Relating the Expression of Soil Redoximorphic Features to Soil Texture, pH, and Cation Exchange Capacity

Three laboratory studies were performed to elucidate the influence of soil\ntexture, pH, and cation exchange capacity (CEC) on the concentration of ferrous Fe in\nsoil solution and the resulting expression of soil redoximorphic features. The objectives\nwere: 1) assess the buffering effects of CEC on ferrous Fe concentration in soil solution,\n2) evaluate the effects of pH on the concentration of ferrous Fe in soil solution, and 3)\nobserve the expression of redoximorphic features in soils with varying texture and CEC.\nThe studies concentrated on seasonally wet soils from the Texas Gulf Coast\nPrairie. Selected soils included Alfisols and Vertisols with characteristics ranging from\ncoarse-loamy to very-fine in texture, strongly acidic to neutral in soil reaction, and\nsiliceous, mixed, and smectitic in mineralogy. The soils included the Pledger clay\nmicrolow (acidic, fine-textured), Pledger clay microhigh (neutral, fine-textured), China\nclay (acidic, fine-textured), Cieno loam (acidic, fine-loamy), Orelia sandy clay loam\n(neutral, fine-loamy), Gessner fine sandy loam (acidic, coarse-loamy), and Orelia fine\nsandy loam (neutral, coarse-loamy).\nThe studies provided the following information: 1) fine-textured soils with\nhigher CEC contained more ferrous Fe in solution, 2) ferrous Fe concentrations in the\nacidic fine-loamy and coarse-loamy soils were higher than the neutral soils for the same textural class, 3) acidic and neutral fine-textured soils contained more ferrous Fe in\nsolution than the remaining soils, 4) the highest percentage of redox concentrations was\nobserved in the acidic, fine-textured soil, 5) the acidic fine-loamy and coarse-loamy soils\nexhibited a greater percentage of Fe depletions, and 6) a higher percentage of redox\nfeatures were observed by micromorphic analysis (i.e., point counts under a binocular\nstereoscopic microscope) than by macromorphic descriptions. This research showed\nthat differing soil characteristics affect the reductive dissolution and translocation of Fe,\nand subsequent formation of redox features.