USDA Soil Taxonomy - Orders

Orders

• Alfisols — moderately weathered, form under boreal or broadleaf forests, rich in iron and aluminum
• Andisols — form in volcanic ash and defined as containing high proportions of glass and amorphous colloidal materials, including allophane, imogolite and ferrihydrite
• Aridisols — (from the Latin aridus, for “dry”) form in an arid or semiarid climate
• Entisols — do not show any "significant" soil profile development. Minimal soil horizons.
• Gelisols — soils of very cold climates which are defined as containing permafrost within two meters of the soil surface
• Histosols — consist primarily of organic materials
• Inceptisols — form quickly through alteration of parent material
• Mollisols — form in semiarid to semihumid areas, typically under a grassland cover
• Oxisols — best known for their occurrence in tropical rain forest
• Spodosols — typical soils of coniferous or boreal forests
• Ultisols — commonly known as red clay soils
• Vertisols — high content of expansive clay