For use in MLRA 150 of LRR T; for testing in all LRRs with Vertisols and Vertic intergrades.
In Vertisols and Vertic intergrades, a positive reaction to alpha-alpha-dipyridyl that:
a. Is the dominant (60 percent or more) condition of a layer at least 10 cm (4 inches) thick starting at a depth of ≤30 cm (12 inches); or at least 5 cm (2 inches) thick starting at a depth of 15 cm (6 inches) from the mineral or muck soil surface,
b. Occurs for at least 7 continuous days and 28 cumulative days, and
c. Occurs during a normal or drier season and month (within 16 to 84 percent of probable precipitation).
User Notes: The time requirements for this indicator were identified from research in MLRA 150A in LRR T (Gulf Coast Prairies). These requirements or slightly modified time requirements may be found to identify wetland Vertisols and Vertic intergrades in other parts of the Nation. These soils generally have thick dark surface horizons, but indicators A11, A12, and F6 commonly are not evident, possibly because of masking of redoximorphic features by organic carbon. The soils are a special case of the “Problem Soils with Thick, Dark A Horizons” listed in the Corps of Engineers Wetlands Delineation Manual (United States Army Corps of Engineers, 1987). Follow the procedures and note the considerations in Hydric Soils Technical Note 8 (“Use of alpha-alpha-Dipyridyl,”available online at http://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/use/hydric/.