Andisoles, inceptisoles y entisoles de la subcuenca del río Pirrís, Región de los Santos, Talamanca, Costa Rica

eight soil profiles were described and classified on volcanic ash deposits at the upper pirrís river watershed. the soils were classified as andisols and inceptisols of the suborders ustands, udands and ustepts; at the great group level the soils were classified as haplustands, placudands and dystrustepts, belonging to the subgroups dystric haplustands, humic haplustands, aquic haplustands, typic placudands and andic dystrustepts. the topsoil characteristics of many of these soils are fragile, vulnerable to erosion and landslides. in general, these soils are acid, of low fertility status and present recent surface horizons (holocene), but could be underlain by argillic horizons formed during the pleistocene. on recent alluvial terraces from the holocene, another group of seven soil profiles were described. these showlittle morphological development; major soilforming processes in these positions include detachment in the highlands and deposition of particles through river flooding in the lowlands. these soils were classified in the orders entisols and inceptisols, suborders fluvents y ustepts, great groups ustifluvents, dystrustepts and haplustepts, finally belonging to the subgroups typic ustifluvents, fluventic dystrustepts, fluventic haplustepts and humic dystrustepts. most entisols present coarse textures (sandy loam) while in the inceptisols the clay content is dominant (clay loam, sandy clay loam and clayey textures). a third group of soils were described in a rim around intrusive materials of miocene to pleistocene origin, dated to be 8 to 11 ma. on these metamorphic materials inceptisols were formed, showing high rock and stone contents. most of these soils are shallow, acid and of yellowish colors, due to the illuviation, lixiviation, humus formation, weathering and erosion dominating soil forming processes in this area.