What is Soil - Earth and Environmental is Soil •Soil is a complex ... Effects of Particle Sizes ... •What determines the composition of a soil? •Mostly the bedrock, erosion, organic stuff ...
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What is Soil
Soil is a complex mixture of weathered rock, minerals, organic material (both living & decaying), water, and air.
Different soils have different amounts.
What might change the amounts?
On average, soil has the following ratios: 45% minerals & rocks
5% organic material
How is Soil Produced?
Weathering of rocks and minerals
Deposits of sediments washed/blown to the site
Decomposition/actions of living things.
Weathering of Rock
Weathering is the physical or chemical breakdown of rock into smaller pieces
These pieces may be large or too small to see!
Two types of weathering:
Physical breakdown of rock
Chemical composition of the rock does not change
Plant & Animal Activity
When rocks come to the surface, pressure on them is reduced.
This can allow cracks to form, and the rocks break apart.
When water flows into the cracks in rocks & freezes.
Why does this split the rocks?
Abrasion When rocks broken from other processes
collide and break even more.
Happens because of gravity, ice, running water, or windwait, how does wind do this?
Plant & Animal Activity Plant roots act like ice to split rocks
Animals, mostly ones that burrow, expose other rocks for further weathering.
Chemical reactions break the minerals in the rock into different materials
Oxidation When elements
in the rock combine with Oxygen, and break off as new compounds.
Usually happens in rocks with iron
Produces a red color
When chemicals in the rock react with water, causing some of the minerals to break away from the rock.
Often happens with metals like Potassium & Aluminum
Carbonation When CO2 gets into water it makes Carbonic Acid
This acid can stick to some minerals and form compounds that are washed away by water.
This often happens to limestone.
Some living things produce acids that are released to the environment.
These acids can make cracks in rocks and start the weathering process.
Examples: Lichens & mosses
Nitrogen & Phosphorus from fossil fuels get into the air and combine with rainwater
This rainwater weathers rock more rapidly than normal rain.
Formation of Soil
When new rock is exposed, soil begins to form.
This newly exposed rock is known as Bedrock.
Formation of Soil Weathering begins to break the bedrock into
This layer of partially weathered rocks, above the bedrock, is known as Regolith.
The size of soil particles also affects the characteristics of a soil.
Soils are usually categorized by the amounts of each type of particle that they have.
Clay: less than 0.0002mm
Silt: 0.0002mm 0.05mm
Sand: 0.05mm 2mm
Effects of Particle Sizes
The size of soil particles affects how much water & air the soil can hold.
The smaller the particles, the less the soil can hold.
However, if the soil is made entirely of larger particles, the water will run right through the soil!
We measure particle sizes by measuring Porosity.
The measure of the volume of pores and distance of pores
Effects of Particle Sizes
Infiltration: the rate at which water from precipitation or other sources flows into the soil
Saturation:The amount of water and air
that can move through soilWater Water
High permeability Low permeability
The formation of soil in different areas produces different layers.
These layers are called Horizons.
The composition and depth of horizons is measured by looking at a Soil Profile.
What changes a Soil Profile?
What determines the composition of a soil?
Mostly the bedrock, erosion, & organic stuffbut what determines these?!?
Climate mostly affects the layers of a soil, but not the materials found in the soil.
In general, climates that have all 4 seasons have all the layers of soil.
What is erosion?
The movement of weathered materials from one location to another.
Soisnt this the same as weathering?
No! Weathering helps to build soil, soil erosion destroys soil.
What Causes Soil Erosion?
Human Actions can speed up the process!
Humans & Erosion
So, how do humans affect this Soil Erosion thing?
Development for housing/buildings
Farmingthis is the big one
Humans & Erosion
Farming can expose a lot of lose soil to erosion.
This soil is the O and A horizonswhy are these important?
These contain most of the organic material in the soil, which plants and animals need to survive.
Is Erosion Really a Problem?
Areas of serious concern
Areas of some concern
Stable or nonvegetative areas
What can we do to prevent Erosion?
Hillsides are plowed in curves that follow the shape of the land.
Prevents water from flowing straight down.
Crops are planted in alternating bands.
This way, the whole area is not filled with row crops that dont cover all the land.
Hills are carved into flat steps.
This prevents water from flowing rapidly down the hill.
Planting a crop to harvest 1 year, and one to leave in place the next year.
Often combined with strip and contour farming.