Tokul soil

The Tokul soil series are Andisol soils formed by volcanic ash and loess over a dense glacial till. The soils are found in the Puget lowland forests and western foothills of the Cascade Range, along the Puget Trough, which stretches from south of Seattle to the Canadian border. Tokul soils are the designated state soil of Washington state.[1]

They are named after Tokul Creek, a small tributary of the Snoqualmie River in eastern King County near Fall City, Washington and Snoqualmie Falls.

Profile

The Tokul soil series has the following profile:[2]

  • Surface layer: organic material
  • Subsurface layer: gravelly medial loam
  • Subsoil - upper: gravelly medial fine sandy loam
  • Subsoil - lower: gravelly sandy loam

Tokul soils have an organic surface, rich in decaying plant matter from the prevalent coniferous forest debris in the area. Below this, a dark-brown, organic rich, gravelly loam creates a fertile and well-drained layer, into which plant roots penetrate. This brown-reddish sub-layer, which extends 1–2 feet (0.30–0.61 m) below the surface, is strongly influenced by volcanic ash and has high concentrations of manganese and iron. Lower still is the grayish, dense glacial till, which then was overlaid with volcanic ash and loess, or wind-blown sediment.[3][4]

The state has over 1,000,000 acres (4,000 km2) of Tokul soils on the western side of the Cascade mountains.[5] Hundreds of other volcanic soils make up the rest of Washington's soils.[1]

Plant Habitat

Tokul soils are among the most productive in the world, supporting the state's rich coniferous, which are dominated by Douglas fir and western hemlock, the state tree of Washington.[6][7]

During wet periods, moisture builds up above the layer of dense glacial till, which can create unstable steep slopes. The soil series is threatened by displaced top soil as a result of development and agriculture due to lower humus content caused by tilling and digging.[8]

Washington state soil

The Tokul soil series was selected by the Washington Society of Professional Soil Scientists as the official soil of Washington.[2][1] While the soil series has not yet been officially designated as the state soil by the state legislature, it is recognized by the USDA Natural Resources Conservation Service (NRCS) and many other agricultural and pedological organizations as the designated representative soil of Washington state.[2]

Washington was the first state to recognize an Andisol, or a soil formed in volcanic ash, as the state soil.[7]

See also

References

  1. ^ a b c "Tokul - Washington State Soil" (PDF). NRCS. USDA. Retrieved 16 March 2026.
  2. ^ a b c "TOKUL SERIES". USDA. Retrieved 16 March 2026.
  3. ^ "Tokul: Washington State Soil" (PDF). Soil 4 Teachers. Soil Science Society of America. Retrieved 16 March 2026.
  4. ^ "The Soil That Makes Washington Oh So Evergreen" (PDF). WSU Master Gardener Program of Thurston County. Washington State University Master Gardener Program. Retrieved 16 March 2026.
  5. ^ Lucas, M. D.; Ross, R. M.; Swaby, A. N. (2014). he Teacher-Friendly Guide to the Earth Science of the Western US (PDF). Ithaca, NY: Paleontological Research Institution. p. 252. Retrieved 16 March 2026.
  6. ^ "Super Soils". Washington Grown. Retrieved 16 March 2026.
  7. ^ a b "State Soils - Washington". Smithsonian National Museum of Natural History. Retrieved 16 March 2026.
  8. ^ Lovejoy, Ann (April 19, 2023). "Washington's super state soil needs a little help". Kitsap Sun. Retrieved 16 March 2026.
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