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Soil Genesis and Development, Lesson 5 - Soil Classification and Geography

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5.9 - Ultisols

Ultisols are intensely weathered soils of warm and humid climates. They are typically formed on older geologic locations in parent material that is already extensively weathered.

Ultisols have accumulated clay minerals in the B horizon. While generally low in natural fertility (basic cations, Ca2+, Mg2+, and K+) and high in soil acidity (H+, Al3+) the clay content of Ultisols gives them a nutrient retention capacity greater than that of Oxisols, but less than Alfisols or Mollisols.  Ultisol soils can be agriculturally productive with inputs of lime and fertilizers.

Large areas of Ultisol are found in the southeastern USA, China, Indonesia, South America, and equatorial regions of Africa.

Soil Order Key Characteristics U.S. Order Distribution Map Profile Examples


Click on the image to study, and click on the expanded image to read the detail.


  • Intensely weathered soils of humid areas
  • Form on older geologic locations in weathered parent materials
  • Contain subsurface clay accumulations (claypans).
  • Low in natural fertility (Ca2+, Mg2+, and K+) and high in soil acidity (H+, Al3+)
  • Can be agriculturally productive with inputs of lime and fertilizers 
  • Occur extensively in the southeastern USA, China , Indonesia, South America, and equatorial regions of Africa
  • Extent of world ice-free land area: 8%


Further Details

 Cecil Series 

Cecil Series, North Carolina State Soil

USDA details

More information

All images courtesy of USDA-NRCS

Question 17:  Oxisols and Ultisols are both intensely weathered soils. What is a major difference between them that impacts their potential agricultural productivity?

A.   amount and type of clay accumulation in the B horizon
B.   climate and rainfall patterns where they are formed  
C.   native vegetation at location where they form      
D.   topography or drainage issues
E.   time since deposition of parent material



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