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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
Why is soil important?
- It is the growing medium for our food
- Purifies our waste
- Home to plants and animals
How long can it take to form one inch of topsoil?
How much can an earthworm work for a year?
A ton of soil
What is soil made up of?
- Mineral grains
- 25% is air
- Organic matter
What are the factors of soil formation?
- Parental Material
How does climate help soil formation?
The greater the rainfall amount, the more rapid the rate of both weathering and erosion
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
How does parent material help soil formation?
- Grain size
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
What does soil thickness mean?
Reflects the balance between rates of soil production and rates of downslope soil movement
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
What are the transformations of soil?
- Decomposition of organic matter
- Humification to form complex organic matter
- Weathering of rocks
What is decomposition?
Breakdown of soil organic matter to form soluble compounds that can be absorbed or leached
Primary layers of soil
- Weathered bedrock
What is on Ao horizon?
Highly decayed organic material (Humus)
What does humus do?
Gives topsoil a rich brown color
What happens in A horizon?
What is leaching?
Carries minerals down into the lower soil horizons
What is on B-horizon or subsoil?
Where the leached minerals end up
Why do coastal plains have no bedrock?
Instead it has layers of sand, clay and gravel because the sea level changes over time
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
- Sandy particles - can be seen
- Silt - feel powdery and don't hold together when went
- Clayey - smallest soil particle
What are the major nutrients found in fertile soils?
What helps maintain the balance of nutrients?
What is physical weathering?
Breaks rocks into small mineral particles
What is chemical weathering?
Dissolves and changes mineral at the Earth's surface
What is saprolite?
Weathered rock that retains remnant rock structure
What limits soil development?
- Rapid erosion
- Slow evolution
What do landslides do?
Redistribute and mix material creating uneven surfaces and topographic variability
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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