Available water capacity (AWC) refers to the volume of water held per volume of soil that is available for plant uptake. This water typically occurs between suction levels of ~ -10 kPa (field capacity) and -1,500 kPa (wilting point). The capacity for water storage is given in centimeters of water per centimeter of soil for each soil layer. The capacity varies, depending on soil properties that affect retention of water. The most important properties are the content of organic matter, soil texture, bulk density, and soil structure, with corrections for salinity and rock fragments.
Available water capacity is an important factor in the choice of plants or crops to be grown and in the design and management of irrigation systems. It is not an estimate of the quantity of water actually available to plants at any given time. Available water supply (AWS) is computed as AWC times the thickness of the soil. For example, if AWC is 0.15 cm/cm, the available water supply for 25 centimeters of soil would be 0.15 x 25, or 3.75 centimeters of water.
The rasters originate from the Gridded SSURGO (gSSURGO) database, a National Cooperative Soil Survey (NCSS) SSURGO product in the format of an Environmental Systems Research Institute, Inc. (ESRI®) file geodatabase. Both SSURGO and gSSURGO are considered products of the NCSS partnership. SSURGO generally has the most detailed level of soil geographic data developed by the NCSS in accordance with NCSS mapping standards (1:15,840 scale) and is stored in a vector format which display soil map unit delineations. The gSSURGO product was generated by creating a 10-m resolution raster of the original SSURGO vector data. The soil property tabular data are stored in the National Soil Information System (NASIS) database. For each soil layer, AWC is recorded as three separate values in the database. A low value and a high value indicate the range of this attribute for the soil component. A “representative” value indicates the expected value of this attribute for the component. For this soil property, only the representative value is used.
The zip file contains the base GeoTIFF soil property rasters, OVR pyramid files (reduced resolution for faster display), AUX auxiliary files (Raster color map, statistics, histogram, table, pointer to pyramid file, coordinate system, transformation, projection information), TFW world files (GeoTIFF coordinate system information), and a LYRX file (stored symbology for viewing in ArcGIS Pro v 2.2 or later) and a LYR file (stored symbology for viewing in ArcGIS for Desktop), and associated metadata in a DOCX file.
Metadata – Sources – Limitations
Produced by: Meyer Bohn, Joshua McDanel, and Bradley Miller January (2019)
Created with the gSSURGO mapping toolset for ArcGIS for Desktop 10.6. Available for download at:
Raster Format: 10-m resolution GeoTIFF, 32-bit floating point
Projection: NAD83 UTM Zone 15N
Extent – West: -96.801571 East: -90.007463 North: 43.644364 South: 40.302683
Soil Survey Staff. 2018. Natural Resources Conservation Service. United States Department of Agriculture. Gridded Soil Survey Geographic (gSSURGO) Database for Iowa. Accessed 27 Oct 2018.
Use limitations: See “Sources of Apparent Error on Existing Soil Maps”. Soil Survey Staff. 2018. Soil Survey Manual – Ch. 4: Soil Mapping Concepts. Natural Resources Conservation Service. United States Department of Agriculture. Available at:
Scale Range: Not intended for use at scales larger than an order 2 Survey (1:12,000 to 1:31,680).
- 0 – 5 cm • 5 – 20 cm
- 0 – 20 cm • 20 – 50 cm
- 0 – 30 cm • 50 – 100 cm
- 0 – 100 cm • 100 – 150 cm
- 0 – 150 cm • 150 – 200 cm
- 0 – 200 cm