Classification and Genesis of Spodosols in the Central Appalachians

Seventeen well-drained pedons were sampled in Pennsylvania and northern West Virginia. Sixteen of the pedons had well-expressed Spodosol morphology while one had very marginal Spodosol morphology. These pedons were classified according to Soil Taxonomy and the Canadian soil classification system. The degree of spodic horizon development in relation to soil temperature was examined. Only three of the 17 pedons studied met the chemical criteria of Soil Taxonomy for Spodosol identification, while 13 met the chemical criteria of the Canadian system. Three pedons were examined for cracked coatings on sand grains and dark pellets of coarse-silt size; all three pedons qualified as Spodosols on the basis of these criteria. These data indicate that more emphasis should be placed on the field criteria described in Soil Taxonomy and less on the chemical criteria or that the chemical criteria should be amended. The spodic horizon (Bh and Bir) in each of the 17 pedons contained the largest amount of illuvial Al, Fe, and C of the various horizons of the soil. As the mean annual soil temperature (MAST) of these soils increased, the Fe (pyrophosphate extracted) and C (total organic) content of the spodic horizon decreased (correlation coefficients of −0.70 and −0.46, respectively). The thickness of the spodic horizon was also related to soil temperature. There was a weak correlation (r = −0.31) of decreased thickness with increased MAST. In addition, Al (pyrophosphate extracted) content in the spodic horizon and the depth to the top of the spodic horizon showed a very weak correlation to MAST (correlation coefficients of −0.27 and 0.23, respectively). Although weak, these correlations show that Al, Fe, and C accumulate in spodic horizons of well-drained soils in colder areas of the Appalachians to a greater extent than in warmer areas, and result in a more strongly expressed Spodosol in the cooler areas. The lack of stronger relationships may be a reflection of the effect of varying vegetation types (e.g., hemlock vs. maple) in the mixed hardwood-conifer forest that was the natural vegetation of these soil pedons, or of varying vegetation during the development of these soils.