Characterization and Classification of Floodplain Soils in the Porto Alegre Metropolitan Region, Rs, Brazil

Abstract

In the Porto Alegre metropolitan region (PAMR) there are a significant proportion of floodplain soils, mainly Planosols and Gleysols, in relation to upland soils. This study aimed to evaluate the morphological, chemical and physical characteristics, and to classify floodplain soils in the PAMR. Six soil profiles were evaluated under different sedimentary lithologies and drainage classes, and samples were collected for chemical and physical analyzes. Two orders of mineral soils (Planosols and Gleysols) and one order of organic soil (Organosols) were identified. The soils were moderately deep to deep and stratified. In mineral soils hue ranged between 7.5YR and 2.5Y, with the occurrence of Bg, Btg or Cg gley horizons, while in organic soil the colors were neutral. Sand and silt were the predominant particle sizes according to the origin sedimentary deposits. The organic carbon content was negatively related to soil density and positively related to soil specific surface area and with soil cation exchange capacity. Soil chemical characterization showed expressive variation in bases, aluminum and sodium saturation. Ki index and Fe (CBD) /Fe (H2SO4) ratio indicated a low soil weathering degree. The different sedimentary lithologies and the soil hydromorphism degree were the main factors related to differences in morphological, physical and chemical characteristics of soils in the PAMR.Index terms: Hydromorphic soils; quaternary sediments; specific surface area. RESUMONa região metropolitana de Porto Alegre (PAMR) é expressiva a proporção de solos de várzea em relação aos solos de terras altas, com predomínio de Planossolos e Gleissolos. Este estudo objetivou caracterizar a morfologia, a física e a química, e classificar taxonomicamente solos em posições de várzea na PAMR. Foram abertas seis trincheiras em relevo plano, sob diferentes litologias sedimentares e classes de drenagem,onde foram realizadas a descrição morfológica dos perfis de solos e a coleta de amostras para as análises físicas e químicas.Foram identificadas duas ordens de solos minerais (Gleissolo e Planossolo) e uma orgânica (Organossolo). Os solos foram moderadamente profundos a profundos e estratificados. Nos solos minerais a matiz variou entre 7,5YR e 2,5Y, com ocorrência de horizontes gleizados Bg, Btg ou Cg, enquanto no Organossolo as cores foram neutras. A granulometria dos solos, com predominância das frações areia e silte, variou conforme os depósitos sedimentares de origem. A expressiva amplitude dos teores de C orgânico mostrou relação negativa coma densidade do solo, e positiva com a área superficial específica e a capacidade de troca de cátions. Os atributos químicos também se mostraram discriminantes entre os solos avaliados, com ocorrência de distrofismo e eutrofismo, variações amplas dos teores de Al 3+ trocável e ocorrência de caráter solódico. Nos solos minerais o índice Ki e a relação Fe (CBD) /Fe (H2SO4) indicaram um grau incipiente de desenvolvimento dos solos. O material de origem e o grau de hidromorfismo foram os principa...

Potentialities and limitations of Planosols with distinct depths of diagnostic horizon

“…This is an advantage for plant development, provided that there are no other limiting factors. There are reports of the occurrence of dystrophic Planosols in Brazil (Silva Neto et al, 2015;Oliveira Júnior et al, 2019), but eutrophic Planosols like those found in this study have been described in the semiarid region (Ferreira et al, 2016).…”

Spatial Disaggregation of Multi-Component Soil Map Units Using Legacy Data and a Tree-Based Algorithm in Southern Brazil

“…The average accuracy of the IPDS areas was 72.7 %, and was 100, 75, and 50 % for the Plintaquults, Albaquults, and Aquents, respectively (Table 4). These accuracies were satisfactory, considering the greater difficulty in mapping these areas in comparison to better drained areas because of the significant heterogeneity of soils inherent to hydromorphic environments (Coringa et al, 2012;Guimarães et al, 2013;Silva Neto, 2015). Moreover, the terrain variations are small in these areas, which makes it more difficult to differentiate soil classes using terrain variables.…”