Soil Series Atlas

The 12 soil orders

U.S. Soil Taxonomy groups every soil into twelve orders. Here is the mapped area, share and number of series for each, largest first. The orders guide compares their typical profiles.

  1. MollisolsSoils with a thick, dark, organic-rich topsoilMapped area435.60 million acresShare27.3%Series7,593
  2. AlfisolsModerately leached soils with a clay-enriched subsoilMapped area276.47 million acresShare17.3%Series4,001
  3. EntisolsYoung soils with little or no horizon developmentMapped area196.15 million acresShare12.3%Series3,003
  4. UltisolsStrongly weathered, leached soils with a clay-enriched subsoilMapped area189.13 million acresShare11.8%Series1,278
  5. InceptisolsYoung soils with weakly developed horizonsMapped area182.19 million acresShare11.4%Series3,264
  6. AridisolsSoils of dry climatesMapped area154.28 million acresShare9.7%Series2,777
  7. SpodosolsAcid soils with a subsoil of humus and iron or aluminumMapped area59.20 million acresShare3.7%Series717
  8. VertisolsClay soils that shrink and crack when dryMapped area42.57 million acresShare2.7%Series481
  9. HistosolsOrganic soils: peat and muckMapped area30.60 million acresShare1.9%Series358
  10. AndisolsSoils formed in volcanic ash and similar materialMapped area20.47 million acresShare1.3%Series1,093
  11. GelisolsSoils with permafrostMapped area8.26 million acresShare0.5%Series123
  12. OxisolsVery highly weathered soils of the tropicsMapped area490,795 acresShare<0.1%Series61