Soil-saprolite-landscape relationships in the Piedmont and Blue Ridge Highland regions of Virginia

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Virginia Agricultural Experiment Station


Various methods and techniques were used to examine soil variability and soil-saprolite-landscape relationships in Virginia. Variability analysis indicates that for the overall study, most soil variability is attributable to differences between study sites or between horizons, with minimal amounts due to landscape position. Substantial lateral variability occurs within horizons, indicating a strong need for subsampling within horizons of the same pedon. Although some soil-saprolite transition horizons appear structureless in the field, soil micromorphology indicated evidence of pedogenic process within these horizons. Soil-saprolite transition horizons were designated as either BCt, BC, or CB, depending on the amount of oriented clay, and rates of change with depth of clay, DCB extractable Fe, and sand. Summit and backslope soils have essentially the same morphology and degree of profile development. Soil reconstruction indicates that sand weathering and clay eluviation/illuviation are the major soil-forming processes occurring within these soils. Footslope soils are less developed than are associated summit and backslope soils, with both depositional and pedologic processes contributing to soil formation and development. Saprolite thickness decreases from summit to footslope. Thicker saprolite at the summit is apparently related to the greater stability of the summit position compared to associated backslope and footslopes. Saprolite reconstruction indicates 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 are either Al or Si. Initial soil formation occurs at a faster rate than that of saprolite formation, but after substantial profile development, soil formation is reduced to a rate below that of saprolite formation, and saprolite accumulates below the solum.