Organic soils of Malaysia their classification and mapping

Organic soils are estimated to occupy about 2.6 million hectares in Malaysia. These estimates, however, exclude soils mapped as organic clays and mucks, which in some cases qualify as organic soils, and the organic soils which occur at high altitudes. One of the problems faced in the mapping, classification and estimation of the extent of organic soils in Malaysia is the different definitions used to define organic soils in Peninsular Malaysia, Sabah and Sarawak. Over the last few years interest in organic soils of Malaysia has increased especially in Sabah and Sarawak after the successful economic cultivation of oil palm on these soils in Peninsular Malaysia using special management. However, efforts to transfer this agrotechnology from Peninsular Malaysia to Sabah and Sarawak are hampered by the differences in the definitions, classification and mapping of organic soils in the three regions. The objective of this paper is to review the existing definition, classification and mapping of organic soils in Malaysia. The paper proposes completely revised definitions, criteria and methodology for the mapping and classification of organic soils of Malaysia. This paper outlines completely new definitions and classification of organic soils of Malaysia as proposed by Paramananthan (1998). This new unified classification while based on the structure of Soil Taxonomy (Soil Survey Staff, 1975) has been modified to suit Malaysian conditions so as not to upset existing soil series/families already in use in Malaysia. The criteria used in this classification include : soil temperature regime, thickness of organic deposits, nature of the dominant material in the subsurface tier, nature of the underlying substratum reaction class, origin of the organic deposit, ash content and the presence/absence of wood in the profile. The Field Legend for Soil Surveys in Malaysia (Paramananthan, 1987) has been used in the mapping of both mineral and organic soils in Malaysia. This paper proposes a revised Field Legend for Organic soils of Malaysia for use exclusively to map organic soils. The criteria to be used include the mode of occurrence and soil temperature regime, the thickness of organic soil materials, the nature of the subsurface tier, the presence of sulfidic materials or sulfuric horizon, nature of the underlying substratum, origin of the organic deposits and the presence/absence of wood in the profile. The paper concludes by presenting four hypothetical cross-sections cross organic soil, Keys to the Identification of Organic Soils of Malaysia and a table summarising the characteristics of the 32 organic soils mapped to-date in Malaysia.