Table 1.
Order | Description | Area (%)a | Common subsoil constraints |
---|---|---|---|
Alfisols | Soils from semi-arid to humid regions, typically developed under hardwood forest cover, with subsurface accumulation of clay | 9.6 | Hypoxia, hardness, temperature |
Andisols | Developed from volcanic ash | 0.7 | Mn toxicity, low P |
Aridisols | Desert soils without water for plants | 12 | Hardness, salinity/sodicity, low P |
Entisols | Soils with minimal evolution, as in eroded or accumulation regions. No subsurface horizons | 16.2 | – |
Gelisols | Permafrost (frozen soil) within 100cm from the surface | 8.6 | Temperature, low P, Mn toxicity |
Histosols | Organic rich, generally in cold latitudes | 1.2 | Hypoxia, low P, temperature, low Ca |
Inceptisols | Soils with weakly developed subsurface horizons | 9.8 | – |
Mollisols | Thick dark surface horizon | 6.9 | Hardness, hypoxia, temperature |
Oxisols | Soils from tropical regions, highly weathered, deep, and uniform profiles | 7.5 | Acidity (low P, low Ca, K, Mg, Al, and Mn toxicity) |
Spodosols | Bleached horizon over grey-brown (spodic) horizon | 2.5 | Hypoxia, acidity (low P, low Ca, Al, and Mn toxicity) |
Ultisols | Weathered soils with low base saturation (low fertility) in subsurface | 8.5 | Acidity (low P, low Ca, K, Mg, Al, and Mn toxicity), hypoxia, hardness |
Vertisols | Shrink and swell soils, that is soils that exhibit temporal variability in volume | 2.4 | Hypoxia, hardness |
a Percentage of the total land area (1.3×108 km2); rows sum to 86%—the remainder (~14%) is from rock and ice-covered regions (Wilding, 2000).