SURGO Soil Map Units SCTDD

Soil map units are the basic geographic unit of the Soil Survey Geographic Database (SSURGO). The SSURGO dataset is a compilation of soils information collected over the last century by the Natural Resources Conservation Service (NRCS). Map units delineate the extent of different soils. Data for each map unit contains descriptions of the soil’s components, productivity, unique properties, and suitability interpretations. Each soil type has a unique combination of physical, chemical, nutrient and moisture properties. Soil type has ramifications for engineering and construction activities, natural hazards such as landslides, agricultural productivity, the distribution of native plant and animal life and hydrologic and other physical processes. Soil types in the context of climate and terrain can be used as a general indicator of engineering constraints, agriculture suitability, biological productivity and the natural distribution of plants and animals. Data from the gSSURGO databasewas used to create this layer. To download ready-to-use project packages of useful soil data derived from the SSURGO dataset, please visit the USA SSURGO Downloader app. Dataset Summary Phenomenon Mapped: Soils of the SCTDD region Geographic Extent: SCTDD counties Coordinate System: NAD 1983 Tennesee State Plane Source: USDA Natural Resources Conservation Service, https://landscape11.arcgis.com/arcgis/rest/services/USA_Soils_Map_Units/featureserver Update Frequency: Annual Publication Date: December 2025 Data Dictionary Attributes Key fields from nine commonly used SSURGO tables were compiled to create the 173 attribute fields in this layer. Some fields were joined directly to the SSURGO Map Unit polygon feature class while others required summarization and other processing to create a 1:1 relationship between the attributes and polygons prior to joining the tables. Attributes of this layer are listed below in their order of occurrence in the attribute table and are organized by the SSURGO table they originated from and the processing methods used on them. Map Unit Polygon Feature Class Attribute Table The fields in this table are from the attribute table of the Map Unit polygon feature class which provides the geographic extent of the map units. Area Symbol Spatial Version Map Unit Symbol Map Unit Table The fields in this table have a 1:1 relationship with the map unit polygons and were joined to the table using the Map Unit Key field. Map Unit Name Map Unit Kind Farmland Class Interpretive Focus Intensity of Mapping Iowa Corn Suitability Rating Legend Table This table has 1:1 relationship with the Map Unit table and was joined using the Legend Key field. Project Scale Survey Area Catalog Table The fields in this table have a 1:1 relationship with the polygons and were joined to the Map Unit table using the Survey Area Catalog Key and Legend Key fields. Survey Area Version Tabular Version Map Unit Aggregated Attribute Table The fields in this table have a 1:1 relationship with the map unit polygons and were joined to the Map Unit attribute table using the Map Unit Key field. Slope Gradient - Dominant Component Slope Gradient - Weighted Average Bedrock Depth - Minimum Water Table Depth - Annual Minimum Water Table Depth - April to June Minimum Flooding Frequency - Dominant Condition Flooding Frequency - Maximum Ponding Frequency - Presence Available Water Storage 0-25 cm - Weighted Average Available Water Storage 0-50 cm - Weighted Average Available Water Storage 0-100 cm - Weighted Average Available Water Storage 0-150 cm - Weighted Average Drainage Class - Dominant Condition Drainage Class - Wettest Hydrologic Group - Dominant Condition Irrigated Capability Class - Dominant Condition Irrigated Capability Class - Proportion of Mapunit with Dominant Condition Non-Irrigated Capability Class - Dominant Condition Non-Irrigated Capability Class - Proportion of Mapunit with Dominant Condition Rating for Buildings without Basements - Dominant Condition Rating for Buildings with Basements - Dominant Condition Rating for Buildings with Basements - Least Limiting Rating for Buildings with Basements - Most Limiting Rating for Septic Tank Absorption Fields - Dominant Condition Rating for Septic Tank Absorption Fields - Least Limiting Rating for Septic Tank Absorption Fields - Most Limiting Rating for Sewage Lagoons - Dominant Condition Rating for Sewage Lagoons - Dominant Component Rating for Roads and Streets - Dominant Condition Rating for Sand Source - Dominant Condition Rating for Sand Source - Most Probable Rating for Paths and Trails - Dominant Condition Rating for Paths and Trails - Weighted Average Erosion Hazard of Forest Roads and Trails - Dominant Component Hydric Classification - Presence Rating for Manure and Food Processing Waste - Weighted Average Component Table – Dominant Component Map units have one or more components. To create a 1:1 join component data must be summarized by map unit. For these fields a custom script was used to select the component with the highest value for the Component Percentage Representative Value field (comppct_r). Ties were broken with the Slope Representative Value field (slope_r). Components with lower average slope were selected as dominant. If both soil order and slope were tied, the first value in the table was selected. Component Percentage - Low Value Component Percentage - Representative Value Component Percentage - High Value Component Name Component Kind Other Criteria Used to Identify Components Criteria Used to Identify Components at the Local Level Runoff Class Soil loss tolerance factor Wind Erodibility Index Wind Erodibility Group Erosion Class Earth Cover 1 Earth Cover 2 Hydric Condition Hydric Rating Aspect Range - Counter Clockwise Limit Aspect - Representative Value Aspect Range - Clockwise Limit Geomorphic Description Non-Irrigated Capability Subclass Non-Irrigated Unit Capability Class Irrigated Capability Subclass Irrigated Unit Capability Class Conservation Tree Shrub Group Soil Slip Potential Susceptibility to Frost Heaving Concrete Corrosion Steel Corrosion Taxonomic Class Taxonomic Order Taxonomic Suborder Great Group Subgroup Particle Size Particle Size Mod Cation Exchange Activity Class Carbonate Reaction Temperature Class Moist Subclass Soil Temperature Regime Edition of Keys to Soil Taxonomy Used to Classify Soil California Storie Index Component Key Component Table – Weighted Average Map units may have one or more soil components. To create a 1:1 join, data from the Component table must be summarized by map unit. For these fields a custom script was used to calculate an average value for each map unit weighted by the Component Percentage Representative Value field (comppct_r). Slope Gradient - Low Value Slope Gradient - Representative Value Slope Gradient - High Value Slope Length USLE - Low Value Slope Length USLE - Representative Value Slope Length USLE - High Value Elevation - Low Value Elevation - Representative Value Elevation - High Value Albedo - Low Value Albedo - Representative Value Albedo - High Value Mean Annual Air Temperature - Low Value Mean Annual Air Temperature - Representative Value Mean Annual Air Temperature - High Value Mean Annual Precipitation - Low Value Mean Annual Precipitation - Representative Value Mean Annual Precipitation - High Value Relative Effective Annual Precipitation - Low Value Relative Effective Annual Precipitation - Representative Value Relative Effective Annual Precipitation - High Value Days between Last and First Frost - Low Value Days between Last and First Frost - Representative Value Days between Last and First Frost - High Value Range Forage Annual Potential Production - Low Value Range Forage Annual Potential Production - Representative Value Range Forage Annual Potential Production - High Value Initial Subsidence - Low Value Initial Subsidence - Representative Value Initial Subsidence - High Value Total Subsidence - Low Value Total Subsidence - Representative Value Total Subsidence - High Value Crop Productivity Index Esri Symbology This field was created to provide symbology based on the Taxonomic Order field (taxorder). Because some mapunits have a null value for soil order, a custom script was used to populate this field using the Component Name (compname) and Mapunit Name (muname) fields. This field was created using the dominant soil order of each mapunit. Horizon Table Each map unit polygon has one or more components and each component has one or more layers known as horizons. To incorporate this field from the Horizon table into the attributes for this layer, a custom script was used to first calculate the mean value weighted by thickness of the horizon for each component and then a mean value of components weighted by the Component Percentage Representative Value field for each map unit. K-Factor Rock Free Esri Soil Order These fields were calculated from the Component table using a model that included the Pivot Table Tool, the Summarize Tool and a custom script. The first 11 fields provide the sum of Component Percentage Representative Value for each soil order for each map unit. The Soil Order Dominant Condition field was calculated by selecting the highest value in the preceding 11 soil order fields. In the case of tied values the component with the lowest average slope value (slope_r) was selected. If both soil order and slope were tied the first value in the table was selected. Percent Alfisols Percent Andisols Percent Aridisols Percent Entisols Percent Gelisols Percent Histosols Percent Inceptisols Percent Mollisols Percent Spodosols Percent Ultisols Percent Vertisols Soil Order - Dominant Condition Esri Popup String This field contains a text string calculated by Esri that is used to create a basic pop-up using some of the more popular SSURGO attributes. Map Unit Key The Mapunit key field is found throughout SSURGO and provides a primary link between the geographic and tabular data. Map Unit Crop Yield Table The Map Unit Crop Yield Table has a 1:1 relationship with the map unit polygons. Selected attributes from this table were extracted and joined to the table using the Map Unit Key field. All values are in Bushels/Acre except for cotton which is in pounds/acre. Corn – nonirrigated Corn – irrigated Cotton – nonirrigated Cotton – irrigated Soybeans – nonirrigated Soybeans – irrigated Wheat – nonirrigated Wheat – irrigated Value Added Look Up Table(gSSURGO) The fields in this table have a 1:1 relationship with the map unit polygons and were joined to the table using the Map Unit Key field. The first 5 fields from this table provide access to the National Commodity Crop Productivity Index (NCCPI) Version 3 - weighted average index for major components. NCCPI is a model that uses inherent soil properties, landscape features and climatic characteristics to assign ratings for dry-land commodity crops. This index ranks soil productivity from 0.1-1.0 with more productive soils having higher values. For more information on how these values are calculated see theUser Guide for the National Commodity Crop Productivity Index. NCCPIv3 – Corn NCCPIv3 – Soy NCCPIv3 – Cotton NCCPIv3 – Small Grains NCCPIv3 – All Other fields from theValue Added Look Up Table: Root Zone Depth – earthy major components - cm Root Zone Available Water Storage – earthy major components - mm Droughty Soil Landscapes – earthy major components - this attribute uses a value of 1 for drought vulnerable soils and 0 for non‐ droughty soils. Potential Wetland Soil Landscapes - the proportion of the mapunit that is potentially a wetland. Values of 999 indicate a map unit that is primarily water. Horizon Table Saturated Hydraulic Conductivity (KSAT) - This field was calculated by selecting the least transmissive horizon of the dominant component for each mapunit. The values are in units of Micrometers per second (μm/s).