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.
Highlights
The Alisol class in the international soil classification of the “World Reference Base for Soil Resources” (FAO), is characterized by the presence of an argillic horizon that has a cation exchange capacity (CEC) value of 24 cmolc kg-1 clay or greater, associated with base saturation of less than 50 % in most of the argillic horizon (IUSS Working Group WRB, 2014)
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 moist consistency ranged from firm in the Bt horizons to friable in the C horizon and Cr layerin the profiles derived from Clayey siltstone
Summary
The Alisol class in the international soil classification of the “World Reference Base for Soil Resources” (FAO), is characterized by the presence of an argillic horizon that has a cation exchange capacity (CEC) value of 24 cmolc kg-1 clay or greater, associated with base saturation of less than 50 % in most of the argillic horizon (IUSS Working Group WRB, 2014). The WRB Alisols are mainly included in the “Argissolo” classes of the Brazilian Soil Classification System (SiBCS), according to Embrapa (2013), and are considered a broadly distributed soil with intermediate agricultural potential. The effective soil depth in Alisols is not generally a limiting factor for agricultural use since the depth usually exceeds 150 cm. In soils developed from sandstone parent materials, thinness of the soil requires proper management to prevent environmental damage to the aquifer
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