Differentiating Erosional Versus Depositional Parent Material Using Terrain Attributes in the Arkansas River Valley (MLRA 118A).

Society is increasing its demands for more intense soil property maps and soil functional interpretations. Given that parent material is a primary factor affecting soil properties, an accurate map of its distribution is essential for creation of a more detailed soil map. The purpose of this study was to develop methods to create a parent material map of erosional versus depositional areas using digital terrain attributes, as a first step toward creating a digital soil map. Redistribution of parent material via erosion and sedimentation is especially apparent in the Arkansas Valley and Ridges. Eroding soils are shallow to bedrock and contain many coarse fragments, while depositional soils are comprised of silty pedisediment (i.e. hillslope sediment) moved by sheet erosion from nearby uplands. In order to create a model of parent material differences, a 5 meter digital elevation model was used to generate several terrain attributes such as slope, curvature, topographic wetness index, multi-resolution valley bottom flatness, topographic position index, relative elevation, vertical distance to channel network, terrain ruggedness, and geomorphons. These terrain attributes were analyzed for their ability to differentiate erosional from depositional areas of the landscape on an 890 hectare research center in Logan County, AR. The parent material map was generated with two units: depositional areas of pedisediment, and residual, erosional areas. Residual areas are characterized by a topographic position index greater than 1.5, multi-resolution valley bottom flatness less than 3, or vertical distance to channel network greater than 15 (m). The map was validated by field sampling and comparison with a modern National Cooperative Soil Survey map. Using digital terrain attributes to differentiate parent material as part of a hierarchical approach within digital soil mapping enables development of a precise, consistent map over large extents that can be used to set constraints on subsequent soil property maps.