These soils have mainly formed under the forests and they have a subsurface horizon in which clays have accumulated.
Alfisols are primarily located in temperate humid and subhumid regions of the world and that combination of generally favorable climate and high native fertility allows Alfisols to be very productive soils for both agricultural and silvicultural (tree growing) development.
Alfisols are divided into five suborders: Aqualfs, Cryalfs, Udalfs, Ustalfs, and Xeralfs; which are defined alphabetically in other parts of this unit.2. From the U.S. Soil Taxonomy soil-order classification system.
3. Etymology: from alf, an abbreviation for aluminum and ferrum, "iron".
Alfisols are arable (cultivatable) soils with water content adequate for at least three consecutive months of the growing season.
Before cultivation, the soils are covered with natural broad-leaved deciduous forest vegetation, sometimes interspersed with needle-leaved evergreen forest or with grass.
Occupying just under ten percent of the nonpolar continental land area on earth, they are found primarily in cool, moist regions of the Northern Hemisphere (the north-central United States and north-central Europe extending into Russia) and in subhumid or Mediterranean climatic regions of both hemispheres (western Africa south of the Sahara, northeastern Brazil, and southern Australia).
The principal agricultural crops grown on Alfisols are corn (maize), wheat, and wine grapes.
Alfisols typically present well-developed, contrasting soil horizons (layers) depleted in calcium carbonate but enriched in aluminum-bearing and iron-bearing minerals.
Below the surface horizon, there is a region with significant accumulation of translocated (migrated) layer silicate clay.
This area which is called the argillic horizon, is characterized by a relatively high content of available calcium, magnesium, potassium, and sodium ions.
Alfisols are lower in humus content than Mollisols (a similar soil order) and do not have the calcium carbonate accumulation of that soil type
They are less extensively leached of metal ions and develop in cooler climates than the Ultisols, a clay-rich soil order of warmer regions.