Soil Series Classification

Taxonomy

• Different regions of the world, including the United States and Europe, developed soil maps as a way to gain information about the types of crops to plant in certain areas and about other land management uses. As a way to map soil types, soils had to be classified. At the top of the taxonomic scale, soils are loosely categorized according to five basic soil-typing factors. As the taxonomic scale descends, soils are categorized with greater specificity. Although the United States and other regions use slightly different classification and taxonomic categories, scientists are still able to map soils and determine the best use for an area.

Soil Characteristics

• The five basic characteristics used to determine a soil order are the type of parent material, the amount of organic material in the soil, the speed at which weather breaks down parent rock, the terrain and the age of the soil. Parent materials can be volcanic rock, clay, limestone, sandstone or even glacial debris. Parent rock can be exposed to intense sun, intense cold, wind, rain and other environmental conditions that can either slow down or speed up the parent material's degradation process. This weathering influences the character of the soil. Organic matter, in the form of decaying animal and plant material, also contributes to the soil's characteristics and pH levels. Soil at a higher elevation may weather faster than low-lying soils; elevation and exposure also play a role in soil's structure. Finally, soil ages. Old soils have been degraded while new soils are recently formed from parent material. Old soils have higher metallic content and poorer structure than new soils. All of these factors are taken into consideration when categorizing and mapping soil.

Series

• Within the United States' soil taxonomy system, there are 19,000 known soil series. A soil series is the lowest, and most specific, category of soil. The reason for the high number of soil series is because of the many differences among soils that occupy the same area. Soil at the top of a slope, for instance, can have a texture and weathering patterns that are different from those of the soil at the slope's bottom, even when the distance between them is only a few meters or yards.

Considerations

• Soil surveys are conducted regularly. Soil changes occur whenever climate conditions change, and after volcanic eruptions, earthquakes and floods. Soil also changes over time, and the change is influenced by the kinds of crops grown in the soil, by the construction taking place on the soil's surface and by whether or not the area is highly trafficked. At the higher-order levels, the soil's category is unlikely to change from year to year or decade to decade, but at the more specific, soil series level, the categorization is more fluid.