FRACTAL BEHAVIOUR IN PARTICLE-SIZE DISTRIBUTIONS AS INFLUENCED BY SOIL PROPERTIES AND DETERMINATION METHOD

Authors: STANCHI, S - U. OF TURIN, ITALY; BONIFACIO, E - U. OF TURIN, ITALY; ZANINI, E - U. OF TURIN, ITALY; Pachepsky, Yakov

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2006
Publication Date: 4/2/2006
Citation: Stanchi, S., Bonifacio, E., Zanini, E., Pachepsky, Y.A. 2006. Fractal behaviour in particle-size distributions as influenced by soil properties and determination method. Soil Science. 171:383-292.

Interpretive Summary: Soil texture is the important soil property that greatly influences soil functioning and use. Soil texture is characterized by the size distribution of primary particles, e. g. sand, silt, and clay. Primary particles are often glued together with binding agents such as sparingly soluble salts and organic compounds. The glued particles form large soil structural units, i.e. aggregates and peds. Various treatments are in use to destroy the bonds between primary soil particles and soil aggregates prior measuring the particle size distribution. The treatments lead to the fragmentation of soil material. The modern fragmentation theory uses the fragmentation fractal dimension as a convenient parameter of fragmentation processes. The objective of this work were (a) to use the fragmentation fractal dimension to quantify the effect of two different pre-treatments on the relative abundance of primary particles of various sizes, and (b) to find soil properties that affect the applicability of the ideal fragmentation theory to soils. Paired particle-size distribution determinations with and without removal of organic and inorganic binding agents were made for 85 samples of soils from various genetic and textural classes found in the Southern Italy. Total of 20 chemical and physical properties of soil was measured in the same samples. Only 35% of the samples conformed the fragmentation theory after pre-treatment, while 52% did when the aggregating agents were not removed. The applicability of the fragmentation theory to soils was primarily defined by fine silt content, and influenced by contents of coarse silt, coarse sand, and exchangeable calcium content.

Technical Abstract: The fragmentation fractal dimension has been used to characterize soil particle-size distributions. Deviations from strict self-similarity were often reported. In particle-size distribution determination, different dispersion and pre-treatment methods can create different fragmentation. The objectives of this work were: a) to investigate fractal behaviour of soil as influenced by the presence of the fragmentation-enhancing pre-treatment before particle-size distribution determination; b) to predict the presence/absence of the fractal behaviour from soil chemical and physical properties by applying discriminant analysis and classification trees and comparing the efficiency of the two methods. Paired particle-size distribution determinations with and without removal of organic and inorganic binding agents were made for 85 samples of soils from various genetic and textural classes found in the Southern Italy. Total of 20 chemical and physical properties of soil was measured in the same samples. Discriminant analysis and classification trees were applied to predict the presence or absence of the fractal scaling in particle-size distribution from soil basic properties. Only 31 samples displayed strict fractal behaviour after pre-treatment, while 44 did when the aggregating agents were not removed. Classification trees rendered better prediction of the presence of the strict fractal behaviour of soil particle-size distributions for each of the determination methods as compared with the discriminant analysis. The presence of the strict fractal behaviour was primarily defined by fine silt content, and influenced by contents of coarse silt, coarse sand, and exchangeable calcium content.