PHYSICAL AND CHEMICAL-PROPERTIES OF SAVANNA SOILS IN NORTHERN BOLIVIA

Soil samples from a savanna in northern Bolivia were examined as part of the first detailed study on the regional vegetation consisting of a mosaic of grassland and shrubland, forest islands, palm swamps, and floodplain vegetation. Soil texture, pH, organic carbon, total nitrogen, exchangeable cations, cation exchange capacity, and base saturation of 29 pedons were determined. The pedons fit into five soil classes of the FAO-System (Cambisols, Ferralsols, Gleysols, Luvisols, and Fluvisols) and were tentatively placed in four orders of Soil Taxonomy (Inceptisols, Oxisols, Alfisols, and Entisols). The soil samples were taken from three vegetation formations, or land units. Most soils under (1) non-flooded grassland, shrubland, and forest as well as from under (2) moist grassland were clay loams, whereas some soils of (3) river floodplains were clays. The forest soils had a pH range of 5.5 to 6.9. All other soils were more acidic, with a pH range of 4.0 to 5.5. The cation exchange capacity rarely exceeded 10 meq/100 g in the mineral soil of all pedons. The base saturation and total exchangeable bases, especially Ca, were generally higher in forest soils compared to the soils of grass- and shrubland. A higher bare saturation was also recorded in the soils from whitewater river floodplains compared to soils flooded by small clearwater rivers. It is believed that frequent burning and grazing gradually changed the non-flooded forest soils into grassland soils which have a lower nutrient status.