Soil of the Piedmont

The dominant soil order in the Piedmont is the Ultisol, which is comprised mainly of the great group Hapludults. The latter are not as thickor as highly weathered as the Paleudults, the great group most common on the Coastal Plain. Hapludults have an argillic B horizon attaining thicknesses as great as 1.5 m and are free-draining soils. They have relatively low base saturation and are moderately to strongly acid throughout the pedon. Natural fertility is not as low asin Paleudults, howeversubsurface horizons are loamy to clayey in texture. The marked increase in clay content of the argillic horizon is largely due to movement of clay minerals from the surface horizons. Hapludults contain a wide variety of clay minerals. Clay minerals of the kaolinitic type are most common, but 2:1 lattice minerals are also present (Buol 1973).

Ireland and others (1939) found a strong relationship between soil characteristics and gully erosion in the Piedmont of South Carolina. Igneous or metamorphic rock bedrock rich in feldspar and silica becomes more intensely weathered than rock rich in magnesium and iron, and the saprolite of the former is thus much more subject to gullying than is that of the latter. An important factor affecting gully development is the great difference in erodibility between the clay-rich B horizon and the underlying saprolite. The latteris much more erodible. During the early stage of erosion, the gully erodes downward through the A and B horizons. Cutting in this stage is relatively slow.When the gullyreaches into the C and growth of the gully greatly accelerates. This stage is characterized by the headward migration of an overfall and plunge pool and by rapid caving of the walls and deepening of the channel.

According to Trimble (1972, 1974, 1975), soil erosion on the southern Piedmont is among the severest in the nation. Estimates based on analysis of truncated soil profiles indicate that since 1700 A.D. (the beginning of significant European agriculture) the average depth of erosion has been 144 mm in North Carolina and, 244 mm in South Carolina. An estimated 20 percent of the North Carolina and 40 percent of the South Carolina Piedmont were essentially ruined for agriculture. The causes include highly erosive land use, the intense nature of the rainfall in this region, and the vulnerability of the saprolite to erosion. Since the 1930s this erosion has greatly diminished, owing to the decline of agriculture in the southern Piedmont and the institution of soil conservation practices. The legacy of this erosion remains, however, particularly for Piedmont streams.