Introduction - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 2

Table 1.1 Abbreviated descriptions of diagnostic horizons at various levels in Soil Taxonomy
Horizon Brief description

Epipedons
Anthropic Human disturbance, moderately thick, dark-colored, abundant organic C and
phosphate, low n-value
Folistic Thick, unsaturated organic materials
Histic Thick organic soil materials
Melanic Thick, andic properties, dark-colored, very high organic C
Mollic Thick, dark-colored, highly base saturated, enriched in organic C
Ochric Pale, low organic matter, or thin
Plaggen Human disturbance, thick, dark-colored, abundant organic C, raised surface,
artifacts, or spade marks present
Umbric Same as mollic but less base saturation
Subsurface horizons
Agric Moderately thick, compacted horizon below plow sole

Albic Subsurface horizon 1 cm thick, light-colored, eluvial, leached of clay, Fe oxides

Argillic Accumulation of illuvial, high-activity silicate clays, presence of clay bridges or

coatings

Calcic Moderately thick, abundant CaCO 3 , lack of cementation

Cambic Minimal but visible subsurface development, does not meet requirements of other

horizons

Duripan Subsurface horizon cemented by Si

Fragipan Subsurface horizon that is brittle, reversibly cemented, slakes in water, breaks with

characteristic snap, restricts rooting

Glossic Subsurface horizon reflecting degradation of an argillic horizon with zones of E and

Bt materials

Gypsic Subsurface horizon enriched but not cemented by gypsum

Kandic Accumulation of low-activity clays, evidence of illuviation not necessary

Natric Accelerated clay illuviation due to dispersive properties of Na

Ortstein 25 mm thick with cemented spodic materials

Oxic Enriched in Fe, Al oxides and low-activity clays
Petrocalcic Moderately thick, abundant CaCO 3 , cemented
Petrogypsic Subsurface horizon cemented by pedogenic gypsum
Placic

Subsurface layer

>

Subsurface layer 1-25 mm thick with cemented spodic materials, barrier to roots

Salic Subsurface horizon enriched in salts more soluble than gypsum

Sombric Subsurface horizon enriched in organic C, dark-colored, strongly leached

Spodic Illuvial accumulation of organic matter and Al (with or without Fe), dark-colored,

low base saturation (acidic)

and umbric (Gelisols, Inceptisols, Ultisols) horizons. Ortstein (Spodosols) is the
only diagnostic horizon used strictly at the family level.
Table 1.4 shows use of diagnostic epipedons among the 12 orders in ST. For
example, the histic epipedon is used in 12 orders and categories in ST, followed
by the mollic (9), umbric (8), folistic (6), and others. Diagnostic epipedons are
used 11 times in the Inceptisols, followed by the Gelisols (7), Andisols (6), and
others. Diagnostic epipedons are used 2, 4, 14, and 28 times at the order, suborder,
great-group, and subgroup levels, respectively.