UltisolArticle Free Pass Ultisol, one of the 12 soil orders in
the U.S. Soil Taxonomy. Ultisols are reddish, clay-rich, acidic
soils that support a mixed forest vegetation prior to
cultivation. They are naturally suitable for forestry, can be
made agriculturally productive with the application of lime and
fertilizers, and are stable materials for construction projects.
Occupying just over 8 percent of the nonpolar continental land
area on Earth, they are found in humid temperate or tropical
regions, including the southeastern United States and China, and
in the humid tropics in South America and Africa. Ultisols are
found in geologically old landscape settings. They are
characterized by a humus-rich surface horizon (the uppermost
layer), by a layer of clay that has migrated below the surface
horizon, and by a nutrient content low in available calcium,
magnesium, potassium, and sodium. The well-developed,
extensively leached soil horizons are enriched in kaolin-group
clay minerals and in metal oxides and appea