Short description of WRB soil groups common in Sweden

Page reviewed:  08/06/2026

In many cases, the identification of soil groups requires an assessment of soil colour.

Colour determination is carried out by comparing the soil sample with a standardised colour chart: the Munsell® Soil Color Chart.

The WRB soil groups described here are used in the frequency maps on the page Soils.

The chart is constructed using colour samples classified by means of three parameters:

  • Hue, which describes the colour of the soil sample in relation to the colours red (R), yellow (Y), green, blue and purple (the latter three colours are not used within the National Forest Soil Inventory). A higher number indicates a yellower colour on the relevant colour charts: 5YR, 7.5YR and 10YR;
  • Value, which determines how light or dark the colour is. A higher number indicates higher lightness;
  • Chroma, which is a measure of colour intensity (saturation). A higher number indicates greater saturation.

Each colour sample in the colour chart has a specific designation, for example “10YR 3/1”, where the hue is 10YR, the value is 3 and the chroma is 1. Colour determination is carried out on a well-moistened soil sample and not in direct sunlight. A rule of thumb is that the soil sample should have the same moisture content as when rolling the soil for texture determination. All colour criteria stated therefore refer to a moist sample.

Terms in italics in the text below are explained under Diagnostic horizons, properties and materials.

Histosol

Soils consisting of organic material that are:
  • 10 cm or thicker from the ground surface to bedrock, or to the upper surface of a layer with stones and boulders whose voids are filled with organic material;

or

  • 40 cm or thicker, with an upper boundary within 40 cm of the ground surface (if another soil layer overlies the organic material).
Most Histosols in Sweden are bog or fen peat soils.

Leptosol

Shallow soils with bedrock within 25 cm of the ground surface, or soils with a very low content (< 20 vol-%) of fine material (< 2 mm) within 75 cm, and without a spodic horizon.

Gleysol

Gleysols are soils in which a high groundwater table and the presence of organic material cause reducing conditions for shorter or longer periods in a soil layer at least 25 cm thick, beginning within 40 cm of the upper boundary of the mineral soil. This leads to the formation of gley colours. The soil may have an odour reminiscent of liquefied petroleum gas.

Podzol

Soils in which the podzolisation process has resulted in weathering of the surface of mineral soil particles in the upper part of the mineral soil (the E horizon or eluvial horizon) and an accumulation of humus, aluminium and iron (hydr)oxides in the B horizon (the illuvial horizon). For soils to be classified as Podzols, the accumulation in the B horizon must be sufficiently strong to meet the criteria for a spodic horizon. This means that soils with a clearly developed E and B horizon—but without a diagnostic spodic horizon—are classified instead as Arenosols or Regosols.

Umbrisol

Umbrisols have a thick and well-developed dark-coloured A horizon, often with a distinctly high concentration of organic matter. The A horizon has a moderately to well-developed aggregate structure (an umbric or mollic horizon). The A horizon may be overlain by a litter/S layer and an Of layer with a thickness of less than 10 cm.

Cambisol

Cambisols develop in medium- to fine-textured soils. The soil profile is relatively weakly developed, and transitions between horizons are often gradual due to intensive activity by earthworms and other burrowing soil fauna. This, together with the fine texture, leads to an aggregate structure. Horizon development has progressed to the extent that there is a clear difference in structure between the B and C horizons, i.e. the requirements for a cambic horizon are fulfilled. The cambic horizon must begin within 50 cm of the ground surface and have its lower boundary at least 25 cm below the surface.

Arenosol

Arenosols are sedimentary soils with a high or low degree of sorting (moraines are therefore excluded from Arenosols). Arenosols are characterised by a very high proportion (≥ 70 wt-%) of sorted coarse silt, medium sand and/or coarse sand in the fine earth fraction (< 2 mm) down to one metre below the ground surface. The proportion requirement increases if clay is present, for example to 85 wt-% at a clay content of 15 wt-%. The total thickness of layers with finer texture than coarse silt must be less than 15 cm. The coarse texture leads to weak development of A, E and B horizons, low water-holding capacity and high permeability. The content of gravel, stones and boulders within 1 m of the ground surface must be less than 40 vol-%, but is normally much lower and consists mainly of gravel.

Regosol

Regosols have such weakly developed horizons that they do not meet the requirements for any of the diagnostic horizons or other criteria typical of the other soil groups. Regosols are a common soil group in Sweden. Texture may range from clay to coarse sand. Note, however, that if the texture is dominated by sand plus coarse silt, Arenosol is a possible soil group, and if the content of gravel, stones and boulders exceeds 80 vol-%, the soil is classified as a Leptosol. 

Contact

  • Johan Stendahl, head of department and researcher
    Biogeochemistry of Forest Soils