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Fractal Characterization of Soil Aggregation and Fragmentation as Influenced by Tillage Treatment

Department of Agronomy, University of Kentucky, Lexington, KY 40546-0091

*Corresponding author (eperfect{at}ca.uky.edu).

ABSTRACT

Parameters are needed to quantify tillage-induced changes in soil structure. Our objective was to see if fractal parameters from ped mass- and number-size relations could be applied to quantify such changes. Soil from long-term conventional (moldboard plow, MP, plus two passes with a disk harrow, DH) and no-till (NT) plots on a Maury silt loam (fine, mixed, mesic Typic Paleudalf) was air dried and sieved into six size classes ranging from 0.5–1 to 16–31.5 mm. The mass percentage and weight of 100 peds in each size class were used to calculate the mean mass per ped and number of peds as a function of scale. Fractal equations were then fitted to both data sets (R² always 0.99). The resulting parameter estimates were D_m (mass fractal dimension) and k_m (mass of an aggregate of unit length) for the mass-size relation, and D_t (fragmentation fractal dimension) and k_f (number of fragments of unit length) for the number-size distribution. Significant tillage effects were observed for D_m, D_f, and k_f. The D_m increased from 2.88 for NT to 2.94 for MP and DH, suggesting differential compaction of large aggregates by plowing and disking. The D_f was always less than the D_m, as predicted by theory. Soil fragmentation was least for NT (D_f = 2.02) and greatest for MP (D_f = 2.55); for DH, the D_f = 2.15 suggesting that disking broke up large fragments and/or coalesced small fragments following plowing. The k_f, which was shown to be nonlinearly related to the D_f, was least for MP and greatest for NT. Similar studies on other soils are needed to test the general applicability of these fractal relations to soil structure.

Kentucky Agric. Exp. Stn. Contribution no. 96-06-027.

Received for publication April 15, 1996.

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