By Dave Lindbo, North Carolina State University
To identify, understand, and manage soils, soil scientists have developed a soil classification or taxonomy system. Like the classification systems for plants and animals, the soil classification system contains several levels of detail, from the most general to the most specific. The most general level of classification in the United States system is the soil order, of which there are 12.
Each order is based on one or two dominant physical, chemical, or biological properties that differentiate it clearly from the other orders. Perhaps the easiest way to understand why certain properties were chosen over others is to consider how the soil (i.e., land) will be used. That is, the property that will most affect land use is given precedence over one that has a relatively small impact.
The 12 soil orders all end in "sol" which is derived from the Latin word "solum" meaning soil or ground. Most of the orders also have roots that tell you something about that particular soil. For example, "molisol" is from the Latin "mollis" meaning soft.
The 12 soil orders are presented below in the sequence in which they “key out” in the U.S. Department of Agriculture’s dichotomous Soil Taxonomy system.
- Gelisols: Frozen
- Histosols: Organic, wet
- Spodosols: Sandy, acidic
- Andisols: Volcanic ash
- Oxisols: Very weathered
- Vertisols: Shrink and swell
- Aridisols: Very dry
- Ultisols: Weathered
- Mollisols: Deep, fertile
- Alfisols: Moderately weathered
- Inceptisols: Slightly developed (young)
- Entisols: Newly formed
Each state and territory in the United States has a representative soil, like a state flower or bird. To find your state/territory soil, go to the NRCS State Soils page.