Illinois Suite of Maps

Contents 

• Soil Order
• Prime Farmland
• Hydric Soils
• Floodplain Soils
• Drainage Class
• Potential Tile Drainage Extent
• Potential Native Vegetation
• Productivity Index
• Ecotypes

Soil Order

• Mollisols are soils formed under prairie vegetation, characterized by dark, surface horizons
• Alfisols are soils formed under forest vegetation
• Entisols are young soils, typically alluvial or disturbed, that show limited signs of soil development
• Inceptisols show more signs of soil development than Entisols
• Histosols are organic soils

Prime Farmland

 Prime farmland is land that has the best combination of physical and chemical characteristics for producing food, feed, forage, fiber and oilseed crops.

Farmland of statewide importance is land other than prime farmland or unique farmland but that is also highly productive.

Hydric Soils

 Hydric soils are soils that are saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions in the upper part. They make up part of the criteria for the identification of wetlands.

Floodplain Soils

Soils that are classified as 'fluvic' at the suborder or subgroup level in Soil Taxonomy, or have a flooding phase in the soil map unit name. 

Drainage Class

Potential Tile Drainage Extent

This map is an interpretation of the soil groups in the Illinois Drainage Guide. It was assumed that very poorly and poorly drained soils that are rapidly permeable to moderately slowly permeable would be very likely to be tile drained. Soils that are somewhat poorly drained, that are rapidly permeable to moderately slowly permeable are likely to be tile drained. Soils that are slowly or very slowly permeable are unlikely to be tile drained. This has not been verified and is to only be used as a general guide. 

Potential Native Vegetation

Taxonomic classification, based on soil taxonomy was used to predict native vegetation. Native in this case would be considered the period of time after transition from a tundra biome ~12,000BP, after the last glacial advance, to forest and grassland biomes. General interpretation rules:

• - Alfisol order - Woodland
• - Mollic subgroups of the Alfisol order - Savanna
• - Mollisol order - Prairie
• - Entisol order - Woodland
• - Inceptisol order - Woodland
• - Histosol order - Marshland

Alluvial soils were interpreted as being Woodland independent of soil classification. This is a generalization, but given the dynamic nature of alluvial systems, there wasn't an adequate way to differentiate the variable vegetation types that may have been present on these types of soils prior to widespread settlement.

Productivity Index

Map is based on the Soil Productivity Index for optimal levels of management as described in Bulletin 811, developed by the University of Illinois. Areas that are white were not rated and include water bodies, disturbed soils or soils that commonly have flooding of long duration. Local officials are responsible for the assignment of a Productivity Index for each soil map unit within a county. This map was developed by NRCS for descriptive purposes only. 

Ecotypes