Pore shape, size distribution and orientation in Bt horizons of two Alfisols with and without cohesive character from Brazil

Abstract

This study aimed to evaluate the morphometry and orientation of the pores in Bt horizons with and without cohesive character in two soils of the Coastal Tableland of the Ceará state, Brazil. In two Alfisols, undisturbed samples were collected in the Bt horizons with and without cohesive, in two directions (horizontal and vertical), and cardboard boxes. Disturbed samples were also collected. Regarding the undisturbed samples, those of the rings were used to determine soil water retention curve (used to determine total porosity, macro- and microporosity, and pore size distribution curve) and soil bulk density, whereas those of the cardboard boxes were used to obtain random 12 × 15 mm photomicrographs and, from them, pore size and pore size distribution. Porosity data were analyzed considering a completely randomized design, in 2 × 2 factorial scheme (two horizons; two sampling orientations), with seven replicates. Micromorphometry data, in which there was no replication for the statistical analysis, were analyzed based on the numerical values derived from the photomicrographs. In general, horizons with cohesive character have lower total porosity and there was no significant difference of this attribute between the soil samples collected horizontally and vertically. With respect to the shape, there were rounded, elongated and complex pores, and rounded shapes had highest occurrence. It was concluded that, regardless of the cohesion level in the Bt horizons, there are significantly more rounded pores in comparison to the other shapes. Regardless of the orientation in the soil, there is good pore size distribution at both cohesion levels of the Bt horizons. At both cohesion levels of the Bt horizons, total porosity does not differ according to soil sampling orientation. However, the total volume of pores and macropores is significantly smaller in horizons with cohesive character.