Download CHAPTER 12 – SOIL NOTES

CHAPTER 12 – SOIL NOTES
What is Soil?
_Soil__ is a mixture of _weathered bedrock_ and decayed _organic __ material. The organic material is
called Humus.
_Soil__ by volume, on the average consists of_ 45%__ mineral, _25%__ water, 25%__ air, and _5%__
organic matter.
Factors That Influence The Development of Soil
1.
_Parent material__- organic and mineral material in which soil formation begins
2.
_Topography - unprotected soils on slopes tend to be thin and less fertile.
3.
_Climate __ - most important factor
4.
Living organisms- plant and animal activity can affect soil development.
-Mosses and lichens release acids that break down soil.
- Animals burrow into the ground and break up soil and let
in more air and water into the soil. This helps speed up the
breaking down of rock.
5.
_Time__- required for soil development.
The result of all of these forces is that soil develops into _layers __ known as __horizons_____.
These horizons together are known as a __soil profile______.
HORIZONS OF A MATURE SOIL PROFILE
-Soil provides support, nutrients,
and water for plants.
-Plants get the nutrients Nitrogen,
Potassium, and Phosphorus from
soil
__O Horizon___ - consists of _leaf _ litter and __organic___ material - _Humus___. _dark__ in color.
__A Horizon __ - _Topsoil___. __Dark __ in color and has varying amounts of __organic___ matter.
- most productive layer of the soil.
As water moves down through the topsoil, many soluble minerals and nutrients dissolve. This process is called
Leaching. The dissolved materials _leach __ downward into lower horizons.
_B Horizon___ - _Subsoil __. _Light __ in color and low in organic matter.
_C Horizon___- partially __weathered___ parent material.
_R Horizon __ - __Bedrock or Parent material___
**THE FIRST STEP IN THE FORMATION OF SOIL IS THE WEATHERING OF THE BEDROCK.
-A soil whose parent material is the bedrock beneath the soil is called Residual Soil.
- Soil that forms from materials transported by winds, rivers, and glaciers is called Transported Soil.
Soil Erosion - removal of soil by wind, water, ice or gravity.
Mass Movements - refers to the downward movement of weathered material (soil and rock) by gravity.
Landslide - term commonly used for the movement of a mass of bedrock or loose soil and rock down a steep
slope.
- Tend to occur after heavy rain or in the spring when large amounts of snow are melting.
- Greater risk in regions near volcanoes or in earthquake prone regions.
Types of Landslides
1. Creep - slow movement of soil down a slope. It will cause fence posts, poles, mailboxes and other
fixed objects to lean downhill. Occurs with repeated freezing and thawing temperatures.
2. Slump - blocks of land tilt and move downhill along a surface that curves into the slope.
3. Earthflow - mass of weathered material that has been saturated with water flows downhill. Some take
place relatively quickly or may last for a period of years.
4. Mudflow - rapid movement of water that contains large amounts of clay and silt. They tend to occur in
drier regions that experience infrequent but heavy rainfall.
5. Lahars - mudflows that accompany volcanoes.
Types of Soil Erosion by Water
1.
__Rill_______ - series of small channels on a slope.
2.
__Sheet______ - removal of thin layer of soil from a large area.
3.
__Gully______ - large, wide channels
4.
__Splash_____ - direct movement of soil by splashing.
Eutrophication_____ - process where water bodies receive excess nutrients that stimulate excessive plant
growth.
Controlling Soil Erosion
1.
__Terracing_____________
2. Contour Farming
3. Windbreaks