Browsing by Author "Stolt, Mark H."
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- An approach to studying soil-landscape relationships in VirginiaStolt, Mark H. (Virginia Tech, 1990)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 soil formation was shown to occur at a faster rate than 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. Reconstruction analysis was found to be a valuable tool in studying soil-landscape relationships.
- Changing the hierarchical placement of soil moisture regimes in Soil TaxonomyStolt, 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.
- Manganese-coated IRIS to document reducing soil conditionsRabenhorst, Martin C.; Drohan, Patrick J.; Galbraith, John M.; Moorberg, Colby; Spokas, Lesley; Stolt, Mark H.; Thompson, James A.; Turk, Judith; Vasilas, Bruce L.; Vaughan, Karen L. (Wiley, 2021-09-01)Iron-coated indicator of reduction in soils (IRIS) devices have been used for nearly two decades to help assess and document reducing conditions in soils, and official guidance has been approved for interpreting these data. Interest in manganese (Mn)-coated IRIS devices has increased because Mn oxides are reduced under more moderately reducing conditions than iron (Fe) oxides (which require strongly reducing conditions), such that they are expected to be better proxies for some important ecosystem services like denitrification. However, only recently has the necessary technology become available to produce Mn-coated IRIS, and the need is now emerging for guidance in interpreting data derived from Mn IRIS. Ninety-six data sets collected over a 2-yr period from 40 plots at 18 study sites among eight states were used to compare the performance of Mn-coated IRIS with Fe-coated IRIS and to assess the effect of duration of saturation and soil temperature as environmental drivers on the reduction and removal of the oxide coating. It appears that the current threshold prescribed by the National Technical Committee for Hydric Soils for Fe-coated IRIS is appropriate for periods when soil temperatures are warmer (>11 °C), but is unnecessarily conservative when soil temperatures are cooler (5–11 °C). In contrast, Mn-coated devices are particularly useful early in the growing season when soil temperatures are cool. Our data show that when using a threshold of 30% removal of Mn oxide coatings there is essentially 100% confidence of the presence of reducing soil conditions under cool (<11 °C) conditions.
- Soil Taxonomy Proposals for Acid Sulfate Soils and Subaqueous Soils Raised by the 8th International Acid Sulfate Soils ConferenceWessel, Barret M.; Galbraith, John M.; Stolt, Mark H.; Rabenhorst, Martin C.; Fanning, Delvin S.; Levin, Maxine J. (2017-12-11)The 8th International Acid Sulfate Soils Conference presented examples and discussions for classification of ‘acid sulfate soils’ and related issues for ‘subaqueous soils’. When these soils are disturbed or exposed, the sulfides (predominantly pyrite) react with oxygen to produce sulfuric acid; soil materials that do this to a great extent are recognised as ‘sulfidic materials’ in Soil Taxonomy. Soil Taxonomy describes physical and chemical properties and thresholds for incubation of sulfidic materials for acidification, and has developed definitions for features and materials commonly seen in these soils. However, based on discussions and examples from field tours the conference has several proposals to modify and add to existing definitions, such as adding new subgroups, defining sulfuric materials and editing the definition of the sulfuric horizon. These changes are centred on improving the interpretative value of taxa in Soil Taxonomy as well as use and management recommendations and their value in soil survey products.
- Soil-saprolite-landscape relationships in the Piedmont and Blue Ridge Highland regions of VirginiaStolt, Mark H.; Baker, James C.; Simpson, Thomas W. (Virginia Agricultural Experiment Station, 1994)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.