Characteristics and genesis of preferential flow paths in a piedmont ultisol

Numerous methods have been used to characterize the size and abundance of macropores in soils. Few of these studies, however, have attempted to determine what portion of the soil column is involved with water flow or to propose a mechanism by which the preferential flow paths are formed. This study was initiated to describe the abundance and characteristics of preferential flow pathways in a Typic Kanhapudult, commonly found on ridges in the Piedmont region of the southeastern USA and to determine their genesis. Forty 15-cm-diameter columns, 60 cm, in length were collected from a conventionally tilled field for identification and evaluation of preferential flow paths. Flow paths were identified using methylene blue dye and the morphology of dye-stained and undyed areas was evaluated. Pore size and abundance for dye-stained and undyed areas were evaluated by image analysis, and fabric of the two areas was described from impregnated blocks and thin sections. Most of the Ap and BA horizons of this soil contributed to flow. Only the lower part of the BA horizon and the Bt horizon had appreciable areas that were undyed, suggesting preferential flow. The dye-stained areas had slightly less clay than undyed areas. Dye-stained areas, however, had about five times more pore area than undyed areas, most of which had pores > 0.25-mm equivalent diameter. Common circular morphology of dye-stained areas and the open fabric of sod in these areas with occasional fecal pellets suggest that dye-stained areas in this soil have been biologically modified. The biological modification is attributed to tree roots and burrowing animals during the period of soil development on old and stable landscapes in the region.