soil order

The reddish color an ultisol soil is due to 
chemical weathering of iron and aluminum.

Photo credit: NRCS
Used with permission

A Soil Order is the highest level of classification in the USDA Comprehensive Soil Classification System. Soil orders are distinguished on the basis of diagnostic horizons.  (See also andisol, alfisol, spodosol, aridisol, mollisol, ultisol, oxisol, inceptisol, entisol, histosol)

Suggested Web Sites:

• National Soil Survey Center -USDA NRCS