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

What is Soil? Soil is the loose, weathered material on Earth’s s surface in which plants can grow Soil is created from broken down bedrock Bedrock is 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

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

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

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 Matter is the remains of once living organisms (plants and animals)

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

Bedrock: solid rock below soil 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

What is Leaching? Leaching is 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

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)

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