University of Idaho College of Agricultural and Life Sciences Plant, Soil & Entomological Sciences Soil & Land Resources
Soil Orders
Soil Links
  Gelisols    Histosols    Spodosols    Andisols    Oxisols    Vertisols    Aridisols    Ultisols    Mollisols    Alfisols    Inceptisols    Entisols

Ultisols (from Latin ultimus, "last") are strongly leached, acid forest soils with relatively low native fertility. They are found primarily in humid temperate and tropical areas of the world, typically on older, stable landscapes. Intense weathering of primary minerals has occurred, and much Ca, Mg, and K has been leached from these soils. Ultisols have a subsurface horizon in which clays have accumulated, often with strong yellowish or reddish colors resulting from the presence of Fe oxides. The 'red clay' soils of the southeastern United States are examples of Ultisols.

Ultisols occupy ~8.1% of the global ice-free land area and support 18% of the world's population. They are the dominant soils of much of the southeastern US and occupy ~9.2% of the total US land area.

Because of the favorable climate regimes in which they are typically found, Ultisols often support productive forests. The high acidity and relatively low quantities of plant-available Ca, Mg, and K associated with most Ultisols make them poorly suited for continuous agriculture without the use of fertilizer and lime. With these inputs, however, Ultisols can be very productive.

Ultisols are divided into 5 suborders: Aquults, Humults, Udults, Ustults, and Xerults. Click here for more information about these suborders. Click here to view a map of their distribution in the US.

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Click on map to view larger image
<< back to Soil Orders list Ultisol example #1 >> 
1. Umbraquult
Coastal Plain of North Carolina
2. Typic Hapludult
western Arkansas
3. Kanhapludult landscape
North Carolina
4. Typic Kanhapludult
North Carolina
5. Kandiudult landscape
North Carolina
6. Typic Kandiudult
North Carolina
7. Plinthic Kandiudult
8. Plinthite blocks
If you have any comments, suggestions, or questions about the 12 Soil Orders web site,
please contact
Dr. Paul McDaniel  at the Soil Science Division,
University of Idaho, Moscow, ID 83844-2339.