Lecture 4b Soil Forming Factors

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Lecture 4bSoil Forming Factors

• Parent Material
• Climate
• Vegetation
• Topography
• Time
• Soils vary from place to place because the
  intensity of the factors is different at
  different locations.

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Soil Forming Factors - Biotic (Vegetation)

• Animal - Soil Mixing earthworms, crawfish,
  scorpions, moles, gophers this mixing can
  result in the destruction of horizons.

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Botic (cont.)

• Vegetation - Additon of Organic Matter (OM).
• Prairie OM added to upper 2 ft. of soil due to
  fibrous root system of grass plants.

Ap
A
AB
Bg
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Biotic (cont.)

• Forest OM added to upper 4 due to yearly leaf
  fall to surface of soil.

A
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Prairie - Border Biotic Factor

• Prairie - Border soils (oak savannahs) have the
  influence of the prairie and forest due to
  changes in vegetation over the past 8000 years
  the soils have been both under prairie and forest.

Ron E. VanNimwegen
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Dyad

• Describe your experience of being in a native or
  restored prairie or an old growth forest. What
  was unique about this experience?

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SFF - Topography or Landscape Position

• Catena - A series of soils with different
  horizons due to differences in their depth to the
  water table
• Drainage classes
• Well-drained
• Moderately well-drained
• Somewhat poorly drained
• Poorly drained

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Catena Natural Soil Drainage Classes

• NOTE Natural drainage refers to depth to water
  table not permeability.
• Natural Soil Drainage Classes
• Well Drained - mottles begin gt 4 ft.
• Moderately well drained - mottles gt 3 ft.
• Somewhat poorly drained -
  mottles gt 2 ft
• Poorly drained - dark surface
  - gray colors in subsoil below
  surface (red mottles)

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Drainage Classes (depth to water table)
gray mottles
gray colors below A
gray mottles in brown B
Mod.well Dr.
mottles gt 4 feet
Well Drained Somewhat
Poorly Poorly Drained
Drained
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Topography erosion deposition
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Summit and Backslope

• Summit will have minimum erosion and maximum soil
  development (greatest horizonation).
  
• Backslope will be similar to summit unless slope
  is gt 20.

summit
backslope
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Shoulder

• Greatest erosion - least water infiltration -
  greatest runoff - minimal soil development.

Ap Bw Bk BC C
shoulder
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Footslope

• Deposition of materials from upslope - may be
  near water table - may have greatest leaching due
  to water from upslope and rainfall.

Ap A1 A2 A3 AB Btg
Upslope Sediments
footslope
Water
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Aspect

• Direction the slope faces - important when slope
  is gt than 10 . Noticeable in SE MN.
• North Slope 1. colder soils, 2. less
  evaporation , 3. more leaching thus more soil
  development
• South Slope 1. warmer soils, 2. more
  evaporation, 3. less leaching thus less soil
  development.

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Aspect

• Direction the slope faces
• Important when slope gt 10

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Hillslope in SE Minnesota
North Facing Slope - more trees - more soil
develop- ment.
South Facing Slope (open, fewer trees)
Less soil development
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Soil Forming Factor - Time

• Vegetation and Climate act on the Parent Material
  and Topography over Time.
• The age of a soil is determined by its
  development and not the actual number of years it
  has been developing.
• How long it takes for a soil to become old
  depends on the intensity of the soil forming
  processes or intensity of the other 4 soil
  forming factors.

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Age Sequence

• Youth

• Juvenile

A
A Bw C
C
Old Age Senile
Mature
Adult
A E Bt1 Bt2
A E Bt C
A E Btqm Bqm
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Factors that retard soil profile development

• low rainfall
• high lime content
• high clay content
• steep slopes
• cold temperature
• severe erosion

• low humidity
• high quartz
• hard rock
• high water table
• constant deposition
• mixing by animals

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Factors that Slow Soil Formation

• Climate
• Low rainfall
• Low humidity
• Cold temperature

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Factors that Slow Soil Formation

• Biota
• Mixing by animals or man

Human made soil Suborder ARENT
anthropogenic factor human influence on soil
formation Direct plowing, manuring, liming.
Indirect changing soil forming factors
deforestation, relief, parent material.
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The Effects of Management on the Interactions
Between Plants and Soils

• In this example, heavy continuous grazing
  followed by drought produces positive feedbacks
  between vegetation and soil properties that
  enhance physical, chemical, and biological
  degradation processes.
• These feedbacks lead to the following
• a) a decrease in soil organic matter and an
  increase in size of bare spaces,
• b) a decrease in soil aggregate stability and
  resistance to erosion,
• c) a loss of topsoil and a decrease in
  infiltration,
• d) an additional loss of grass and increase in
  shrubs, which cause the feedback loop to
  continue.
• (Figure modified from Bird et al., 2001.)

• Arrow represent physical, chemical, and
  biological degradation

Desert grass displaced by shrubs. Soil OM
decreases and Size of bare space increases.
Aggregate stability and resistance to erosion
decrease Topsoil and fertility lost and
infiltration decreases.
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What happens to a soil with time

• Loss of nutrients ( bases) lower pH or soil
  becomes more acid
• Increase in concentration of iron or soil becomes
  redder
• Increase in clay content or old soils have more
  clay
• Deeper weathering into the parent material
• Oldest soils in US are on high terraces and
  alluvial fans of the mountains in the western
  U.S.

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Oldest soils in United States
Durixeralf - California
Petroargid Arizona
Petrocalcic
A Bk Bkm C
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Petroargid - New Mexico
A
BA
Bt
Btk
Bkm
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Stonehenge was not built in one single step, but
rather in four separate stages, dating from
approximately 3100BC to 1500BC.
The End
Neolithic peoples originally inhabited the
fertile landscape as farmers. Their crops,
however, quickly depleted the
chalky soil of the Salisbury Plain.