Calculate the "Profile Darkness Index" by the method of Thompson & Bell (1996) "Color index for identifying hydric conditions for seasonally saturated mollisols in Minnesota" DOI: 10.2136/sssaj1996.03615995006000060051x. The Thompson-Bell Index has been shown to reflect catenary relationships in some Mollisols of Minnesota (generally: wetter landscape positions = thicker, darker surfaces).

thompson.bell.darkness(
  p,
  name = guessHzDesgnName(p),
  pattern = "^A",
  value = "m_value",
  chroma = "m_chroma"
)

Arguments

p

A single-profile SoilProfileCollection (e.g. via profileApply())

name

Column name containing horizon designations used to find A horizons (default: first column name containing 'name')

pattern

Regular expression to match A horizons (default: "^A" which means horizon designation starts with A)

value

Column name containing horizon color values (default: "m_value")

chroma

Column name containing horizon color chromas (default: "m_chroma")

Value

A numeric vector reflecting horizon darkness (lower values = darker).

References

Thompson, J.A. and Bell, J.C. (1996), Color Index for Identifying Hydric Conditions for Seasonally Saturated Mollisols in Minnesota. Soil Science Society of America Journal, 60: 1979-1988. doi:10.2136/sssaj1996.03615995006000060051x

Author

Andrew G. Brown