Characterization of Soil Structure and Pore Architecture From the Aggregate to Horizon Scale.

Soil structure and the corresponding pore architecture affect the stability of land surfaces against both wind and water erosion, influence water retention and thus plant available water, mineral weathering, and soil water flux, and may be important for understanding the distribution of soil carbon.  Measurements of mass and volume of soil aggregates show that, in many cases, a fractal relationship exists between the size of an aggregate and its density.  While fractal models have been used to characterize this relationship, they have been applied on relatively small aggregate volumes (<6 cm³) because of the difficulty in obtaining accurate, non-destructive volume measurements of larger, irregularly-shaped peds.  Recent applications of multistripe laser triangulation (MLT) technology, which yield high-resolution (120 µm), three-dimensional digital models, show that the volume and thus density of these relatively large peds can now be accurately measured.  This project investigates the application of a MLT scanner to characterize the relationship between the mass and volume of soil aggregates and structural peds across a range of scales.  Two locations in northeastern Kansas were chosen, soils described using traditional methods, and samples taken from two morphological horizons at each site.  In addition, MLT scans were made of cleaned pit faces and monoliths were extracted to assess horizon-scale relationships.  Volumes of aggregates and small peds were determined by volume displacement in two non-mixing liquids; volumes of the larger peds were determined from MLT scan results.  Soil structure was characterized using parameters derived from fractal models fit to the data.  The resulting model parameters and tests of significance will be presented.