PST 2310 SOIL Technology Chapter 1: The Importance of Soil Chapter 2: Soil Origin and Development

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PST 2310 SOIL TechnologyChapter 1 The
Importance of SoilChapter 2 Soil Origin and
Development
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The Importance of Soil

• Soil shapes human history
• Egyptians 4000 years ago, Nile river
• The dust bowl 1930s, due to soil misuse
• World population doubles every 40 years
• Soil is non-renewable in our life time

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Soil Is a Life-supporting Layer of Material

• Core, mantle, crust, atmosphere
• Crust, rock is 50 miles thick
• Atmosphere is 170 miles thick
• Soil is thin layer in between

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Oxygen

• Plant roots need oxygen to grow.
• Temperature Our temperate climate ranges between
  40 to 85 degrees.
• Water, cycles from one stage to next, one
  location to next.
• Carbon, converted by photosynthesis.
• Nutrients, cycle through the soil.

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Photosynthesis Respiration

• Photosynthesis
• 6CO212H2O light energy --gtC6H12O66O26H2O
• Respiration
• C6h12o66o2---gt.6co26h2oenergy (691 cal/mol)

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SOIL A 3-PHASE SYSTEM

• Solid phase (45)
• Liquid phase (25)
• Gas phase (25)
• Organic matter (5)

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SOIL PHASES
5 O.M.
25 air
45 mineral
25 H20
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Agricultural Uses of Soil

• Cropland
• Grazing land
• Forest
• Other, especially landscape usage

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Nonagricultural Uses of Soil

• Recreation
• Foundations
• Shrink-swell potential
• Load bearing capacity
• Waste disposal
• Building materials

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Land Use in the United States

• Rangeland
• 132 Million
• Acres

Pasture 132 million (8) Urban land 92 million
A. (6) Other land 55 million acres (4)

• Cropland
• 382 Million
• acres

• Forestland
• 395 Million
• Acres

• Conservation, 34 M, (2)

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Soil Origin and Development

• The soil body
• Pedon, a small body of soil 10 to 100 sq ft
• Poly pedon, a collection of pedons

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Pedons

• Pedon C

• Pedon A

• Pedon B

• Pedon A

• Pedon B

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Soil Formation

• Physical weathering
• Frost Wedging
• Chemical Weathering
• Solution
• Hydrolysis
• Oxidation
• Root wedging

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Soil Formation and Root Wedging
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Rocks and Minerals

• Igneous rock.
• From volcanic activity.
• Sedimentary rock, deposited by wind or water.
• Sandstone
• Limestone
• Metamorphic rock.
• Sedimentary rock changed by pressure etc.

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Rocks and Minerals

• Sedimentary rock
• Igneous rock
• Metamorphic rock

quartzite
quartzite
basalt
ocean
sandstone
Mud sand
sandstone
marble
limestone
marble
limestone
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Rocks and minerals

• Picture page 20

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Rocks and Minerals

• Parent Material Glacial Ice
• Wind Water
• Gravity Organic deposits
• Climate Organisms
• Topography Time

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Parent Material

• Residual soils
• Formed in place
• Formed slowly

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Glacial Ice

• Carried materials of much of North America,
  1,000,000 to 10,000 years ago
• Glacial drift,deposits left at melting
• Glacial till, dropped in place, no sorting
• Glacial outwash, sorted
• Lacustrine, lake deposits

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Wind

• Eolian deposits, soil deposited by wind
• Loess, wind deposited silt

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Eolian Wind Deposited Soil
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Water

• Alluvial soils deposited in moving fresh water
• Alluvial fans, form just below hills
• Levees, soil deposited in low ridges along a
  river bank
• Floodplains, large flat areas, soil settles out
• River terrace, when a river cuts a new path and
  leaves old area high and dry

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Alluvial Fan
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Water

• Marine sediments, form in the ocean
• Deltas, where a river meets the ocean and leaves
  deposits at the mouth

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Delta River Soil Deposits
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Gravity

• Colluvium, parent materials slid down a slope
• Talus, sand and rocks that collect at the foot of
  a slope

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A Talus Slide
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Organic Deposits

• Minerals soils contain less than 20 organic
  material
• Organic soils contain 20 or more organic
  materials, usually form under water
• Low oxygen under water retards decay

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Mineral Soils
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Climate

• Temperature affects speed of chemical reactions
• Reactions occur mostly above 60 degrees F
• Rainfall leaches materials deeper into the soil

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Effects of Climate

• Cooler temp
• More o.m.

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Effects of Climate
Forest Grassland Desert mixed
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Topography

• Steepness of slope effects water movement.
• Steep or south slopes are drier than gentle or
  north slopes.
• The top of a slope is drier than the bottom.
• Steep slopes promote erosion.
• Low spots gather soil and have higher O.M.

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Time

• Soil formation can be in as little as a hundred
  years with good conditions
• Under poor conditions, soil formation will take
  hundreds of years

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The Soil Profile

• The master soil horizons are
• A,B,C
• In order from the top down the horizons are
  O,A,E,B,C, and R

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The O horizon

• The O horizon is formed from wholly or partially
  decayed organic matter
• Usually occurs in undisturbed soil

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The A horizon

• Called topsoil by most growers
• Surface mineral layer where organic matter
  accumulates
• Looses clay, iron to leaching
• Best environment for growing crops

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The E horizon

• Zone of greatest eluviation
• Clay, chemicals are leached to lower level
• Light in color
• Usually found in sandy forest soils in high
  rainfall areas

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The B horizon

• Subsoil
• Zone of accumulation, or illuviation
• Collects materials leached out of the A horizon
• Lower O.M.
• A,E, B are called solum

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Subdivisions of Master Horizons

• As soils age, they develop more layers than basic
  horizons
• Assume letter of both I.e.AB
• May also be identified by lower case letter that
  tells specific trait
• Further subdivision using number after lower case
  letter, I.e. Bt1 meaning two distinct layers in
  the B horizon

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• Undecomposed o.m.

Oi

• Oa

• Decomposed o/m.

• Leached mineral horizon

A

• Zone of maximum leaching

E
EB

• Transitional layer similar to E or A

• Transitional layer similar to B

BE

• Zone of maximum accumulation

B
BC

• Transitional layer between B C

• Horizon similar to parent material

C
R

• Igneous, sedimentary or metamorphic rock