Soil-Landscape Relationships in Virginia: I. Soil Variability and Parent Material Uniformity

Abstract

Relationships between soil development and parent material or landscape position can often be hidden or confounded by soil variability. Variability in particle size and elemental composition was examined in soils within four representative toposequences in Virginia. The objectives were to partition total variability, describe lateral variability within horizons of the same pedon, and evaluate parent material uniformity. Total variability was partitioned among study sites, landscape positions, horizons, and random effects. Variability attributed to landscape position was minimal (<8%), suggesting that parent material differences or horizon differentiation may be more important in explaining spatial variability in soils than landscape position. Lateral variability was substantially higher in C horizons, than in associated Bt and near-surface horizons. These differences are related to the weathering and pedogenesis occurring in these horizons resulting in an increase in the degree of order of the soil constituents. Mean coefficients of variation ranged from 8 to 34% for particle size data, and 10 to 30% for elemental data, indicating considerable lateral variability and supporting the need for multiple sampling within horizons. Lithologic discontinuities were difficult to recognize without obvious field evidence. Differences in distributions of clay-free sand and Zr, or ratios of Ti/Zr and sand/silt for residual soils were related to differential weathering rates or slight variations in the parent rock.