Spatial arrangement of soil pores determines soil structure and is important to model soil processes. Geometric properties of individual pores can be estimated from thin sections, but there is no satisfactory method to quantify the complexity of their spatial arrangement. The objective of this work was to apply a multifractal technique to quantify properties of ten contrasting soil pore systems. Binary images (500 by 750 pixels, 74.2 μm pixel−1) were obtained from thin sections and analyzed to obtain f(α) spectra. Pore area and pore perimeter were measured from each image and used to estimate a shape factor for pores with area larger than 0.27 × 106 μm2 Mean area of the lower (MAL) and upper (MAU) one‐half of cumulative pore area distributions were calculated. Pore structures with large (MAU > 10 × 106 μm2) and elongated pores exhibited “flat” f(α)‐spectra typical of homogenous systems (three soils). Massive type structure with small (MAU < 1 × 106 μm2) rounded and irregular pores resulted in asymmetric f(α)‐spectra (two soils). Well defined and symmetric f(α)‐spectra were obtained with soil structures having elongated pores of intermediate size (1 × 106 < MAU < 10 × 106 μm2) clustered around relatively small structural units (five soils). Multifractal parameters defining the maximum of the f(α)‐spectra were correlated to total porosity (P < 0.001), and silt content (P < 0.05). This study demonstrates that the spatial arrangement of contrasting soil structures can be quantified and separated by the properties of their f(α)‐spectra. Multifractal parameters quantifying spatial arrangement of soil pores could be used to improve classifications of soil structure.

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Surrnelo, M. J. ext Pnorz, R. 1987

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Earthworm activity is believed to be beneficial for the maintenance of good soil structure; however, some research suggests that it promotes soil degradation. Factors affecting the contribution of casting activity to aggregate stability were assessed by measuring clay dispersibility in casts produced by Lumbricus terrestris L. and Lumbricus rubellus Hoff. in laboratory cultures when provided alfalfa (Medicago sativa L.), bromegrass (Bromus inermis Leyss.), red colver (Trifolium pratense L.), or corn (Zea mays L.) leaves or no food. Fresh, moist casts were 26 to 41% more dispersible than uningested, moist soil. Aging reduced dispersibility of moist casts produced under alfalfa, red clover, and corn leaf diets and after 32 d casts were 26% more to 16% less dispersible than uningested, moist soil. Casts aged moist and analyzed after air drying were unaffected by aging but were 9% more to 49% less dispersible than uningested, dried soil. The effects of aging and drying increased as cast organic carbon content increased, therefore L. rubellus casts, which contained more incorporated organic matter than those of L. terrestris, were less dispersible than L. terrestris casts for most treatments. The initial dispersibility increase was due to interparticle bond disruption caused by ingestion and peristalsis. Restoration and improvement in stability was probably due to thixotropic hardening and bonding of clay with incorporated organic debris. Because fresh worm casts are highly dispersible, surface casting activity in areas exposed to raindrop impact may contribute to soil erosion and crusting. Casting activity should enhance soil aggregate stability if casts are aged or dried before being subject to dispersion.

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