Introduction - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 9

Table 1.7 Soil-forming processes in relation to diagnostic horizons, properties, and materials by
order in Soil Taxonomy

Diagnostic horizon,
properties, material

Representative
horizon sequence Soil order Soil-forming processes

Alfisol Argillic horizon (high base

status)

Argilluviation biological
enrichment of base
cations

A/E/Bt/C

Andisol Melanic epipedon andic

properties

Andisolization A/Bw/C

Andiscol Natric horizon Solonization, solodization A/Eg/Btm/Bk/

By/C

Calci, petrocalcic horizon Calcification A/Bkm/Ck

Gypsic, petrogypsic horizon Calcification A/Cym/Cy

Argillic horizon Argilluviation A/E/Bt/Ck

duripan Silicification Az/Cz

Satic horizon [aridic
soil-moisture regime]

Salinization Az/Cz

Histosol Histic materials Paludization Oi/Oa/Oe

Mollisol Mollic epipedon (high base

status)

Melanization biological
enrichment of base
cations

A/Bt/C

Spodosol Spodic materials placic

horizon albic horizon

Podzolization base cation
leaching

Oa/E/Bh/Bs/C

Ultisol Argillic (low base status) Argilluviation base cation

leaching

E/Bt/C

Vetisol (Slickensides, cracks) Vertization A/Css

Getisol Gellic materials Cryoturbation O/Bgil/Cf

Inceptisol Cambic (plus others) Weak soil formation A/Bw/C

Entisol (None) Very weak soil formation A/C

All orders
(except
Aridisols)

Reductimorphic features
[aquic soil-moisture
regime]

Gleization A/Bg/Cg

(None) Anthropic, plaggen horizons Anthrosolization Ap/Bw/C

Source: Bockheim and Gennadiyev ( 2000 )

calcic/petrocalcic soils from gypsic/petrogypsic soils. Perhaps calcification should
refer to calcic/petrocalcic horizons and gypsification be introduced for gypsic/
petrogypsic horizons.

Acknowledgments Alfred Hartemink kindly prepared Tables 1.4 and 1.5 .

References

Bockheim JG, Gennadiyev AN (2000) The role of soil-forming processes in the definition of taxa
in Soil Taxonomy and the World Soil Reference Base. Geoderma 95:53-72
IUSS Working Group WRB (2007) World reference base for soil resources 2006, first update
2007. World Soil Resources Report number 103. FAO, Rome