Descriptive Name (units) - definition - data type

• State - The name of the State - character
  
• County - The name of the County - character
  
• Soil survey area name - The name given to the specified geographic area (e.g., soil survey area) - character
  
• Soil survey ID - A symbol that uniquely identifies a single occurrence of a particular type of area (e.g Lancaster Co., Nebraska is NE109) - character
  
• Map Unit Symbol - The symbol used uniquely identify the soil map unit in the soil survey - character
  
• Component name - The correlated name of the map unit - character
  
• Component percent (%) - The percentage of the component of the map unit - integer
  
• Soil Order - The soil order of the soil component name - character
  
• Local Phase - A phase criterion used at a local level to help identify soil components - character
  
• Texture of the Soil Surface - An expression, based on the USDA system of particle sizes, for the relative proportions of various size groups - character
  
• Soil Loss Tolerance (T factor) (Tons/acre/year) - The maximum amount of erosion at which the quality of a soil as a medium for plant growth can be maintained - integer
  
• Albedo of the bare dry surface soil - The estimated ratio of the incident shortwave (solar) radiation that is reflected by the air dry, less than 2 mm fraction of the soil (unitless) - float
  
• Surface Slope (%) - The difference in elevation between two points - float
  
• Surface Fragment Cover (m3/m3) - The fraction of the surface area covered by rock greater than 2.0 mm - float.
  
• Depth to Bedrock (cm) - The observed depth to the top of the bedrock layer - float.
  
• Depth to Restrictive Layer (cm) - The distance from the soil surface to the upper boundary of a restrictive layer - float.
  
• Depth to Top of Horizon (cm) - The distance from top of the soil to the top of soil horizon - integer
  
• Depth to Bottom of Horizon (cm) - The distance from top of the soil to the base of soil horizon - integer
  
• Clay (%) - Mineral particles less than 0.002 mm in equivalent diameter as a weight percentage of the total soil - float
  
• Sand (%) - Mineral particles 0.05 to 2.0 mm in equivalent diameter as a weight percentage of the total soil - float
  
• Coarse Sand (%) - Mineral particles 0.5 to 1.0 mm in equivalent diameter as a weight percentage of the total soil - float
  
• Medium Sand (%) - Mineral particles 0.25 to 0.5 mm in equivalent diameter as a weight percentage of the total soil - float
  
• Fine Sand (%) - Mineral particles 0.10 to 0.25 mm in equivalent diameter as a weight percentage of the total soil - float
  
• Very Fine Sand (%) - Mineral particles 0.05 to 0.10 mm in equivalent diameter as a weight percentage of the total soil - float
  
• Rock fragments by volume (%) - The volume of the horizon occupied by 2 mm or larger fraction - integer
  
• Bulk Density 1/3 Bar (Mg/m³) - The oven dried weight of the less than 2.0 mm soil material per unit volume at a tension of 1/3 bar - float
  
• Bulk Density Oven Dry (Mg/m³) - The oven dried weight of the less than 2.0 mm soil material per unit volume - float
  
• Water 1/3 Bar (%) - The amount of soil water retained at a tension pf 1/3 bar (33 kPa), expressed as a percentage of the less than 2 mm, oven-dry soil weight - float
  
• Water 15 Bar (%) - The amount of soil water retained at a tension pf 15 bar (1500 kPa), expressed as a percentage of the less than 2 mm, oven-dry soil weight - float
  
• Saturated Hydraulic Conductivity (μm/s) - The amount of water that would move vertically through a unit area of saturated soil in unit time under unit hydraulic gradient - float
  
• Cation Exchange Capacity (meq/100 g) - The amount of exchangeable cations that a soil can adsorb either at pH 7.0 or the sum of NH4OAc extractable bases plus KCl extractable aluminum is used - float. If the soil has a pH < 5.5, the column is blank, otherwise the effective cation exchange capacity will be listed.
  
• Organic matter (%) - The amount by weight of decomposed plant and animal residue expressed as a weight percent of the soil material - float
  
• Calcium carbonate equivalent (%) - The quantity of Carbonate (CO3) in the soil expressed as CaCO3 as a weight percentage of the < 2 mm soil - integer
  
• Soil Reaction - pH (unitless) - A numerical expression of the relative acidity or alkalinity of a soil. The pH will be listed as determined by the 1:1 soil to water method or as determined by the 0.01M calcium chloride method. - float.
  
• Linear extensibility percent (%) - The linear expression of the volume difference of the natural soil fabric at 1/3 or 1/10 bar water content and oven dryness. The volume change is reported as a percent change for the whole soil. - float
  

Downloading Soil Data

This section describes how to download soil data from the NRCS Soil Data Mart and how to extract it for use within WEPS. A Microsoft Access database is available for importing the data in the export file. You must have Microsoft Access 97 or later installed on your PC.

Soil data for NRCS and most other users in the US, is currently available for download from the NRCS Soil Data Mart at: http://soildatamart.nrcs.usda.gov/ . Soil survey data that is exported from the Soil Data Mart is in what is referred to as "SSURGO" (Soil Survey Geographic) format. To obtain soil data for a Soil Survey Area of interest, go to the Soil Data Mart and click 全elect State' at the top of the Soil Data Mart screen. Select the desired state then click 全elect Survey Area' or 全elect County'. Select the soil survey area, then click 船ownload Data'. On the download screen select 禅abular Data Only', select the version of Microsoft Access on your computer, and enter your e-mail address, then click 全ubmit Request'. You will see a message stating "Your request has been logged. At a later time you will receive an e-mail with a link to download the export file. The format of an export file name is: soil_ssasymbol.zip, where ssasymbol is the soil survey symbol of the corresponding soil survey area.

After the export file has been copied to your PC, it must be unzipped using either WinZip or a similar program. For additional information, please see the file named README.txt in the root directory that is created by unzipping the export file. For additional soil survey areas, each zip file should be copied and unzipped into individual directories. When an export file is unzipped, the following directory hierarchy is produced in the directory to which the export file was unzipped:

The top level directory contains the following files:

soil_metadata_ssasymbol.txt - Federal Geographic Data Committee (FGDC) metadata in plain ASCII format.

soil_metadata_ssasymbol.xml - the same FGDC metadata in XML format.

readme.txt - a text file containing additional information.

The root directory will also contain a zipped, empty MS Access SSURGO template database, if one was requested as part of the download. The non-extension part of the zipped template database file name varies, but if one was included, it will be the only file in the top level directory with an extension of "zip". This file should be unzipped as well.

The directory "tabular" contains any tabular data that was requested. The directory "spatial" contains any spatial data that was requested. Note that spatial data is not required or recommended (due to file size) for WEPS. It is possible to request tabular data from the Soil Data Mart, without including the corresponding spatial data, and vice versa.

Tabular data is provided as a set of ASCII delimited files. Each file corresponds to a table in the SSURGO 2.1 data model. The tabular data isn't particularly useful until it has been imported into the MS Access SSURGO template database. Current Soil Data Mart downloads include a template database. If a template database was not included in the export file, you can download one from the following URL:

http://soildatamart.nrcs.usda.gov/templates.aspx

Load the template file into MS Access. A 全SURGO Import' screen will display asking for the full path to the tabular data directory. Type the full path of the tabular directory and click 前K'. A list of database tables will appear and a folder will be created in the top level directory (with the non-extension part of the template name). At the same time, an MS Access database file (*.mdb) which contains the data required for WEPS, will be created in the template folder. To import more than one soil survey area into a single MS Access database, run the Import macro specifying the full path to the directory the SSURGO data was uncompressed into. Repeat the Import macro for each area desired. When done, save the template database with the imported data to a new name (*.mdb).

Using SSURGO Data With WEPS

Within WEPS, open the "Configuration" window, then click the "Directories" tab. Fill out the full path and SSURGO soil database file name (*.mdb) for "Soil DB" and close the configuration window. Selecting the Soil Template folder at the bottom of the main WEPS screen will display the list of soil survey areas to choose from. Select the desired soil survey area and select the soil map unit and component for the simulation run. If the SSURGO database is not populated with data required by WEPS you will get an error message when selecting that soil. More detailed information on selecting soils, see the "Interface Reference: Choosing a Soil" section of the WEPS User Manual.