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Soil Formation and Composition EQ: How do you scientifically describe soil? How is soil formed? G2-2 Soil Formation • Soil- the loose, weathered material on Earth’s surface in which plants can grow • 3 steps to soil formation 1)Begins as bedrock (solid layer of rock beneath the soil) 2)Breaks down (weathering) 3)Mixes with other materials EQ: How do you scientifically describe soil? How is soil formed? G2-2 Soil Composition • Soil – a mixture of rock particles, minerals, decayed organic material, air and water • Rock particles- sand, silt, clay • 2 factors affect the rock particles and minerals found in a soil - bedrock EQ: How do you scientifically - type of weathering describe soil? How is soil formed? G2-2 Soil Composition • Humus – dark colored substance that forms as plant and animal remains decay – Creates space in soil for air and water – Rich in nutrients for plants: • nitrogen, sulfur, phosphorus, and potassium EQ: How do you scientifically describe soil? How is soil formed? G2-2 Soil Color • Color of soil can vary from gray, yellow, deep red brown to black. EQ: How do you scientifically describe soil? How is soil formed? G2-2 Soil Texture • Size of particles. • Rub soil between your fingers to test. • Different names are given to soils depending on the proportion of sand, silt, and clay. • Every soil on earth is defined as sand, silt, clay. EQ: How do you scientifically describe soil? How is soil formed? G2-2 Soil Texture Pebbles/gravel are NOT considered soil! G2-2 EQ: How do you scientifically describe soil? How is soil formed? Soil Texture is: • grainy -large-sized pieces and feels gritty, like sand. • silky -medium-sized pieces and feels powdery, like silt. • sticky -small pieces and feels gummy, like wet clay. EQ: How do you scientifically describe soil? How is soil formed? G2-2 Soil Consistency EQ: How do you scientifically describe soil? How is soil formed? • how easily the soil clumps can be broken apart. The soil consistency is • loose - soil breaks apart when held. • friable - soil breaks apart with a small amount of pressure from one finger. • firm - soil breaks apart with a lot of pressure between two fingers. G2-2 EQ: How do you scientifically describe soil? How is soil formed? Soil Horizons • A layer of soil that differs in color and texture from the layers above or below it G2-2 Soil Horizons • Scientists classify soil into 3 horizons – A Horizon - topsoil-crumbly, dark brown soil – B Horizon – subsoil- contains clay and other particles washed down from A. Contains little humus – C Horizon – contains partly weathered rock G2-2 EQ: How do you scientifically describe soil? How is soil formed? Rate of Soil Formation • Depends on the climate and type of rock – Warm and rainy climate – soil develops quickly – Cold and dry climate – soil develops slowly EQ: How do you scientifically describe soil? How is soil formed? G2-2 Life in soil- organisms mix the soil, create spaces, make humus . • Plant “litter”, a loose layer over the soil where plants shed leaves or die • Decomposers, organisms that break down the remains of dead plants and animals live in the soil • Bacteria, fungi, earthworms, snails and beetles EQ: How do you scientifically describe soil? How is soil formed? G2-2 Soil Types in the United States • Scientists classify soil based on: – Climate – Common plants found in the region – Soil composition EQ: How do you scientifically describe soil? How is soil formed? G2-2 Class Work and Homework • Classwork: Copy questions 1-5 on notebook paper. • Homework: Questions 1-5 using notes. See page G55. G2-2
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