SOILS ON QUATERNARY TERRACES OF THE TALLAPOOSA RIVER, CENTRAL ALABAMA

Abstract

Fluvial terrace chronosequences provide excellent opportunities for evaluating pedogenesis. We evaluated soil development on Quaternary terraces of the Tallapoosa River of central Alabama. Our objective was to ascertain pedogenic markers for these relatively low terraces. Past studies and other evidence suggest landscape ages ranging from contemporary floodplains to mid- to late Pleistocene terraces. The six pedons evaluated ranged from Typic Udifluvents and Fluventic Dystrudepts on the floodplain to fine-loamy and coarse-loamy Typic Paleudults on relatively higher terraces. Soil physical properties (particle size, bulk density, 15 bar H 2 O content), soil chemical properties (total and extractable elements, cation exchange capacity, Fe and Al extractions, heavy mineral content), morphological properties, and micromorphological properties were evaluated. Many soil physical and chemical properties (averaged for B horizons) are related to the soil chronosequence, including properties established in earlier studies as being indicative of soil development. The effective cation exchange capacity and cation exchange capacity 100 g -1 clay (P ≤ 0.05 and 0.01, respectively), oxalate-extractable Fe (P ≤ 0.05), oxalate-extractable Fe/dithionite extractable Fe (P ≤ 0.10), and total K/total Ti (P ≤ 0.05) all decreased at higher levels. In addition, Mehlich extractable Cu (P ≤ 0.10), Fe (P ≤ 0.05), and Zn (P ≤ 0.05), along with total Mg (P ≤ 0.01), Mn (P ≤ 0.10), and Ca (P ≤ 0.10) decreased with higher terrace levels. Principal component analysis and cluster analysis indicated that soils on terrace levels 5500 years B.P. are similar. The first principal factor, which accounted for 65% of the variance and is composed of both chemical and physical properties, separated terrace levels satisfactorily. The results are generally consistent with decreasing inherent fertility with increasing soil development.