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Unit 4 Hydric Soil Lecture 2 - An Introduction to Hydric...

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1 An Introduction to Hydric Soils and Hydric Soil Terminology by: Wade Hurt, USDA, NRCS, NSSC/ University of Florida, Gainesville, Florida and based on deliberations of: The National Technical Committee for Hydric Soils (NTCHS). Hydric Soil Definition A soil that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part (Federal Register. July 13, 1994). “that formed under” means that there are such things as drained hydric soils; that the presence of ditches do not alter the status of a hydric soil. “saturation, flooding, and ponding” tells us there are three conditions for wetness. These 3 conditions of wetness are utilized differently. “during the growing season” will be applied differently for different applications. “develop anaerobic conditions” tell us that a hydric soil need not be reduced but only lack oxygen. “in the upper part” is vague enough to allow interpretations that vary from region to region and from climate to climate. Growing Season Growing Season: The portion of the year when soil temperatures are above biologic zero 5 degrees C (41 degrees F) at 50 cm (19.7").
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2 How to Determine a Hydric Soil “Hydric Soil List” – Based on known characteristics of a soil series and the criteria established for hydric soils. “Field Indicators” – Determine by field investigation of soil at a given location. Hydric Soil List: Most hydric soil lists are created by comparing the hydric soil criteria with data in a published soil survey. Hydric Soil List First the criteria are compared to the data to identify several soils that have data ranges (water table, flooding, ponding) that are within the criteria ranges. Next the detailed map unit descriptions are read to identify possible hydric soil inclusions. Lastly a hydric soil list is created.
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3 Inherent Problems with Hydric Soil Lists – Mapping scale often to broad for detailed use – Spatial variability/heterogeneity in soil series characteristics – Attributes of “type” soil series reported in the soil survey may differ slightly from that at the site.
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