Soil Formation and Weathering
CH 10 uvm.edu

It’s not just dirt?
• Medium for plant growth (food, feed, fiber)
• Mechanical support for living organisms
• Regulates water flow (runoff, infiltration, storage, recharge)
• Provides nutrients & cycles nutrients
• Acts as filter (physical, chemical & biological)

How is soil formed?
• Parent rock material breaks down into smaller and smaller pieces.
• Pieces are changed chemically by weathering.
• Weathering changes rock at deeper and deeper levels.
• Eventually different layers or zones (horizons) are noticeable

Soil
• Loose material at Earth’s surface capable of supporting plants with root systems
• Mixture of:
– Small mineral fragments
– Decaying organic material
– Water
– Air
– Organisms physicalgeography.net

Soil http://www.organicgardeninfo.com/soil.html

Soil food web
From Miller’s Living in the Environment

Soil horizons
• O horizon
– Leaf litter
• A horizon
– topsoil
• B horizon
– subsoil
• C horizon
– parent material eoearth.org

• Clay
< .002 mm
• Silt
< .06 mm
• Sand
.06 mm – 2 mm
Soil texture http://140.254.84.203/wiki/index.php/Fines

Soil texture chart

How is soil formed?
• Mechanical weathering
– Breakdown of rocks into smaller pieces by physical means
• Chemical weathering
– Breakdown of rocks into smaller pieces by chemical reactions

Mechanical weathering
• Ice
• Abrasion
• Wind
• Water
• Gravity
• Plants
• Animals

Chemical weathering
• Water
• Acid in rainwater
• Acid in groundwater
• Air

Soil types in different biomes
From Miller’s Living in the Environment

Soil types in different biomes
From Miller’s Living in the Environment

Tropical Rain Forest
• Thin, nutrient poor soils
• Heavy rains leach nutrients from soil
• Plants use nutrients very rapidly, so few nutrients are in soil

Desert
• Slow rate of chemical weathering, so soil created slowly
• Salts build up because there is little water to dissolve them & wash away

Temperate forest & grassland
• Much weathering occurs due to much rain
• Freeze/thaw breaks apart rocks
• Rain causes chemical weathering
• Most nutrient rich soils in the world

Arctic
• Chemical weathering occurs slowly due to little precip.
• Soils occur slowly
• Thin soil = few plants
• Decomposition happens slowly due to cold

Soil Erosion
• http://www.maine.gov/dep/blwq/doceducation/dirt.htm
http://www.otsego.org/conservationdistrict/erosion.htm

• Erosion in Africa is widespread http://www.shef.ac.uk/research/stories/engineering/27.html

Soil erosion
• Overused soils > fewer nutrients > fewer plants > exposed soils > wind & water carry away soil > people go hungry
• Desertification = land degradation = areas that are now unable to support crops

Stream side erosion http://www.newechotarivers.org/about-the-oostanaula/ecological-threats • http://www.newechotarivers.org/about-theoostanaula/ecological-threats

Soil Conservation
• Contour plowing http://teachers.sduhsd.k12.ca.us/hherms/herms/GEOLOGY/conservatio n/desertification.htm

Soil Conservation
• Buffers along streams http://www.treehugger.com/files/2010/10/the-global-battle-toconserve-and-rebuild-soil.php

• Terracing
Soil Conservation http://factoidz.com/terracing-an-environmentfriendly-agricultural-approach
/

• Satellite image of circular crop fields characteristic of center pivot irrigation in Kansas (June 2001). Healthy, growing crops are green. Corn would be growing into leafy stalks by late June. Sorghum, which resembles corn, grows more slowly and would be much smaller and therefore, possibly paler. Wheat is a brilliant gold as harvest occurs in June. Fields of brown have been recently harvested and plowed under or lie fallow for the year.

Vermicomposting turning kitchen scraps to soil
• http://kids.niehs.nih.gov/worms.htm

Homework
• Read pages 278 - 297

Output
• Soil horizons activity