Soil Distribution / Distribución de Suelo
In the Willamette Valley, two of the twelve soils are present, Mollisols (suborder Xerolls) and Ultisols (suborder Humults)1.

Mollisols are soils occurring in grassland ecosystems1. Characterized by a fertile, dark surface horizon, Mollisols are considered to be some of the most important and productive soils for agriculture in the world2. The suborder Xerolls occur in temperate areas where summers are dry and winters are moist2.

Ultisols are soils occurring in forests and are typically acidic because of leaching2. With higher amounts of clay in the surface, Ultisols occur in humid temperate and tropical areas2. These soils are important for productive forests but are not suited for agriculture because of the need for fertilizer and lime and with this addition may be used for that purpose2. The suborder Humults are higher in organic matter, meaning they require less of additional substances such as lime for productive agriculture2.

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1. Olsen, G. (1981) Soils and the environment (New York, NY: Dowden & Culver, Inc.)
2. McDaniel, P. (2008) The twelve soil orders. Available at (accessed June 2008).

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