Sunday, 6 November 2005 - 3:00 PM
7-8

Spatial Variation in Soil Texture in a Savanna Ecosystem.

Heather M. Jahnsen1, Thomas W. Boutton1, Charles T. Hallmark1, Donna Prochaska1, X. Ben Wu1, and Steven R. Archer2. (1) Texas A&M University, Agronomy Club, Dept. Soil & Crop Sciences, College Station, TX 77843-2474, (2) University of Arizona, School of Renewable Natural Resources, 325 Biological Sciences East, Tucson, AZ 85721-0043

Soil texture is a fundamental ecosystem property that modulates the availability and cycling of water and nutrients. Although it is generally accepted that spatial variability in texture results from interactions between topography, hydrologic processes, and vegetation patterns, few studies have examined this variability at the landscape scale. This study quantified spatial patterns of soil particle size distribution in relation to topography and vegetation in a savanna landscape at the TAES La Copita Research Area 65 km W of Corpus Christi, TX. Upland vegetation is comprised of discrete clusters and groves of woody vegetation embedded in a grassland matrix. Lower-lying portions of the landscape are dominated by closed-canopy drainage woodlands. Soil cores (2.5 x 15 cm) were collected at 1 m intervals along a 309 m transect extending from upland into lowland portions of the landscape. Transect points were located using GPS. Soil particle size distribution was determined by the pipet method. Upland portions of this landscape (grasslands, clusters, groves) consisted of fine sandy loams, whereas lower-lying portions of the landscape consisted of sandy clay loams (drainage woodlands) and clay loams (playas). Clay and silt were both more abundant in the lower elevations along the transect, probably reflecting the translocation of these fine particle size fractions from uplands to lowlands in runoff during the process of landscape evolution. Fine fractions of both silt and clay became more concentrated in lowlands, while coarse silt and clay fractions were more constant in their distribution along the transect. Woody plants were most abundant on sandy clay loams and clay loams in the lowlands, but grasslands were only found in fine sandy loam uplands. Thus, soil texture may influence plant distribution here. These patterns of soil particle size distribution likely influence the storage and dynamics of water and nutrients in this savanna landscape.

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