The Aggeric Epipedon: A Proposed Amendment to Soil Taxonomy

Results of field and laboratory studies in Thailand have shown that some man-made epipedons have less than 250 mg kg⁻¹ citric acid soluble P₂O₅ as required for the definition of an anthropic epipedon. They are lower in organic carbon and are less than 50 cm thick as defined for the plaggen epipedon. These man-made epipedons occur extensively, particularly in floodplains in Thailand and the soils used for both agricultural production and constructional purposes. However, they are not described in Soil Taxonomy, apparently because they have not been fully characterized. The term “Aggeric epipedon” is hereby proposed for these epipedons, created artificially by excavation and subsequent dumping of soil materials, as an amendment to Soil Taxonomy. Soils with this type of epipedon are recognized in the revised legend of the FAO/UNESCO Soil Map of the World published in 1988 as Cumulic Anthrosols. The Aggeric epipedon include man made surface layers which shall be 40 cm or more thick, it should have lower organic carbon content to differentiate it from the plaggen epipedon and a P₂O₅ value of less than 250 mg kg⁻¹ in citric acid to differentiate it from the anthropic epipedon. The proposed epipedon does not affect the classification of soils with a plaggen or anthropic epipedons.