1. The Influence of Parent Material On The Genesis of the Miles Soil Series J. J. Parsley 1 ; D.C. Weindorf 2 ; R. Wittie 1 1 Tarleton State University; 2 Louisiana State University AgCenter The Miles soil series is the sixth most commonly mapped soil in the state of Texas. Soils mapped as this series total 665,816 ha in area, and within Texas span 34 counties from south-central regions to the panhandle of the state (A.L. Stahnke, personal communication, 2005) (Fig 1). The Miles series is a benchmark soil; defined as a soil of vast extent; and occupying a key rank in soil classification. Additionally, benchmark soils are agronomically, and ecologically important. A good understanding of benchmark soils allows a better understanding, classification and description of other soils, and guides the development of soil surveys. Map units (MU) currently described as Miles do not fit within the range of characteristics (ROC) given in the official series description (OSD). The Miles series has been mapped across different parent materials and geologic landforms. Each impart unique characteristics to soils. Map units previously correlated as the Miles series were studied on the basis of parent material to determine if these MU were within the ROC for the series. The objectives of this study were to: 1) identify, describe, and sample twelve Miles series pedons over four parent materials, 2) conduct physical and chemical laboratory analyses to characterize and classify the soils, 3) investigate the relationship among soil morphology, soil properties, soil parent materials, and landforms for these soils to develop soil-landscape model(s), and 4) determine the relationship between the soil- landscape model(s) and the soil map units associated with these twelve pedons. Fig.1. Geographic mapping extent by county of the Miles soil series in Texas with delineated study site counties. (Soil Survey Staff, 2007) Soil Survey Staff. 2007. Geographic mapping extent by county of the Miles soil series in Texas. ArcGIS 9.2 rendering. USDA-NRCS. Abilene, TX. Zylman, J., D.C. Weindorf, R. Wittie, A. McFarland, and T. Butler. 2005. Field-Truthing of USDA-NRCS Soil Survey Geographic Data on Hunewell Ranch, Erath County, Texas. Soil Survey Hor. 46(4):135-145. The authors would like to acknowledge Tarleton State University for facility usage, and research stipend. Also, acknowledgements go to the Natural Resource Conservation Service for technical expertise, assistance, and being the primary funding agency for the project. Parent MaterialAge of Deposition Method of Deposition Depositional Environment Residuum208 - 230 Ma BPAlluvialVast Stream Flooding Old Alluvium1.8 - 23.8 Ma BPAlluvial Valley FillSemi-Arid/Sub-Humid Young AlluviumOngoingStream/Strath TerraceStream Flooding and Erosion Aeolian10 - 12,000 yr BPWindIntense Droughts Three sites were identified for each of the four parent materials based upon previous pedon descriptions and field work. Miles soils confirmed on each unique parent material were excavated with a backhoe to a minimum 210-cm depth. A complete pedon description was made followed by sample collection for lab analysis. Laboratory analyses conducted on the samples for all horizons included coarse fragment percentage, electrical conductivity, pH, and particle-size analysis. Calcium carbonate equivalent was performed on selected horizons. Additionally, organic carbon and citrate available phosphate were performed only on the upper 18-cm of each pedon. Field and laboratory data collected was individually ranked against criteria set forth in the Miles series ROC as a match, partial match, or no match (Zylman et al., 2005). The individual criterion rankings were then averaged by pedon, and parent materials. These rankings were then developed into total percent matches. As expected, negligible differences were observed between individual pedons, but distinct differences were found between parent materials. Based upon tested Miles criteria and pedons, the closest overall match (85%) to the Miles ROC was residuum parent material. Old and young alluvium followed with little difference between the two at 74%, and 76%, respectively. Aeolian parent material was least like the Miles soil with only 63% of evaluated features matching the Miles soil. From the parent material separations seen between the tested pedons a preliminary Miles soil model was developed within the study site counties. For this model, soil parent material characteristics were correlated with the underlying geology directly beneath and at a specific distance from each sample site. This preliminary model was then extrapolated over the entire mapping extent of the Miles series in Texas, showing probable locations where Miles soils would have these traits (Fig 2). Fig. 2. Extrapolation of preliminary Miles soil model over Miles series mapping extent in Texas.