Soil Taxonomy
•	USA system of soil classification
–	12 major soil orders
•	Then: sub-order, great group, sub-group, family, series
•	Classify soil by common properties
–	Orders based on field properties that are backed by lab data
•	To classify soils at order/sub-order levels, need to identify diagnostic horizons, soil temperature, and soil moisture regimes

Taxonomy 
•	Diagnostic horizons
–	So named because they contain essential characteristics to identify soil
•	Surface (epipedon)
•	Subsurface 
–	Defining characteristics?  Structure, thickness, clay content, etc.
•	Soil moisture and temperature regimes
–	Moisture;based on estimates of depth to which known amount of water will wet in certain amount of time
–	Temperature; mean annual temp at 50cm depth

Taxonomy 
•	From drier to wetter:
–	Aridic; soils in arid climates (soil moist < 90 consecutive days)
–	Ustic; semi-arid climates (soil dry for 90 or more cumulative days)
–	Xeric; soil of Mediterranean climates (wet winters, dry summers)
–	Udic; humid climates, precip and storage > evapotranspiration
–	Perudic; all months water moves through soil, P > PE
–	Aquic; saturated soils

Taxonomy 
•	Temperature 
–	Based on mean annual temp at 50cm depth
•	MAT of soil is approx that of MAT + 1 of air
–	Pergelic; < 0o C 
–	Cryic; 0-8o C (and summer temp restrictions)
–	Frigid; 0-8o C (warmer in summer than Cryic
–	Mesic; 8-15o C
–	Thermic; 15-22o C
–	Hyperthermic; > 22o C

•	Entisol – weakly developed; newly deposited material; occur anywhere (12.3%)
•	Inceptisols – slightly more developed than Entisols; occur anywhere (9.7%)
•	Andisols – volcanic ash (1.7%)
•	Aridisols – dry, deserts; Arizona (8.3%)
•	Vertisols – lots of clay; south-central US (2.0%)
•	Mollisol – fertile, farming; Iowa (21.5%; most extensive soil order of USA)

Cont.
•	Alfisols – more organic matter; PA (13.9%)
•	Spodosols – acidic; conifer forests, New England (3.5%)
•	Ultisols – weathered, old; Louisiana (9.2%)
•	Oxisols – really old, low fertility; Hawaii (0.02%)
•	Histosols – bogs, swamps; north Canada, Arkansas (1.6%)
•	Gelisols – tundra (8.7%)

Link for great website with maps, etc. 

Soil Orders | University of Idaho