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ARS Home » Research » Publications at this Location » Publication #68775
Title: FRACTAL CHARACTERIZATION OF POROSITY IN FIELD SOIL AND PACKED COLUMNS

Author
item Gimenez, Daniel
item ALLMARAS, RAYMOND - 3640-20-00
item NATER, EDWARD - UNIVERSITY OF MINNESOTA
item HIGGINS, DAVID - UNIVERSITY OF MINNESOTA

Submitted to: Groderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soils are porous media whose properties depend largely on the relation between solid and porous phases. Our ability to model soil processes can be enhanced by a proper characterization of pore systems. Fractal geometry is a new tool that is potentially able to characterize different aspects of pores. Hydrological properties such as infiltration are mainly determined by the amount and size distribution of large pores. In agricultural soils those characteristics are periodically modified by tillage and consolidation of rainfall. We applied fractal methods to images of resin-impregnated soil-blocks to characterize roughness and size distribution of large pores. The study includes situations of freshly tilled and somewhat consolidated field soil, as well as laboratory columns packed with various aggregate assemblies. Main conclusions of the paper are that: I) fractal geometry is appropriate to characterize roughness and size-distribution of pores, and; II) there is a functional relation between the fractal dimensions of both properties that can further simplify a description of a pore system. Information in this paper can be used by scientists interested in modeling processes in agricultural soils.

Technical Abstract: Fractal techniques have been applied to model pore system of natural materials. Fractal dimensions characterizing either roughness of a soil-pore outline, Db, or scaling of pore sizes, Dv, has been reported. Our objective was to evaluate Dv and Db for pore systems from field and laboratory samples of a Normania loam. Field samples were from tillage experiments sampled immediately tillage or after crop harvest. Laboratory columns were packed with single aggregate-size fractions with average diameter of 8.6 and 2.8 mm, and two mixtures of six aggregate-size fractions, each covering two ranges: 28.0 to 1.5 mm, and 8.4 to 0.4 mm. Aggregate mixtures were fractal with fractal dimensions of 2.08 and 2.99. Samples from all sources were resin-impregnated and a face/block was cut and polished. Images of UV illuminated faces were obtained at different magnifications. A box-counting technique was applied to area and outline of pores to obtain Dv-box, and Db-box, respectively; Db was also calculated from area-perimeter relations (Db-AP). Box-count data showed two segments. Selection of Dv-box, and Db-box in relation to each segment and to Db-AP is discussed. Values of Db-box vs Dv-box were highly correlated for all samples. Values of fractal dimensions decreased with resolution for laboratory samples, but did not exhibit a defined pattern of variation for field samples. Fractal models are useful in describing pore systems in soil, but consideration should be given to scale and method of determination.