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Chapter 7

ENV100Y5 Chapter Notes - Chapter 7: Parent Material, Hydrosphere, Nitrogen Cycle

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Barbara Murck

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Chapter 7 Textbook Notes
(181) Soil as a system
Soil - complex plant supporting system that consists of disintegrated
rock, organic matter, water, gases, nutrients, and microorganisms.
Fundamental to support life on this planet and provision of food for
Renewable if managed carefully, however currently at risk in many
It's a complex, dynamic mixture - minerals in it are from parent
materials (base geological material in a location, from where the soil is
formed) = determines starting composition of soil
Water %lls open spaces between mineral and particles or organic
matter. Not pure water
Air %lls soil pores - soil gas has O2, N, CO2
Soil meets the de%nition of a ecosystem
Soil formation is complex and slow
Formation begins when parent material is exposed to atmosphere,
hydrosphere, biosphere
Most commonly is bedrock
Most common processes for formation: weathering, erosion, deposition
and decomposition of organic matter
oWeathering = what breaks down a rock and mineral. Small
particles are then the precursors of soil (regolith)
oPhysical/mechanical weathering - breaks rock without triggering
a chemical change in parent material (wind, ice, rain)
oChemical weathering - water or other substances chemically
interact with parent material
oBiological weathering - living things break down parent material
by physical/chemical means
Partial decomposition creates HUMUS - dark, spongy, crumbly mass of
material made of complex organic compounds. Soil with this are
productive of plant life and hold moisture well.
Peat = soil dominated by decayed or compressed organic material
Erosion - movement of particles from location to another
A soil pro%le consists of layers (Horizons)
Soil pro%le - cross-section as a whole from surface to bedrock
Leaching - materials suspended or dissolved in liquid are transported
through the subsurface
oCommonly leached are soluble
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