SOIL: DEFINITION, FORMATION & LAYERS"
What Is Soil? soil - upper-most (relatively thin) layer of Earth s crust, which supports terrestrial plants, animals, & microorganisms basic natural resource that deeply effects every other part of ecosystem composed of 3 main ingredients: minerals organic materials open space filled with water & air HOW DOES SOIL DEVELOP? SOIL: DEFINITION, FORMATION, & LAYERS" 3"
Factors Controlling Soil Formation Over time, 5 major factors control how soil forms climate organisms relief (landscape) parent material time CL.O.R.P.T. SOIL: DEFINITION, FORMATION, & LAYERS" 4"
How Does Soil Develop? develops in response to several factors: parent material " rock & minerals from which soil derives climate " results in weathering of parent material living organisms" help decompose litter & recycle nutrients topography" controls water availability & soil accumulation rate includes drainage, slope direction, elevation, & wind exposure SOIL: DEFINITION, FORMATION, & LAYERS" 5"
Factors influencing chemical weathering organisms" expose rocks to weathering e.g. by burrowing " time" longer a rock is exposed, more weathered it will become " mineral composition" stability depends on strength of chemical bonds e.g. silicate structure (later-formed minerals weather more slowly because stronger bonds) " availability of water" e.g. climate SOIL: DEFINITION, FORMATION, & LAYERS" 6"
Parent Material mineral content determines: nutrients produced (for vegetation) amount of soil produced Thick soil: Igneous Limestone Thin soil: Sandstone Moist temperate environment SOIL: DEFINITION, FORMATION, & LAYERS" 7"
Soil Composition browns/blacks: " high organic content" " whites/grays:" low organic content" " yellows/red: " high Fe content" SOIL: DEFINITION, FORMATION, & LAYERS" 8"
How Does Soil Develop? soil can be considered a nonrenewable resource" parent material is slowly broken down, or fragmented into smaller & smaller particles by biological, chemical, & physical weathering processes takes long time to break down & for organic material to accumulate in soil SOIL: DEFINITION, FORMATION, & LAYERS" 9"
How Does Soil Develop? SOIL: DEFINITION, FORMATION, & LAYERS" 10"
SOIL HORIZONS Soil scientists at work in a soil pit. Photo: John A. Kelley SOIL: DEFINITION, FORMATION, & LAYERS" 11"
Soil Horizons many soils are organized into distinctive horizontal layers called soil horizons" soil profile - vertical section from surface to parent material, showing soil horizons SOIL: DEFINITION, FORMATION, & LAYERS" 12"
Soil Horizons: Main Layers A Horizon (topsoil)" dark; high concentration of organic matter (humus) contains living organisms & inorganic minerals typically thick in grasslands " B Horizon (subsoil)" light-colored (yellowish); litter & nutrient minerals leached from A & E horizons accumulate here (including Fe & Al, humic compounds, & clay) rich in nutrients where rainwater leeched nutrients from topsoil C horizon (weathered parent material)" below roots, often saturated with groundwater, partially broken down inorganic minerals SOIL: DEFINITION, FORMATION, & LAYERS" 13"
Soil Horizons: Main Layers SOIL: DEFINITION, FORMATION, & LAYERS" 14"
Soil Horizons (continued) O Horizon (surface litter)" mostly organic matter & humus; plant liter accumulates & decays thick in deciduous forests & very thin in tundra & deserts A Horizon (topsoil)" dark; high concentration of organic matter (humus) contains living organisms & inorganic minerals typically thick in grasslands E Horizon (zone of leeching)*" dissolved & suspended materials move downward SOIL: DEFINITION, FORMATION, & LAYERS" 15"
Soil Horizons (continued) B Horizon (subsoil)" light-colored (yellowish); litter & nutrient minerals leached from A & E horizons accumulate here (including Fe & Al, humic compounds, & clay) rich in nutrients where rainwater leeched nutrients from topsoil C horizon (weathered parent material)" below roots, often saturated with groundwater, partially broken down inorganic minerals R Horizon (bedrock or parent material)" SOIL: DEFINITION, FORMATION, & LAYERS" 16"
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