Aridisols: Types of Desert Soil, Profile and Layers

What makes a soil an Aridisol

NRCS’s definition is about water: Aridisols are too dry for the growth of mesophytic plants. Soluble material often moves and builds up inside them, and the University of Idaho lists what accumulates in their subsurface horizons: clays, calcium carbonate, silica, salts and gypsum.^[2][3]

NRCS names the horizons that can mark an Aridisol: a calcic, cambic, gypsic, natric, petrocalcic, petrogypsic or salic horizon, a duripan, or an argillic horizon.^[2]

Mesophytic plants are those adapted to neither very wet nor very dry ground. The same dry climate holds back weathering, and Aridisols often carry salt, gypsum or carbonates, in hot and cold deserts alike. The name comes from the Latin aridus, dry, and the order covers about 12% of the world’s glacier-free land, including some of the dry valleys of Antarctica.^[1]

Types of desert soil

NRCS describes seven Aridisol suborders, and five of them are defined by the layer that has built up: an argillic or natric horizon, a calcic horizon, a duripan, a gypsic horizon or a salic horizon. The other two are the least developed Aridisols and the cold ones:^[2]

• Argids have an argillic or natric horizon, but not a duripan or a gypsic, petrocalcic, petrogypsic or salic horizon. Most are rangeland or wildlife habitat; some are irrigated cropland.
• Calcids have a calcic or petrocalcic horizon, with calcium carbonate in the layers above. They’re in the Western States.
• Cambids show the least soil development of the order. They’re mostly in Washington State.
• Cryids are the Aridisols of cold areas, with a cryic temperature regime, at high elevations in mountain valleys and basins in Idaho.
• Durids have a duripan. The largest extent is in Nevada and Idaho.
• Gypsids have a gypsic or petrogypsic horizon and are mostly in the Southwestern States.
• Salids have a salic horizon and are mostly in Utah and Nevada. As a rule they’re unsuitable for farming unless they’re leached of salts.^[2]

The Durids’ duripan is a subsurface layer that silica has cemented; our soil horizons page covers it with the other restrictive layers.^[4]

Deserts also hold Entisols

Not every desert soil is an Aridisol. Even in Arizona, Nevada, New Mexico and Utah, where Aridisols are the leading order, they cover 34.5% to 49.3% of the soil acres, and Entisols, soils with no diagnostic horizons, take another 17.1% to 28.7%:^[5][6]

Share of each state’s soil acres that have a recorded order.

The desert soil profile and its layers

Aridisol topsoil is thin. The A horizon has a median thickness of just 3.5 inches (9 cm), against 6.3 inches (16 cm) for all US soils, and the B horizon below it starts at a median 3.1 inches (8 cm). The most common sequences are A–B (49.5 million acres), A–B–C (28.4 million acres) and A–B–R (17.1 million acres); bedrock (R) turns up in 22.8% of described profiles, at a median 18.1 inches (46 cm) where it does.^[5]

A horizon’s name records what has built up in it. A desert profile’s B horizon can carry any of these lowercase suffixes, each naming what has accumulated:^[3][7]

The diagnostic layers, in the Keys’ terms

Calcic horizon:

an illuvial horizon of secondary calcium carbonate.

Petrocalcic horizon:

an illuvial horizon where secondary calcium carbonate or other carbonates have accumulated so far that the horizon is cemented or indurated.

Gypsic horizon:

a horizon where gypsum has accumulated or been transformed to a significant extent.

Salic horizon:

a horizon of salts more soluble than gypsum in cold water.

Natric horizon:

a subsurface horizon with significantly more silicate clay than the horizons above it, where sodium’s dispersing effect has sped up the clay’s movement; its criteria include an exchangeable sodium percentage of 15 or more (or a sodium adsorption ratio of 13 or more).^[4]

What Aridisols are like

Aridisols are well drained, alkaline and low in organic matter. 90.5% of their acres are well drained, and 78.3% have an alkaline first mineral layer; moderately alkaline is the most common class, at 46.5%. The median pH, 7.9, is the highest of any order, and the median organic matter, 0.85%, is the lowest.^[5][8][9]

The first mineral layer is most often sandy loam (38.9%), loam (30.9%) and silt loam (10.2%), and where a parent material is recorded it’s mostly alluvium (61.3%), residuum (10.7%) and eolian (wind-blown) sand (9.3%). B horizons show up on 93.8% of described profiles.^[5]

Can you farm Aridisols?

Only with water brought in. Because of the dry climate they form in, the University of Idaho notes, Aridisols aren’t used for crops unless irrigation water is available.^[3]

In the survey, just 0.1% of Aridisol acres are prime farmland, against 12.5% of all US soil acres, but 8.2% would be prime if irrigated, drained or protected from flooding. 91.5% of rated acres sit in land-capability Classes VI–VIII. Across the rated acres the hazard is most often a shallow, droughty or stony root zone (subclass s, 42.0%), then erosion (subclass e, 31.3%) and climate (subclass c, 25.7%).^[5][10][11]

The prime farmland checker gives USDA’s farmland class for one address.

Where Aridisols are in the US

Nevada has the most Aridisol acres, 29.9 million, then New Mexico (28.3 million) and Arizona (28.1 million). As a share of each state’s own soil, Aridisols reach a quarter or more in five states:^[5]

Most widespread Aridisol series

The top series, Reagan (Texas), Upton (Texas) and Gunsight (Arizona), link to their official descriptions.^[5][12]

Download the Aridisols data (CSV)

Aridisols compared with other orders

Of the 11 orders with surface figures, Aridisols have the thinnest median topsoil and the most alkaline median surface.^[5][9]

Histosols show a dash: their surface is organic material (peat or muck), so a topsoil (A) or surface pH median would describe mineral soil beneath it.

Frequently asked questions

What are Aridisols?

Soils too dry for mesophytic plants, common in the world’s deserts, with subsurface horizons where clay, calcium carbonate, silica, salts or gypsum have accumulated.^[2][3]

What types of soil are found in deserts?

Aridisols lead, at 34.5% to 49.3% of the soil acres in Arizona, Nevada, New Mexico and Utah, and Entisols take 17.1% to 28.7%. Aridisols split by what has built up in them: Argids (an argillic or natric horizon), Calcids (calcic), Durids (a duripan), Gypsids (gypsic) and Salids (salic), plus the little-developed Cambids and the cold Cryids.^[2][5]

What does a desert soil profile look like?

A thin A horizon, a median 3.5 inches (9 cm) in Aridisols, over a B horizon that starts a median 3.1 inches (8 cm) down. The most common sequence is A–B, and bedrock turns up in 22.8% of described profiles.^[5]

What are the layers of desert soil called?

The B horizon takes a suffix for what has built up: Bk for calcium carbonate, By for gypsum, Bz for salts more soluble than gypsum, Bn for sodium, Bq for silica and Bt for clay. A carbonate layer cemented hard is a petrocalcic horizon.^[7][4]

Are all desert soils Aridisols?

No. Even where they lead, in Arizona, Nevada, New Mexico and Utah, Aridisols cover 34.5% to 49.3% of the soil acres; Entisols cover 17.1% to 28.7% and other orders the rest.^[5]

Can you grow crops on Aridisols?

Only with irrigation. 0.1% of Aridisol acres are prime farmland, but 8.2% would be prime if irrigated, drained or protected.^[3][5][10]

What does ‘Aridisol’ mean?

It comes from the Latin aridus, dry.^[1]