Editing Humus (section)

==Horizons==
Humus has a characteristic black or dark brown color and is organic due to an accumulation of organic carbon. Soil scientists use the capital letters O, A, B, C, and E to identify the master [[soil horizon]]s, and lowercase letters for distinctions of these horizons. Most soils have three major horizons: the surface horizon (A), the subsoil (B), and the substratum (C). Some soils have an organic horizon (O) on the surface, but this horizon can also be buried.<ref>{{cite journal |last1=Gerlach |first1=Renate |last2=Fischer |first2=Peter |last3=Eckmeier |first3=Eileen |last4=Hilgers |first4=Alexandra |title=Buried dark soil horizons and archaeological features in the Neolithic settlement region of the Lower Rhine area, NW Germany: formation, geochemistry and chronostratigraphy |journal=[[Quaternary International]] |volume=265 |pages=191–204 |doi=10.1016/j.quaint.2011.10.007 |url=https://www.academia.edu/77065464 |access-date=20 October 2024 }}</ref> The master horizon (E) is used for subsurface horizons that have significantly lost minerals ([[eluviation]]). Bedrock, which is not soil, uses the letter R. The richness of soil horizons in humus determines their more or less dark color, generally decreasing from O to E, to the exception of deep horizons of podzolic soils enriched with [[colloid]]al humic substances which have been [[Leaching (pedology)|leached]] down the soil profile.<ref>{{cite journal |last1=Sanborn |first1=Paul |last2=Lamontagne |first2=Luc |last3=Hendershot |first3=William |title=Podzolic soils of Canada: genesis, distribution, and classification |journal=[[Canadian Journal of Soil Science]] |volume=91 |issue=5 |pages=843–80 |doi=10.4141/cjss10024 |doi-access=free }}</ref>