland.
              1.3 Build the dike across the slope to prevent water. This method is for the upland.
       Not : Mechanical method takes much money and a lot of techniques.
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