The humus type Mor develops on soils with very low base saturation and poorly decomposable litter, for example, from spruce, pine, bilberry, cranberry, or heather. A high CN ratio and phenol content of the litter reduce its decomposability. In Mor, biological mixing by endogeic and anecic earthworms is absent. Litter decomposition takes place exclusively in the organic surface layers and is very slow and incomplete. Mor, developed from spruce needle litter, is characterised by very abrupt transitions between the single organic surface horizons as well as between the organic surface layer and the mineral soil. During the separation of distinct horizons in an organic surface layer monolith, the horizons detach easily from each other even under low tensile stress. Organic fine material accumulating in the Oh horizon is compact (Okh) or can even be broken into sharp-edged pieces (Osh). Organic layers of Mor humus forms enhance podzolisation of the mineral soil due to the translocation of mobile humic substances by seepage water. The CN ratio in the Oh horizon is mostly >25, and the CP ratio is >400. The typical characteristics of the humus form type Mor are:
Ol and Of horizons are present;
Osh horizon or Okh horizon is present; and
an acidic bleached horizon (Ee-Ah horizon, Ah-Ee horizon or Ee horizon) is present.
ARM Moder-like Mor
ART Typical Mor
ARF Moist Mor