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.

          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. 

          2. Planting method for soil and water conservation

          Growing plants across the slope with the varions mulch (suitable for the area) as the following method : 

                    2.1 Planting bushes with leguminous crops for soil maintenance Plant bushes with leguminous crops such as horse tamarind mixed with Mahae bean in the ratio of 1: 1. Plant it in a row and the row space is 50 cm. Plant it as conservation strip across the slope. The strip space is 8-10 m.

                    2.2 Planting grasses strip Planting grasses strip across the slope and the strip space is 8-10 m. Select various grasses like Ruzi, Zettaria, Napia, Barhere and Ginny and plant it as a strip with 1 m. width. For vetiver grass, plant it in one row and the plant space is 5-10 cm.

                    2.3 Planting mixed crops Empty area between conservation strips is used for Planting farm crops, vegetables, flowers and trees according to the area types. Plant mixed crops such as planting farm crops or vegetables before planting leguminous crops (peanut, blackbean, mung bean, Jackbean) for rotation. Its purpose is to reclaim soil for sustainable landuse.

          For other management for soil and water conservation, there should be soil preparation and growing plants in the rows according to the slope area. Apply crop residue as the mulch and soil amendmends. Planting with less soil preparation will decrease soil erosion and it is an effective way for landuse.

Table : Soil management for growing various plants