Soil Composition and Formation PDF

SOILS  ◦ 14.1 Describe the composition of soil. At the end 14.2 Assess your soil type. ◦ ◦ 14.3 Explain how soil is formed. of this ◦ 14.4 Describe contrasting soils in Ireland chapter, soil. you will ◦ 14.5 Explain how...

SOILS  ◦ 14.1 Describe the composition of soil. At the end 14.2 Assess your soil type. ◦ ◦ 14.3 Explain how soil is formed. of this ◦ 14.4 Describe contrasting soils in Ireland chapter, soil. you will ◦ 14.5 Explain how soil and vegetation are interconnected. be able to: ◦ 14.6 Describe the exploitation of soil as a natural resource. KEYWORD CONNECTIONS Composition of Soil ◦Mineral matter ◦Humus ◦Air ◦Water ◦Living organisms This Photo by Unknown Author is licensed under CC 1. Mineral matter o Largest component of soil. o It comes from bedrock that has been broken down by the processes of weathering and erosion. o Stones, sand, clay and silt. 2. Humus o Humus is a dark, jelly-like substance that is rich in nutrients. o It forms when dead plants and leaves decay on top of the soil. o This process is called humification. o Living organisms then mix this material through the soil…such as worms. o Humus helps bind soil together and increases the fertility of soil. 3. Air Air is found in the spaces between soil particles. It is essential for plant growth, as it supplies oxygen and nitrogen. It also enables living organisms to survive in soil. 4. Water Water is an important component of soil, as it helps plants to grow. Water dissolves the minerals and nutrients in the soil, which allows plants to absorb them through their roots. 5. Living organisms Earthworms and insects live in soil. They burrow through the soil, allowing water and air to pass through. This burrowing action helps to mix the soil. Microorganisms such as bacteria and fungi also live in soil. They help to break down dead plants to form humus. This increases soil fertility. ASSESS YOUR SOIL TYPE. Soil texture Clay Silt Sand Clay particles are the Silt particles are Sand particles are larger – smallest, at less than 0.002 smaller than sand but this is why they settled first mm in diameter! The small bigger than clay. in your jar. The sand allows particle size makes These drain well but water to drain freely from clay stick together. This can get waterlogged the soil, so it is good for results during heavy rainfall. farming. If there is too much in a heavy, usually sticky sand, however, leaching A soil that is mostly soil. may occur, or the soil may sand and silt will be Clay soils are difficult to dry out in summer. good for farming. plough, so they are usually used for dairy farming. If the water in your jar is still muddy after a day, it is because clay particles are Soil acidity How acidic a soil is affects which plants grow well in a soil. A soil may be acid or alkaline (basic). Soil acidity is measured on the pH scale. The pH scale runs from 0 (most acid) to 14 (most alkaline). Plants grow well in soils with a pH of 6.5. If a soil is too basic (pH greater than 8), it may need fertiliser added to it to make it more suitable for planting crops. Soils that are too acid (pH lower than 6) may need to have lime added to them. Lime is made from limestone and is alkaline. Alkalines neutralise acids. How Soil is Formed 1. Bedrock 2. Relief Bedrock is broken down by Relief is the shape of the land – upland or weathering. lowland. It provides the mineral matter for Highland areas are wetter, so there is the soil. more water in the soil. This can lead to leaching or to soil becoming Some rocks weather slowly (e.g. waterlogged. granite), whereas others break down quickly (e.g. limestone). There is less plant life in highland areas because of the harsh climate. This means that it takes longer for soil to form in a granite area. This means there is less humus. The type of rock also affects the Lowland areas tend to have deeper, well- characteristics of the soil. drained soils. 3. Climate 4. Human activity Rainfall and temperature determine the Human activity affects the rate at which the parent rock is broken composition and quality of down by weathering and erosion. soil. In cold areas, freeze-thaw action slowly Ploughing, irrigation breaks down rock. This results in thin schemes and the use of soils developing. fertilisers can make soil more fertile. In hot areas, chemical weathering breaks down material rapidly to form The removal of vegetation deep soils. and the overuse of soil can stprip it of nutrients and In wet areas, leaching washes minerals make it less fertile. and nutrients deep into soils, causing them to become infertile. This can also lead to soil erosion. In dry areas, soils can become so dry Soils in Ireland Ireland has four main soil types: Peat soil (found in bogs) Gley (a heavy waterlogged soil) Brown earths Podzols Soil Profiles ◦ A soil profile is a cross- section down through a soil. ◦ It shows the layers that make up the soil. ◦ These layers are called horizons.  Soil Type Podzol Grey Colour Areas that were once covered by coniferous Formed forests in Cold, wet, upland areas Wexford, Cork and Galway Limited leaf litter (leaves). Excessive rainfall causes leaching. Soil processe Leaching also forms a hard, impermeable layer s of nutrients, called hardpan; this makes the soil waterlogged – water cannot drain out of the soil Infertile soil and slightly acidic Uses Only suitable for forestry or rough grazing of sheep or goats Soil type Brown Soils Dark brown Colour Areas once covered in deciduous trees Ireland’s most common soil Formed in Midlands, south, east of Ireland Humification of plentiful supply of plant litter Soil Rich humus and moderate rainfall processes supply the soil with nutrients Fertile, well-drained soil Uses Good for arable or pastoral farming Soil type Peat soils Black Colour Limited plant litter available Cold, wet, upland areas and lowland Formed hollows in Mountain locations and in the midlands Limited leaf litter High levels of rainfall lead to Soil waterlogging processes Humus doesn’t decay fully Leaching occurs Infertile soil Only suitable for coniferous forestry or Uses rough grazing of sheep Soil type Gleys Blue-grey Colour Cold regions with high rainfall Impermeable bedrock or high Formed in percentage of clay Ulster, north midlands, Clare, Limerick Poorly drained Waterlogging occurs Soil Poor humus processes Infertile soil Uses Only suitable for grazing of sheep Podzol Brown Peat soil Gleys soil How soil and vegetation are interconnected ◦Soil forms part of an ecosystem or biome. ◦An ecosystem is an area where plants, animals and other organisms interact with the physical landscape and climate. ◦Soil and plants interact in an ecosystem as part of the Nutrient Cycle. ◦The Nutrient Cycle describes how nutrients move between soil and plants and back again. Nutrients are elements such as nitrogen, carbon and iron. 1. Nutrients enter the soil from the parent material and from the atmosphere. 2. Plants absorb nutrients from the soil. When leaves fall from plants, they decay to form humus. Nutrients from humus enter the soil and the cycle repeats itself. 3. If there is too much rainfall, leaching may happen. This stops plants from absorbing nutrients. 4. If nutrients are not available to plants, they cannot thrive and they cannot provide enough plant litter for a rich humus. The soil becomes infertile. 5. The Nutrient Cycle shows us that plants and soils are dependent on each other. Impact of Overgrazing in Ireland Overgrazing is when too many animals graze in a limited space and remove the plant cover from soil. This exposes the soil to wind and rain, which can remove Irelandthe topsoil, joined the causing soil erosion. EU in 1973. The EU gave financial support (money) to farmers with sheep which led to a huge increase in the number of sheep in Ireland. In Mayo and Galway alone, there were 2 million sheep. Up to 30 per cent of upland areas became at risk from overgrazing putting pressure on vegetation. Loss of vegetation can lead to soil erosion and mass movement. In 2003, up to 80 mm of rain fell in north Mayo over a two-hour period. More than 40 individual landslides and mudflows resulted. Houses were cut off, roads were washed away and bridges were destroyed.  Overcropping: When soil is farmed too heavily, nutrients are not replaced, the soil can lose its fertility - soil erosion Farming the same crop on the same land all of the time – can cause a loss of soil quality. The soil uses up certain nutrients that need to be replaced by artificial fertilisers. In developing countries (poorer countries), farmers may not be able to afford these fertilisers. Deforestation: Deforestation is the cutting down of trees. As the world’s population increases, the demand for wood and for food increases. Illegal logging in Brazil has left soils exposed to the weather. Poor farming methods have also caused soil to become exhausted. Climate change Rapid change in the Earth’s climate as a result of burning fossil fuels In some regions, climate change has caused increased rainfall. Climate change will make some regions experience less rainfall - drought. Drought causes desertification – the spread of a desert into previously fertile land, e.g. the Sahel in Africa. The Sahel is a semi-arid region just south of the Sahara Desert in Africa. Much of the Sahel is experiencing desertification. Once sand blows onto fertile land, it destroys it, and the land can no longer be cultivated. Effects of desertification 1. Long periods of drought have led to famine, which has resulted in the deaths of many people. 2. Millions of animals have also died due to drought and famine. 3. Large areas of once-fertile land have been eroded and are no longer suitable for agriculture. 4. Many people have been forced to migrate in search of food. This puts pressure on land elsewhere. Solutions of desertification 1. Irrigation schemes and deeper wells provide water for agriculture - preserve the water content of soils. 2. Stone lines are lines of stone that trap water when it rains - prevents soil from being washed away. 3. Restrictions on herd sizes help to reduce overgrazing. 4. Planting trees, drought-resistant grasses and other plants reduces soil erosion. The roots of these plants help to bind the soil together and prevent the soil from Impact of Human Activity on Soils in Brazil ◦ Tropical red soils are rusty-red in colour and are very deep – between 20 and 30 m ◦ Tropical red soils are found close to the equator in places with a tropical or equatorial climate. ◦ The hot, wet weather in these regions causes rapid chemical weathering. Formation of tropical red soils 1. The hot and humid climate causes intense chemical weathering, which breaks down rock. A deep soil horizon forms. 2. The parent material is red because it contains large quantities of iron oxide, which ‘rusts’ when weathered. 3. Tropical plants grow and produce a lot of plant litter. High temperature and humidity causes rapid decay and produces a rich humus. 4. Leaching washes nutrients into the topsoil. Rapid decay means the humus decays too quickly, however: only a thin upper layer of tropical red soils is fertile. 5. Tropical red soils are altered by human activity. Overgrazing exposes the soil, and the upper fertile layer is eroded. Over-farming leads to soil erosion. Soil erosion in Brazil Soil erosion is increasing as trees are felled for timber and mining. Plant litter is no longer available to the soil. The humus layer is removed. The nutrient cycle is destroyed. As the tree canopy layer is removed, the soil is baked and dried in the direct sunlight. Rainfall runs off this soil easily, as it cannot soak into the ground. Deep grooves called gullies are cut into the soil by rainfall. Tree roots no longer hold the soil together. In upland areas, landslides and mudslides occur. When land is cleared for farming, the rich plant litter of the tropical rainforest is replaced by grass for grazing cattle.