Soil Variability in Different Landscape Positions in the Porto Alegre Botanical Garden, Southern Brazil

Abstract

Knowledge of soil characteristics in areas where activities related to the environment are developed, such as Porto Alegre Botanical Garden (JB-PoA), is a fundamental condition for the sustainable use of this natural resource. The objective of this study was to characterize, classify and evaluate some issues about soil formation in Porto Alegre Botanical Garden, as well as relate their distribution on the landscape according to environmental characteristics. For the morphological description and collecting samples four profiles were selected (P1 to P4), located in the summit-shoulder transition, backslope, footslope and toeslope, respectively. Granulometric distribution of the P1 and P3 profiles indicated sharp textural gradient, with presence of textural and "plânico" B horizons, respectively, according to Brazilian System of Soil Classification. There is predominance of low values of pH, and low base saturation, with exception of P4, indicating probable deposition of solution material at this area. The Fed/Fes relationship was greater in the profile located in the summit-shoulder transition (P1), indicating higher weathering. The Feo/Fed relationship increased in P3 and P4 profiles, indicating greater participation of iron oxides of low crystallinity in reducing environment. The occurrence of some pedogenic processes may be inferred, like lessivage in P1 (Ultic Hapludalf), due to clay skins and higher values of fine clay:total clay relationship in subsurface; ferrolysis and gleization, by low pH value and high Feo/Fed relationship in E and EB horizons of P3 (Oxyaquic Hapludalf), being the last also present in P4 (Humaqueptic Endoaquent), indicating gleization occurrence.