Porosity and structure in Brazilian hardsetting soils: an evaluation by 2D-image analysis
Abstract
Limited knowledge about the hardsetting attribute in soils of the southeast and northeast regions of Brazil have restricted the exploitation of expressive agricultural areas, especially with eucalyptus, citrus and sugarcane. Aiming to evaluate how hardsetting behavior is manifested in terms of structural organization and distribution of pore shape and size classes, three hardsetting horizons were sampled in Dystrophic Yellow Argisols (Ultisols) in the Coastal Tablelands and submitted to micromorphological analysis. To this end, intact, vertically oriented soil blocks were collected from each hardsetting horizon. The blocks were impregnated with resin and fluorescent pigment and then cut into thin sections. A detailed study of pore classes was conducted by 2-D image analysis in eight captured images of thin sections, which represented approximately 80% of the total surface of the sections. By image analysis, it was possible to evaluate the distribution of pore area and number, as well as shape, size and preferential orientation (direction) in relation to the block surface. Our findings confirm the hypothesis that hardsetting horizons in the coastal tablelands of Brazil are similar regarding structural organization and pore network, and that pore size can be modified by soil management practices. The number and distribution of pore size classes revealed that the pore network in hardsetting soils exhibits random distribution and that the elongated pores are reduced in length owing to their low interconnectivity.
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