IAS NOVA Interactive Atlas
Soils of the World
Read the living skin of Earth—from deeply weathered tropical profiles and black grassland soils to desert crusts, peatlands, volcanic ash soils and frozen ground.
Definition
Soil is a dynamic natural body made of mineral and organic matter, water, air and living organisms, arranged into layers or horizons by soil-forming processes. The map groups the 32 WRB Reference Soil Groups into 17 readable teaching categories and cross-references the 12 USDA Soil Taxonomy orders. It is a world-scale learning map, not a substitute for a detailed soil survey.
Learn with the map: Open it in FULL SCREEN, choose a soil environment or type, and hover, tap or use the Index to compare formation, profile, fertility and land use across representative regions.
How soils form and why they differ
Soil is the biologically active interface between rock, air, water and life. Its colour, texture, structure, chemistry and horizons record the combined influence of climate, organisms, relief, parent material and time—often remembered as CLORPT.
Explore the five soil-forming factors
Select a factor to see the strongest world-scale relationship it creates.
Climate: the broad zonal control
Temperature and moisture regulate chemical weathering, organic decomposition and leaching. This helps create broad belts from tropical Ferralsols to polar Cryosols.
Map signal: humid tropics favour deep weathering; drylands favour salt, carbonate or gypsum accumulation.
Seventeen major soil categories used on the map
The names prioritise WRB Reference Soil Groups and give close USDA Soil Taxonomy equivalents where a useful broad comparison exists. The two systems are not one-to-one translations.
Ferralsols | Oxisols
Profile: very deep, red/yellow and strongly weathered.
Setting: old, stable humid tropical landscapes.
Use: low natural nutrient reserves; productive with careful liming and fertilisation.
Acrisols | Ultisols
Profile: acidic, clay-enriched subsoil with low base status.
Setting: humid tropical and subtropical forest margins.
Use: erosion and acidity constrain farming.
Nitisols
Profile: deep red, well-structured, shiny clay aggregates.
Setting: tropical highlands, commonly on basic volcanic rocks.
Use: often better physical properties than other old tropical soils.
Lixisols/Luvisols | Alfisols
Profile: clay transferred into a base-richer subsoil.
Setting: seasonally dry tropics and temperate forest belts.
Use: moderate to good agricultural potential where erosion is controlled.
Podzols | Spodosols
Profile: pale E horizon over dark organic-metal accumulation.
Setting: cool, moist, acidic sandy material under conifers or heath.
Use: acidic and naturally nutrient-poor.
Chernozems/Phaeozems | Mollisols
Profile: thick, dark, humus-rich surface horizon.
Setting: mid-latitude grasslands.
Use: among the world’s most productive grain soils.
Kastanozems and Calcisols
Profile: chestnut surface with secondary carbonate accumulation.
Setting: dry steppe and semi-arid grassland.
Use: moisture limits yield; irrigation may raise salinity risk.
Aridisols, Arenosols and desert soils
Profile: weak organic surface; carbonates, gypsum or salts may accumulate.
Setting: deserts and very dry shrublands.
Use: water scarcity is the main limit.
Solonchaks and Solonetz
Profile: excess soluble salts or exchangeable sodium.
Setting: closed basins, arid lowlands and poorly managed irrigation zones.
Use: requires drainage, salt control and sometimes gypsum.
Vertisols
Profile: dark expanding clay with deep cracks and slickensides.
Setting: seasonal wet-dry climates on clay-rich material.
Use: fertile but difficult to till and drain.
Fluvisols | alluvial Entisols
Profile: young, stratified river deposits with little horizon development.
Setting: floodplains, deltas and active valleys.
Use: often fertile, densely settled and flood-prone.
Gleysols
Profile: grey-blue colours and mottles caused by prolonged saturation.
Setting: depressions and high water-table plains.
Use: drainage-sensitive wetlands and pasture.
Histosols
Profile: thick organic material or peat.
Setting: cool bogs and tropical peat swamps where decomposition is slow.
Use: major carbon stores; drainage causes subsidence and emissions.
Cryosols | Gelisols
Profile: permafrost-affected material with freeze-thaw disturbance.
Setting: Arctic and sub-Arctic landscapes.
Use: fragile, poorly drained and highly climate-sensitive.
Andosols | Andisols
Profile: dark, porous volcanic-ash material with strong phosphate retention.
Setting: volcanic arcs and plateaus.
Use: excellent structure but phosphorus management is often needed.
Leptosols and Regosols
Profile: shallow, stony or weakly developed.
Setting: steep mountains, eroding slopes and young deposits.
Use: grazing, forestry and watershed protection often suit them better than tillage.
Cambisols | Inceptisols
Profile: moderately developed young soil with an altered subsoil.
Setting: widespread temperate and upland landscapes.
Use: potential varies mainly with texture, depth, slope and climate.
Read a soil profile from O to R
| Horizon | What it contains | Diagnostic clue |
|---|---|---|
| O | Fresh to decomposed organic litter | Common under forest or in peat-forming sites |
| A | Mineral material mixed with humus | Biological activity and darker colour |
| E | Eluviated, leached mineral layer | Pale because clay, iron or organic matter moved out |
| B | Altered or illuviated subsoil | Accumulation of clay, iron, aluminium, humus, carbonates or salts |
| C | Little-altered parent material | Weathered sediment or rock beneath the solum |
| R | Hard bedrock | Continuous rock rather than soil material |
Processes that create diagnostic soil patterns
Ferralitisation
Intense tropical weathering and leaching remove silica and bases, leaving iron- and aluminium-rich material.
Podzolisation
Acid organic compounds mobilise humus, iron and aluminium from E to spodic B horizons.
Calcification
Evaporation and limited leaching concentrate calcium carbonate in dry grassland or desert subsoil.
Gleisation
Waterlogging removes oxygen; reduced iron gives grey-blue colours with rusty mottles.
Salinisation
Evaporation, saline groundwater or irrigation concentrates soluble salts in the root zone.
Melanisation
Humus becomes intimately mixed with mineral material, darkening a biologically active surface horizon.
Vertisation
Shrink-swell clays crack, churn and form slickensides as wet and dry seasons alternate.
Lessivage
Dispersed clay moves downward from an upper horizon and accumulates in a clay-enriched subsoil.
Why dark colour does not tell the whole fertility story
Plant productivity depends on nutrient supply, pH, organic carbon, rooting depth, texture, structure, drainage, salinity and climate. Management can improve some constraints but may worsen others.
| Constraint | Typical soil setting | Management principle |
|---|---|---|
| Acidity and aluminium toxicity | Acrisols, Ferralsols, Podzols | Limit erosion; use adapted crops, organic inputs and carefully targeted lime |
| Low nutrient reserves | Strongly weathered or sandy soils | Recycle biomass and match nutrients to crop demand |
| Waterlogging | Gleysols, some Vertisols and floodplains | Protect wetlands or provide controlled drainage suited to the landscape |
| Salinity/sodicity | Solonchaks, Solonetz and irrigated drylands | Improve drainage, leach safely and manage sodium where feasible |
| Erosion | Leptosols, cultivated slopes, bare tropical soils | Maintain cover, slow runoff and reduce disturbance |
India within the world soil pattern
| Indian teaching group | Broad world correlation | Major distribution and clue |
|---|---|---|
| Alluvial soils | Fluvisols and young Entisols | Indo-Gangetic-Brahmaputra plains and coastal deltas; layered river deposits |
| Black soils (regur) | Vertisols | Deccan Trap region; clayey, shrink-swell and moisture-retentive |
| Red and yellow soils | Acrisols, Lixisols and related tropical soils | Peninsular uplands; iron colours and generally low humus |
| Lateritic soils | Ferralsols and strongly weathered tropical groups | High-rainfall uplands of Western/Eastern Ghats and northeast; strongly leached |
| Arid soils | Aridisols, Arenosols and Calcisols | Thar and northwest; sandy, low humus, locally calcareous or saline |
| Forest and mountain soils | Leptosols, Cambisols, Podzols and others | Himalaya and hill systems; strong vertical and slope variation |
| Saline/alkaline and peat/marsh soils | Solonchaks/Solonetz and Histosols/Gleysols | Arid basins, poorly drained coasts, wetlands and local peatlands |
Protect the thin, living resource
Major degradation pathways
- Water and wind erosion
- Organic-carbon and nutrient decline
- Salinisation and sodification
- Compaction, sealing and waterlogging
- Acidification and contamination
Conservation principles
- Keep soil covered and roots living
- Reduce unnecessary disturbance
- Rotate crops and add organic matter
- Farm along contours and protect buffers
- Match irrigation, drainage and nutrients to site
Soils of the world quiz
1. Which set lists the classic soil-forming factors?
CLORPT summarises climate, organisms, relief, parent material and time.
2. Which soil is most closely associated with humid tropical, deeply weathered landscapes?
Ferralsols are strongly weathered, iron-rich soils of old humid tropical surfaces.
3. A thick dark, humus-rich grassland surface is characteristic of:
Dense grass roots and strong biological cycling build dark mollic or chernic surface horizons.
4. Which process creates a pale E horizon over an organic-metal-enriched B horizon?
Podzolisation transfers organic matter, iron and aluminium downward from a bleached E horizon.
5. Which soil commonly develops deep seasonal cracks?
Expanding clays make Vertisols shrink, crack and churn during wet-dry cycles.
6. Why are many Fluvisols agriculturally important?
Floodplains and deltas receive renewed sediment, but flood risk remains a major constraint.
7. Which pair stores unusually large amounts of soil carbon?
Peat accumulation and frozen conditions slow decomposition, conserving large carbon stocks.
8. Why is a 17-category world soil map a generalisation?
The WRB has 32 Reference Soil Groups, and detailed maps contain inclusions and local variation too fine for this world view.
Frequently asked questions
What are the major soils of the world?
Major world-scale groups include tropical Ferralsols and Acrisols, forest Luvisols and Podzols, grassland Chernozems and Kastanozems, dryland Aridisols and saline soils, Vertisols, Fluvisols, Gleysols, Histosols, Cryosols, Andosols, Leptosols and Cambisols.
How many soil types are recognised globally?
The WRB 2022 system recognises 32 Reference Soil Groups. USDA Soil Taxonomy recognises 12 soil orders. Each system subdivides these broad units into more detailed classes.
What is the difference between WRB and USDA Soil Taxonomy?
They are independent diagnostic classification systems with different hierarchies and definitions. Broad correlations are useful for learning, but most names are not exact equivalents.
Which are the most fertile soils in the world?
Chernozems and many Mollisols are famous for thick, fertile grassland topsoil. Many Fluvisols are also productive. Fertility still depends on climate, drainage, depth and management.
Why are many tropical soils nutrient-poor despite lush forests?
Warm, wet conditions cause strong weathering and leaching, while a large share of nutrients circulates rapidly through living biomass and surface litter rather than remaining stored in mineral soil.
What is the difference between soil texture and structure?
Texture is the proportion of sand, silt and clay. Structure is the way particles bind into aggregates such as crumbs, blocks or prisms.
How does soil salinity develop?
Salinity develops when soluble salts accumulate because evaporation exceeds leaching, groundwater is saline, drainage is poor or irrigation adds salts without adequate removal.
Why are world soil-map boundaries approximate?
Soils change over short distances with slope, drainage, parent material and land use. A readable global atlas must merge fine survey units into representative teaching regions.
Authoritative references and further reading
- FAO: Harmonized World Soil Database version 2.0
- FAO: HWSD v2.0 technical report
- IUSS Working Group WRB: World Reference Base history and 2022 edition
- IUSS Working Group WRB: Reference Soil Groups
- USDA NRCS: Soil classification and Soil Taxonomy
- USDA NRCS: The twelve soil orders
- ISRIC: SoilGrids global soil-property maps
