5.7 - Alfisols | Soil Genesis and Development, Lesson 5 - Soil Classification and Geography

Alfisols are found in cool to hot humid areas, and in the semiarid tropics; they are formed mostly under forest vegetation, but also under grass savanna. Extensive areas of Alfisols are found in the Mississippi and Ohio River valleys in the USA, through Central and Northern Europe into Russia, and in the South-central region of South America.

Alfisols generally show extensive profile development, with distinct argillic (clay) accumulations in the subsoil. Extensive leaching often produces a light-colored E horizon below the topsoil.

Generally fertile and productive, these soils typically have a high concentration of nutrient cations (Ca, Mg, K, and Na) and form in regions with sufficient moisture for plants for at least part of the year. Natural fertility and productive capacity of Alfisols is considered to be greater than that of Ultisols, but less than that of Mollisols.

Key Characteristics: Alfisols

Found under forest and savanna vegetation
Clay accumulations in subsoil horizons
Often are leached below topsoil (E horizon)
Generally fertile, with high base saturation%.
Comparable in productivity to Mollisols and Ultisols.
Extensive in humid mid-latitudes
Extent of world ice-free land area: 10%

**U.S. Order Distribution Map for Alfisols.** ***Image courtesy of USDA-NRCS***

**Further Detail by the NRCS**

Quiz

Question

What type of Native Vegetation is most commonly associated with formation of soils of the Alfisol Order?‏

A. Tallgrass prairie

Incorrect: Native vegetation and biota make up one of the five main soil-forming factors significant in Alfisol formation. Check the description in this section for more information.

B. Deciduous forest

Correct: Alfisols are formed mostly under native deciduous vegetation, but also under grass savanna.

C. Coniferous forest

Incorrect: Native vegetation and biota make up one of the five main soil-forming factors, significant in Alfisol formation. Check the description in this section for more information.

D. Sage and scrub brush

Incorrect: Native vegetation and biota make up one of the five main soil-forming factors, significant in Alfisol formation. Check the description in this section for more information.

E. Tropical rainforest

Incorrect: Native vegetation and biota make up one of the five main soil-forming factors, significant in Alfisol formation. Check the description in this section for more information.

Looks Good! Correct: Alfisols are formed mostly under native deciduous vegetation, but also under grass savanna.

Question

What sequence of horizons could be expected to be found in a well-developed (mature), unplowed Alfisol soil profile?‏

A. A – B – C

Incorrect: Check the colors of the soil layers in the profile pictured above. Dark colors indicate organic matter, while lighter colors may indicate the presence of leached soil.

B. O – B – C

Incorrect: Check the colors of the soil layers in the profile pictured above. Dark colors indicate organic matter, while lighter colors may indicate the presence of leached soil.

C. O – A – E – B – C

Correct: Accumulation of surface litter forms an organic and potentially acidic 'O' horizon that promotes leaching of organic matter, clay, and nutrients in the topsoil layers below it.

D. A – E – B – C

Incorrect: Check the colors of the soil layers in the profile pictured above. Dark colors indicate organic matter, while lighter colors may indicate the presence of leached soil.

Looks Good! Correct: Accumulation of surface litter forms an organic and potentially acidic 'O' horizon that promotes leaching of organic matter, clay, and nutrients in the topsoil layers below it.