Primary diagnostic horizons of soil

U.S. Soil Taxonomy defining features FAO soil group system

Epipedons

histic thick organic layer histic

. mollic thick, dark, neutral to alkaline mollic

ochric pale or thin ochric

. umbric thick, dark, acidic umbric

Subsurface horizons

argillic clay mineral deposition argic

. cambic in situ mineral weathering only cambic

oxic highly weathered; aluminum oxide,

iron oxide, and kaolin clay deposition ferralic

. spodic aluminum oxide, iron oxide,

and humus deposition spodic