Annexes

Annex 1 - Key to Reference Soil Groups
Annex 2 - Diagnostic horizons, properties and material
Annex 3 - Qualifiers (formative elements for naming soil units)
Annex 4 - Suggestions for ranking qualifiers in soil unit names

Annex 1
Key to Reference Soil Groups

Concepts

The World Reference Base for Soil Resources identifies `diagnostic soil horizons', `diagnostic soil properties' and `diagnostic soil materials'. See Annex 2 for definitions.

Diagnostic soil horizons are internally uniform soil layers delimited by gradual, clear or abrupt upper and lower limits (`boundaries') and characterized by one or more soil characteristics and/or properties occurring over a specific depth.
Diagnostic soil properties are complex soil attributes that involve several soil characteristics and reflect present or past soil forming mechanisms. For example, `gleyic properties' refer to soil characteristics such as `rH-value =< 19', `dark blue colour if in contact with potassium ferric cyanide' or `strong red colour if sprayed with a,a-dipyridyl solution in 10% acetic acid' and to dynamic oxidation-reduction processes of a periodic nature.
that `soil characteristics' are single-value soil attributes that can be observed/measured in the field or laboratory. Soil characteristics include class attributes such as colour, texture or structure class, and discrete attributes expressed in one numerical value such as `soil depth in cm', `soil-pH' or `nominal cation exchange capacity in cmol(+)/kg'.
Diagnostic soil materials are defined as `materials that reflect the original parent materials, in which pedogenetic processes have not yet been so active that they left a significant mark. They comprise anthropogenic, calcaric, fluvic, gypsiric, organic, sulfidic and tephric soil material'

The World Reference Base for Soil Resources defines `Soils' by the vertical combination of soil horizons, properties and/or characteristics occurring within a defined depth and by the vertical organization (`sequence') of soil horizons.

Key to Reference Soil Groups

Soils having a histic or folic horizon, and

either 10 cm or more thick from the soil surface to a lithic or paralithic contact;
or 0 cm or more thick and starting within 30 cm from the soil surface; and
having no andic or vitric horizon starting within 30 cm from the soil surface.

HISTOSOLS (HS)

Other soils having one or more cryic horizons within 100 cm from the soil surface.

Cryosols (CR)

Other soils,

either having a hortic, irragric, plaggic or terric horizon 50 cm or more thick;
or having an anthraquic horizon and an underlying hydragric horizon with a combined thickness of 50 cm or more.

Anthrosols (AT)

Other soils,

either limited in depth by continuous hard rock within 25 cm from the soil surface;
or having a mollic horizon with a thickness between 10 and 25 cm directly overlying material with a calcium carbonate equivalent of more than 40 percent;
or containing less than 10 percent (by weight) fine earth from the soil surface to a depth of 75 cm; and
having no diagnostic horizons other than a mollic, ochric, umbric or yermic horizon.

Leptosols (LP)

Other soils,

having a vertic horizon within 100 cm from the soil surface; and
having, after the upper 20 cm have been mixed, 30 percent or more clay in all horizons to a depth of 100 cm or more, or to a contrasting layer (lithic or paralithic contact, petrocalcic, petroduric or petrogypsic horizons, sedimentary discontinuity, etc.) between 50 and 100 cm; and
having cracks¹ which open and close periodically.

Vertisols (VR)

Other soils,

having a thickness of 25 cm or more; and
having fluvic soil material starting within 50 cm from the soil surface; and
having no diagnostic horizons other than a histic, mollic, ochric, takyric, umbric, yermic, salic or sulfuric horizon.

Fluvisols (FL)

Other soils,

having a salic horizon starting within 50 cm from the soil surface; and
having no diagnostic horizons other than a histic, mollic, ochric, takyric, yermic, calcic, cambic, duric, gypsic, or vertic horizon.

Solonchaks (SC)

Other soils,

having gleyic properties within 50 cm from the soil surface; and
having no diagnostic horizons other than an anthraquic, histic, mollic, ochric, takyric, umbric, andic, calcic, cambic, gypsic, plinthic, salic, sulfuric, or vitric horizon within 100 cm from the soil surface.
having no abrupt textural change within 100 cm from the soil surface.

Gleysols (GL)

Other soils,

having a vitric or an andic horizon starting within 25 cm from the soil surface; and
having no diagnostic horizons (unless buried deeper than 50 cm) other than a histic, fulvic, melanic, mollic, umbric, ochric, duric, or cambic horizon.

Andosols (AN)

Other soils,

having a spodic horizon starting within 200 cm from the soil surface, underlying an albic, histic, umbric or ochric horizon, or an anthropedogenic horizon less than 50 cm thick.

Podzols (PZ)

Other soils,

either having a petroplinthic horizon starting within 50 cm from the soil surface;
or having a plinthic horizon starting within 50 cm from the soil surface;
or having a plinthic horizon starting within 100 cm from the soil surface underlying an albic horizon or a horizon with stagnic properties.

Plinthosols (PT)

Other soils,

having a ferralic horizon at some depth between 25 and 200 cm from the soil surface; and
having no nitic horizon within 100 cm from the surface; and
having no layer, which fulfils the requirements of an argic horizon and which has 10 percent or more water-dispersible clay within 30 cm from its upper boundary unless the soil material has geric properties or contains more than 1.4 percent organic carbon.

Ferralsols (FR)

Other soils,

having a natric horizon within 100 cm from the soil surface.

Solonetz (SN)

Other soils,

having an eluvial horizon or materials having loamy sand or coarser textures, the lower boundary of which is marked, within 100 cm from the soil surface, by an abrupt textural change associated with stagnic properties; and
having no albeluvic tonguing.

Planosols (PL)

Other soils,

having a mollic horizon with a moist chroma of 2 or less if the texture is finer than sandy loam, or less than 3.5 if the texture is sandy loam or coarser, both to a depth of at least 20 cm, or a mollic horizon which has these chromas directly below a plough layer; and
having concentrations of secondary carbonates starting within 200 cm from the soil surface; and
having no petrocalcic horizon between 25 and 100 cm from the soil surface; and
having no secondary gypsum; and
having no uncoated silt and sand grains on structural ped surfaces.

Chernozems (CH)

Other soils,

having a mollic horizon with a moist chroma of more than 2 to a depth of at least 20 cm or directly below any plough layer; and
having concentrations of secondary carbonates within 100 cm from the soil surface; and
having no diagnostic horizons other than an argic, calcic, cambic, gypsic, petrocalcic, petrogypsic or vertic horizon.

Kastanozems (KS)

Other soils,

having a mollic horizon; and
having a base saturation (in 1 M NH₄OAc at pH 7.0) of 50 percent or more and having no secondary carbonates to at least a depth of 100 cm from the soil surface, or to a contrasting layer (lithic or paralithic contact, petrocalcic horizon) between 25 and 100 cm; and
having no diagnostic horizons other than an albic, argic, cambic or vertic horizon.

Phaeozems (PH)

Other soils,

having a gypsic or petrogypsic horizon within 100 cm from the soil surface; and
having no diagnostic horizons other than an ochric horizon, a cambic horizon, an argic horizon permeated with gypsum or calcium carbonate, a vertic horizon or a calcic or petrocalcic horizon underlying the gypsic or petrogypsic horizon.

Gypsisols (GY)

Other soils,

having a duric or petroduric horizon within 100 cm from the soil surface.

Durisols (DU)

Other soils,

having a calcic or petrocalcic horizon within 100 cm of the surface; and
having no diagnostic horizons other than an ochric or cambic horizon, an argic horizon which is calcareous, a vertic horizon or a gypsic horizon

Calcisols (CL)

Other soils,

Having, within 100 cm from the soil surface, an argic horizon with an irregular upper boundary resulting from albeluvic tonguing into the argic horizon.

Albeluvisols (AB)

Other soils,

having an argic horizon, which has a cation exchange capacity (in 1 M NH₄OAc at pH 7.0) of 24 cmol(+) kg^-1 clay or more, either starting within 100 cm from the soil surface, or within 200 cm from the soil surface if the argic horizon is overlain by loamy sand or coarser textures throughout; and
having alic properties in most of the layer(s) between 25 and 100 cm from the soil surface; and
having no diagnostic horizons other than an ochric, umbric, albic, andic, ferric, nitic, plinthic or vertic horizon.

Alisols (AL)

Other soils,

having a nitic horizon starting within 100 cm from the soil surface; and
having gradual or diffuse horizon boundaries; and
having no ferric, plinthic or vertic horizon within 100 cm from the soil surface.

Nitisols (NT)

Other soils,

having an argic horizon, which has a cation exchange capacity (in 1 M NH₄OAc at pH 7.0) of less than 24 cmol(+) kg^-1 clay in some part, either starting within 100 cm from the soil surface, or within 200 cm from the soil surface if the argic horizon is overlain by loamy sand or coarser textures throughout, and
having less than 50 percent base saturation (in 1M NH₄OAc at pH 7.0) in the major part between 25 and 100 cm.

Acrisols (AC)

Other soils,

having an argic horizon with a cation exchange capacity (by 1 M NH₄OAc at pH 7.0) equal to or greater than 24 cmol(+) kg^-1 clay, either starting within 100 cm from the soil surface, or within 200cm from the soil surface if the argic horizon is overlain by loamy sand or coarser textures throughout.

Luvisols (LV)

Other soils,

having an argic horizon starting within 100cm from the soil surface, or within 200 cm from the soil surface if the argic horizon is overlain by loamy sand or coarser textures throughout.

Lixisols (LX)

Other soils,

having an umbric horizon; and
having no diagnostic horizons other than an anthropedogenic horizon less than 50 cm thick, an albic horizon or a cambic horizon.

Umbrisols (UM)

Other soils,

either having a cambic horizon;
or having a mollic horizon;
or having one of the following diagnostic horizons:
- an andic, vertic or vitric horizon starting between 25 and 100 cm below soil surface, or
- a plinthic, petroplinthic, salic or sulfuric horizon starting between 50 and 100 cm below soil surface, in the absence of loamy sand or coarser materials above these horizons.

Cambisols (CM)

Other soils,

having a texture which is loamy sand or coarser either to a depth of at least 100 cm from the soil surface, or to a plinthic, petroplinthic or salic horizon between 50 and 100 cm from the soil surface; and
having less than 35 percent (by volume) of rock fragments or other coarse fragments within 100 cm from the soil surface; and
having no diagnostic horizons other than an ochric, yermic or albic horizon, or a plinthic, petroplinthic or salic horizon below 50 cm from the soil surface.

Arenosols(AR)

Other soils.

Regosols (RG)

¹ A crack is an open space between gross polyhedrons. Cracks may be filled mainly by granular materials from the soil surface but remain open in the sense that the polyhedrons are separated.