Official Guidance Maps for Appropriate Application of Hydric Soil Field Indicator F21 Red Parent Material: National and Regional User Notes.

Hydric soil Field Indicator, F21 Red Parent Material (RPM) (developed from the original TF2 indicator) has been approved for nationwide testing for identification of problematic red soils (derived from certain parent materials) that are resistant to redox-induced color changes. These soils most often do not manifest the low chroma colors typically associated with hydric soils. Because the morphological requirements of the indicator are relatively minimal, (7.5YR or redder hues; 10% redox concentrations and depletions in combination), suspected red soils must “qualify” as being resistant to color change by having Color Change Propensity Index (CCPI) values less than 30. Currently there is no glossary or list of problematic RPM soils and no formal guidance regarding where use of the F21 indicator is appropriate. Therefore, an effort was begun, in collaboration with the USDA-NRCS, USACE, and KSSL, to collect and identify (via CCPI analysis) all problematic RPM soils and their derivative parent materials across the country, and to generate guidance maps for the appropriate application of the F21 RPM indicator. From CCPI analyses of more than 1250 individual soil samples (correlated with USDA-NRCS gSTATGO and relevant USGS datasets), a variety of lithology and soil groups from four major regions (Mid-Atlantic, Great Lakes, South Central, and Desert Southwest and Rocky Mountains), have been mapped which identify areas where problematic RPM likely exist and where application of the F21 indicator is appropriate. Based on these efforts, it appears that the problematic RPM occurs in association with lithified, sedimentary, “red bed” deposits rich in the mineral hematite, and in the alluvial, colluvial, and glacial materials derived from them. This poster will present F21 RPM guidance maps for each of the various regions where problematic RPM occurs and will also present updated user notes.