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Influence of Soil Properties on the Statistical Characterization of Dry Aggregate Strength

Dep. of Land Resource Science, Univ. of Guelph, Guelph, ON, N1G 2W1, Canada

A. P. da Silva

Escola Superior de Agricultura ‘Luiz de Queiroz’, Univ. of Sao Paulo, Piracicaba, Sao Paulo, Brazil

* Corresponding author ( eperfect{at}lrs.uoguelph.ca).

ABSTRACT

Dry aggregate strength measurements, important in tillage and erosion studies, are often analyzed statistically using the Weibull model. The parameters of this model, and ß, characterize the absolute strength and the spread of strengths, respectively. Information is lacking on the influence of soil properties on values of and ß. We measured dry aggregate strength as the specific rupture energy (E in J g^–1) of 40 aggregates in two size classes (4–8 and 8–16 mm) from 36 locations along a 500-m transect across four soil types with a wide range of physical and chemical properties (e.g., 8.0–72.6% sand content). Estimates of and ß were obtained by fitting Weibull's model to these data using nonlinear regression. The and ß values were lognormally and normally distributed, respectively. The mean log() was -2.4 and the mean ß was 1.3. Multiple regression analysis was used to relate log() and ß to soil properties. The resulting regression equations explained 93% of the variation in log() and 60% of the variation in ß. The log() increased with decreasing aggregate size and sand content and increasing organic matter content. The ß increased (indicating a narrower range of strength values) with decreasing log() and aggregate size. The regression equations were validated by predicting the cumulative relative frequency distribution of E for aggregates from a different site where independent measurements of E were available for comparison. A good agreement (R² 0.91) was obtained between predicted and observed values of E.

Received for publication January 3, 1994.

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