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Sifting through the Soil : Determining London’s Local Soils Soil Soil is like a skin over the earth’s crust, and is essential in enhancing life on earth. There are six main contributors to soil: - Parent rocks and sediments Climate Landscape Vegetation and living creatures Time Man 2 Copyright, legal, version number? Parent Material • Gradually rocks break down into smaller pieces under the effects of rainfall, snow, freeze and thaw cycles. • The parent rock or sediment is the main factor responsible for the texture of the soil and is also important in determining the pH of the soil and how rich it is in nutrients. • For example – Shale clay – Sandstone sand 3 Copyright, legal, version number? Climate • The two main climatic influences: – Temperatures increase the rate at which the breakdown of the underlying rock takes place and also the release of nutrients into the soil. – Rainfall and snowmelt break down rock to form soil and distribute soil nutrients. • In hot, wet climates such as the tropics soils tend to be deep. • In cold, artic areas the soils tend to be thin and poorly developed. 4 Copyright, legal, version number? Landscape • Landscapes generally affect the depth or thickness of soils. • Steep slopes often have shallow soils because soil is easily washed down the hillsides into the valleys below. • Flat land such as that in valley bottoms, flood plains, or low lying plains have deeper soils. 5 Copyright, legal, version number? Vegetation • Vegetation aids in creating soils as acids released by the roots of some plants act to breakdown the rock on which soil is forming. • Once the rocks have been broken down into smaller materials, the vegetation is able to supply its dying remains as a source of nutrients to help enhance the soil while adding organic matter. 6 Copyright, legal, version number? Soil Organisms • Organisms begin to set up their homes in the soil from the moment it begins to form. • The main role of organisms in soil is to recycle the organic matter and release nutrients in what is called “castes.” • Organisms also create pores within the soil to allow air circulation and add architecture to the soil. 7 Copyright, legal, version number? Time • It takes a long time for soils to develop from rock and existing sediments. • The oldest soils are currently located in South Africa. Elsewhere, soil is relatively young due to periods of geologic disturbance. 8 Copyright, legal, version number? Humans • Farmers have cultivated the land for centuries and in most cases the soil has been managed well. • In some parts of the world however; soils have been damaged. For example: – Cutting down parts of the tropical rainforest, decreasing organic material – Cultivation of crops on steep slopes creating erosion – Deterioration of natural nutrient content, as the focus is largely on fertilizers in commercial agriculture 9 Copyright, legal, version number? Quick Quiz! • Answer the following on a piece of paper: 1. 2. 3. 4. 5. 6. 10 Name all of the soil forming factors. What does parent material provide? How does climate influence soil formation? Why is vegetation important in soil formation? How do humans influence soil? Other than an earthworm, name a soil organism. Copyright, legal, version number? Soil Horizons • A soil horizon is approximately parallel to the surface, having distinct characteristics produced by soil forming processes. • Soil horizons are used to classify the soil and make interpretations about its quality and stability. 11 Copyright, legal, version number? O-Horizon • Organic layers of decaying plant and animal tissues. • Typically within a woodland area there are three distinct organic layers: 1. Leaves, needles and twigs (Oi) 2. Partially decomposed layer (Oe) 3. Dark layer of decomposed humus (Oa) 12 Copyright, legal, version number? A-Horizon • A mineral horizon at or near the surface in which an accumulation of humified organic matter is mixed with mineral material. • This horizon exhibits obliteration of all or much of the original rock structure. 13 Copyright, legal, version number? E-Horizons • A horizon in the upper part of the soil. It is light coloured and leached. • The light colour is due to the natural colour of the dominant quartz and sand grains. • The main feature is the loss of silicate clay, iron, or aluminum, leaving a concentration of sand and silt particles. 14 Copyright, legal, version number? B- Horizons (Subsoil) • Horizons which are dominated by the obliteration of all or much of the original rock structure. • Contain illuvial concentrations of clay, iron, aluminum, humus, gypsum, silica, and other minerals. • Well drained soils have the brightest colour development within the B-Horizons. • Usually 2-3 feet below the surface. 15 Copyright, legal, version number? C-Horizons (Substratum) • A horizon which excludes hard bedrock. • Hardly affected by the soil forming processes and have changed very little since the time they were deposited. • This layer lacks colour, however, geologic layering or strata is often present. 16 Copyright, legal, version number? R-Horizons • Horizons containing hard bedrock. • Typically requires large machinery to break through. • Common R-Horizon materials consist of granite, basalt, quartzite, limestone and sandstone. 17 Copyright, legal, version number? Activity In groups of four, choose a local soil to research during class. Using the internet, determine why the soils are located where they are in London. Assess the benefits and issues associated with each type of soil. Present your findings to the class. 18 Copyright, legal, version number? Soil Types • There are various different types of soil in London, all created from the eight factors mentioned above: • • • • • 19 Alluvium Clay Organics Sand-Gravel Silt Copyright, legal, version number? 20 ACTIVITY Characterizing Your Soil 21 Copyright, legal, version number? Plot the Soil Type • Based on classmates results and presentations of their soil type, fill in the map of London with the O and A soil horizons found. Be sure to pin point where each sample came from. 22 Copyright, legal, version number? What did you think about the lesson? • • • • • What did you learn? What did you love? What do you want to learn more about? What was boring? How would you make the lesson better? 23 Copyright, legal, version number?