Morphology and taxonomy classification of Neossolos and saprolites derived from volcanic rock of the Serra Geral formation in Rio Grande do Sul, Brazil.

摘要

The soil types Neossolos Litolicos (Leptosols) and Neossolos Regoliticos (Regosols) have been poorly studied in Brazil, due to their relatively low potential for agricultural use. Consequently the morphological description of Neossolos in the field is also hampered, particularly in terms of contacts between soil, saprolite and rock, and their classification in the Brazilian Soil Classification System. The purpose of this study was: to define morphologically the contact between soil, saprolite and rock in Neossolos; generate data of the saprolite layer and test an inclusion in the suborder Neossolos Litolicos and Neossolos Regoliticos; and evaluate the diagnostic attributes and classes available in the Brazilian Soil Classification System for the of Neossolos Litolicos and Regoliticos derived from volcanic rocks of the Serra Geral formation in Rio Grande do Sul, State, Brazil. Five profiles of litho-climosequence were analysed. The contacts were characterized based on the straight shovel excavation test associated to analyses of saprolite fracture and weathering classes. The contacts related to the presence of saprolite layers identified in the profile are not taken into consideration in the Brazilian Soil Classification System. Diagnostic attributes for the classification of Neossolos Regoliticos were proposed as well as a change of the term from "Regolitico" to "Saprolitico". New classes were also suggested for the third categorical level, based on information such as soil position and saprolite contact, excavation resistance and cracking level of the material. The proposed diagnostic attributes and classes allowed a more adequate classification of Neossolos derived from volcanic rocks in the State of Rio Grande do Sul.