SOIL!! :D
Chapter 14
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Geologic Processes
Crust - Extremely thin, less-dense solid.
Mantle - Makes up majority of earth, and surrounds a small core of iron.
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Outermost portion is solid.
 Crust and solid outer mantle collectively known as the lithosphere.
 Asthenosphere is a thin layer below the outer mantle capable of
plastic flow.
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Geologic Processes
Plate Tectonics - _________________________________________________________
_______________________________________________________.
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Heat from earth core causes movement.
 Plates are pulling apart in some areas, and colliding in others.
 Building processes counteracted by processes tending to tear down land.
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Geological Processes
Weathering - ____________________________________________________________
_______________________________________________.
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_______________ - Results from physical forces reducing size of rock particles
without changing the chemical nature of the rock.
 Freezing and Thawing Cycles
 Erosion from Wind and Moving Water
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Weathering
_______________ - Involves the chemical alteration of rock in such a manner that it is
more likely to fragment or be dissolved.
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Rock fragments exposed to atmosphere may oxidize, or otherwise chemically
change.
Soil and Land
Land - Portion of world not covered by water.
Soil - ___________________________________________________________________
__________________________________________________.
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Good Agricultural Soil:
 45% Mineral
 25% Air
 25% Water
 5% Organic Matter
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Soil Formation
Soil formation begins with fragmentation of ____________________________ .
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Ancient layers of rock, or more recent deposits from lava flows or glacial activity.
First organisms to gain a foothold in weathered parent material also contribute to soil
formation.
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Lichens form pioneer community.
 Decomposition of lichens further alters underlying rock.
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Soil Formation
_______________ - Decaying organic material.
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Mixes with top layers of rock particles, and supplies needed nutrients to plants.
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Creates crumbly soil which allows adequate water absorption and drainage.
Burrowing animals bring nutrients up from deeper soil layers, improving soil fertility.
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Other Factors Influencing Soil Formation:
_______________
_______________
_______________
_______________
_______________
_______________
_______________
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Soil Properties
_______________ - Determined by the size of mineral particles within the soil.
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Too many large particles leads to extreme leaching.
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Too many small particles leads to poor drainage.
 Gravel >2.0
 Sand
0.05 - 2.0
 Silt
0.002-0.05
 Clay
< 0.002
mm
mm
mm
mm
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Soil Properties
_______________ - Refers to the way various soil particles clump together.
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In good soils 2/3 of intra-soil spaces contain air after excess water has drained.
 Friable - Crumbles easily.
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Protozoa, nematodes, earthworms, insects, algae, bacteria, and fungi are typical
inhabitants of soil.
Soil Profile
_______________- A series of horizontal layers of different chemical composition,
physical properties, particle size, and amount of organic matter.
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Each recognizable layer of the profile is known as a horizon.
Soil Horizons
_______________- Litter - Un-decomposed or partially decomposed organic material.
_______________- (Topsoil) Uppermost layer - contains most of the soil nutrients and
organic matter.
_______________- Formed from leaching darker materials.
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Not formed in all soils.
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Usually very nutrient poor.
Soil Horizons
_______________- (Subsoil) Underneath topsoil. Contains less organic matter and
fewer organisms, but accumulates nutrients leached from topsoil. Poorly developed in
dry areas.
_______________- Weathered parent material, very little organic material.
_______________- Bedrock
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Soil Profiles
Over _______________________________________________. However, most
cultivated land can be classified as either grassland or forest soil.
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Grassland Soils - Usually have a deep A Horizon - low rainfall limits topsoil
leaching.
 A Horizon supports most root growth.

Soil Profiles
Forest Soils - ____________________________________________________________
________________________________. (High rainfall areas)
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Tropical Rainforests
 Two features of great influence:
 High Temperatures

______________________________.
 High Rainfall

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______________________________.
Soil Erosion
Erosion - ___________________________________________________________.
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Worldwide removes 25.4 billion tons/yr.
 Made worse by deforestation and desertification.
 Poor agricultural practices increase erosion and lead to the transport of
associated fertilizers and pesticides.
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Soil Erosion
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Most current agricultural areas ________________________________________.
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Wind erosion may not be as evident as water erosion, but is still common.
 Most common in __________________________________.
 Great Plains of North America have had four serious bouts of wind
erosion since European Settlement in the 1800s.
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Soil Conservation Practices
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When topsoil is lost, fertility is reduced or destroyed, thus fertilizers must be used to
restore fertility.
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________________________________________________________.
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Over ________ of U.S. land is suitable for agriculture, but only _________ does
not require some form of soil conservation practice.
Soil Conservation Practices
Agricultural Potential
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Worldwide:
 _______ land surface is suitable for crops.
 _______ in permanent pasture.
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United States:
 _______ land surface suitable for crops.
 _______ in permanent pasture.
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African Continent:
 _______ land surface suitable for crops.
 _______ can be used for pasture.
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Soil Conservation Practices
Contour Farming - ________________________________________________________
_____________________________________________________.
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Useful on gentle slopes.
Strip Farming - ___________________________________________________________
_____________________________________________________.
Terracing - ______________________________________________________________.
–
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Good for very steep land.
Soil Conservation Practices
_______________ - Depressions in sloping land where water collects and flows off the
land.
–
Channels movement of water.
_________________ - Planting of trees or other plants that protect bare soil from full
force of the wind.
–
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Reduces wind velocity decreasing the amount of soil that can be carried.
Conventional vs. Conservation Tillage
Plowing has multiple desirable effects:
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Weeds and weed seeds are buried or destroyed.
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Crop residue is turned under.
 Decays faster and builds soil structure.
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Leached nutrients brought to surface.
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Cooler, darker soil brought to top and warmed.
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Problem:
Each trip over the field is an added expense to the farmer, and at the same time
increases the amount of time the soil is open to erosion via wind or water.
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________________________ - Uses less cultivation to control weeds and
prepare soil, but generally leaves 15-30% of soil surface covered with crop
residue after planting.
Problem:
Conservation Tillage - Further reduce amount of disturbance and leaves 30% or more of
soil surface covered with crop residue.
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Mulch Tillage - ____________________________________________.
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Strip Tillage - _________________________________________.
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Ridge Tillage - ______________________________________.
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No Till - ____________________________________________.
Positive Effects of Reduced Tillage
___________________________________________________.
___________________________________________________.
___________________________________________________
__________________________________________________.
Double - cropping
___________________________________________________-.
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Drawbacks of Conservation Tillage
_________________________________________________.
Crop residue reduces _________________________________________________.
Accumulation of plant residue can ________________________________- requiring
more insecticides and fungicides.
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Protecting Soil on Non-Farm Land
By using appropriate soil conservation practices, much of the land not usable for crops
can be used for grazing, wood production, wildlife production, or scenic and
recreational purposes.