RELATIONSHIP OF SOIL PROPERTIES TO PARENT MATERIAL AND LANDSCAPE POSITION IN EASTERN MADRE DE DIOS, PERU

Properties of soils in the eastern part of Madre de Dies, Peru, were c haracterized and related to landscape position and parent material tex ture. Level uplands, dissected side slopes and recent flood plains dom inate the topography in this region. Soil textures vary from clayey to sandy, depending on the texture of sedimentary materials from which e ach pedon formed. Parent material textural variation is a result of di fferences in the energy of the meandering rivers that deposited the an cient alluvium. Fourteen soil profiles were described and sampled in t he field and analyzed in the laboratory. Data for eight soil profiles representative of the region are presented here. The profiles include soils formed in both sandy and fine-textured parent materials and soil s with moisture status ranging from well drained to poorly drained. So il moisture conditions vary with position on the landscape, such that as distance from streams increases, average depth to the fluctuating w ater table decreases. Redoximorphic features are present in all minera l soils. The average depth to redoximorphic features is least in locat ions furthest from streams. Soils in landscape positions that are poor ly or somewhat poorly drained contain significant amounts of plinthite . In all soils, kaolinite is the dominant mineral in the < 0.2 mu m fr action, while quartz is the dominant mineral in very fine and fine san d fractions. All soils have low cation exchange capacity (CEC), low ba se saturation, and acid pH. Coarse-textured spodic soils with well dev eloped zones of iron and organic matter translocation are formed in re cent sand deposits of flood plains of 2nd-order streams. Organic soils are found in the wetlands associated with flood plains of some 3rd-or der streams. Most properties of these soils appear to be controlled by the textures of their sedimentary parent materials and by their posit ion on the landscape. The soils classify as Paleustults, Plinthaquults , Kandiustults, Placaquods and Troposaprists according to Soil Taxonom y. New subgroups of Paleustult are proposed. (C) 1998 Elsevier Science B.V.