5.14 - Vertisols

Vertisols are soils with a high content of clay minerals that shrink and swell as they change water content. The clay minerals adsorb water and increase in volume (swell) when wet and then shrink as they dry, forming large, deep cracks. Surface materials fall into these cracks and are incorporated into the lower horizons when the soil becomes wet again. As this process is repeated, the soil experiences a mixing of surface materials into the subsoil that promotes a more uniform soil profile.

Vertisols are usually very dark in color, with widely variable organic matter content (1 – 6%). They typically form in Ca and Mg rich materials such as limestone, basalt, or in areas of topographic depressions that collect these elements leached from uplands. Vertisols are most commonly formed in warm, subhumid or semi-arid climates, where the natural vegetation is predominantly grass, savanna, open forest, or desert shrub. Large areas of Vertisols are found in Northeastern Africa, India, and Australia , with smaller areas scattered worldwide.

Key Characteristics:  Vertisols

• Soils with high content of shrinking/swelling clay minerals.
• Self-mixing due to shrink-swell of clay minerals
• Dark colored with variable organic matter content (1 – 6%)
• Typically form in limestone or basalt, or in topographic depressions.
• Most commonly formed in warm, subhumid or semi-arid climates.
• Large areas are found in Northeastern Africa, India, and Australia, with smaller areas scattered worldwide.
• Extent of world ice-free land area: 2%