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Characteristics and Genesis of Preferential Flow Paths in a Piedmont Ultisol

^a USDA-ARS 1420 Experiment Station Rd. Watkinsville, GA, 30677
^b Miller Plant Sciences Bldg. Dep. of Crop and Soil Sciences Univ. of Georgia Athens, GA 30602

View larger version (27K): [in this window] [in a new window]   Fig. 1. Depth distribution of mean clay content and dyed-stained area. The number associated with each depth is the number of columns contributing to the mean. The error bar represents one standard error of the mean. Horizon boundaries indicated on the figure represent typical depths found in the Piedmont region of the southeastern USA.

View larger version (171K): [in this window] [in a new window]   Fig. 2. Horizontal faces of column slices: (A) Ap horizon at 10 cm, (B) BA horizon at 20 cm, (C) BA horizon at 35 cm, and (D) Bt horizon at 55 cm; b = undyed B horizon fragment, u = undyed areas, c = circular dyed area, l = thick elongate dyed area, s = linear dyed area assumed to be associated with a structural face. Column diameter was 15 cm.

View larger version (21K): [in this window] [in a new window]   Fig. 3. Clay percentage in dye-stained and undyed soil. The numbers beside each pair of points represent the number of samples contributing to the mean from dyed and undyed areas within a specific depth range. The mean at 10 cm represents samples from various slice depths within the Ap horizon. Means at lower depths represent samples from slice depths from a 15-cm depth increment. The error bar represents one standard error of the mean. Horizon boundaries indicated on the figure represent typical depths found in the Piedmont region of the southeastern USA.

View larger version (15K): [in this window] [in a new window]   Fig. 4. Size distribution of mean pore area for dye-stained and undyed soil as determined by image analysis. Means represent samples from all column depths, n for dye-stained material = 52; n for undyed material = 27. The error bar represents one standard error of the mean.

View larger version (152K): [in this window] [in a new window]   Fig. 5. Micrographs of dye-stained and undyed soil from Ap and BA horizons: (A) thin section, under partially polarized light, of Ap horizon at 6 cm, (B) polished block of dye-stained soil from BA horizon at 37 cm, (C) polished block of BA horizon at 28 cm showing fecal pellets (arrow), and (D) polished block of undyed soil from BA horizon at 28 cm; c = channel, d = dye-stained soil, s = sand grain, u = undyed soil, v = void. Bar length = 5 mm.

View larger version (151K): [in this window] [in a new window]   Fig. 6. Micrographs of polished blocks from Bt horizon: (A) 50-cm depth, (B) 55-cm depth, (C) 48-cm depth, and (D) undyed soil at 55-cm depth showing structural voids plugged with clay and Fe oxides (arrow); d = dye-stained soil, u = undyed soil, f = fecal material, v = voids. Bar length = 5 mm.

View larger version (100K): [in this window] [in a new window]   Fig. 7. Schematic representation of biologic modification of soils in this study. Horizon boundaries indicated on the figure represent typical depths found in the Piedmont region of the southeastern USA.