Introduction

The Natural Resources Conservation Service (NRCS) U.S. Department of Agriculture has the federal responsibility for the National Cooperative Soil Survey (NCSS) and federal leadership for collecting, storing, maintaining, and distributing soils information in the United States. The Federal Geographic Data Committee (FGDC) and the Office of Management and Budget have formally assigned the responsibility for national coordination of digital soils data to the NRCS. The NRCS has established 3 digital soil geographic data bases (NATSGO, STATSGO, and SSURGO) representing different intensities of soil mapping. Common to each data base is the linkage to a soil interpretation (attribute) record data base, which gives the proportionate extent of the component soils and their properties for each map unit. With these digital data bases, users can store, retrieve, analyze, and display soil data in a highly efficient manner, as well as integrate the data with other spatially referenced resources in a geographic information system (GIS).

Three types of information are included in soil information systems:

  • Soil maps (polygons, data points)
  • Tables of data (soil attribute information)
  • Metadata (description of the soil data such as source of data, quality, characteristics)

National Soil Information System (NASIS)

NASIS is designed to manage and maintain soil data from collection to dissemination for the National Cooperative Soil Survey. It is a tool to help create and maintain soil surveys. NASIS maintains the hierarchical structure of soil survey data, through the use of table-oriented editors.

The requirements for NASIS are:

  • Enable collectors of soil information to record efficiently their actual observations of soils
  • Flexible input
  • Availability of detailed primary soil property data
  • Dynamic updating
  • Integrated systems
  • Statements or measures of reliability of the data included

NASIS supports soil survey in 3 ways:

  • Support field operations to gather new information efficiently in compliance with standards
  • Apply expert knowledge to make information usable for an increasing variety of purposes
  • Make information readily available to meet the needs of a wide variety of users

NASIS has 3 types of geographic data bases:

  • National Soil Geographic Data Base (NATSGO)
  • State Soil Geographic Data Base (STATSGO)
  • Soil Survey Geographic Data Base (SSURGO)

National Soil Geographic Database (NATSGO)

NATSGO used primarily for national, regional, and multi-state resource assessment, planning, and monitoring. The boundaries of the major land resource area (MLRA) and land resource regions were used to form the NATSGO data base. The MLRA boundaries were developed primarily from state general soil maps. Map unit composition for NATSGO was determined by sampling done as part of the 1982 National Resource Inventory. Sample data were expanded for the MLRAs, with sample design being statistically significant to state parts of the MLRAs. The NATSGO map was digitized at a scale of 1 : 750,000 and is distributed as a single data unit for the U.S. coverage.

 

State Soil Geographic Database (STATSGO)

STATSGO omprises state general soil maps made by generalizing the detailed soil survey data. The level of mapping is designed to be used for broad planning and management (county, state, regional, and national resource planning).

STATSGO is a digital general soil association map developed by the National Cooperative Soil Survey. It consists of a broad based inventory of soils and non-soil areas that occur in a repeatable pattern on the landscape and that can be cartographically shown at the scale mapped. The soil maps for STATSGO are compiled by generalizing more detailed soil survey maps. Where more detailed soil survey maps are not available, data on geology, topography, vegetation, and climate are assembled, together with Land Remote Sensing Satellite (LANDSAT) images.

Map unit composition for a STATSGO map is determined by transecting or sampling areas on the more detailed maps and expanding the data statistically to characterize the whole map unit. The data set consists of georeferenced digital map data and computerized attribute data. The map data are collected in 1-by 2-degree topographic quadrangle units and merged and distributed as statewide coverages. The soil map units are linked to attributes in the Map Unit Interpretations Record relational data base which gives the proportionate extent of the component soils and their properties.

Purpose: STATSGO depicts information about soil features on or near the surface of the Earth. These data are collected as part of the National Cooperative Soil Survey. STATSGO was designed primarily for regional, multi-county, river basin, State, and multi-state resource planning, management, and monitoring. STATSGO data are not detailed enough to make interpretations at a county level. This soil survey product is not designed for use as a primary regulatory tool in permitting or citing decisions, but may be used as a reference source. The STATSGO database contains information on map unit acreage and on the proportionate extent of the components in each map unit. It also contains soil property and interpretation data for each map unit component.

The approximate minimum area delineated is 625 hectares (1,544 acres), which is represented on a 1:250,000-scale map by an area approximately 1 cm by 1 cm (0.4 inch by 0.4 inch). A scale of 1:250,000 means that 1 inch on the map represents 4 miles in nature. The smallest map units are about 2.3 square miles in size. Linear delineations are not less than 0.5 cm (0.2 inch) in width. The number of delineations per 1:250,000 quadrangle typically is 100 to 200, but may range up to 400. Delineations depict the dominant soils making up the landscape. Other dissimilar soils, too small to be delineated, are present within a delineation.

Map Unit Delineations are closed polygons that are generally geographic mixtures of groups of soils and nonsoil areas. The map unit ID uniquely identifies each closed delineation, map unit. Each map unit ID is linked to a map unit name. The map unit ID is also the key for linking information in the Map Unit Interpretations Record tables. Map Unit Delineations are described by the Map Unit Interpretations Record data base. This attribute data base gives the proportionate extent of the component soils and the properties for each soil. The data base contains both estimated and measured data on the physical and chemical soil properties and soil interpretations for engineering, water management, recreation, agronomic, woodland, range and wildlife uses of the soil. The Soil Map Unit Interpretations Record data base consist of the following relational tables:

  • codes (data base codes) – stores information on all codes used in the data base
  • comp (map unit component) – stores information which will apply to a specific component of a soil map unit
  • compyld (component crop yield) – stores crop yield information for soil map unit components
  • forest (forest under story) – stores information for plant cover as forest under story for soil map unit components
  • interp (interpretation) – stores soil interpretation ratings (both limitation ratings and suitability ratings) to soil map unit components
  • layer (soil layer) – stores characteristics which apply to soil layers for soil map unit components
  • mapunit (map unit) – stores information which applies to all components of a soil map unit
  • plantcom (plant composition) – stores plant symbols and percent of plant composition associated with components of soil map units
  • plantnm (plant name) – stores the common and scientific names for plants used in the data base
  • rsprod (range site production) – stores range site production information for soil map unit components
  • taxclass (taxonomic classification) – stores the taxonomic classification for soils in the data base
  • windbrk (windbreak) – stores information on recommended windbreak plants for soil map unit components
  • wlhabit (wildlife habitat) – stores wildlife habitat information for soil map unit components
  • woodland (woodland) – store information on common indicator trees for soil map unit components
  • woodmgt (woodland management) – stores woodland management information for soil map unit components
  • yldunits (yield units) – stores crop names and the units used to measure yield

Soil Survey Geographic Database (SSURGO) – Soil Data Mart

SSURGO – Soil Data Mart is the most detailed level of soil mapping done by the National Resource Conservation Service (NRCS). Soil maps in the SSURGO data base are made by field methods, using observations along soil delineation boundaries and traverses and determining map unit composition by field transects. Aerial photographs are interpreted and used as the field map base. Maps are made at scales ranging from 1 : 15,840 to 1 : 31,680 (commonly 1:24,000). SSURGO data are collected and archived in 7.5 minute topographic quadrangle units, and distributed as complete coverage for a soil survey area usually consisting of 10 or more quadrangle units. This data base is used primarily for farm and ranch conservation planning; range and timber management; county planning; and watershed resource planning and management. SSURGO can be also used to assess land use potential and to identify potential wetland areas.

Map Unit Interpretation Records (MUIR)

MUIR data is a collection of soil and soil-related properties, interpretations, and performance data for a soil survey and its map units, map unit components, and component layers. It is a dataset which can be used at the regional and national level.

MUIR data should be used in conjunction with soil survey maps. The soil survey maps indicate the geographic location and extent of the soil map units within the soil survey area. Mapping scales generally range from 1:12,000 to 1:31,680. The maps meet or exceed the national NRCS mapping specifications. MUIR data is intended to be used by landowners, county and local governments, and other natural resource managers for basic land use planning. It is not intended to be used for site-specific land use suitability determinations, such as approval, and sizing of septic tank absorption fields.

Most MUIR data exists in the database as a range of soil properties, depicting the range for the soil survey area. Data is obtained from a combination of field observations, site descriptions and transects, and laboratory analyses. In making the soil survey, soil scientists observed landforms and landscape features, such as the steepness, length, and shape of slopes; the general pattern of drainage; the kinds of crops and native plants growing on the soils; and the kinds of bedrock. They observed and studied many soil profiles. Samples of some of the soils in the area were collected for laboratory analyses and for engineering tests. Soil boundaries were drawn on the soil maps and a locally tailored MUIR data base was constructed, based on those observations and the resulting landscape model the soil scientist developed.

Goal is to replace all MUIR data by SSURGO. However, in some States MUIR are the only available digital soil data at county scale.

Soil Series

This database contains the taxonomic classification of each soil series identified in the United States, along with other information about the soil series such as office of responsibility, series status, dates of origin and establishment, and geographic areas of usage. Information such as soil texture, bulk density, available water capacity, soil reaction, and organic matter is included for each major layer of the soil profile.

Web link:
Official Soil Series Description

National Soil Characterization Database (NSSC)

This database currently contains analytical data for more than 24,000 pedons of U.S. soils and about 1,100 pedons from other countries. The Soil Survey Laboratory (SSL), National Soil Survey Center collected the data, which include data that may or may not represent the central concept of a soil series or map unit and pedons sampled to bracket a range of soil properties with series or a landscape.