Fractal parameters of pore surfaces as derived from micromorphological data: effect of long-term management practices

Differences between soils in their porosity need to be quantified to diagnose changes related to management practices or to pedogenesis. Micromorphological data give abundant information on soil pore arrangement whereas fractal geometry presents tools to quantify irregular and rugged boundaries characteristic to soil pores. The objective of this work was (a) to verify applicability of the fractal scaling to irregular pore outlines revealed on soil thin sections, and (b) to test the capability of fractal parameters to reflect an influence of management practices on soil porosity. We sampled Comly silty loam soil in plots where nitrogen was supplied from conventional fertilizer sources, manure, legumes, and in uncultivated plots under grasses where no nitrogen has been supplied. Using slit-island technique, we have shown that fractal scaling was applicable to soil pore outlines revealed on thin sections. Piecewise-linear log-log relationships were found between pore area and pore perimeter. Small pores with areas less than 10−9 m2 had fractal dimension D1 between 1.06 and 1.12. Pores with areas exceeding 10−9 m2 had fractal dimension D2 between 1.42 and 1.51. The boundary between two ranges corresponded to the boundary between vughy and rounded pores. Pores with rugged fractal outlines represent 15–30% of total pore number and provide 86–98% of the total visible pore area. Management practices affected only the number and the area of large elongated pores. Value of D2 was larger in samples from the legume plots than in samples from other plots.

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