Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/25/1997
Publication Date: N/A
Citation: N/A Interpretive Summary: Soil structure in agricultural soils is the result of fragmentation by tillage and aggregation by physical and biological processes. The size distribution of fragments, as well as their density and surface roughness, are important for modeling the mechanics of fluids moving over the surface and into a freshly tilled soil. Thus, our ability to model soil processes in freshly tilled soil can be enhanced by a proper characterization of soil fragments. We applied fractal geometry to characterize mass distribution, surface roughness, and size- distribution of soil fragments collected from freshly tilled soils. The main conclusions of this study are that: i) fractal geometry was appropriate to characterize roughness, and size distribution of fragments, and ii) distribution of mass within fragments was not fractal. We suggest that all parameters of fractal models contain information to characterize soil fragments in freshly tilled soil. We propose to relate fragment- and pore-size distributions and to use topothesy (a parameter of a fractal model of surface roughness) to study the relationship between fragment-size distribution and surface roughness of fragments. Information in this paper can be used by scientists interested in modeling processes in freshly tilled soils.
Technical Abstract: The use of fractals on freshly tilled soil has been tested only briefly. The objectives of this research were to test the applicability of fractal fractal models on mass- and number-size distributions, and on surface roughness of soil fragments produced by tillage; and to evaluate relationships among parameters of these fractal models. Fragments were were sampled from the soil surface of three soil management experiments on a Normania clay loam: (1) moldboard, chisel, and disc as primary tillage tools, (2) three primary/secondary tillage sequences, and (3) three crops followed by the same primary/secondary tillage sequence. Air dried samples were sieved to obtain eight fragment-size fraactions with average dimaters ranging from 0.4 to 28.0 mm. Mass-size raltions from size fractions and individual fragments indicated a non-fractal distribution of mass; but soil management influenced the estimated mass of fragments; but soil management influenced the estimated mass of fragments of unit diameter, km. Two-dimensionl roughness of fragment surfaces, measured on thin sections, was fractal with dimensions, Ds, between 1.02 and 1.18. Soil management effect was only manifested on disc tillage that produced the highest Ds among primary tillage tools. Fragment number-size distributions were fractal with the fragmentation fractal dimension, Df, between 2.14 and 3.19 and sensitive to management effects. The number of fragments of unit diamter, kf, was inversely related to km, but relationships Df-kf and Df-Ds were not consistent with fragmentation fractal models. It is suggested that models of the rilled layer should focus on relations between number-size distributions of pores and fragments.