Saturday, 15 July 2006

Geomorphology and Parent Material Relationships: Refining Second Order Soil Surveys in Kansas Using GIS and Terrain Analysis.

DeAnn Presley1, Michel D. Ransom1, and W.A. Wehmueller2. (1) Kansas State Univ, 2004A Throckmorton Plant Sciences Center, Dept of Agronomy, Manhattan, KS 66506-5501, (2) USDA-NRCS, 760 South Broadway, Salina, KS 67401

The east central portion of Kansas is largely comprised of alternating, level beds of Permian and Pennsylvanian shale and limestone. Upland soils in this region have a complex genesis, often contain one or more paleosols, and form in multiple parent materials including loess, colluvium, residuum, and possibly ancient alluvium. In this study the objective is to examine and refine the spatial distribution and genesis of selected series as second order soil surveys are updated. The series of interest include the Irwin series which is mapped on interfluves and benches as well as paleoterraces and classify as fine, smectitic, mesic Udertic Argiustolls. The Ladysmith series is mapped on both uplands and paleoterraces, and these soils classify as fine, mixed, superactive, mesic Pachic Argiustolls. Upland soil parent materials were historically described as clayey sediments, such as residuum, while recent field and micromorphological investigations have described the stratigraphy as loess over hillslope sediment over a paleosol formed in shale or limestone residuum. Clayey sediments used in soil descriptions have also included old alluvium, when the series were mapped on broad, flat paleoterraces. In the current study, terrain analysis methods were performed in a Geographic Information System (GIS) environment in order to systematically identify the landscape features that exist where the soils of interest are currently mapped. Thirty meter digital elevation models (DEMs) were obtained from the National Elevation Dataset (NED). Soil Survey Geographic Data was obtained from the United States Department of Agriculture Natural Resources Conservation Service (USDA-NRCS) Soil Data Mart website. This data had an original mapping scale of 1:24,000. The compound topographic index (CTI) index was calculated for the study area, as CTI is often used as a proxy for landscape position. Large CTI values indicate areas that are relatively lower on the landscape, and small CTI values indicate higher, more upland positions. Terrain analysis was performed in two manners. It was preliminarily performed for the study area as a whole, which encompasses 25 counties in Kansas. It is understood that this “global” approach is not the most accurate, since it includes numerous drainage basins. Rather, the goal was to identify zones in Kansas where major differences in soil series and CTI values and thus, geomorphology, existed. Visual differences were noticeable in the resulting CTI/series distribution maps. In the eastern portion of the study area, Irwin and Ladysmith soils appeared to be mapped on dissected, upland landscapes that were not closely associated with modern river systems. In the western part of the study area, however, broad flat areas with relatively high CTI values were observed. Globally, the mean CTI value for Irwin and Ladysmith soils were 3.3 and 4.5, respectively. This was not surprising, as Ladysmith soils are most commonly associated with paleoterraces, while Irwin is most commonly mapped on higher landscape positions, such as interfluves and benches. Field sampling is in progress and will be performed in several counties. Terrain analysis was also performed on a more localized basis for each of the study areas, which normally encompass between 64 to 256 hectares per site. One of the Chase County study sites in the easternmost portions of the study area is 192 hectares in size, with relief ranging from 450 meters in the northwest area to 340 meters in the southeast area, which is approximately 1.2 kilometers from the present-day channel of the Cottonwood River. At this study site, mean CTI values were 3.9 and 4.4 for the Irwin and Ladysmith soils, respectively. Again, this was not surprising given that Ladysmith soils are usually mapped on a lower landscape position than Irwin soils. Interestingly, both series were located on areas that spanned the scaled CTI range of values from 1 to 9. That is, in this drainage area the soils were mapped on a wide range of slope positions. However, these soils have a long and complex genesis, and in the field complex slopes were observed. This likely explains the wide range in CTI values for both series. Terrain analysis is one tool that can be used to systematically evaluate relationships between soils, parent materials, and geomorphic positions. The goal is to ensure that the soil series concepts are applied consistently across the entire mapping extent. Research results will be provided to the Kansas NRCS, with a possible outcome being the modification of second order soil surveys in Kansas.

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