Xanthic- and Rhodic-Acrudoxes under cerrado vegetation: differential internal drainage and covarying micromorphological properties

Abstract

Soil internal drainage plays a major role in soil genesis, and it is mostly dependent on topography. However, the existence of sedimentary and meta-sedimentary rock strata with variable dip angle allows for strong differences in internal drainage for identical topographies, which result in a marked differentiation in the properties of overlain soils. This work aimed to investigate the micromorphology of soils formed from different dip angles of rock strata and their relationships to internal drainage, in Minas Gerais, Brazil. Over horizontal strata, a Xanthic Acrudox lacking hematite and with blocky structure has developed. Over strata with 45° dip angle, strong drainage has resulted in intense desilication, forming a Rhodic Acrudox having hematite and with strong fine granular structure. Micromorphological analyses showed that both soils contain relict nodules which are probably being dissolved in the current environment, whereas only the Xanthic Acrudox has nodules in current processes of formation due to slower drainage. The Cr horizon of both soils, but mainly the Xanthic Acrudox, presented a much slower saturated hydraulic conductivity than the respective overlying horizons, which was associated with a pattern of poorly connected fissural pores as seen in thin sections. The Cr horizon of the Rhodic Acrudox showed a matrix impregnated by Mn and Fe oxides in an unusual pattern of microlamination and hypocoatings that appear to be unstable, dissolving in the current, strongly drained environment. The soil color is a reliable indicator of such differential pedogenesis in these conditions. Index terms: Soil genesis; xanthization; rubefication; plinthite; saprolith. RESUMOA drenagem interna desempenha um importante papel na gênese de solos e é principalmente dependente da topografia. Contudo, a existência de estratos de rochas sedimentares e meta-sedimentares com ângulo de inclinação variável permite forte diferença na drenagem interna em locais de topografia semelhante, o que resulta em marcante diferenciação de propriedades dos solos acima. Este trabalho teve como objetivo investigar a micromorfologia do solo com estratos de rochas com diferentes ângulos de inclinação e suas relações com a drenagem interna dos solos, em Minas Gerais, Brasil. Sobre estratos horizontalizados, formou-se um Latossolo Amarelo ácrico típico sem hematita e de fraca estrutura média em blocos subangulares. Sobre estratos com ângulo de inclinação de 45°, a drenagem forte resultou em intensa dessilicatização, formando um Latossolo Vermelho ácrico contendo hematita e de estrutura forte muito pequena granular. As análises micromorfológicas mostraram que ambos os solos contêm nódulos reliquiais que estão provavelmente sendo dissolvidos no ambiente atual, enquanto somente o Latossolo Amarelo possui nódulos em processo de formação, devido à drenagem mais lenta. Os horizontes Cr de ambos os solos, mas principalmente do Latossolo Amarelo, apresentaram condutividade hidráulica saturada muito menor do que os horizontes sobrejacentes, em as...

Hydrosedimentological modeling in a headwater basin in Southeast Brazil

“…In the basin, the classes of Latossolo (Oxisol) (45.1 % of the area), Cambissolo (Inceptisol) (38.2 %), and Argissolo (Ultisol) (15.4 %) are predominant; rock outcrop and Neossolo Litólico (Entisol) occupy, respectively, 0.7 and 0.6 % of the area (Figure 1c). The Latossolos (Oxisols) present in MRB are formed in intensely weathered parent material with a physically well-structured soil, which confers a high permeability and thus greater resistance to water erosion (Curi et al, 1994;Skorupa et al, 2016). This soil has low soil erodibility, and Silva et al (2009) suggested a value of 0.0032 Mg h (MJ mm) -1 for this parameter.…”

Land-use influence on the soil hydrology: An approach in upper Grande River basin, Southeast Brazil

“…In addition, the geology of these areas can contribute to the low Ko values. Chagas et al (1997) and Skorupa et al (2016) studied two contrasting Oxisols in Minas Gerais, Brazil, and reported that the orientation of their parent material layers had great influence on drainage of those soils. They observed that the orientation of metaphelitic rock layers interferes with soil drainage.…”

“…In situations where such orientation is horizontal (Red-Yellow Latosols and Yellow Latosols) there is a more restricted drainage. Where the orientation of the layers is inclined (Red Latosols), water infiltration is facilitated and provides better drainage in the Red Latosols with greater "solum" thickness (Chagas et al, 1997;Skorupa et al, 2016).…”

Preconsolidation stress of gibbsitic and kaolinitic Oxisols under a multipractice conservationist coffee system

“…However, the most Oxisols are susceptible to compaction under machine traffic (Ajayi et al, 2009a,b;Severiano et al, 2013;Andrade et al, 2017;Guimarães Júnnyor et al, 2019;Ferreira et al, 2020), even with different proportions of oxide/kaolinite in the clay fraction (weathering soil). Meanwhile, when used conservation techniques to cultivated this soils, improvements in the soil physical quality can occur, due to the increases of aggregates stability (Severiano et al, 2013;Iori et al, 2013;Silva et al, 2016;Vollant-Tuduri et al, 2005).…”