World Reference Base for Soil Resources

The World Reference Base for Soil Resources (WRB) is the international standard taxonomic soil classification

Soil classification

Soil classification deals with the systematic categorization of soils based on distinguishing characteristics as well as criteria that dictate choices in use.- Overview :...

system endorsed by the International Union of Soil Sciences (IUSS). It was developed by an international collaboration coordinated by the International Soil Reference and Information Centre

International Soil Reference and Information Centre

World Soil Information, established in 1964 is an independent foundation with a global mandate, funded by the Netherlands Government, and with a strategic association with Wageningen University and Research Centre.Our aims:...

(ISRIC) and sponsored by the IUSS and the FAO

Fão

Fão is a town in Esposende Municipality in Portugal....

via its Land & Water Development division. It replaces the previous FAO soil classification

FAO soil classification

The Food and Agriculture Organization of the United Nations developed a supra-national classification, also called World Soil Classification, which offers useful generalizations about soils pedogenesis in relation to the interactions with the main soil-forming factors. It was first published in...

.

The WRB borrows heavily from modern soil classification concepts, including USDA soil taxonomy

USDA soil taxonomy

USDA Soil Taxonomy developed by United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters and in several levels: Order, Suborder, Great Group, Subgroup, Family, and Series.- Example of...

, the legend for the FAO Soil Map of the World 1988, the Référentiel Pédologique and Russian concepts. The classification is based mainly on soil morphology

Soil morphology

Soil morphology is the field observable attributes of the soil within the various soil horizons and the description of the kind and arrangement of the horizons. C.F...

as an expression pedogenesis

Pedogenesis

Pedogenesis is the science and study of the processes that lead to the formation of soil ' and first explored by the Russian geologist Vasily Dokuchaev , the so called grandfather of soil science, who determined that soil formed over time as a consequence of...

. A major difference with USDA soil taxonomy

USDA soil taxonomy

is that soil climate is not part of the system, except insofar as climate influences soil profile characteristics. As far as possible, diagnostic criteria match those of existing systems, so that correlation with national and previous international systems is as straightforward as possible.

The WRB is meant for correlation of national and local systems. The level of detail corresponds to USDA soil taxonomy subgroups, without the soil climate information. It is not detailed enough for mapping at scales larger than about 1:200k, although proposal have been made to couple WRB with substrate information to map at 1:50k in regional studies.

Key to the WRB reference soil groups (2006)

Identification key to the 32 reference soil groups:

1.	Soils with thick organic layers:	Histosols (HS)
2.	Soils with strong human influence
	Soils with long and intensive agricultural use:	Anthrosols Anthrosols An Anthrosol in the FAO World Reference Base for Soil Resources is a type of soil that has been formed or heavily modified due to long-term human activity, such as from irrigation, addition of organic waste or wet-field cultivation used to create paddy fields.... (AT)
	Soils containing many artefacts:	Technosols Technosols A Technosol in the FAO World Reference Base for Soil Resources is a new type of soil that combines soils whose properties and pedogenesis are dominated by their technical origin... (TC)
3.	Soils with limited rooting due to shallow permafrost or stoniness
	Ice-affected soils:	Cryosols (CR)
	Shallow or extremely gravelly soils:	Leptosols Leptosols A Leptosol in the FAO World Reference Base for Soil Resources is a very shallow soil over hard rock or highly calcareous material or a deeper soil that is extremely gravelly and/or stony. Leptosols cover approximately 1.7 billion hectares of the Earth's surface. They are found from the tropics to... (LP)
4.	Soils influenced by water
	Alternating wet-dry conditions, rich in swelling clays:	Vertisols (VR)
	Floodplains, tidal marshes:	Fluvisols Fluvisols A Fluvisol in the FAO World Reference Base for Soil Resources is a genetically young soil in alluvial deposits . Apart from river sediments, they also occur in lacustrine and marine deposits.... (FL)
	Alkaline soils:	Solonetz Solonetz Solonetz is a type of soil in FAO soil classification. They have, within the upper 100 cm of the soil profile, a so-called "natric horizon" . There is a subsurface horizon , higher in clay content than the upper horizon, that has more than 15% exchangeable sodium... (SN)
	Salt enrichment upon evaporation:	Solonchaks (SC)
	Groundwater affected soils:	Gleysols Gleysols A Gleysol in the FAO World Reference Base for Soil Resources is a wetland soil that, unless drained, is saturated with groundwater for long enough periods to develop a characteristic gleyic colour pattern... (GL)
5.	Soils set by Fe/Al chemistry
	Allophanes or Al-humus complexes:	Andosols Andosols Andosols are soils found in volcanic areas formed in volcanic tephra. In some cases can andosols also be found outside active volcanic areas. Andosols cover an estimate of 1-2% of earth's ice-free land surface... (AN)
	Cheluviation and chilluviation:	Podzols (PZ)
	Accumulation of Fe under hydromorphic conditions:	Plinthosols (PT)
	Low-activity clay, P fixation, strongly structured:	Nitisols (NT)
	Dominance of kaolinite and sesquioxides:	Ferralsols (FR)
6.	Soils with stagnating water
	Abrupt textural discontinuity:	Planosols (PL)
	Structural or moderate textural discontinuity:	Stagnosols (ST)
7.	Accumulation of organic matter, high base status
	Typically mollic:	Chernozems (CH)
	Transition to drier climate:	Kastanozems (KS)
	Transition to more humid climate:	Phaeozems (PH)
8.	Accumulation of less soluble salts or non-saline substances
	Gypsum:	Gypsisols Gypsisols Gypsisols in the FAO World Reference Base for Soil Resources are soils with substantial secondary accumulation of gypsum . They are found in the driest parts of the arid climate zone.In the USDA soil taxonomy they are classified as Gypsids , in the Russian soil classification they are called... (GY)
	Silica:	Durisols Durisols A Durisol in the FAO World Reference Base for Soil Resources is a very shallow to moderately deep, free-draining soil of arid and semi-arid environments, that contain cemented secondary silica in the upper metre of soil. Durisols are internationally known as "hardpan soils" or "dorbank" or they... (DU)
	Calcium carbonate:	Calcisols Calcisols A Calcisol in the FAO World Reference Base for Soil Resources is a soil with a substantial secondary accumulation of lime. Calcisols are common in calcareous parent materials and widespread in arid and semi-arid environments... (CL)
9.	Soils with a clay-enriched subsoil
	Albeluvic tonguing:	Albeluvisols Albeluvisols An albeluvisol in the FAO World Reference Base for Soil Resources is a soil with a thin, dark surface horizon on a bleached subsurface horizon that tongues into a clay illuviation horizon. The Bt horizon has an irregular or broken upper boundary resulting from the tonguing of bleached soil... (AB)
	Low base status, high-activity clay:	Alisols Alisols Alisols define a soil group within the World Reference Base for Soil ResourcesProperties include having an argic horizon, which has a specific cation exchange capacity; a predominantly alic properties zone between 250mm and 1000 mm from the soil surface; and no diagnostic horizons other than... (AL)
	Low base status, low-activity clay:	Acrisols (AC)
	High base status, high-activity clay:	Luvisols (LV)
	High base status, low-activity clay:	Lixisols Lixisols Lixisols are soils with subsurface accumulation of low activity clays and high base saturation. They develop under intensive tropical weathering conditions.... (LX)
10.	Relatively young soils or soils with little or no profile development
	With an acidic dark topsoil:	Umbrisols (UM)
	Sandy soils:	Arenosols (AR)
	Moderately developed soils:	Cambisols Cambisols A Cambisol in the FAO World Reference Base for Soil Resources is a soil with a beginning of soil formation. The horizon differentiation is weak... (CM)
	Soils with no significant profile development:	Regosols Regosols A Regosol in the FAO World Reference Base for Soil Resources is very weakly developed mineral soil in unconsolidated materials. Regosols are extensive in eroding lands, in particular in arid and semi-arid areas and in mountain regions... (RG)

WRB 98 soil groups

Code	Soil type	Brief description
AC	Acrisol Acrisol An acrisol is a type of soil as classified by the Food and Agriculture Organization. It is clay-rich, and is associated with humid, tropical climates, such as those found in Brazil, and often supports forested areas. It is one of the 30 major soil groups of the World Reference Base for Soil Resources...	Red, brown or yellow coloured soil, develops in areas of intense weathering, has a clay rich B horizon
AB	Albeluvisol
AL	Alisol
AN	Andosol	Soil developed from volcanic material, are young immature soils, characteristics depend on type of volcanic material
AT	Anthrosol
AR	Arenosol	Sandy soil with no more profile development than a A horizon
CL	Calcisol	Soil with a substantial secondary accumulation of lime
CM	Cambisol	Transformation of soil matter (Fe particularly) in situ In situ In situ is a Latin phrase which translated literally as 'In position'. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may... without moving in profile. Mostly brownish color.
CH	Chernozem Chernozem Chernozem , also known as "black land" or "black earth", is a black-coloured soil containing a high percentage of humus 7% to 15%, and high percentages of phosphoric acids, phosphorus and ammonia...	Fertile black-coloured soil Soil Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics... containing a high percentage of humus, phosphoric acid Phosphoric acid Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way... s, phosphorus Phosphorus Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks... and ammonia Ammonia Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
CR	Cryosol	Soil in permafrost Permafrost In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of... areas, exhibits cryoturbation Cryoturbation In gelisols , cryoturbation refers to the mixing of materials from various horizons of the soil right down to the bedrock due to freezing and thawing.Cryoturbation occurs to varying degrees in most gelisols... and is usually rich in organic matter
DU	Durisol Durisol Durisol may refer to:* a trade name for Cement-bonded wood fiber* Durisols, soil type...	Soil of some arid and semi-arid environments, contains cemented secondary silica
FR	Ferralsol	Red to yellow soil rich in iron and aluminium, common in temperate to tropical humid areas
FL	Fluvisol Fluvisols A Fluvisol in the FAO World Reference Base for Soil Resources is a genetically young soil in alluvial deposits . Apart from river sediments, they also occur in lacustrine and marine deposits....	Soil developed above flood plain sediments, A horizon is commonly directly above C horizon
GL	Gleysol
GY	Gypsisol
HS	Histosol Histosol In both the FAO soil classification and the USA soil taxonomy, a histosol is a soil consisting primarily of organic materials. They are defined as having or more of organic soil material in the upper . Organic soil material has an organic carbon content of 12 to 18 percent, or more, depending on...	Soil consisting primarily of organic materials, common in wetland Wetland A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions.... s
KS	Kastanozem
LP	Leptosol	Shallow soil over bedrock Bedrock In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil... , calcareous Calcareous Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:... material or a deeper soil that is gravel Gravel Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble... ly or stony, common in mountains
LX	Lixisol
LV	Luvisol
NT	Nitisol
PH	Phaeozem	Sod organic-accumulative
PL	Planosol Planosol A planosol in the FAO World Reference Base for Soil Resources is a soil with a light-coloured, coarse-textured, surface horizon that shows signs of periodic water stagnation and abruptly overlies a dense, slowly permeable subsoil with significantly more clay than the surface horizon...
PT	Plinthosol
PZ	Podzol	Soil that presents significant podzolization Podzolization Podzolization is the comprehensive name for the process of mobilization and precipitation of dissolved organic matter, together with aluminum Al and iron Fe as they are leaching down from the A and E horizons to the B horizon . Through this process the overlying eluvial horizons are getting bleached... , common in coniferous forests
RG	Regosol
SC	Solonchak Solonchak Solonchak is pale or grey soil type found in arid to subhumid, poorly drained conditions. The word is Russian for "salt marsh" in turn from Russian sol , "salt"....
SN	Solonetz Solonetz Solonetz is a type of soil in FAO soil classification. They have, within the upper 100 cm of the soil profile, a so-called "natric horizon" . There is a subsurface horizon , higher in clay content than the upper horizon, that has more than 15% exchangeable sodium...
UM	Umbrisol Umbrisol An Umbrisol in the FAO World Reference Base for Soil Resourcesis a soil with a dark topsoil and in which organic matter has accumulated within the mineral surface soil to the extent that it significantly affects the behaviour and utilization of the soil...	Soil with a dark topsoil and in which organic matter Soil organic matter Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds... has accumulated significantly within the mineral surface soil
VR	Vertisol Vertisol In both the FAO and USA soil taxonomy, a vertisol is a soil in which there is a high content of expansive clay known as montmorillonite that forms deep cracks in drier seasons or years. Alternate shrinking and swelling causes self-mulching, where the soil material consistently mixes itself, causing...	Shows significant and recurrent swelling with water, high content of expansive clay Expansive clay Expansive clay is a clay that is prone to large volume changes that are directly related to changes in water content.The mineral make-up of this type of soil is responsible for the moisture retaining capabilities. Soils with smectite clay minerals, including montmorillonite, have the most dramatic...

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