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Soil Classification

Irish soils are classified using a three-level system, moving from general to very specific. These levels are the:

  • Great Soil Groups,
  • Subgroups
  • Soil Series.

This structure helps organise the wide variety of soils by grouping similar ones together.

Great Soil Groups

At the highest level are the Great Soil Groups. These are soils that share common characteristics and have formed under similar environmental conditions, especially climate and vegetation, over a large geographic area. Each Great Group has a similar arrangement and development of soil horizons (layers).

There are 11 Great Soil Groups in Ireland are outlined in the Table below. To learn more about each click on the link.

Criteria Great Group
Soils with thick organic layers 1.      Ombrotrophic Peat
2.      Minerotrophic Peat
Shallow or extremely gravelly soils 3.      Rendzina
4.      Lithosol
Soils influenced by water 5.      Alluvial
6.      Groundwater Gley
7.      Surface-water Gley
Soils affected by Fe/Al chemistry increase 8.      Podzol
9.      Brown Podzolic
Soils with clay enriched subsoil 10. Luvisols
Relatively young, or soils with little profile development 11. Brown Earth

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Soil Subgroups

Each Great Group is further divided into subgroups, which provide a more detailed understanding of the soil. Subgroups are based on the kind and arrangement of soil horizons, and they reflect both the main characteristics of the Great Group and any variations or transitions toward other soil types.

Subgroups are especially important because they give the most information about soil processes. They show what is actively happening in the soil, such as waterlogging, leaching, or human influence.

To define subgroups, soil scientists use diagnostic features, which are key characteristics observed in the soil profile. There are nine main diagnostic features recognised in Ireland, including things like a peaty surface (histic), waterlogging from groundwater (gleyic), poor drainage (stagnic), or the movement of iron and aluminium (spodic). Other features include calcareous (lime-rich) soils, humic (organic-rich) surfaces, artificially drained soils, cutover peat soils, and soils heavily modified by humans (anthropic).

Soil Series

The most detailed level of classification is the soil series. A series consists of soils within a subgroup that are very similar in their physical and chemical properties. These include characteristics such as colour, texture, structure, consistency, and mineral composition, as well as how these features are arranged in the soil profile.

Soil series are usually named after the place where they were first identified, such as a town or townland. This makes them specific to real locations.

Series are defined in a hierarchy that includes the Great Group, subgroup, texture, and parent material (the material from which the soil developed).

Soil Associations

In mapping soils across Ireland, soil series are grouped into soil associations. A soil association is a collection of related soil series found in a similar landscape. It typically includes one dominant soil (the major soil) and one or more minor soils.

The association is named after the dominant series.  The interactive soil map of Ireland outlining the soil types of Ireland can be viewed at  Irish Soil Information System.

11 Great Soil Groups in Ireland

Ombrotrophic peat

  • Thick organic (>40cm) layer
  • Rain-fed
  • pH <4
  • Located in lowland (raised bog) or upland (blanket bog) areas   

Minerotrophic peat

  • Thick organic (>40cm) layer
  • Groundwater-fed
  • Poor decomposition and pH >4.5
  • Located near streams, hollows or other areas with high groundwater table

Rendzina

  • Shallow <30cm and often very stoney
  • Calcareous bedrock; pH>7
  • Mainly found in the west of Ireland and Burren

Lithosol

  • Shallow <30cm and often very stoney
  • Acidic parent material; pH<6.5
  • Located in mountain landscapes

Alluvial

  • Forms in floodplains of waterbodies
  • Often waterlogged for prolonged periods
  • Distinct layers of soil material from deposits
  • Found throughout the country

Groundwater gley

  • High groundwater table
  • Prolonged periods of waterlogging within 40cm of surface
  • Grey uniform colour (gleying) or mottling through profile
  • Often found near rivers or hollows between drumlins

Surface water gley

  • Poorly drained with slowly permeable subsurface layer that impedes drainage
  • Subsoil dense or with high clay content
  • Seasonal prolonged waterlogging of top 40cm causing mottling
  • Common in the south west and in border counties

Podzol

  • Pale nutrient-poor acidic mineral topsoil overlain with a dark peaty layer
  • Organic acids from vegetation result in nutrient leaching (particularly Fe/Al) from surtace layers
  • Found at higher altitudes

Brown podzolic

  • Formed in acidic conditions
  • Tends to be free-draining
  • Found mainly in the south of the country

Luvisol

  • Clay enriched subsoil
  • Good agricultural soils with good nutrient retention
  • Moderately to imperfectly drained
  • Widely distributed

Brown earth

  • Young soils with little profile development
  • Well drained with good nutrient retention
  • Most widely cultivated soils in Ireland