Mass fractal dimensions of soil aggregates from different depths of a compacted Vertisol

There is limited information on the application of fractal concepts to Vertisols. The objectives of this study were to: (i) test the applicability of the fractal fragmentation theory to Vertisols and (ii) see whether the parameters of fractal models reflect differences in soil management and with depth. The soil was sampled at 0-10, 10-20, and 20-40 cm depths in early May 1998, 15 days after the rice harvest. Undisturbed clods were taken, submerged in ethanol and air-dried prior to sieving, seven size classes were selected ranging from 0.25-0.5 to 7.0-10.0 mm. Aggregate bulk density was measured from six selected aggregates from each size class by a combination of kerosene and paraffin methods. Fractal equations fitted the experimental data reasonably well, the coefficient of determination, R-2, was more than 97% for the log-linear regression and 83% for non-linear estimation. There were no differences between the fractal parameters with soil depth. The density-size relation showed a scale-variant behaviour. Fractal theory could be a valuable tool for the study of Vertisols. From the point of view of fractal parameters, the three soil depths were in the same condition after crop harvest. It is suggested that the bulk density of an aggregate of unit length could be used as a measure of soil compaction. (C) 2001 Elsevier Science B.V. All rights reserved.