The recent shift in soil tillage from conventional to no-tillage systems in Brazil alters the soil system dynamics. In soils cultivated under the no-tillage system the relations are established and preserved over the course of time, which increases the functional complexity of the system, while under the conventional system often destroys these relationships. Some questions have risen about the reliability of sampling the so-called "arable soil layer" (0-20 cm) for soil acidity quantification in the no-tillage system due to the formation of acidity, organic matter and nutrient gradients in the top soil, besides modifications in the magnitude of the relationships between indicators and acidity types. To verify this type of relationships in no tillage systems, a study was conducted in six fields, in two layers (0-10 cm and 0-20 cm) of an Oxisol (Typic Hapludult) of the Planalto region in the state of Rio Grande do Sul. Representative soil samples were collected from 20 sites of each crop field and soil acidity was analyzed in the laboratory. The relationship between soil acidity types and indicators was not affected by the soil layer. For the no-tillage system in the region under study, both layers (0-10 cm or 0-20 cm) represent a reliable basis for lime recommendation.
potential and active acidity; aluminum; aluminum saturation; base saturation
