Ultisols are old, strongly weathered soils that have experienced extensive leaching but are generally less weathered than Oxisols. They are common in humid temperate and subtropical regions, where rainfall has removed much of the calcium, magnesium, potassium, and sodium from the soil. Ultisols are typically acidic, contain a clay-rich subsoil, and have moderate to low natural fertility.
These soils usually require lime to raise pH and fertilizers to replace nutrients removed by crops. Compared with Oxisols, Ultisols retain more weatherable minerals and generally have a higher cation exchange capacity (CEC), making them somewhat easier to improve for agriculture. Large areas of the southeastern United States are dominated by Ultisols.
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