Soil Formation & Classification: (Keywords: (Metamorphic Rock,…
Soil Formation & Classification:
Igneous Rocks are formed when magma cools and solidifies above the earth's crust e.g. Granite, Basalt.
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 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 involves the breakdown of rocks into sediments (Small particles);
Heating and cooling
Activity of animals & roots
Chemical weathering brings about a chemical change during the decomposition process;
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.
Hydration is the addition of water to a rock mineral. It happens after oxidation where iron oxide is formed.
Solution is when metal ions such as potassium, sodium & calcium dissolve in water.
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 are where plants & animals contribute humus when they die. Microorganisms break this down further into nutrients which improve soil fertility.
Topography is the slope of the landscape & has a direct impact on the moisture content of the soil.
Climate is where temperature & precipitation can contribute to the physical weathering (Heating & cooling) & chemical weathering (Hydrolysis, solution & carbonation) of rocks.
Time is the length of time the above four factors have impacts on soil formation.
Parent material is the original rock from which the soil was made has a big influence on its texture.
This is not always present, due to the absence of vegetation. It consists of organic material.
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.
This is known as subsoil. It's normally a lighter colour than topsoil, except where minerals have been leached & have accumulated in this horizon.
This contains parent material & is rocky in nature.
This is bedrock & is solid.
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.
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 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.
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.