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Slide 2 Slide 3 Why is soil important? There are different types of soil, depending on its composition. These support different types of plants and influence the ecosystem that develops. separating the Earths crust from the living environment supporting the growth of plants recycling nutrients from dead organisms providing a habitat for organisms such as bacteria and worms. Soil is an essential part of the ecosystem : Slide 4 What is soil? Soil is made up of 5 components: 40% 22.5% living organisms dead organic matter (humus) 5% 10% eroded rock fragments water air Slide 5 How is soil created? 1. Erosion of the underlying parent rock Soil is created in two main stages: 2. Production of topsoil This is where the other components are added. The accumulation of organic matter is affected by the climate and topology of the area. Fragments of rock accumulate at the site of erosion. These are the source of minerals in the soil. The mineral composition of the soil therefore depends on the type of parent rock. Slide 6 The Rock Cycle Slide 7 Uses of soil Soil is a source of minerals. Plants produce their own food, but have to obtain minerals from the environment. Plants growing on soils that are lacking in minerals often show symptoms related to deficiencies. Most plants grow in soil. Soil provides anchorage to hold the plant in one place. Soil also provides plants with water. Plants obtain water via their roots. Soil traps water, providing a reliable supply for plants. Slide 8 True or false? Slide 9 Slide 10 Slide 11 Slide 12 Note: clays are microscopic in size ! Slide 13 Clay minerals photographed with an electron Microscope. Note: they are plate or flake like and are stacked on top of each other. They are electrically charged and act like magnets that attract and hold plant nutrients. Slide 14 Soil Properties Texture - Determined by the size of mineral particles within the soil. Too many large particles leads to extreme leaching. Too many small particles leads to poor drainage. Slide 15 Oxygen and water Most of the organisms living in soil require oxygen and water for respiration. The amount of water and oxygen that a soil can hold depends on the soils structure and texture. Air can only remain in the spaces that are not filled with water. Waterlogged soils have very low oxygen levels. This is beneficial to anaerobic bacteria but not to aerobic organisms. Large soil particles have large spaces between them, and water can drain away rapidly. Smaller particles have smaller spaces and retain more water. Sandy soil Clay soil Slide 16 Soil Structure Soil structure can be changed by compaction: 1. When subjected to pressure, pores can collapse and total pore space decreased 2. compaction reduces permeability of soil to water and air Slide 17 Infiltration Rate The rate of gravitational flow of water through soil is referred to as the infiltration rate. Soil with a high infiltration rate is easily leached. These soils can quickly become infertile without the addition of fertilizers When soil become dry, water can be drawn upward from the water table by capillary action. Slide 18 Permeability vs. Porosity Permeability is a measure of how quickly water infiltrates soil. Highest in soil with large pores sandy soils Lowest in soil with small pores clay Porosity is a measure of the space between particles of the soil. Clay has the greatest porosity Sand has the lowest porosity Porosity has an inverse relationship to permeability. Slide 19 Earthworms Earthworms are present in most soil throughout the world, except in Antarctica. They improve its quality by: burrowing through the soil, which mixes and aerates it, and improves drainage breaking up large pieces of organic matter by dragging it into the soil, and consuming parts of it. Soil and matter pass through their intestines and emerge as castings. Castings are higher in mineral content than topsoil. They increase the surface area of the material which is available for decomposition by bacteria and fungi. Slide 20 Neutralizing acidic soil The pH of soil influences plant growth. Acidic conditions can affect enzyme function in soil organisms and alter the availability of mineral ions. Acidic soils often occur in areas of higher rainfall because the alkaline calcium is leached out. Farmers add lime to neutralize acidic soil, a process which is called liming. Lime is a mixture of calcium compounds. Liming releases carbon dioxide into the atmosphere. This may contribute to global warming. Slide 21 Slide 22 Alfisol: Spodsol:Mollisol Slide 23 oxisol aridsol Slide 24 Erosion - Wearing away and transportation of soil by wind, water, or ice Slide 25 Slide 26 Slide 27 Slide 28 Slide 29 Slide 30 Slide 31 How did the Canyon Lands of Utah form? Slide 32 Sheet Erosion Slide 33 Slide 34 The Problem of Soil Erosion A. Topsoil is eroding faster than it forms on about 1/3 f the worlds cropland. B. Losing topsoil makes soil less fertile and less able to hold water. C. Sediment is the largest source of water pollution 1. It clogs irrigation ditches, boat channels, reservoirs and lakes. 2. It causes the water to heat up by absorbing solar energy causing fish to die. 3. Increases flood risk by filling in streams and rivers. Slide 35 The Problem of Soil Erosion D. 2/3 of the seriously degraded lands are in Asia and Africa. E. In the U.S., 1/3 of the nations original prime topsoil has been washed or blown into streams, lakes, and oceans by over cultivating, over grazing and deforestation. Slide 36 Slide 37 Slide 38 Desertification: A.Causes : 1. Overgrazing 2. Deforestation 3. Surface mining 4. Irrigation techniques that lead to increased erosion 5. Salt build up and water logged soils (remember the lab?) 6. Farming on land with unsuitable terrain or soils 7. Soil compaction by farm machinery and cattle hoofs Slide 39 Desertification: B. Consequences: 1.Worsening drought 2.Famine 3.Declining living standards 4.Swelling numbers of environmental refugees whose land is too eroded to grow crops or feed livestock. Slide 40 Desertification: C. Solutions: 1.Reduce overgrazing, deforestation, and the destructive forms of planting, irrigation, and mining. 2.Planting trees and grasses to anchor soil and hold water. 3.Removing salt from the soil. D. Soil Erosion Act of 1935: U.S. established the Soil Conservation Service Slide 41 Soil Conservation Figure 14-21 A. Tillage farming 1. Conventional tillage farming: land is plowed and then soil is broken and smoothed to make a planting surface. 2. Conservation tillage farming: disturb the soil as little as possible. Slide 42 Other methods: 1. Terracing: series of broad level terraces 2. Contour planting: planting crops in rows across rather than up and down the slope 3. Strip cropping: a row of crops alternates in strips with another crop. 4. Alley cropping: several crops are planted together in strips or alleys between trees and shrubs. 5. Gully reclamation: planting of shrubs, trees to prevent water runoff that forms gullies Slide 43 Slide 44 Slide 45 Slide 46 Slide 47 Alley Cropping Slide 48 Gully Reclamation Slide 49 Soil Conservation Practices 8. Windbreaks - Planting of trees or other plants that protect bare soil from full force of the wind. Slide 50 Other methods: 7. PAM: a chemical added to water during the 1 st hour of irrigation. Negative PAM particles bond to positive clay particles and increase cohesiveness of surface soil particles. 8. 1985 Farm Act: established a strategy for reducing soil erosion in the U.S. Slide 51 How can soil fertility be maintained? A. Organic fertilizers B. Inorganic fertilizers Slide 52 Average annual erosion rates in the United States Erosion in tons per acre per year Cultivated Cropland Water 5 Wind 3.5 Rangeland --- Water 1.5 Wind 1.7 Forestland --- Water 1 Slide 53 The Dust Bowl Slide 54 Salinization 1.Irrigation water contains small amount of dissolved salts. 2. Evaporation and transpiration leave salts behind 3. Salt builds up in soil Waterlogging 1. Precipitation and irrigation water percolate downward 2. Water table rises