Two‐dimensional porosity of crusted silty soils: Indicators of soil quality in semiarid rangelands?
2011
Miralles Mellado, Isabel | Cantón Castilla, María Yolanda | Solé Benet, Alberto
Little is known about the morphological characteristics of pores in soil crusts. The objective was to characterize the two-dimensional (2D) porosity (amount, shape, size, and area of pores) of soil crusts to ascertain their potential as indicators of soil quality for natural crusted soils. The 2D-porosity was described in thin sections and measured by image analysis of polished resin-impregnated soil blocks. Physical soil crust and incipient biological soil crusts appear to be the lowest-quality soils in terms of number of pores (average of 131–133 cm−1) and area occupied by pores or meso-macroporosity (3.5–4.2%). Their most abundant pore types were small unconnected rounded pores. Soil crust infiltration coefficients (65–72% annual) were among the lowest and their high erosion rates (81–204 g m−2 yr−1) were not only due to their lower total porosity, but also to their pore shapes and sizes. Biological soil crusts appear on higher-quality soil, where the higher the organic C content, the more evolved the soil crust is (with lichens and cyanobacteria). Such soil crusts have better developed pore-systems with specific meso- and macropore morphologies, for example, large, interconnected elongated and irregular pores. Biological soil crusts (BSCs) dominated by lichens have the largest meso-macroporosity (up to 23.65%) due to the predominance of elongated pores. In many cases, infiltration is low (46–57%) because the biological crusts are somewhat detached from the soil underneath, but the armouring effect decreases erosion rates (7–23 g m−2 yr−1). Soil crust pore numbers, size, and shape were useful indicators of soil quality.
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