Unit 4.2: Soil Formation and Erosion

Soil

mix of geologic and organic components (sand, silt, and clay)

Humus

broken down biomass that is the main organic part of soil

Ammonium, phosphates, nitrates

main soil nutrients

Weathering

breakdown of rocks into smaller pieces

Erosion

transport and deposition of weathered rock fragments by wind and rain

Soil formation from below

weathering of parent material produces smaller and smaller fragments that make up geologic/inorganic part of soil

Soil formation from above

breakdown of organic matter adds humus to soil and erosion deposits soil particles from other areas, adding to soil

O-Horizon

layer of organic matter on top of soil

A-Horizon

topsoil; layer of humus and minerals from parent material that has the most biological activity

B-Horizon

subsoil; lighter layer below topsoil, mostly made of minerals with little to no organic matter

C-Horizon

least weathered soil that is closest to the parent material, sometimes called bedrock

Soil Degradation

the loss of the ability of soil to support plant growth

Loss of Topsoil

tilling and loss of vegetation disturb soil and make it more easily eroded by wind and rain

Compaction

compression of soil by machines, grazing livestock, and humans reduces ability to hold moisture

Nutrient Depletion

repeatedly growing crops on the same soil removes key nutrients over time, which reduces the ability to grow future crops

Parent Material

effects soil pH and nutrient content

Topography

steeper slopes cause too much erosion and more level ground effects deposition

Climate

effects the rate of organic breakdown (warmer speeds it up) as well as weathering, erosion, and deposition (precipitation)

Organisms

fungi, worms, and bacteria in the soil aid in the breakdown of organic matter