12 Soil Orders

Oxisols

• nutrient deficient for crops

• get red color from oxidized iron

• occur in tropical rainforest within 25 degrees north and south of the equator

• takes up 7% of the land area (nonpolar) on Earth

• oxic horizon, no argillic horizon, highly weathered

Ultisols

• strongly leached, acidic forest soils with relatively low fertility

• found in humid, temperate and tropical areas, typically on older, more stable landscapes

• make up 8% of global (ice-free) land

• argillic or kandic horizon, low base saturation

Vertisols

• clay/smectite rich soils that shrink and swell with changes in moisture content

• grassland soils that are rich in lime

• take up 2% of (ice-free) global land

• high in swelling clay; deep cracks when soil is dry

Gelisols

• soils of very cold climates that contain permafrost on the first 2m of surface

• found in high-latitude polar regions and localized areas at high mountain elevations

• take up 9% of (ice-free) global land

Mollisols

• about 50% of soils in IL are mollisols

• soils of grassland ecosystems characterized by thick, dark surface horizon

• take up 7% of (ice-free) global land

• fertile soil results from long-term addition of OM derived from grass roots

Ardisols

• soils that form in arid/ semi-arid climates and occupy around 1/3rd of Earth’s land surface

• biomass input is limited so OM doesn’t accumulate

• accumulation of salts on surface can lead to salinization

• take up about 12% of (ice-free) global land

Histosols

• composed mainly of organic matters

• form in places where poor drainage inhibits the decomposition of plant and animal remains

• aka peats and mucks and form in bogs and marshes

• occur mostly in boreal, arctic and subarctic regions

Alfisols

• moderately leached soils with relatively high native fertility

• formed primarily under forests and clays have accumulated in subsurface horizons

• found in temperate humid and subhumid regions in the world, used intensively for agriculture

• take up about 10% of (ice-free) global land

Andisols

• dark/black soils formed in volcanic ash

• high nutrient retention and often nutrient poor

• typically dominated by amorphous colloids

• make up about 1% of (ice-free) global land

Spodosols

• acid soils characterized by a subsurface accumulation of humus that is complexed with Al and Fe

• course parent material and light colored E horizon

• develops over centuries as water from seasonal precipitation helps translocate upper material

• make up about 4% of (ice-free) global land

Entisols

• found in rocky, mountainous regions; river valleys, river plains and deltas

• little to no morphological development except A horizon

• no diagnostic soil horizon, mostly undisturbed parent material

• make up about 18% of (ice-free) global land

Inceptisols

• found in semiarid to humid conditions

• contain B horizon

• have thin surface horizons and develops slowly because of fast weathering as it develops

• weathering morphological features formed and destroyed continuously

• make up about 15% of (ice-free) global land