Click on any point in Pennsylvania to see the "soil order" at that location outlined and identified.
The area outlined in red shows a "suborder" (see definition below), but only its "order" is identified.
A "soil order" is the most general level for categorizing types of soil. There are twelve types of soil at this level in the entire world, four of which occur in Pennsylvania. Each soil order is then subdivided into more detailed categories at multiple levels. The next levels below the soil order are: the "suborders," then come the "great groups," then the "subgroups," then the "families" and the "series." Soil scientists further differentiate soils within a series based on the land's slope. The most detailed designation is referred to as a "mapping unit."
The NRCS link in the Credits section below will take you to more detailed descriptions.
|Alfisols are the most productive soils, formed over carbonate rocks at lower elevations in the Piedmont and Ridge and Valley physiographic provinces, and over limestone and other bedrock in some areas of the Central Lowland and Appalachian Plateau physiographic provinces. Their greater proportions of clay-sized particles improves water retention, and their greater alkalinity is a boost to many crops.
|Ultisols are less productive productive than alfisols, unless fertility is added, and occur over non-carbonate sedimentary rocks as well as over igneous rocks. They occur in the upland areas of the Piedmont physiographic province, in some parts of the Ridge and Valley physiographic province, covering the nearly entire New England physiographic province, and in much of the Appalachian Plateau physiographic province. They are similar in structure to the alfisols, but beneficial minerals have been more thoroughly dissolved and removed from the topsoil.
|Entisols are very poorly formed soils because they are developing over recent deposits of sediment in river valley floodplains. Since floods can occur at any time, these soils do not get a chance to mature and develop horizons. Adding fertility can make them productive, but must be repeated for every crop.
|Inceptisols are similar to entisols in that they are forming over material that does not represent native bedrock or over bedrock that does not easily break down. Even where the soils are deep, they develop little fertility in their topsoil.
|Areas Lacking Soil
|Areas identified this way may have a soil layer but it does not contain characteristics that allow it to be classified as any of the established soil orders. This includes river and lake beds, but also urban areas in which the earth has been extensively excavated or otherwise disturbed.
|US Census website.
|Miller, E. Willard 1995. "Soil Resources." Chapter 5 in Miller, E. Willard (ed.) A Geography of Pennsylvania. pp. 67-73.
|"The Twelve Orders of Soil Taxonomy:" USDA Natural Resources Conservation Service.
|PA map source:
|PA Spatial Data Access.
|Map and webpage created by:
|Dr. Geiger, 2016, 2020, 2023.