Determination of an Appropriate Geometrical Model for Soil Aggregates Based Upon Specific Surface Area Scaling

The appropriate geometrical form of soil aggregates is important for modeling soil hydraulic and mechanical properties. To investigate this topic, specific surface are (SSA) measurements were conducted on soul aggregates obtained from two sites. Differing long-term agricultural practices at the two sites resulted in nine distinct soil treatments. Each of the soil treatments was fractionated into five size classes and the SSA of each class was measured using the nitrogen adsorption technique. The measured data were then compared to simulated SSA results. To accomplish this, six geometrical models were developed, using either Euclidean or fractal geometry, to predict the SSA sealing as a function of size. There models predict that as aggregate size increases, the SSA either remains constant (with a scaling exponent of zero) or decreases (with an integer exponent of minus one or non-integer exponent of between 0 and -1). The determination of an appropriate model did not rely solely on SSA scaling. Other physical treatments in order to more finely discern between the different models. The presence or absence of these properties had major implications as to which geometrical model was most appropriate. By comparing the SSA scaling data with the particle- and pore-size distribution measurements it was apparent that the most appropriate geometrical model for soil aggregates is a pore-solid fractal. This study gives support to the idea that soil aggregates are fractal in nature.