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Indicator: Acres of High Quality Soils

Data and Data Discussion provided by Sustainable Seattle

Upstream Indicators
  •   Urbanization and Impervious Surface Changes --- The number of acres of urban land, clear-cut, and regenerating forest have increased in King County since 1986. Acres of grass and deciduous, mixed and coniferous forest have decreased. Acres of rural forests and privately owned working forests have declined in recent years  (view data graph)
  •   Organic Farm Trends --- The number of certified organic farms in King County has more than tripled from 7 in 1995 to 23 in 2002, and remained relatively constant since then. The amount of acreage in organic production increased substantially in 2007.   (view data graph)
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Downstream Indicators
  •   303d Listed Watercourses --- Although approximately 50% of watercourses included on the 1998 Washington State 303(d) list have been de-listed, the total number of listed water segments has increased in the past decade. The most significant increase in listings has occurred with regards to temperature.   (view data graph)
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Related Goals

Sustainability Snapshot:

By converting farmland to urban uses, we are robbing ourselves of our most productive soil resources. A study of the impacts of urban development on soil resources found that residential, commercial, and industrial development, known as "urban sprawl," appear to have the greatest impacts on the better agricultural soils. Floodplains, for example, offer rich fertile lands for agriculture but are also very desirable for housing and commerce. Most of the floodplains in the central Puget Sound region have been drained, levied and paved over. A consequence of this urbanization process is a growing dependence on ever greater yields per unit area on the poorer soils that remain available for agriculture and an increasing reliance on more distant food sources.

Sustainability Trend:

While the amount of land being farmed has been relatively stable in recent years, there are continuing pressures on farmland being used for other purposes.

Data Discussion

The Indicator Defined

Acres of high quality soils based on suitability for food, feed, fiber, forage and oilseed crop production.

Data Interpretation/Evaluation

The Natural Resources Conservation Service (NRCS) classifies farmland by the extent to which different soils are suited for food, feed, fiber, forage, and oilseed crop production. In King County, soils are classified as follows: prime farmland; farmland of statewide importance; prime farmland if drained; prime farmland if irrigated; prime farmland if drained and either protected from flooding or not frequently flooded during the growing season; prime farmland if irrigated and either protected from flooding or not frequently flooded during the growing season; and not prime farmland.   The difference between prime farmland and farmland of statewide importance is …

Figure 1 shows a general overview of the urban land use area, prime farmland (suitable soil area for farming), and the county's topographical relief (elevation). On the eastern side of the county, there is a large variation of elevation, making land less favorable for agricultural production. Fertile soil areas meander through the mountains along tributaries and rivers.  Beginning in the middle of the county, soil suitability becomes more favorable as elevation decreases and the flood plains of major rivers form.  Prime farming areas extend north-south through the county, but diminish further westward with urbanization. Prime farmland in King County, including that under the urban overlays, totals 1,560,524.6 acres. 

Figure 2 shows soils in King County classified by the aforementioned suitabilities with an urban boundary overlay.  Most high quality soils in King County fall in the 'farmland of statewide importance' classification, and tend to correlate with large floodplains and low elevation.  The urban boundary overlay is included to give the viewer an indication of how much land has been consumed by urban land use.

Data Source and Limitations

Soil data accessed from NRCS (http://websoilsurvey.nrcs.usda.gov), and edited in ArcEditor. The data was collected in two separate soil surveys in the King County Region. Shapefiles were obtained from Washington Department of Financial Management, King County Conservation District, Washington State Department of Transportation, U.S. Department of Commerce TIGER files, USGS Elevation Data.

 

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