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| Oxisol | |
|---|---|
| Name | Oxisol |
| Type | Highly weathered tropical soil |
| Climate | Humid tropical, subtropical |
| Parent material | Basalt, granite, volcanic ash, alluvium |
| Profile | Deep, well-drained, kaolinitic horizons |
| Dominant minerals | Iron oxides, aluminum oxides, kaolinite |
| Drainage | Well to poor depending on topography |
Oxisol Oxisol are deeply weathered tropical soils notable for intense leaching and concentration of iron and aluminum oxides. Found across tropical and subtropical regions, they are central to discussions of land use, biodiversity, and soil science because of their unique chemistry and global distribution.
Oxisol are defined in soil taxonomies as highly weathered, low-activity mineral soils dominated by oxides and low cation-exchange capacity; they appear in classifications such as the United States Soil Taxonomy, the World Reference Base for Soil Resources, and national systems in countries like Brazil, India, Australia, Gabon, Congo, Cameroon, Indonesia, Malaysia, Colombia, Peru, Bolivia, Venezuela, Ecuador, Zambia, Zimbabwe, Mozambique, Madagascar, Thailand, Vietnam, Philippines, Papua New Guinea, Costa Rica, Panama, Honduras, Nicaragua, Kenya, Tanzania, Uganda, Rwanda, Burundi, Côte d'Ivoire, Ghana, Nigeria, Senegal, Mali, Chad, Sudan, Eritrea, Djibouti, Somalia, Saudi Arabia, Oman, Yemen, United Arab Emirates, Qatar, Bahrain, Kuwait, Iran, Iraq, Syria, Jordan, Israel, Lebanon, Turkey, Greece, Spain, Portugal, Italy, France, Germany, Poland, Ukraine, Russia, Kazakhstan, Mongolia, China, Japan, South Korea, North Korea, Taiwan, Sri Lanka, Bangladesh, Pakistan, Nepal, Bhutan, Maldives (occurrence variable by region). Their principal biogeographic settings include the Amazon Basin, the Congo Basin, the Guyana Shield, the Brazilian Highlands, the Guiana Highlands, parts of the Indonesian Archipelago, and ancient cratons in West Africa and Northern Australia.
Oxisol formation results from prolonged chemical weathering under warm, humid conditions associated with climates described by Köppen climate classification types such as Af, Am, and Aw. Parent materials like basalt, granite, and volcanic ash undergo laterization processes first recognized during colonial-era surveys by explorers and geologists linked to institutions like the Royal Geographical Society and the Smithsonian Institution. Characteristic features include deep red to yellow coloration from hematite and goethite, abundance of secondary minerals such as kaolinite, gibbsite, and iron oxides, and horizons with low natural fertility yet high physical stability. Important contributors to their study include researchers affiliated with the Food and Agriculture Organization, International Union of Soil Sciences, United States Department of Agriculture, Embrapa, CSIRO, INRAE, University of São Paulo, Wageningen University, University of California, Davis, and University of Reading.
Within the USDA soil taxonomy, Oxisol correspond to orders defined by diagnostic horizons like kandic or oxic horizons; comparable units in the WRB include Ferralsols and Plinthosols. Key measurable properties used in classification are base saturation, cation-exchange capacity, particle-size distribution, organic carbon content, and exchangeable aluminum; analytical methods are standardized by organizations such as the International Organization for Standardization and national laboratories at institutions like CSIRO and USDA NRCS. Physical properties—granular structure, high porosity, and often deep profiles—contrast with chemical properties—low phosphorus retention and high aluminum toxicity—which influence crop choices and reclamation strategies promoted by agencies like FAO, CGIAR centers including CIP, CIAT, IRRI, and universities such as CIMMYT partners.
Ecosystems on these soils include lowland rainforests of the Amazon rainforest, the Congo rainforest, tropical savannas like the Cerrado and Campos Rupestres, and montane forests on shields and plateaus. Biodiversity hotspots such as the Atlantic Forest, Madagascar dry deciduous forests, Eastern Afromontane, Sundaland, and Mesoamerican biodiversity hotspot often sit on Oxisol, shaping conservation priorities of organizations like Conservation International, WWF, IUCN, Nature Conservancy, BirdLife International, and national parks agencies like ICMBio in Brazil. Traditional land uses include shifting cultivation practiced by indigenous groups documented by researchers at Smithsonian Tropical Research Institute and Museu Paraense Emílio Goeldi, while modern uses span cattle ranching, soybean and oil palm production driven by corporations such as Bunge Limited, Cargill, ADM, Wilmar International, and plantation projects supported by development banks including the World Bank and Inter-American Development Bank.
Restoring or maintaining fertility on these soils relies on practices promoted by extension services and research institutions like Embrapa, CSIRO, IRRI, CIMMYT, and universities including USP and UFPA: lime application to ameliorate acidity and aluminum toxicity; phosphate fertilization using sources evaluated in trials at CIAT and CIP; integrated soil fertility management combining organic residues, green manures, and biochar studied by teams at ETH Zurich, University of Oxford, and University of Copenhagen. Agroforestry systems modeled after projects at CATIE, World Agroforestry Centre (ICRAF), Heifer International, and Slow Food networks help rebuild soil organic matter and sustain smallholder livelihoods supported by NGOs like Oxfam and CARE International. Crop breeding programs at Embrapa, CIMMYT, and IRRI target varieties adapted to low-phosphorus conditions and aluminum tolerance.
Oxisol regions play major roles in global biogeochemical cycles, carbon storage, and climate regulation; research collaborations among IPCC, NASA, NOAA, European Space Agency, JAXA, UK Met Office, and academic consortia inform policy on deforestation and carbon accounting. Conservation strategies integrate protected area networks designated under conventions such as the Convention on Biological Diversity and the Ramsar Convention and are implemented by agencies including ICMBio, SERNANP, SINAC, and transnational initiatives like the Amazon Cooperation Treaty Organization. Restoration science draws on work by The Nature Conservancy, WRI, GCF, and research programs at Yale School of the Environment, Harvard Forest, and Princeton University to reconcile agricultural expansion with biodiversity goals exemplified by projects in the Xingu River basin and the Pantanal.
Category:Soils