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Land Rehabilitation and Soil Erosion Control

Collecting data from all over the world a large number of measures for soil and water conservation has been found; what measure should be used at any one area depends on the country’s or community’s region, climate, terrain, land use, along with the culture.
Land Development Department (LDD) has mission in soil and water conservation and prevention of degradation of soil and land resources of the country; many studies have been conducted to find the most suitable methods and systems for soil and water conservation since 1963. Studies have been done to find methods and systems to suit the country’s problems, land use, society, culture and economy. It can be said that the agency has found the most suitable soil and water conservation methods and systems for use in majority of soils and land resources in Thailand.

Definition and Meaning of “Soil and Water Conservation”
        The definition and meaning of ‘Soil and Water Conservation’ has been given by many people, based on those developed in foreign countries, especially the United States. Then the definition has been modified to relate to Thailand’s situation.

Land Development Department’s Committee on Standard of Soil and Water Conservation Works had considered the definition given by Dr. Samran Sombatpanit and Mr. Sophon Sangwichian of the Division of Soil and Water Conservation (at that time) together with the definitions from other countries and concluded that the definition of ‘Soil and Water Conservation’ should be “The most effective land use emphasizing soil erosion prevention to retain soil fertility and to confine (keep) water in the area as much as possible”, and the definition of “Soil and Water Conservation System” should be “The combination of methods for soil erosion control along with water and humidity confinement to the area for the most effective and sustainable land use.”

Classification of Soil and Water Conservation Measures
Soil and water conservation measures can be classified by operation methods into
three types as follows:
1. Mechanical or Engineering Measures. For this type, terrain conditions must be
            adjusted by constructing each method such as ‘diversion’ (คันดินเบนน้ำ), ‘absorption
            bank’ (คันดินเก็บกักน้ำ), ‘field terrace’ or ‘bank’ (คันดินแบบต่าง ๆ), ‘bench terrace’ 
            (ขั้นบันไดดิน), ‘hillside ditch’ (คูรับน้ำรอบเขา), ‘waterway’ (ทางระบายน้ำ), ‘reservoir’ \
            (อ่างเก็บน้ำ), ‘farm pond’ (บ่อน้ำในไร่นา), ‘gully control’ (บ่อดักตะกอน), ‘check dam’
            (อาคารควบคุมน้ำ), ‘land remodelling & reshaping’ (การปรับรูปแปลงนา) and so on.
2. Vegetative Measures. 
            The terrain conditions need not be adjusted, as they use natural methods by
            planting specific plants in hedgerows such as leucaena (Acacia leucocephala)
            mixed with pigeon pea (Cajanus cajan), vetiver grass (Chrysopogon zizanioides),
            wind break strips and contour trash lines.
3. Agronomic Measures.
            farmers have been doing; they are cover cropping, green manure cropping, contour
            cropping, strip cropping, inter-cropping, multiple cropping, crop rotation, contour
            ploughing, fertilizer application, liming and mulching with various materials.

Soil and Water Conservation Systems
There are three soil and water conservation systems that the LDD has developed and provided for the farmers; they are as follows:
1. Highland Soil and Water Conservation System. Highland is the land 500 m or more
            above the sea level or with more than 15% slope, most of them being watershed
            area and forests.
2. Upland Soil and Water Conservation System. Upland refers to foothill slope areas
            that are less than 500 meter above the sea level or 3-15% slope, most of them
            being used for cash cropping, fruit orchards and pasture.
3. Lowland Soil and Water Conservation System. Lowland is the land connected to 
            foothill slope, normally less than 3% slope and occasionally waterlogged.Most
            of the land is used for growing rice, vegetables or diversified farming/ mixed
            farming. A typical problem in lowland is the impeded drainage of overland flow, as
            water may accumulate from run off from upland and highland and also underground
            water and rainfall.
4. Each soil and water conservation system. consists of several soil and water
            conservation measures, which vary by terrain conditions and specific problems.
            Therefore, surveying, analysis and planning along with the study of local farmers’
             needs must be conducted before designing and constructing soil and water
             conservation and management systems.

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