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What is soil?
Solid earth material that has been altered by physical, chemical and organic processes so that it can support rooted plant life
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Why is soil important?
- It is the growing medium for our food
- Purifies our waste
- Home to plants and animals
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How long can it take to form one inch of topsoil?
100 years
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How much can an earthworm work for a year?
A ton of soil
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What is soil made up of?
- Mineral grains
- 25% is air
- Organic matter
- Bacteria
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What are the factors of soil formation?
- Climate
- Organisms
- Parental Material
- Topography
- Time
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How does climate help soil formation?
The greater the rainfall amount, the more rapid the rate of both weathering and erosion
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How do organisms help soil formation?
- Plant and animal activity produces humic acids that are powerful weathering agents
- They stabilize soil profiles and tend to increase erosion
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How does parent material help soil formation?
- Chemistry
- Mineralogy
- Grain size
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How does topography help soil formation?
- Ground slope (the steeper the surface slope, the more likely any eroded material is to be transported out of the system)
- - soils on hillslopes reach about 1m thickness while soils on flat surfaces, tend to thicken through time
- Elevation
- Aspect
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What does soil thickness mean?
Reflects the balance between rates of soil production and rates of downslope soil movement
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How does time help soil formation?
- Development and destruction of soil profiles
- Typical reaction rates are slow, the longer a rock unit has been exposed, the more likely it is to be weathered
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What are the transformations of soil?
- Decomposition of organic matter
- Humification to form complex organic matter
- Weathering of rocks
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What is decomposition?
Breakdown of soil organic matter to form soluble compounds that can be absorbed or leached
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Primary layers of soil
- Topsoil
- Subsoil
- Weathered bedrock
- Bedrock
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What is on Ao horizon?
Highly decayed organic material (Humus)
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What does humus do?
Gives topsoil a rich brown color
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What happens in A horizon?
Leaching
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What is leaching?
Carries minerals down into the lower soil horizons
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What is on B-horizon or subsoil?
Where the leached minerals end up
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Why do coastal plains have no bedrock?
Instead it has layers of sand, clay and gravel because the sea level changes over time
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What is the best soil texture for growing things?
- Loam -mixture of clay and silt
- Contain a good supply of nutrients, necessary for the organisms living in the soil
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Grain sizes
- Sandy particles - can be seen
- Silt - feel powdery and don't hold together when went
- Clayey - smallest soil particle
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What are the major nutrients found in fertile soils?
- Nitrogen
- Potassium
- Phosphorus
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What helps maintain the balance of nutrients?
Organic matter
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What is physical weathering?
Breaks rocks into small mineral particles
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What is chemical weathering?
Dissolves and changes mineral at the Earth's surface
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What is saprolite?
Weathered rock that retains remnant rock structure
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What limits soil development?
- Rapid erosion
- Slow evolution
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What do landslides do?
Redistribute and mix material creating uneven surfaces and topographic variability
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Methods to control soil erosion
- Conservation tillage - crop residues are left in the ground
- Crop rotation
- Contour plowing - fields are plowed in curves
- Strip cropping - placing closely sown crop under a loosely sown crop
- Terracing - to catch downhill runoff
- Shelter belt - to control blowing dust of the semiarid plains
- Greenbelts - using shrubs and trees as boundaries
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