Saturday, 15 July 2006

Classification and Mapping of Soils of Sri Lanka for Sustainable Land Management.

Ranjith B. Mapa1, Anil R. Dassanayake1, Robert G. Eilers2, and Tee B. Goh2. (1) Soil SCience Society of Sri Lanka, Department of Soil SCience, University of Peradeniya, Peradeniya, Sri Lanka, (2) Canadian Society of Soil Science, Western Land resource Group, 362A Ellis Building, University of Manitoba Campus, Manitoba, MB R3T 2N2, Canada

Sri Lanka is a tropical Island in the Indian Ocean consisting of a land area of 65,525 km2 which is a predominantly agricultural. When the arable land is considered, the land man ratio is low as 0.15 ha, showing the pressure on agricultural land. There is a prime need to identify more productive land, which should continue with agriculture, while the unfertile lands should be released for non-agricultural activities. The soil resource of the country should be characterized and classified according to internationally accepted systems, and inventorized leading to a soil data base that could be used for many applications. The soil map and the Handbook of the Soils of Sri Lanka published in 1972 consist of Great Soil Groups according to the local classification system. Therefore, the objective of this paper is to highlight recent advances of Soil Classification according to international methods and development of a soil data base for sustainable land management in Sri Lanka.

For more detailed classification the three rainfall zones, Wet, Intermediate and Dry zones, receiving a mean annual rainfall of higher than 2500 mm, from 1750 to 2500 mm and less than 1750 mm respectively were considered separately. As the Wet zone supports mainly the export agriculture as well as 75% of the population, it was considered first and then followed by the Intermediate zone and dry zone. This study started in 1995 and continued to year 2005. A total of 28 bench mark pedons in the Wet Zone, 40 and 54 pedons in the Intermediate and Dry zone were characterized. These benchmark sites were geo-referenced using a global positioning system for easy interaction with other databases. The field characterization consists of topography, drainage, parent material, present land use, agro-ecological regions, etc. The soil profile was described according to FAO system and major soil horizons were identified. Soil physical properties including soil texture, bulk density, saturated hydraulic conductivity, wet and dry aggregate stability, and water retention were characterized using standard methods. The chemical properties characterized were soil pH, cation exchange capacity, base saturation, exchangeable bases including Ca, Mg, K and Na, organic carbon content electrical conductivity, total N and available P.

Using these data the soils were classified according to the Soil Taxonomy and FAO systems. The hard copy of the data base is available as fact sheets for the researchers and as publications in English and two local languages for the students in Soil Science and general public. The soils have been mapped at a getter scale than before and the soil map for the Wet Zone at a scale of 1:250,000 and for the Intermediate zone at 1:50,000 are available.

The soil map and the database generated by this study is presently used for many applications as indicative land suitability maps at zonal level to match the soil parameters with the crop requirements. Its usage in land use planning and crop zoning would be vital as it could be integrated with other geographical databases such as agro-climatology, physiogrphy and other terrain characteristics. Some of the examples of applications include soil erosion hazard maps, derived maps for drainage, slope, Soil Series and textural classes for given districts, risk of ground water contamination with agro-chemicals as 2.4-D and carbofuran. The database could be updated when new information is generated and could be used interactively with other similar databases.

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