Representative Elementary Area Determinations through Digital Photography, Image Analysis, and Soil Color.

Photography has been a welcome tool in assisting to document and convey qualitative soil information.  Greater availability of digital cameras with increased information storage capabilities has promoted novel uses of this technology in investigations of water movement patterns, organic matter content, and soil mineralogy.  When coupled with image analysis software, the utility of digital cameras can be increased to answer additional questions related to pedofeature characterization.  The determination of a Representative Elementary Area (REA) still remains a critical information need for soil scientists so that measurements are independent of sample size and account for spatial heterogeneity.  This research used a digital camera and image classification software to identify soil redoximorphic features by groupings of Munsell ^© color in 40 cm² areas from subsurface horizons of claypan soils located in northcentral Missouri, U.S.A.  Soils included in this research were characterized by a large clay content (>50%) in argillic horizons, consisting of smectitic clay minerals.  Fifty pedons from two cropped fields (25 per field) were sampled in order to span a range of depth to argillic horizon and upslope contributing area.  Soil redoximorphic features identified by color were quantified by areal, shape, and interspersion metrics.  The relative change in metrics was determined for 16 image sizes ranging from 2.5 cm² to 40 cm², at 2.5 cm² area increments.  The relative change in metrics was subsequently used to determine if an REA for low chroma and high chroma soil redoximorphic features was met for varying metrics, soil depths, and soil series.  Examination of relative changes to metric values helped define an REA for future assessments of soil feature trends across claypan soil landscapes.  Interdisciplinary soil science fields requiring quantifiable measures of soil pedofeatures may greatly benefit from determining these appropriate scales relative to research questions.