A Digital Morphometric Method for Quantifying Ped Shape.

Soil structure is the arrangement of soil particles into repeating patterns known as ‘peds’. Ped shape is an important property because it has considerable influence over several soil processes, such as infiltration, root penetration, preferential flow, and solute transport. Despite the host of methods employed to quantify other soil morphological properties, such as color and texture, ped shape quantification remains elusive as only qualitative and subjective categories such as platy, granular, blocky, or prismatic are used in their description. Existing methods attempting to quantify soil structure in general, such as X-ray computed tomography, utilize laboratory techniques that have limitations on sample size and resolution, thus, restricting the range of ped shape expression. Our goal was to develop a tool to quantify ped shape using morphometrics created from published digital photographs of soil profiles and structure specimens. Ped shape was quantified by manually outlining distinct examples of soil peds from high-resolution photographs and calculating a host of morphometrics from the resulting silhouettes using image analysis software. In addition, we used the same method to quantify ped shape from heuristic diagrams and three-dimensional scans of peds in order to assess both idealized and multiple orientations of peds, respectively. The calculated morphometrics for each ped shape were assembled into a database for quantifying ped shape. A survey was designed to poll expert judgment in order to properly classify the shape of peds in the database. Our findings and the potential of this method for transforming typical categorical and subjective descriptions of peds into continuous quantitative shape data will be discussed. This approach provides an opportunity for analyzing soil structure at broader scales than is currently possible and for reanalyzing existing photographs without the need to resample.