Resumen

Properties of soils in the eastern part of Madre de Dios, Peru, were characterized and related to landscape position and parent material texture. Level uplands, dissected side slopes and recent flood plains dominate the topography in this region. Soil textures vary from clayey to sandy, depending on the texture of sedimentary materials from which each pedon formed. Parent material textural variation is a result of differences in the energy of the meandering rivers that deposited the ancient alluvium. Fourteen soil profiles were described and sampled in the 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 soils with moisture status ranging from well drained to poorly drained. Soil moisture conditions vary with position on the landscape, such that as distance from streams increases, average depth to the fluctuating water table decreases. Redoximorphic features are present in all mineral soils. The average depth to redoximorphic features is least in locations furthest from streams. Soils in landscape positions that are poorly or somewhat poorly drained contain significant amounts of plinthite. In all soils, kaolinite is the dominant mineral in the <0.2 μm fraction, while quartz is the dominant mineral in very fine and fine sand fractions. All soils have low cation exchange capacity (CEC), low base saturation, and acid pH. Coarse-textured spodic soils with well developed zones of iron and organic matter translocation are formed in recent sand deposits of flood plains of 2nd-order streams. Organic soils are found in the wetlands associated with flood plains of some 3rd-order streams. Most properties of these soils appear to be controlled by the textures of their sedimentary parent materials and by their position on the landscape. The soils classify as Paleustults, Plinthaquults, Kandiustults, Placaquods and Troposaprists according to Soil Taxonomy. New subgroups of Paleustult are proposed