Soil Formation 6.E.2.3 Explain how the formation of soil is related to the parent rock type and the environment in which it develops.
What is soil? A loose mixture of weathered rock, organic material, air and water
Soil Texture This refers to the size of the particles: Sand (The largest particle size) Silt Clay (The smallest particle size) Loam is a mixture of sand, silt, and clay and is ideal for growing things because the sand lets things flow through the soil and clay hold the water in
Nutrients in the Soil Humus is rich decayed organic material in the topsoil that provides nutrients to plants
Factors that Form Soil CLimate Organisms Relief/Topography Parent Material Time These factors affect the processes which affect the soil formation
Climate The weathering rates are greatly affected by rainfall and temperature. Higher rainfall - increased weathering Higher temperature - increased weathering Tropical rainforest have highest rate of energy (nutrients in the soil) and dessert has the lowest
Organisms Organisms work to mix the soil physically by moving soil but also by adding or depleting nutrients Legumes add nitrates to soil Plants and trees drop their seeds and leaves into the soil
Relief or Topography Erosion and water availability Erosion can cause A and B to be thinned where there is much erosion Near rivers and streams, the layers will be thicker
Parent Material The soil is formed, in part, by the weathered rock in the area. Sandstone - creates sand Shale - creates clay Basalt (extrusive igneous rock)- weathers easily Granite (intrusive igneous rock) - resists weathering
Time As soils mature, they will take on more developed horizons. E horizon can be formed as nutrients from A are leached through the soil As sediments from a stream are deposited, thicker layers can be formed at the delta
Soil Formation Video - Part 1
Soil Formation - Additions to Soil These things can be added to the soil horizon: Precipitation Organic Matter (plants and animals) Salts and other chemicals
Soil Formation - Losses in Soil The soil can have nutrients taken from it: Chemical and nutrient leaching Erosion (top or bottom layers) This can be natural or caused by human use of soil
Soil Formation - Translocation Transportation of materials from one part of the profile to another Caused by water of animals moving things within the layers of soil
Soil Formation - Transformation The breaking down of rock into sediment and eventually creating soil Physical and chemical weathering Clay formation Organic matter/humus
Steps of Soil Formation Step 1: The bedrock forms and this is the bottom layer of soil which is also known as the R horizon Formed by the original rock in the crust Much of this is granite
Steps of Soil Formation Step 2: The bedrock is worn down to weathered bedrock forming the C horizon This is not solid rock but it is also not fine sediment yet
Steps of Soil Formation Step 3: Over time, the weathered rock gets finer creating the first soil horizon A Topsoil - This is the horizon in which the plants grow Rich in nutrients and dark
Steps of Soil Formation Step 4: Nutrients wash out of the topsoil and the subsoil forms. This is called B horizon Light brown color because the nutrients are not as readily available in this layer because the plants have used the nutrients up
Steps of Soil Formation Step 5: Organic material is added on top of the top soil. This is called the litter or O horizon Leaves from trees Debris from plants Decomposing insects and/or animals
E Horizon Not all soil horizons have this layer. This is formed from an intense leaching of nutrients. This would lie between the A and B horizon
Soil Formation Video - Part 2
Rocks and Soil - Bill Nye