Browsing by Author "Lindbo, David L."

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    Changing the hierarchical placement of soil moisture regimes in Soil Taxonomy
    Stolt, Mark H.; O'Geen, Anthony T.; Beaudette, Dylan E.; Drohan, Patrick J.; Galbraith, John M.; Lindbo, David L.; Monger, H. Curtis; Needelman, Brian A.; Ransom, Michel D.; Rabenhorst, Martin C.; Shaw, Joey N. (2021-05)
    Soil moisture and temperature are incorporated into Soil Taxonomy through the broad classes of moisture and temperature regimes. Although both are important variables in soil formation and land use, soil temperature regime (STR) is typically applied at the family level, whereas soil moisture regime (SMR) is applied at the suborder level. In this paper, we are questioning whether moving SMR to the family level will create a classification system that is more efficient and provide more information to the user at higher categories. The pros and cons of moving ustic, xeric, and udic SMRs from suborder to family category are discussed. To explore this potential change, we used Shannon diversity (Delta H) as an index of the information gain moving from order to suborder when classifying a soil. The analysis indicated a relatively small Delta H for most of the country considering current suborder classes. The proposed group of suborders, characterized by diagnostic horizons instead of SMR, conveyed a considerably larger Delta H supporting a substantial gain in information if the change was incorporated into Soil Taxonomy. The proposed change also has the potential to reduce the number of subgroup taxa by nearly 50%, without losing any of the current information within each taxa. Counterarguments for the change are that SMRs have soil genesis connotations and provide a way to group similar soils on broad-scale maps. A change in the hierarchy of SMRs within Soil Taxonomy could deemphasize the relevance of soil moisture to soil genesis, morphology, and ecology.
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    Hydropedology of Problematic Interfluve Transported Soils in the Central Virginia Piedmont
    Severson, Erik D. (Virginia Tech, 2016-09-29)
    Interpreting soil wetness in upland transported soils on flat broad summits in the central Piedmont of Virginia containing chroma ≥ 3 redoximorphic features (RMFs) can be difficult. It is imperative to understand their saturation regimes because onsite wastewater disposal systems, which are sited based upon soil evaluations, have failed prematurely when installed into these problematic soils. My objectives were to determine if soil morphology was an accurate predictor of soil wetness and permeability, to differentiate interpretations for colluvial soils from residual soils, and to determine the effect of canopy cover on seasonal wetness. Soil morphology, soil wetness regimes in open and wooded canopies, and in-situ saturated hydraulic conductivity were documented in transported Appomattox, Bentley, Brockroad, Catharpin, and Dothan and residual Clifford, Minnieville, and Penhook soil series at eight sites. Transported soils had average winter water levels, and met 30-day and 20-day NRCS oxyaquic criteria at 81, 66, and 91 cm, respectively. Transported soils with depleted ped faces, Fe- concentrations, and chroma 3 depletions were saturated an average of 41, 23, and 41% of the winter, respectively. Residuum found ≥ 1.5 m beneath transported soils exhibited little saturation, thus confirming epiaquic conditions. Residual soils did not perch water for extended periods; and were saturated for significantly (p<0.001) shorter durations and shallower depths (average 93 and 82 cm for 30-day and 20-day oxyaquic criteria, respectively). Transported soils under clear cuts had significantly (p<0.001) shallower average water levels (79 cm) and 30-day and 20-day oxyaquic conditions (51 and 88 cm, respectively) than wooded locations (87 and 83 cm average water levels and 30-day oxyaquic water table, respectively). In-situ hydraulic testing confirmed the presence of low permeability layers as determined by soil evaluation. Restrictive layers were thicker and less permeable in transported soils than in residual soils. In summary, water perches seasonally for extended periods over thick impermeable layers in transported soils. A recommended best management practice for problematic transported soils would be to not install septic systems in zones of saturation and low permeability, including the 1.5 m below a discontinuity. Drainfield designs should utilize permeable saprolite beneath transported material and an upslope curtain drain.