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| Alfisols | |
|---|---|
| Name | Alfisols |
| Classification | Soil order (USDA) |
| Parent material | Various |
| Climate | Temperate to moist tropical |
| Vegetation | Deciduous forest, grassland |
| Major uses | Agriculture, forestry |
Alfisols
Alfisols are a major order of soils recognized in the United States Department of Agriculture (USDA) Soil Taxonomy and in international systems, associated with temperate to subhumid climates and productive ecosystems. They commonly support deciduous forests and mixed grasslands and are important for cereal, legume, and tree production across many regions. Alfisols are characterized by a subsurface horizon of clay accumulation and relatively high base saturation, making them agriculturally valuable in many landscapes.
In USDA Soil Taxonomy, Alfisols are defined by diagnostic horizons including an argillic, natric, or kandic subsurface horizon and at least 35% base saturation in the upper 100 cm, placing them among the fertile orders recognized alongside Mollisols, Ultisols, Entisols, and Inceptisols. Internationally, analogous categories appear in the World Reference Base for Soil Resources (WRB) as Luvisols, Arenosols, or related Reference Soil Groups depending on texture and carbonate content, while the Canadian System of Soil Classification maps similar classes in its own framework. Suborders in USDA taxonomy divide Alfisols by moisture and temperature regimes, linking to concepts from the Köppen climate classification, the FAO Land Use Classification System, and regional schemes used by agencies such as the Natural Resources Conservation Service.
Pedogenesis of Alfisols involves weathering, eluviation, and illuviation processes under vegetative cover such as broadleaf deciduous forests and savanna ecosystems associated with regions like the Midwestern United States, Central Europe, and parts of India. Clay translocation leads to development of an argillic horizon via physical and chemical mechanisms governed by parent material (e.g., loess, glacial till, alluvium), bioturbation by organisms such as Lumbricus terrestris (earthworms), and leaching influenced by precipitation patterns described in studies from institutions like USDA NRCS and universities such as Iowa State University and University of Wisconsin–Madison. Secondary mineral formation often yields smectite or illite clays, with cation exchange influenced by inputs documented by researchers affiliated with International Union of Soil Sciences and regional soil surveys like those by the Soil Science Society of America.
Typical Alfisol profiles display an A horizon with organic enrichment, an E horizon of eluviation in some suborders, and a B horizon enriched in clay (argillic) or other diagnostic features; colors, structure, and porosity vary by region and parent material seen across landscapes from the Black Sea basin to the Ohio River Valley. Physicochemical properties include moderate to high base saturation, pH ranging from slightly acidic to neutral, and moderate cation exchange capacity; physical behavior under cultivation is influenced by texture class similar to soils studied at institutions like Cornell University and University of California, Davis. Alfisols often exhibit evidence of pedogenic processes such as clay coatings, blocky structure, and root traces referenced in field guides used by agencies including the Natural Resources Canada and the European Soil Data Centre.
Alfisols occupy significant areas in the Midwestern United States, parts of Canada's southern provinces, extensive tracts in Eastern Europe, the Caucasus, much of India's peninsular zones, and regions of South America such as the Pampas. Global mapping efforts by the Food and Agriculture Organization and the International Soil Reference and Information Centre indicate that Alfisol-like soils cover large portions of temperate broadleaf and mixed forest biomes and transitional grassland zones, often overlapping with agricultural belts served by infrastructure networks exemplified by corridors like the Trans-Canada Highway and continental river basins such as the Mississippi River.
Because of their base saturation and structured B horizons, Alfisols support major crops including wheat, maize, soybeans, and tree plantations cultivated in regions influenced by institutions such as the International Maize and Wheat Improvement Center and national ministries like the Ministry of Agriculture and Farmers Welfare (India). Land use regimes range from intensive row-crop agriculture in the Corn Belt to managed forests in regions administered by agencies like the United States Forest Service and the State Forestry Administration (China). Sustainable management practices promoted by organizations including the Food and Agriculture Organization and Conservation International emphasize crop rotation, residue management, and agroforestry systems to maintain structure and fertility.
Alfisols play roles in carbon sequestration and hydrological regulation across watersheds such as the Chesapeake Bay and the Ganges Basin, where soil management affects sediment and nutrient fluxes monitored by programs like the United States Geological Survey and the International Water Management Institute. Erosion, salinization, and depletion of organic matter are key threats addressed through conservation measures championed by groups including the Natural Resources Defense Council and research centers at Wageningen University. Management strategies employ contour farming, cover crops, reduced tillage, and liming where pH amelioration is necessary, often integrated within policy frameworks of bodies like the European Commission and national extension services such as the Cooperative Extension System.
Debates in soil science concern boundaries between Alfisols and neighboring orders such as Ultisols and Mollisols, especially where base saturation gradients and clay mineralogy vary across landscapes studied by teams at USDA ARS, CSIRO, and universities like University of Illinois Urbana–Champaign. Revisions to global classification schemes, including successive editions of the World Reference Base for Soil Resources and updates to Soil Taxonomy, reflect ongoing discourse about diagnostic criteria, pedogenic thresholds, and the representation of anthropogenic modifications explored in symposia by the International Union of Soil Sciences and publications from the Soil Science Society of America.
Category:Soil orders