Soil Formation

What is soil? Soil is the loose covering of broken rock particles and decaying organic matter, called humus, overlying the bedrock of Earth’s surface

Why is soil important? Essential for all life on Earth! We are dependent upon plants, which grow in soil, for food and other basic needs (clothes, etc) Benefits: oxygen from plants, meat from animals dependent on plants for food, filters out pollutants

What lives in soil? All kinds of animals; including: Moles Earthworms (night crawlers) Nemotode (Round worms) Root fungus Bacteria

How Soil Forms… Starts when physical or chemical weathering occurs, breaking rock into smaller and smaller pieces Organisms like bacteria and fungi live on the smaller pieces of rock Over time, the organisms die, decay, and add organic material to the soil.

Soil Profile During soil formation, soil develops layers. A soil profile is a vertical sequence of soil layers. Poorly developed soils show little distinction between layers.

Soil Profile 5 major soil horizons: O, A, B, C, and D Horizon O- this is the top layer, the “organic” layer, made up of dead plant matter Horizon A- high concentrations of organic material and humus are found in the “top soil.”

Soil Profile Horizon B- “subsoil layer” that is enriched with clay material May be red or brown in color as a result of iron oxides Accumulation of clay in B horizon can lead to the formation of hardpan, a very dense layer that may allow little to no water to pass through Horizon A Horizon B

Soil Profile Horizon C contains weathered parent material This layer usually has lots of large rocks mixed in the soil deep underground All horizons may not be present in a given soil Horizon C

Soil Profile Horizon R is solid parent bedrock and is the last layer of the soil horizons Horizon R Bedrock Layer

Soil Texture There are three main types of soil texture: (1) sand (2) silt (3) clay

Sand Larger soil particles Sand does not hold nutrients well Little plant growth (think deserts and beaches)

Silt Medium sized particles Very fertile Holds lot of water

Clay Smaller sized particles Stick together well Inhibits root growth Holds water well Found mostly in piedmont

Soil Texture Relative proportions of different sized particles (clay, silt, and sand) determine a soil’s texture The texture of a soil affects its capacity to retain moisture and its ability to support plant growth CLICK the link below https://www.youtube.com/watch?v=4hW59WZ0EQI

Soil Fertility Soil fertility is a measure of how well a soil can support the growth of plants Factors that affect fertility include: (1) availability of minerals and nutrients (2) number of microorganisms present (3) amount of precipitation available (4) Topography (5) Level of acidity