Truncation and accretion of soil profiles on coastal plain croplands: implications for sediment redistribution

Abstract

Soil stratigraphy and morphology in a small agricultural watershed on the coastal plain at Clayroot, North Carolina, indicate long-term, decadal-scale patterns of the redistribution of sediment. The most dramatic truncation of the soil profile occurs on convex upper slopes, and suggests tillage and aeolian erosion as the major processes of soil loss. Thicker soils immediately downslope from convexities are consistent with redistribution by tillage, but significant aeolian soil loss also occurs from some fields. Thinner, apparently truncated soils were also associated with relatively steeper lower slope areas where contemporary rilling was observed. The presence of thicker, cumulic soils at toeslopes where small fans are observed at rill termini and about a half meter of alluvium in drainage ditches indicates that water erosion is also quite prominent. Distinctive soil stratigraphy is found in areas of aeolian deposition, where podzolization in sandy surface deposits has created compound soil profiles. On convex slopes, tillage and wind erosion result in net soil loss, with the former dominating on wetter soils and when plowing occurs, and aeolian processes dominating on drier hilltops and when no-till or minimum tillage practices are followed. Soils are thicker immediately downslope from convexities, with thinner soils and rill erosion on lower slopes. Thickened soils and colluvial deposition in the form of thin fan deposits occur at toeslopes and in depressions. The borders of fields often have thicker soils because of aeolian deposition. Water, wind, and tillage processes are all significant in soil redistribution at the Clayroot site, with relative importance in space and time controlled by topography, soil properties, seasonal moisture and vegetative cover, and tillage practices.