Umbrisols have one of the smallest share among all Reference Soil Groups of Europe, found in southern part of the continent.
The Umbrisol Reference Soil Group belongs to the set of mineral soils conditioned by a (sub)humid temperate climate. Soils in this Reference Soil Group occur in cool, humid regions, mostly mountainous and with little or no soil moisture deficit, on weathering material of siliceous rock; predominantly in late Pleistocene and Holocene deposits.
Umbriols occupy about 1 million km2 throughout the world.
The central concept of Umbrisols is that of deeply drained, medium-textured soils with a dark, acid surface with high organic matter content as the most distinguishing feature. Vegetation and climate influence the development of an umbric horizon (a dark colored horizon, with low base saturation). In some cases, an umbric horizon may form quite rapidly while concurrent development of an incipient, non-diagnostic, spodic or argic horizon is slow. This explains why umbric horizons are found in young, relatively undeveloped soils that lack any other diagnostic horizon, or have only a weak cambic horizon. Profile development is strongly dependent on deposition of (significant quantities of) organic material with low base saturation at the soil surface.
The organic material that characterises Umbrisols can comprise a variety of humus forms that have been variously described as acid or oligitrophic mull, moder, raw humus and mor. Organic matter could accumulate because of slow biological turnover of organic matter under conditions of acidity, low temperature, surface wetness, or a combination of these. However, Umbrisols were never cold and/or wet for sufficiently long periods to have developed a diagnostic histic horizon.
Many Umbrisols of the world are under a natural or near-natural vegetation cover. Umbriols are predominantly suitable for forestry and extensive grazing. Under adequate management, Umbrisols may also be planted to cash crops such as cereals, root crops, tea and coffee.
Other national and international classification systems classify these soils as Umbrepts and Humitropepts (Soil Taxonomy), Humic Cambisols and Umbric Regosols (FAO), Sombric Brunisols and Humic Regosols (France).