Micromorphology and Genesis of Soils from Topolitosequences in the Brazilian Central Plateau

Fernando Cartaxo Rolim Neto,Marcelo Metri Corrêa,Roberto Da Boa Viagem Parahyba,Carlos Ernesto Gonçalves Reynaud Schaefer,Anifo Soares Mamudo Ibraimo,Danilo De Lima Camêlo,Anildo Monteiro Caldas

doi:10.1590/18069657rbcs20180219

Abstract

ABSTRACT The micromorphology of deeply weathered soils (Ferralsols/ Latossolos ) from the Central Plateau of Brazil remains little studied, and its affiliation to different parent materials, poorly known. To clarify the processes of soil formation of these acric, gibbsitic, Fe-oxide rich Ferralsols, three lithotoposequences on local ultrabasic to basic intrusive rocks were studied. The influences of mixing and pedobioturbation are evident in all soils, and Ferralsols of the Central Plateau of Brazil are polygenetic, based on the coarse mineral composition, with ultrabasic and metapelitic rock contributions. The typical oxic microstructure with stable microaggregates encompasses a gibbsite/Fe rich micromass with random inclusions of charcoal, allochthonous quartz, Ti-magnetite, and perovskite grains. Shallow Cambisols ( Cambissolos ) on tuffites also display a similar “oxic” microstructure, but a much lower degree of weathering. These Cambisols possesses apatite, and mafic and pelitic minerals as residuals minerals grains, indicating the polygenetic colluvia mixture of different substrates. The common occurrence of perovskite (CaTiO3) as a residual grain in deep-weathered, acric Ferralsols on ultrabasic rocks, not yet reported in the literature, shows an unusual resistant Ca reserve in oxic soils, though nothing is known about its implications to soil fertility.

Highlights

IntroductionThe most weathered and oxic tropical soils are polygenetic, and formed from pre-weathered materials (Tardy and Roquin, 1992; Stoops et al, 1993; Thomas, 1994; Baert and van Ranst, 1997; Schaefer, 2001; Marcelino et al, 2018)
The most weathered and oxic tropical soils are polygenetic, and formed from pre-weathered materials (Tardy and Roquin, 1992; Stoops et al, 1993; Thomas, 1994; Baert and van Ranst, 1997; Schaefer, 2001; Marcelino et al, 2018). They were subjected to cumulative, long-term ferralitization, pedobioturbation, and eventually, other soil-forming processes that led to great Bw horizon development, possessing peculiar micromorphological properties when compared to the soils from temperate regions (Schaefer, 2001). These soil are classified as Oxisols (Soil Survey Staff, 1999), Latossolos (Brazilian Soil Classification System; Santos et al, 2018) or Ferralsols (World Reference Base; International Union of Soil Sciences (IUSS), 2015), and their physical and structural properties are very favorable for root development (Ker, 1997), despite the very low fertility status
The advanced well-formed oxic microstructure of these Ferralsols is due to long-term pedobioturbation, in which resistant primary minerals are randomly incorporated within the homogeneous oxic, acric micromass inherited from the saprolite

Summary

Introduction

The most weathered and oxic tropical soils are polygenetic, and formed from pre-weathered materials (Tardy and Roquin, 1992; Stoops et al, 1993; Thomas, 1994; Baert and van Ranst, 1997; Schaefer, 2001; Marcelino et al, 2018) They were subjected to cumulative, long-term ferralitization, pedobioturbation, and eventually, other soil-forming processes that led to great Bw horizon development, possessing peculiar micromorphological properties when compared to the soils from temperate regions (Schaefer, 2001). Compared to other soil orders, little detailed work has been undertaken on the microstructural and microchemical properties of Ferralsols (Stoops and Buol, 1985; Schaefer et al, 2002; Paisani et al, 2013), despite being required to support genetic and taxonomical studies. Previous studies, such as Miklós (1992), Duarte et al (1996), Muggler and Buurman (1997), Marques (2000), Nunes et al (2000), Schaefer (2001), Paisani et al (2013), and Stoops and Schaefer (2018) have assembled important data on the micropedology of Ferralsols, relating the micropedological features observed with other aspects, such as pedogenesis, geomorphological evolution of the landscape, chemistry and soil fertility, among others

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