Resumo. ABSTRACT The connected fragments of lowland and alluvial deciduous forests present topography with the large pedological and geomorphological variations. Thus, to understand the conditions in these environments, it was studied in details the conditions of soils and landforms present in small tributaries of a watershed in sedimentary geology, in the town of Pantano Grande, Rio Grande do Sul state. In order to assess these variables, it was established 200 plots of 100 m² divided into 40 sampling points with five plots each, the headwaters to the floodplain of the River Jacuí. In each sampling unit, it was collected surface soil samples for the analysis of fertility and granulometric composition. It was determined 16 soil classes until the fourth categorical level by the Brazilian System of Soil Classification and 12 geomorphological and soil compartments. In the ordination analysis, it showed differences between the sampling points of the plain and slopes. The variables altimetry, slope, soil texture, H + Al and CEC were the most important ones in the analysis of environment ordination.