Alabama Landscapes
Soils
Soils of Alabama
Six soil orders occur in Alabama (Figure S1). In order of
decreasing abundance they are Ultisols, Inceptisols, Vertisols, Entisols,
Alfisols and Mollisols. The Inceptisols and Entisols are immature
soils, the rest are mature.
Ultisols are the most common and are characterized by well-developed horizons, a clay-rich B-horizon, and typically red or yellow colored due to the presence of iron. Often leached of nutrients, these soils require fertilizers for optimum plant growth. These are the soils of most forested areas in Alabama.
Figure S1. Major soil orders in Alabama. Black circles N to S: Huntsville, Birmingham, Montgomery, Mobile. Broken black line: approximate physiographic section boundaries. (Simplified from http://www.nrcs.usda.gov/technical/land/lgif/m4025l.gif)
Vertisols, which only occur in the Black Prairie district of the Coastal Plain, are clay-rich, maybe acid or alkaline depending on the parent material, and often have a dark-colored A horizon (hence the name "black belt"). Much of the clay shrinks and swells excessively as it dries or becomes moist. The soils are mainly used for timber, pasture and soybeans.
Inceptisols may have horizons but commonly have lost bases (sodium, calcium, potassium and magnesium), iron and aluminum through leaching and still contain some of the original minerals. Typically they do not contain a clay-rich horizon. In Alabama they occur in the flood plains of the major rivers and the highest regions of the Piedmont Upland.
Entisols have little or no horizon development. They tend to be sandy or very thin.
Mollisols, which are very uncommon in Alabama, have a dark colored surface horizon due to high organic content and are rich in bases.
Alfisols are moderately leached and have a clay-rich horizon.
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