Fractal and compositional analysis of soil aggregation
Visualitza/Obre
Estadístiques de LA Referencia / Recolecta
Inclou dades d'ús des de 2022
Cita com:
hdl:2117/366612
Tipus de documentText en actes de congrés
Data publicació2011
EditorCIMNE
Condicions d'accésAccés obert
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Abstract
A soil aggregate is made of closely packed sand, silt, clay, and organic particles building up
soil structure. Soil aggregation is a soil quality index integrating the chemical, physical, and
biological processes involved in the genesis of soil structure and tilth. Aggregate
size distribution is determined by sieving a fixed amount of soil mass under mechanical stress and
is commonly synthesized by the mean weight diameter (MWD) and fractal dimensions such as the
fragmentation fractal dimensions (D f). A fractal is a rough object that can be broken down into a
number of reduced-size copies of the original object. Equations have been developed to compute
bounded and unbounded scaling factors as measures of fractal dimensions based on
assumptions about average diameter, bulk density, shape and probability of failure of sieved
particles. The log-log relationship between particle diameter and cumulative number or mass of
aggregates or soil particles above a given diameter often shows more or less uniform fractal
patterns. Multi-fractal (slopes showing several D f values ≤ 3) and non fractal
patterns or incomplete fragmentation ( D f < 2 or > 3) have been reported. Scaling
factors are curve- fitting parameters that are very sensitive to the choice of the fractal
domain about breakpoints. Compositional data analysis using sequential binary partitions for
isometric log ratio (ilr)
coordinates with orthonormal basis provides a novel approach that avoids the assumptions
and dimensional constraints of fractal analysis. Our objective was to compare MWD, fractal scaling
factors and ilr coordinates using published data. In the first dataset, MWD was found to be biased
by excessively high weight being given to the largest aggregate-size. Eight ilr coordinates
contrasting micro- vs. macro-aggregates were related to fragmentation fractal dimensions,
most of which were below 2 or above 3, a theoretical impossibility for geometric fractals. The
critical ilr value separating scaling factors 3 and > 3 was close to zero. In a second dataset,
the Aitchison distance computed across ilr coordinates proved to be a useful measure of the
degree of soil aggregation, agradation or degradation against a reference composition such
as that of primary particles, bare fallow or permanent grass. The individual contributions of ilr
coordinates to the Aitchison distance can be interpreted in terms of sign and amplitude and be
related to soil properties and processes mediated by soil aggregation.
CitacióParent, L.E. [et al.]. Fractal and compositional analysis of soil aggregation. A: CODAWORK 2011. "Proceedings of CoDaWork'11: 4th international workshop on Compositional Data Analysis, Egozcue, J.J., Tolosana-Delgado, R. and Ortego, M.I. (eds.) 2011". Barcelona: CIMNE, 2011, ISBN 978-84-87867-76-7.
ISBN978-84-87867-76-7
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