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Soil Formation & Classification: (Keywords: (Metamorphic Rock,…
Soil Formation & Classification:
Keywords:
Metamorphic Rock
Physical Weathering
Sedimentary Rock
Chemical Weathering
Igneous Rock
Igneous Rock:
Igneous Rocks are formed when magma cools and solidifies above the earth's crust e.g. Granite, Basalt.
Sedimentary Rock:
Sedimentary Rocks are formed by layers of sediment deposited at the bottom of the seas and lakes & built up over millions of years & slowly compacted & solidified in the process e.g. Sandstone, Limestone.
Metamorphic Rock:
Metamorphic Rocks are formed from igneous or sedimentary rocks when heat or pressure brings about a change in the rock & its mineral content e.g. Marble, Slate.
Physical Weathering:
Physical weathering involves the breakdown of rocks into sediments (Small particles);
Heating and cooling
Freezing
Activity of animals & roots
Grinding action
Chemical Weathering:
Chemical weathering brings about a chemical change during the decomposition process;
Hydrolysis:
Hydrolysis is the chemical breakdown of a substance when it reacts with water. Hydroxide compounds are formed.
Oxidation & Reduction (OIL RIG):
Oxidation is the loss of electrons from a substance & the addition of oxygen to the substance.
Reduction is when electrons are gained & oxygen is removed from a substance.
O
xidation
I
s
L
oss
R
eduction
I
s
G
ain
Hydration:
Hydration is the addition of water to a rock mineral. It happens after oxidation where iron oxide is formed.
Solution:
Solution is when metal ions such as potassium, sodium & calcium dissolve in water.
Carbonation:
Carbonation is dissolving carbon dioxide in a liquid & forming carbonic acid.
Factors of Soil Formation:
The five factors that affect the formation of soil.
Living Organisms:
Living Organisms are where plants & animals contribute humus when they die. Microorganisms break this down further into nutrients which improve soil fertility.
Topography:
Topography is the slope of the landscape & has a direct impact on the moisture content of the soil.
Climate:
Climate is where temperature & precipitation can contribute to the physical weathering (Heating & cooling) & chemical weathering (Hydrolysis, solution & carbonation) of rocks.
Time:
Time is the length of time the above four factors have impacts on soil formation.
Parent Material:
Parent material is the original rock from which the soil was made has a big influence on its texture.
Soil Profiles:
O horizon:
This is not always present, due to the absence of vegetation. It consists of organic material.
A horizon:
This is commonly known as topsoil. It contains minerals & may have organic matter mixed through it. However, it can experience the effects of leaching & so it may be lacking minerals in certain conditions.
B horizon:
This is known as subsoil. It's normally a lighter colour than topsoil, except where minerals have been leached & have accumulated in this horizon.
C horizon:
This contains parent material & is rocky in nature.
R horizon:
This is bedrock & is solid.
Leaching:
Leaching is a process in which soluble matter such as minerals dissolves in water filtering through soil and is carried downwards. The leached minerals may accumulate at a lower horizon.
Podzolization:
Pozolization occurs in acidic pH conditions where minerals such as iron and aluminum are leached from the A horizon, leaving it bleached in colour. They accumulate in the B horizon, forming an iron-pan that is impermeable to water.
Brown Podzolic Soils:
Brown Podzolic Soils are found in lowland areas overlying acid parents materials. They are suitable for forestry but can also be used for crops and grazing.
Brown Earths:
Brown Earths are found in lowland areas overlying limestone parent materials. They are very suitable for crop production as they require little lime or fertilizer and have good drainage.
Gleys:
The formation of gleys soil is called gleization.
Gleys are poorly drained soils that form in waterlogged conditions. The B horizon has a mottled appearance due to oxidation / reduction of soil.
There are two types of gleys;
Groundwater gleys formed in depressions in the landscape and surface-water gleys found overlying land impermeable to water.