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Soils 3


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Levels in US Classification System
Order, suborder, great group, sub group, family, series
List several diagnostic horizons
Spodic, argillic, oxic, mollic, histic
Spodic diagnostic horizon
B horizon with illuvial accumulation of Fe+3, Al+3 and humas. Bhs or Bs.
Oxic diagnostic horizons
Laterization of everything except Fe+3 and Al+3 weathered away.
An argillic diagnostic horizon
Bt horizon
Twelve soil orders
Alfisols, Andisols, Aridisols, Entisols, Gelisols, Histosols, Inceptisols, Mollisols, Oxisols, Spodosols, Ultisols, Vertisols.
Two soil orders for young soils
Entisols - young, weakly developed, with no B.

Inceptisols - relatively young, more developed than Entisols, might have B.
Typical profiles in an Entisol,
Places where Entisols are typically found.
Ridge tops, recent deposits, beaches, ash, and urban areas.
Soils with permafrost or cryoturbation. Cold or frozen most of the year. Organic or inorganic.
Soils developed from volcanic material
Characteristics of Andisols
Developed from volcanic material. A Horizons that are rich in Al-humic materials. Secondary minerals are predominately amporphous. Range from moderate to well developed.
Dry soils, arid to semi arid. A Horizons with less plant growth. Can have many types of B Horizons, but Bks are common.
List profiles.
"Soft." Have a mollic A horizon. Greater than 50% base saturation with good physical properties. Usually under grasslands. Very fertile.
A B_ C, AC or A E B_ C
List profiles
Has a Bt Horizon. Moderate base saturation (35-50%). Lower fertility than Mollisols but still excellent soil. Common under deciduous forests and grasslands.
A E Bt1 Bt2 C, or A Bt1 Bt2 BC
List Profiles
Old, highly-weathered, acidic soil. Low base saturation (less than 35%). Has a Bt horizon. Lower fertilitiy than Alfisols. Common under forests. Developed in wetter temperate areas or tropical areas with lots of leaching. Easily degraded.

O A Bt1 Bt2 Bt3 C
Orders that are likely to have Bt Horizon
Alfisols, Ultisols
Most highly weathered, old soils. Lateralization with an oxic B horizon. Kaolinite common. A horizon low in organic matter. Common in tropic areas with high rainfall and a stable landscape
Soil orders likely to be found in tropic areas
Oxisols(stable environment), Ultisols (where heavy leaching)
Soil orders likely to be found under grasslands
Mollisols, Alfisols.
Horizons with accumulation of Al-humic matter. What's the difference?
Andisols, Spodisols. Andisols have accumulation in A horizon. Spodisols have illuvial accumulation in B horizon (Bs or Bhs)
Has a spodic horizon (Bs or Bhs) with illuvial accumulations of Fe, Al, O.M.) Usually has an E horizon. Acidic lower in fertility. Found in cooler temperatures, coniferous regions, areas with high leaching, course textured soil. O E Bhs Bs C
Orders that are likely in forests and temperate regions.
Spodisols - coniferous
Ultisols - old and leached
Alfisols - deciduous
High content of shrink swell clay in the upper 7 m of soil. Soil expands and contracts and mixes. Cracks open. Sub humid to semi-arid areas. Deep A horizon.
Orders in arid, semi arid areas
Organic soils (little to no mineral material). Found in water logged areas of any type of climate. Wetlands. When drained, can be very fertile but difficult to manage due to poor properties. Oa Oe Oi
Mollic diagnostic horizon
Thick, dark colored, high base saturation, good structure, very fertile A horizon
"Base" Cations
Na, Ca, K, Mg
Formula for base saturation
Quantity of Base Cations/Cation Exchange Capacity
What is a good base saturation for high fertility?
The three soils orders defined by base saturation and the base saturation %s
Mollisols - greater than 50%
Alfisols - 50-35%
Ultisols - less than 35%
Explain how pH influences base saturation. Why?
A low pH (acidic) leads to low base saturation. Higher pH (more basic) leads to higher base saturation.
When OH increases it pulls H+ off exchange cites and frees sites up for base cations.
The process by which soils are depleted of bases and become acidic.
Define and explain laterization
Intense weathering,high leaching, formation of oxides, rapid decomposition, deep soil. Occurs in high temp high prec good drainage with stable landscape. Remaining soil has lots of oxides, no silica, and is low in nutrients - Bo horizon.
Four processes of soil formation
Additions (water, OM, stuff from air)
Losses (bottom - water, colloidal minerals, nutrients; top - water, erosion, energy, gases)
Translocations (iron, OM.. from one horizon to the next)
Transformation (creation of new minerals from decomposition, weathering)
Define and explain gleization
Occurs in water logged, poorly drained soils. Causes mottles of orange and grey creating either a Bg or Cg horizon.

Results from the reduction of iron (addition of electron) from decomposing organic matter. Occurs when no O2 present. Normally O2 would take up the electrons. Can be mottled because of cycles of wetting/anerobic conditions.
Explain and define podzolization
Formation of Bhs or Bs horizons (Spodic soils) in temperate, cooler, high rainfall locations with coniferous vegetation and course textured soils.

Slow decomposing O horizon releases organic acids which grab onto and leach Fe and Al oxides out of A and E horizons and precipitate them into B horizon as they finish decomposing.

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