12 Sep 2025

Identifying Hydric Soils Using α,α′-Dipyridyl Dye

Purpose: The application of α,α′-dipyridyl dye (pronounced alpha, alpha di-peeri-dill) provides a reliable and defensible mechanism for documenting the presence of reduced iron in support of hydric soil identification and wetland delineation activities. The α,α′-dipyridyl dye has proven particularly useful for identifying hydric soils in naturally problematic, altered, and disturbed soils. The proper application of paper test strips embedded with α,α′-dipyridyl dye further promotes the use of this technique to improve wetland delineation and management. This technical note summarizes the state of the science related to α,α′-dipyridyl dye and provides practitioner recommendations for applying, documenting, and interpreting α,α′-dipyridyl dye in hydric soil and wetland investigations.