An approach to studying soil-landscape relationships in Virginia

Various methods and techniques were used to examine soil-landscape relationships for residual and colluvial soils of Virginia. Soil micromorphology indicated that although some BC and C horizons in the field appeared structureless, evidence of pedogenic process was observed. These were designated as either BCt, BC, or CB horizons depending on the amount of oriented clay and the rates of change with depth of clay, DCB extractable Fe, and sand contents. Soil variability was examined for the overall study, as well as within toposequences, pedons, and individual horizons. Most of the overall variability was attributed to differences between study sites or between horizons, with minimal amounts due to landscape position. Substantial lateral variability occurred within horizons indicating a strong need for subsampling within horizons of the same pedon. Lithologic discontinuities were found to be difficult to recognize without obvious field evidence. Reconstruction analysis was used to examine soil and saprolite formation. Summit and backslope soils were found to be essentially the same in both morphology and degree of profile development. Sand weathering and clay eluviation/illuviation were the major soil forming processes occurring within these soils. Footslope soils were less developed than associated summit and backslope soils, with both depositional and pedologic processes contributing to soil formation and development. Thickness of saprolite was found to decrease. from the summit to the footslope. Thicker saprolite at the summit was apparently related to the greater stability of the summit position compared to the backslope and footslopes. A bucket auger was modified to obtain undisturbed samples of deep saprolite for reconstruction analysis. Saprolite reconstruction indicated that between 20 and 36 % of the mass of the partially weathered rock, which is the precursor to saprolite, is lost during saprolite formation. Most of these losses were either Al or Si. Initial