Soil Classification Key FAO

HISTOSOLS (HS)
Soils having a histic or folic horizon
either
a. 10 cm or more thick from the soil surface to a lithic or paralithic contact
or
b. 40 cm or more thick and starting within 30 cm from the soil surface
and
lacking an andic or vitric horizon starting within 30 cm from the soil surface

CRYOSOLS (CR)
Other soils having one or more cryic horizons within 100 cm from the soil surface

ANTHROSOLS (AT)
Other soils having
either
a hortic, irragric, plaggic or terric horizon 50 cm or more thick
or
an anthraquic horizon and an underlying hydragric horizon with a combined thickness of 50 cm or more

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

VERTISOLS (VR)
Other soils having a vertic horizon within 100 cm from the soil surface;
and
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
cracks2/ which open and close periodically

FLUVISOLS (FL)
Other soils having fluvic soil material starting within 25 cm from the soil surface and continuing to a depth of at least 50 cm from the soil surface
and
no diagnostic horizons other than a histic, mollic, ochric, takyric, umbric, yermic, salic or sulfuric horizon

SOLONCHAKS (SC)
Other soils having a salic horizon starting within 50 cm from the soil surface
and
no diagnostic horizons other than a histic, mollic, ochric, takyric, yermic, calcic, cambic, duric, gypsic or vertic horizon

GLEYSOLS (GL)
Other soils having gleyic properties within 50 cm from the soil surface
and
no diagnostic horizons other than a anthraquic, histic, mollic, ochric, takyric, umbric, andic, calcic, cambic, gypsic, plinthic, salic, sulfuric or vitric horizon within 100 cm from the soil surface

ANDOSOLS (AN)
Other soils having
either
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

PODZOLS (PZ)
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

PLINTHOSOLS (PT)
Other soils having
either
a petroplinthic horizon starting within 50 cm from the soil surface
or
a plinthic horizon starting within 50 cm from the soil surface
or
a plinthic horizon starting within 100 cm from the soil surface when underlying either an albic horizon or a horizon with stagnic properties

FERRALSOLS (FR)
Other soils having a ferralic horizon at some depth between 25 and 200 cm from the soil surface
and
lacking a nitic horizon within 100 cm from the soil surface
and
lacking a layer which fulfils the requirements of an argic horizon and which has in the upper 30 cm, 10 percent or more water-dispersible clay (unless the soil material has geric properties or more than 1.4 percent organic carbon)

SOLONETZ (SN)
Other soils having a natric horizon within 100 cm from the soil surface.

PLANOSOLS (PL)
Other soils having an eluvial horizon, the lower boundary of which is marked, within 100 cm from the soil surface, by an abrupt textural change associated with stagnic properties above that boundary
and
no albeluvic tonguing

CHERNOZEMS (CH)
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 having these chromas directly below any plough layer
and
concentrations of secondary carbonates starting within 50 cm of the lower limit of the Ah horizon but within 200 cm from the soil surface
and
no petrocalcic horizon between 25 and 100 cm from the soil surface
and
no secondary gypsum
and
no uncoated silt and sand grains on structural ped surfaces

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

PHAEOZEMS (PH)
Other soils having a mollic horizon
and
a base saturation (by 1 M NH4OAc) of 50 percent or more and a calcium carbonate-free soil matrix at least to 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
no diagnostic horizons other than an albic, argic, cambic or vertic horizon, or a petrocalcic horizon 1/in the substratum

GYPSISOLS (GY)
Other soils having
either
a gypsic or petrogypsic horizon within 100 cm from the soil surface,
or
15 percent (by volume) or more gypsum, which has accumulated under hydromorphic conditions, averaged over a depth of 100 cm; and
no diagnostic horizons other than an ochric or cambic horizon, an argic horizon permeated with gypsum or calcium carbonate, a vertic horizon, a calcic horizon, or a petrocalcic horizon underlying the gypsic horizon

DURISOLS (DU)
Other soils having a duric or petroduric horizon within 100 cm from the soil surface

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

ALBELUVISOLS (AB)
Other soils having an argic horizon within 100 cm from the soil surface with an irregular upper boundary resulting from albeluvic tonguing into the argic horizon

ALISOLS (AL)
Other soils having an argic horizon, which has a cation exchange capacity (by 1 M NH4OAc) of 24 cmolc 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
alic properties in the major part between 25 and 100 cm from the soil surface
and
no diagnostic horizons other than an ochric, umbric, albic, andic, ferric, nitic, plinthic or vertic horizon

NITISOLS (NT)
Other soils having a nitic horizon starting within 100 cm from the soil surface
and
gradual to diffuse horizon boundaries between the surface and the underlying horizons
and
no ferric, plinthic or vertic horizon within 100 cm from the soil surface

ACRISOLS (AC)
Other soils having an argic horizon, which has a cation exchange capacity (by 1 M NH4OAc) of less than 24 cmolc 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
a base saturation (by 1M NH4Oac) of less than 50 percent in the major part between 25 and 100 cm

LUVISOLS (LV)
Other soils having an argic horizon with a cation exchange capacity (by 1 M NH4OAc) equal to or more than 24 cmolc kg-1 clay throughout

LIXISOLS (LX)
Other soils having an argic horizon

UMBRISOLS (UM)
Other soils having an umbric horizon
and
no diagnostic horizons other than an anthropedogenic horizon less than 50 cm thick, or an albic or cambic horizon

CAMBISOLS (CM)
Soils having
either
a cambic horizon
or
a mollic horizon overlying a subsoil which has a base saturation (by 1 M NH4OAc) of less than 50 percent in some part within 100 cm from the soil surface
or
one of the following diagnostic horizons within the specified depth from the soil surface:
– an andic, vertic or vitric horizon starting between 25 and 100 cm;
– a plinthic, petroplinthic or salic horizon starting between 50 and 100 cm, in the absence of loamy sand or coarser textures above these horizons

ARENOSOLS (AR)
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
less than 35 percent (by volume) of rock fragments or other coarse fragments within 100 cm from the soil surface
and
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, or an argic or spodic horizon below 200 cm depth

REGOSOLS (RG)
Other soils

ENDNOTES
1/ A petrocalcic horizon may be present locally (e.g. the “Tosca” in Argentina). Such petrocalcic horizons are considered to be polygenetic and may best be handled for classification purposes at phase level (e.g. Luvic Phaeozem, Tosca phase).
2/ A crack is a separation between gross polyhedrons. If the surface is strongly self-mulching, i.e. a mass of granules (“grumic”), or if the soil is cultivated while cracks are open, the cracks may be filled mainly by granular materials from the soil surface but they are open in the sense that the polyhedrons are separated. A crack is regarded as open if it controls the infiltration and percolation of water in dry, clayey soil (Soil Survey Staff, 1996). If the soil is irrigated the upper 50 cm has a coefficient of linear extensibility (COLE) of 0.06 or more throughout.

from:http://www.fao.org

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