The Nature of Soil

1. The Nature of Soil Essential Question: What are the characteristics of soil? How does the composition of soil vary?

2. What is Soil? • Soilis the loose, weathered material on Earth’s s surface in which plants can grow • Soil is created from broken down bedrock • Bedrockis the solid layer of rock beneath the soil • When this rock is exposed, it gets weathered or broken down into small particles that forms soil

3. What is soil made up of? • Soil is made up of: • Rock/mineral fragments • Decayed Organic matter • Air • Water • Rock/Mineral fragments are broken down into small particles such as clay, silt, and sand • Most decayed organic material comes from plants, but also from animals when they die • Eventually, this turns into humus, a dark-colored substance that forms as plants and animals decay • Humus contains nutrients that plants need to help them grow • Good soil has an equal mix of humus and weathered rock

4. Different types of Soil: • Soil texture(how it feels) can vary depending on the particle size in the soil • Sand feels coarse and grainy, while clay feels smooth and silky • Soil texture is important for plant growth: • Sandy soils allow water to quickly drain, so plants may not get enough water • Clay soils hold a lot of water, so plants may drown from too much water • Good soil should have equal parts of sand, silt, and clay

5. How does soil form? • Soil forms as rock is broken down by weathering and mixes with other material on the surface. • Soil is constantly being formed whenever bedrock is exposed and weathered. • Plants and animals add organic matter to rock fragments • Organic Matteris the remains of once living organisms (plants and animals)

6. What is a soil profile? • As soil develops it forms layers known as horizons • Horizons are the different layers of soil that differs in color and texture from the layer above or below it • All of the horizons together form a soil profile

7. What is a Soil Profile? O Horizon: layer of loose leaves and organic debris at the surface of the soil A Horizon: the top layer of soil, usually covered with litter, or leaves, twigs, and other organic material B Horizon: the subsoil layer. Lighter in color due to less humus and is less fertile. C Horizon: the parent rock.Mostly weathered rock and is bottom of the soil profile. It is most like the bedrock material. Bedrock: solid rock below soil

8. What is Leaching? • Leachingis the removal of minerals that have been dissolved in water • When it rains, the water picks up minerals and carries them down from the A Horizon to the B Horizon. • C Horizon will hardly ever have minerals in it

9. How do living organisms affect soil? • Some organisms make humus, the material that makes soil fertile • Other organisms mix the soil and make space for water and air • Plants contribute most of the organic remains that form humus • Litter is the loose layer of dead plant leaves and stems of the soils surface • Decomposers are the organisms that break down the remains of dead organisms (fungi, bacteria, worms, etc)

10. What factors affect soil? • Factors affecting soil formation include: • Climate • Slope of land • Types of Rock • Types of Vegetation • How long the rock has been weathered