Region 2: The Interior Highlands

The most common soils in the Interior Highlands are Ultisols, especially in forested, higher-elevation areas. Ultisols are rich in clay, and red in color due to their high iron and aluminum content (Figure 8.18). They are low in fertility, with most nutrients concentrated in the uppermost horizon. Ultisols tend to be acidic and are therefore poorly suited to agriculture, although they can be improved using fertilizer and lime.

Moisture-rich Alfisols of the suborder Udalfs are more common in the lower-elevation portions of this region, especially Missouri. They are fertile and can support a reasonable amount of plant growth.

Other soil types that appear in the Interior Highlands are uncommon. Vertisols occur only in parts of the lower valley of the Arkansas River, and Entisols appear along only a few streams in southern Missouri. Likewise, Inceptisols are rare, occurring only in the lower-elevation parts of Missouri. In stark contrast to the Central Lowland, Mollisols are also extremely rare in this region, and are only found in isolated valleys in Missouri.

Figure 8.18: Vivid red Ultisols are exposed at the surface near a roadside in western Arkansas.