Boundary between Soil and Saprolite in Alisols in the South of Brazil

Abstract

Despite numerous studies conducted on the lower limit of soil and its contact with saprolite layers, a great deal of work is left to standardize identification and annotation of these variables in the field. In shallow soils, the appropriately noting these limits or contacts is essential for determining their behavior and potential use. The aims of this study were to identify and define the field contact and/or transition zone between soil and saprolite in profiles of an Alisol derived from fine sandstone and siltstone/claystone in subtropical southern Brazil and to subsequently validate the field observations through a multivariate analysis of laboratory analytical data. In the six Alisol profiles evaluated, the sequence of horizons found was A, Bt, C, and Cr, where C was considered part of the soil due to its pedogenetic structure, and Cr was considered saprolite due to its rock structure. The morphological properties that were determined in the field and that were different between the B and C horizons and the Cr layer were color, structure, texture, and fragments of saprolite. According to the test of means, the properties that support the inclusion of the C horizon as part of the soil are sand, clay, water-dispersible clay, silt/clay ratio, macroporosity, total porosity, resistance to penetration, cation exchange capacity, fe extracted by DCB, Al, h+Al, and cation exchange capacity of clay. The properties that support the C horizon as a transition zone are silt, Ca, total organic C, and fe extracted by ammonium oxalate. Discriminant analysis indicated differences among the three horizons evaluated.

Field Description and Identification of Diagnostic Qualifiers for Urban Soils in Brazil

“…Saprolite is a residual material at a different stage of alteration, generally with the structure of the parent rock and always susceptible to shovel excavation, being designated as a C or Cr horizon under natural conditions. It has significant water retention and does not allow root penetration, except through fractures that tend to be common (Pedron et al, 2015).…”

Field Perception of the Boundary Between Soil and Saprolite by Pedologists and its Differentiation Using Mathematical Models

“…The fast precipitation of iron during the weathering of iron bearing minerals at the weathering front tends to produce less crystalline oxides, which further, during the pedogenesis, tend to reorganize themselves in more crystalline forms. Therefore, the Fe DCB /Fe OA ratio tends to increase as the profile evolves (Stolt et al, 1991;Pedron et al, 2015).…”

Identification of plinthite or saprolite residue in soils with high textural contrast in the southern Brazil

“…The presence of plinthite or petroplinthite can alter the retention and movement of water (Daniels et al, 1978) and roots in the soil. In addition, they promote limitations to mechanization when close to the soil surface (Miguel et al, 2013;Pedron et al, 2015). In this way, their wrong identification results in a misunderstanding taxonomic and technical classification.…”