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Chapter 7
Soil: loose material derived from rock a complex plant-supporting system consisting of disintegrated
rock, organic matter, water, gases, nutrients, and microorganisms fundamental to the support of life
on the planet & provision of food
x Consists of half mineral matter with varying proportions of organic matter, pore space taken up
by air, water, soil gases
x Organic matter living and dead microorganisms, decaying material from plants and animals
x 1 teaspoonful of soil = 100 million bacteria, 500 000 fungi, 100 000 algae, 50 000 protists
x Habitat for earthworms, insects, mites, millipedes, centipedes, nematodes, sow bugs, other
invertebrates (burrowing mammals, amphibians and reptiles)
x Influences region’s ecosystems, climate, latitude, and elevation
Parent material: base geological matter can include lava or volcanic ash, rock or sediment deposited
by glaciers, wind-blown dunes, sediments deposited by rivers in lakes or ocean, bedrock
x Weathering, erosion, deposition and decomposition (and accumulation) of organic matter
Weathering: physical, chemical, and biological processes that break down rocks and minerals (large Æ
small: regolith are precursors of soils)
Physical weathering (mechanical weathering): breaks rocks down without triggering a chemical change
in the parent material wind and rain, water freezing & expanding
Chemical weathering: when water or other substances chemically interact with parent material warm
and wet conditions, acidic precipitation or groundwater
Biological weathering: when living things break down parent material by physical or chemical means
x Erosion sometimes help form soil transporting material destructive in reducing the amount of
life that a given area of land can support
Humus: a dark, spongy, crumbly mass of material made up of complex organic compounds holds
moisture and are productive for plant life
Peat: dominated by partially decayed, compressed organic material
x Horizon layer of soil
- O(rganic) horizon: organic matter deposited by organisms
- A horizon: topsoil, some organic material mixed with mineral components + organic matter
and humus most nutritive for plants, most vital to ecosystems and agriculture
Leaching: solid particles suspended or dissolved in liquid are transported to another location (minerals
iron, aluminum and silicate clay)
- B horizon: subsoil
- C horizon: consists of parent material unaltered or only slighted altered by the process of
soil formation contains larger rock particles
- R(ock) horizon: parent material
- certain soils have a distinct layer of water (W horizon, e.g. permafrost)
x Soil profile: the cross-section as a whole, from surface to bedrock
1/ Soil colour indicates its composition and sometimes its fertility (red: iron, black or dark brown: rich
in organic matter, pale grey to white: leaching or low organic content)
2/ Soil texture size of particles
Clay: less than 0.002 mm, sticky when moist
Silt: 0.002 - 0.05 mm, even mixture (loam)
Sand: 0.05 - 2 mm, large and do not adhere to one another
Porosity: a measure of the relative volume of spaces within the material
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Document Summary

Soil: loose material derived from rock a complex plant-supporting system consisting of disintegrated rock, organic matter, water, gases, nutrients, and microorganisms fundamental to the support of life on the planet & provision of food. N consists of half mineral matter with varying proportions of organic matter, pore space taken up by air, water, soil gases. N organic matter living and dead microorganisms, decaying material from plants and animals. N 1 teaspoonful of soil = 100 million bacteria, 500 000 fungi, 100 000 algae, 50 000 protists. N habitat for earthworms, insects, mites, millipedes, centipedes, nematodes, sow bugs, other invertebrates (burrowing mammals, amphibians and reptiles) Parent material: base geological matter can include lava or volcanic ash, rock or sediment deposited by glaciers, wind-blown dunes, sediments deposited by rivers in lakes or ocean, bedrock. N weathering, erosion, deposition and decomposition (and accumulation) of organic matter.

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