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Chapter 13/14 revision (soils) - Coggle Diagram
Chapter 13/14 revision (soils)
Soil composition
Living organisms (1%)
Soil is home to creatures such as earthworms, woodlice and slugs.
It is also home to millions of micro-organisms (tiny creatures too small to be seen with the naked eye)
There are more micro-organisms in a teaspoon of soil than there are people on Earth
As animals such as earthworms dig through soil, they break it up and mix it, allowing more water and air to enter the soil
When these creatures die, their remains add nutrients to the soil
Humus (4%)
Organic matter is composed of the remains of dead creatures and plants
It is broken down and mixed into the soil by living organisms
As the organic matter decays, it turns into a dark brown or black substance called humus.
Humus provides nutrients that make the soil particles bind together
Air (25%)
Air fills the spaces (pores) between the mineral particles in the soil.
When worms burrow through the soil, the mix it and also make it easier for water and air to pass through.
It contains oxygen and nitrogen (these are vital for the growth of plants)
Air allows living organisms to survive in the soil
Water (25%)
Water is important for planth growth because it contains dissolved minerals
Plants absorb these minerals through their roots
Water helps bind the soil particles together.
Mineral matter (45%)
It is made up of rock particles that have been broken down due to weathering/erosion
It includes sand, silt and clay
The biggest ingredient in soil composition
How are soils formed?
Vegetation
When vegetation dies, it is broken down and decays to add humus and nutrients to the soil
Deciduous vegetation provides more leaf fall then coniferous trees
Living organisms
Micro organisms such as bacteria and fungi help to break down the dead plant and animal life in the soil, turning it into humus
Parent material (bedrock)
Soils that develop from limestone are more fertile than those that develop from granite or sandstone
The type of rock from which the soil is formed is called the parent material. I
This is what determines the type of soil in an area
For example, granite is slow to break down by weathering, while sandstone breaks down easily and forms soil quickly
Landscape
Upland areas are cold and wet, so soils are often waterlogged.
There is little plant and animal life, so there is less humus.
Climate
Hot climates experience chemical weathering
Cold climates experience freeze-thaw
Temperature and rainfall influence the rate at which the parent rock is broken down by weathering
Time
One of the most important factors in soil formation
It may take up to 400 years for 1cm of soil to form
The longer a rock is exposed to the forces of weathering, the more it is broken down.
Soil profiles
Leaching
Hardpan
If leaching is very servere, minerals such as clay and iron oxide (rust) build up at the bottom of the A horizon
They cement together to form a crust called hardpan
Hardpan is impermeable
Impermeable: Rocks that do not let water soak through them
It causes the soil above it to become waterlogged
Waterlogged: saturated with or full of water.
In wet climates, such as in Ireland, water soaks down through the soil.
As it does so, it washes minerals, humus and nutrients down into the B horizon
Leaching can cause the A horizon to lose its fertility because it washes the nutrients down beyond the reach of plant roots.
Soil horizons
B horizon
Found beneath the A horizon
Subsoil
Lighter in colour
Less humus than the A horizon
It has more stones than the A horizon
It is closer to the parent material
Protected from weathering
C horizon
It is made up of large and small rock particles
It lies directly on top of the solid bedrock
It consists of partially weathered parent material
A horizon
Loose and crumbly
Most organisms live in this layer
Darker than the other layers
High humus content
It is generally the most fertile layer of soil
The upper layer of the soil is called top soil
Bedrock
The hard layer of rock that lies beneath looser rocks and soil
Litter layer
Plant litter
Dead plant material,such as leaves and twigs that has fallen to the ground
If you dig down into the ground as far as the bedrock, you will find a number of different layers. Each layer is called a horizon.
The layers can be seen along road cuttings and other areas where the soil is exposed
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Natural vegetation and soil
How soil influences vegetation
Drainage
Sandy soils are free-draining and can support a wide range of vegetation.
Clay soils become waterlogged and support a limited range of vegetation.
Depth
Deep soils support vegetation with long roots such as deciduous forests.
Shallow soils are limited in the vegetation that they can support (e.g. conifers).
Nutrients
Fertile soils contain a wide range of nutrients, including nitrogen and calcium, and can support a wide range onpf vegetation
Infertile soils can support only a limited range of vegetation.
How vegetation influences soil
Leaching
Vegetation can absorb surface water, thus reducing the amount of leaching.
Without vegetation, the water moves downward in the soil, leaching nutrients.
Soil erosion
Roots bind soil particles together, thus slowing down or preventing soil erosion.
Loss of vegetation cover results in soil being eroded by surface water.
Plant litter
Deciduous trees provide lots of plant litter to form humus and brown earth soils.
Coniferous trees provide little plant litter (mostly needles), leading to the formation of relatively infertile soil
Soil as a natural resource
Soil is an important natural resource
Healthy soil performs numerous functions
Clean water
This is largely the result of water being filtered as it percolates through the soil and rock.
In storing water, soil also assists in the control of flooding.
Soil provides raw materials for industry
Sand for the construction industry
Soil bacteria for antibiotics
Kaolin for the pottery industry
The production of food
For both human and animal use
Soil stores nutrients and gradually releases them to plants and crops
Most important function of soil
Soil is a carbon sink
Along with plants and the oceans, it absorbs and stores carbon
dioxide from the atmosphere.
Soil is a non-renewable resource
It is formed at a rate very much slower than the rate
at which it is being damaged.
Today, one-third of the soil on Earth is either moderately or
highly damaged.
The increased demand for food
The result is soil erosion, desertification, soil pollution and loss of soil fertility.
Poor farming practices
The sustainable exploitation of soil
Soil is a non-renewable resource and is increasingly under pressure
Healthy soil
Stores and filters groundwater
Stores vast quantities of carbon
Grows fibres and trees
Supports innumerable organisms
Produces crops used to feed humans and animals
Provides bacteria from which antibiotics can be developed
The soil crisis
Human factors
Desertification
The areas that are most affected by desertification are those at the edge of existing deserts.
Desertification in the Sahel
Nowhere is desertification more severe than in the Sahel, a region at the southern edge of The Sahara Desert.
Desertification in the Sahel results from a combination of climate change and human activities.
The climate of the Sahel has changed over the last thirty years
Rainfall in the region has become unreliable. Rains ,as come late or may not come at all
As a result several droughts have occurred
Higher temperatures lead to increased evaporation and less condensation
The countries of the Sahel have a high birth rate, leading to rapid population growth and an increased demand for food. This placed increased pressure on the land
Overcropping occurs when land is continuously cultivated, as many farmers change from grazing to growing food crops. The soil does not get time to recover the nutrients that have been taken out by other crops. Without fertilisers, the soil soon loses its nutrients and the crops fail
People need wood for shelter and cooking. This leads to deforestation as people travel from place to place in search of trees and even shrubs. Their roots no longer anchor the soil and soil erosion is speeded up.
People keep large herds of cattle and goats, leading to overgrazing of the land. Overgrazing is caused by grazing too many animals on a piece of land for too long, so it is unable to recover its vegetation.
Soil can be damaged if it is overused; it can lose its nutrients and become infertile. This means vegetation and crops can't grow. The area can become like a desert. This spread of desert conditions is known as desertification.
Solutions to desertification
Desertification can be stopped - or even reversed - if there is good management of soil. Most solutions to desertification in the Sahel are carried out at a local level rather than in the region as a whole
Results of desertification
Hundreds of thousands of people have died because of famine for example in the 1980s
Millions of people have been forced to migrate in search for food or aid. Many of these people still live in refugee camps
Vast areas of land are now unable to support agriculture
Many people have moved into urban areas, leading to the growth of slums
Millions of animals have died
Loss of fertility
Pesticides and other chemicals used on crop plants have helped farmers to increase yields. However, the overuse of some of these chemicals changes the nature of the soil and interferes with the micro-organism population
Monoculture is the continuous production of one type of crop year after year on the same area of land. Chemical fertilisers are used to replace the nutrients absorbed from the soil. Plants are more open to disease, requiring the increased use of pesticides.
Agriculture practices, many on an industrial scale, damage and degrade soil quality.
Climate change
Soil erosion
Soil erosion is the washing away or blowing away of the upper part of the soil cover
When the plant cover is disturbed by cultivation, grazing, deforestation, burning or bulldozing, the soil is exposed to erosion by wind and water. The slow rate of natural erosion is greatly speeded up. Soil is lost at a rate much faster than new soil can be created
Undisturbed by humans, soil usually covered by a canopy of grasses, shrubs and tress. The canopy protects the soil when the rain falls or the wind blows
Soil conservation
Soil conservation is the prevention of soil loss from erosion
or reduced fertility.
It is best done by using sustainable
agricultural practices.
Contour ploughing
How it works
The furrows will be level and can hold rain, preventing run-off and reducing soil erosion
Where it is used
Effective in the large cotton fields and tobacco fields of the southern states of the USA.
What it is
Sloping land is ploughed along the contours rather than up and down the slope
Terrace farming
What it is
Terracing is a method of creating flat areas on hillsides. Mud or stone walls are built and the space behind them is filled with soil.
How it works
When it rains, instead of washing away the soil, the soil stays in place. Nutrients are retained or carried down to the next level.
Where it is used
Popular in Asia for planting rice
Crop rotation
How it works
It increases the yield and the fertility of the soil because the nutrients used by one of the crops are replaced by the different crop in the next year
Where it is used
Beneficial in all crop farming areas
What it is
Growing, for example, a cereal crop and a root crop in the same field on consecutive years
Windbreaks
How it works
Evergreen trees are the best as they provide year-round protection. Trees and hedges slow down surface run-off and keep nutrients in the soil
Where it is used
Effective when combined with strip farming, where different crops, such as cereal and root crops, are grown in long strips in the same field.
What it is
Rows of tall trees that are planted close together around the farmland
Soil types in Ireland
There are four main soil types in Ireland
Peaty soils
Soil characteristics
Apart from water, peat soils contain solid organic matter that decays slowly
The partly decayed solids include roots, stems, leaves and seeds
Very dark in colour and has a spongy texture
Human response
When drained, it is great for growing root crops and salads (think compost)
Harvested as a non renewable source for fuel
An acidic soil that has few nutrients and is not naturally very fertile
Relief, drainage, climate and vegetation
Especially common in areas with high rainfall
Asociated with badly drained lowlands
Found in uplands (blanket bog) and lowlands (raised bog)
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Podzol soils
Soil characteristics
The soil is acidic because of the pine needles
Heavy rainfall causes leaching, and Hardpan may develop. This gives the A horizon a greyish colour
Podzols are very heavy soils and, as a result, are very badly drained
Human response
Limited use for agriculture
Mainly used for rough grazing and forestry
Lacking in nutrients and relatively infertile
Fertility can be improved by the addition of lime (crushed limestone) and fertiliser
Relief, drainage, climate and vegetation
Developed in a Co,d, wet and poorly drained environment
As a result, plant litter decayed very slowly only producing small amounts of humus
Found in both upland and lowland areas, mainly in areas that were covered by coniferous forest.
Brown Earth soils
Soil characteristics
Due to mixing by organisms the A and B horizons blend into one another
Brown Earth soils are well drained
A p,entiful supply of plant litter decayed to form humus, giving the soil its dark brown colour
There is very little leaching
Human response
Suited to a wide range of farming activities, including arable and pastoral
Due to its lowland location, brown Earth land is lost to settlement, transport and industry
The most fertile soils in Ireland
Relief, drainage, climate and vegetation
Developed on the boulder clays deposited after the last ice age
Found in low-lying areas, where the climate is less extreme
Developed in areas that were for melt covered by deciduous forest
Gley soils
Soil characteristics
There is very little bacterial action so humus builds up on the surface
Leaching and Hardpan are problems
Since they have a lot of clay, waterlogging is common. As a result, there is very little oxygen in the pores
Human response
Mainly used for pastoral farming (sheep grazing) and forestry
Fertility can be improved by deep ploughing and the addition of fertiliser
Limited agricultural potential
Relief, drainage, climate and vegetation
These include areas with impermeable bedrock and clay soils, such as floodplains
Many of theseareas are flat, where the water is unable to drain away
Associated with areas where the drainage is poor
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Land use capability
Soil type is the main influence on land use in Ireland. However, land use I also governed by altitude, slope and drainage. As a result of all these factors, there are wide variations in the capability of the land from east to west. The most capable soils are found to the east of the country, with the most limited soils found along the west.
