Sombric-like horizon and xanthization in polychrome subtropical soils from Southern Brazil: implications for soil classification

Author(s)

Chiapini, Mariane ; de Oliveira Junior, Jairo Calderari ; Schellekens, Judith ; de Almeida, Jaime Antonio ; Buurman, Peter ; Vidal-Torrado, Pablo

• Document type: Journal article
• Source: CIENTIA AGRICOL; v. 78, n. 4, p. 13-pg., 2021-01-01.

Abstract

The occurrence of dark subsurface horizons rich in organic matter (OM) associated with polychrome in the B horizon (yellowish over reddish hue) is common in soils from Southern Brazil. The formation of these horizons and the combination with such morphological attributes has not been properly documented, and neither has the cause effect relationship. Four soil profiles with such sombric-like horizons with a yellowish color at the upper part of the B horizon over red subsoil were studied in Southern Brazil. Results from micromorphology, extractable sesquioxide minerals, clay mineralogy and isomorphic substitution of Fe by Al in iron minerals showed that melanization, xanthization, bioturbation, moderate shrinking/swelling and moderate ferralitization were the most evident pedogenetic processes in role. Xanthization is closely related to the sombric-like horizon formation. In the studied area the findings demonstrated that no clay and OM illuviation had taken place. Therefore, the classification of these soils was revisited, so as to take into account the processes that underlie their genesis with emphasis on xanthization, clay illuviation and soil aggregation. The results suggest that the sombric horizon may need redefinition, unless profiles can be found in which illuviation of clay and/or OM can be proven. (AU)

• FAPESP's process: 13/03953-9 - Organic matter dynamics in tropical peatlands (Diamantina, Brasil) - development of molecular proxies to reconstruct environmental changes
• Grantee: Judith Schellekens
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 15/03577-2 - Pedogenesis and molecular characterization of sombric horizons in soils in Tijucas do Sul region - PR
• Grantee: Mariane Chiapini
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 14/23969-0 - Soil organic matter dynamics and its relation to the environment: molecular chemistry (pyrolysis-GC/MS) to understand soil formation in tropical soils
• Grantee: Pablo Vidal Torrado
• Support Opportunities: Regular Research Grants