U.S. Soil Taxonomy

soil order defining characteristics name derivation percent of Earth's land area*

Alfisol moderate leaching; B horizon enriched in clay; humid forest vegetation Pedalfer (C.F. Marbut) 9.77

Andisol volcanic-ash parent material an do (Japanese: "dark soil") 0.73

Aridisol hot, dry climate; weak B horizon aridus (Latin: "dry") 18.53

Entisol little or no horizonation or swelling clay recent 10.61

Gelisol permafrost within 2 metres (approximately

6 feet) of the land surface gelid (Greek: "very cold") —

Histosol organic parent material histos (Greek: "tissue") 1.84

Inceptisol little or no B horizon development inceptum (Latin: "beginning") 21.80

Mollisol thick, soft, black A horizon mollis (Latin: "soft") 5.99

Oxisol hot, humid climate; B horizon enriched in iron and aluminum oxides and kaolinite oxide (French) 7.00

Spodosol cool, humid climate; B horizon enriched in iron and aluminum oxides and organic matter; sandy parent material spodos (Greek: "wood ashes") 3.45

Ultisol warm, humid climate; B horizon enriched in clay; extensive leaching ultimus (Latin: "last") 8.12

Vertisol little or no horizonation; high content of swelling clay vertere (Latin: "to turn") 2.23

*Rock, sand, and bodies of water account for 5.25% of the continental land area in the world between 75° N and 75° S latitude. Gelisols cover about 18 million square km (7 million square miles) largely outside these latitudes, mostly in Russia and Canada.