The classification and genesis of soils with spodic morphology in the Southern Appalachians

Soils with Bs/Bhs horizonation have been known to occur in the Southern Appalachians. Limited soil data, particularly chemical data, have made it difficult to classify these soils in the present classification system using the spodic horizon chemical criteria of Soil Taxonomy (105). This study attempts, in part, to correct this deficiency. Eleven pedons were selected from sites in Tennessee and North Carolina. Laboratory analyses were carried out to determine pH, particle-size distribution, extractable bases, acidity, aluminum, and iron. Two field techniques for spodic horizon identification were also evaluated. The presence of coarse fragments causes tongueing of organic matter in the E horizon and varying expressions of spodic horizon development across the pedon face in the B horizon. The Bs/Bhs horizon in most pedons is characterized by aluminum, iron, organic carbon, and clay accumulation. The present fraser-fir, red spruce and rhododendron vegetation which promotes conditions favorable to the formation of Bs/Bhs horizons interacts with the more potent influence of parent material as a source of clay and cations in producing varying degrees of spodic horizon development in the soils studied. Of the 11 pedons used in this study, two pedons met all the present chemical criteria for Bs/Bhs horizon identification. The most critical spodic horizon criterion is the pyrophosphate aluminum and iron to clay ratio of ≥ 0.2. The high clay content in the Bs/Bhs of most pedons is responsible for reducing the measured value to less than 0.2. Two pedons were classified as Haplorthods while the remaining nine pedons were classified as either Dystrochrepts or Haplumbrepts. Proposals were made to overcome some of the problems that were encountered with the use of the present classification system to classify soils which showed evidences of spodic horizon expression. These proposals include lowering the pyrophosphate aluminum and iron to clay ratio from ≥ 0.2 to ≥ 0.1 for soils with cambic horizons that have a loamy particle-size class in the Bs/Bhs horizons, creating spodic subgroups in Inceptisols and eliminating the depth requirement for frigid soils. These proposals need further study before any consideration is given to their inclusion in Soil Taxonomy (105).