Quaternary Stratigraphy and Dynamic Soil Properties of Loess Derived Soils in Southeastern Iowa

1. Quaternary Stratigraphy and Dynamic Soil Properties of Loess Derived Soils in Southeastern Iowa Brad Oneal, C. Lee Burras, Thanos Papanicolaou, Mostafa Ibrahim, and Jessica Veenstra Department of Agronomy, Iowa State University, Ames, IA 50011 OPTIONALLOGO HERE OPTIONALLOGO HERE Introduction Site Description and Sample Collection Results Loess is the most common surface stratigraphic unit found in Iowa and across the midwestern United States. Several past studies have focused on the stratigraphy and spatial distribution of loess derived soils in Iowa and the surrounding states. Smith (1942), Hutton (1947), and Simonson and Hutton (1954) documented changes in loess depth and properties along transects in the midwest. Ruhe (1954, 1969) deepened these studies, especially for the state of Iowa. More currently, Young and Hammer (2000) modeled changes in soil properties across landscape positions in Missouri that include a loess mantle. Ruhe developed a stratigraphy model of the loess derived soils of Iowa based on his work in western Iowa (Figure 1). It is assumed that the stratigraphic units described in this model are found in loess derived soils across the state of Iowa. However, the deep stratigraphy of loess derived soils in eastern Iowa has never been thoroughly investigated. • The Clear Creek watershed in Iowa County, Iowa was chosen as the research site to test Ruhe’s stratigraphy model for eastern Iowa. General location of the Clear Creek watershed is shown in Figure 2. • 182 pedons were collected from four fields within the watershed (Figure 3). Results Figure 5. Interpolation of epipedon thickness for Field 1. An inverse distance weighted method was applied using ArcGIS software. Table 1. Classification of Clear Creek pedons. The number of pedons described as each series is shown. Conclusions • All stratigraphic units described in Ruhe’s model are found in the • Clear Creek watershed. • A dynamic soil approach is useful for capturing variability of soil properties. • Surface horizon texture, cation exchange capacity, and pH vary according to hillslope position. • Soil properties including particle size, pH, bulk density, cation exchange capacity, and organic carbon content also vary significantly at depth. 1 2 Figure 2. Location of the Clear Creek watershed in Iowa. Map shows depth of loess at summit positions (Ruhe, 1969) Table 2. Mean pH, CEC, BD, OC, C:N, and clay % for surface horizons at varying hillslope positions. A mean value followed by a different letter indicates that the values are significantly different at an α level of 0.05 using a t test. 4 1 2 3 References Hutton, C.E. 1947. Studies of loess-derived soils in southwestern Iowa. Soil Sci. Soc. Am. Proc. 12:424-431. Oneal, B.R. 2009. Quaternary stratigraphy and pedology of Clear Creek watershed in Iowa County, Iowa. MS thesis. Iowa State University, Ames, IA. Papanicolaou, A.N., C. L. Burras, M. Elhakeem and C. Wilson. 2008. Field and laboratory investigations of infiltration on different geomorphic surfaces in a watershed under different land uses. Final Report, USDA-NRCS Natl. Soil Survey Center (USDA contract number 68-3H75-3-122). 69 p. Ruhe, R.V. 1954. Relations of the properties of Wisconsin Loess to topography of western Iowa. Am. J. Sci. 252:663-672. Ruhe, R.V. 1969. Quaternary landscapes in Iowa. Iowa State University Press, Ames Simonson, R.W., and C.E. Hutton. 1954. Distribution curves for loess. Am. J. Sci. 252:99-105. Smith, G.D. 1942. Illinois loess: Variations in its properties and distribution: A pedologic interpretation. Illinois Agric. Experiment Station Bull., 490. Young, F.J. and R.D. Hammer. 2000. Soil-landform relationships on a loess-mantled upland landscape in Missouri. Soil Sci. Soc. Am. J. 64:1443-1454. Figure 1. Hillslope stratigraphy model of loess derived soils in southern Iowa. Adapted from Ruhe (1969). Study Objectives Figure 3. Location of the four sampling sites within the Clear Creek watershed. • Test the validity of Ruhe’s stratigraphy model using the Clear Creek watershed. • Spatially link soil properties and stratigraphy with a GIS-dynamic soil approach. • Compare variation in soil properties across different land uses.* • Integrate soil properties with Ksat data from University of Iowa and NRCS infiltration study (Papanicolaou et al., 2008).* • * Objectives 3 and 4 are not discussed in this poster. Characterization • Soil cores were described and classified to the series level. Soil physical and chemical properties were determined for selected horizons. • Analyzed properties by horizon include: • Particle Size • Bulk Density (BD) • Organic Carbon Content (OC) • pH • Cation Exchange Capacity (CEC) • Stable Aggregate Content Figure 4. Number of strata observed in 35 pedons to depth.