Soil Science 120 Final Study Guide
-Gordon Rees with correct answers
2025
How is soil defined? - correct-answers-"Three dimensional Natural body Composed of mineral
Give the six components of the definition of soil discussed in class. - correct-answers-● Three
Dimensional
● Natural Body
● Composed of mineral and/or Organic Material
● At Earth's Surface
● Vertically differentiated
● Modified by soil-forming Factors
Why do we care about soil? Give several examples of soil functions. - correct-answers-●
Medium for Plant growth
● Systems for water supply and purification
,● Biological habitats
● Nutrient recycling system
● Engineering medium
● Carbon Storage
What is a "typical" soil composition? - correct-answers-● Typical soil composition is 25% air and
25% water in pore space and 45% mineral and 5% organic material for the soil solids
Compare/contrast mineral vs organic soil material - correct-answers-Mineral:
○ "broken-down rocks"
○ Inorganic chemistry
○ Not from living organisms
Organic:
○ "decomposed life"
○ Organic chemistry
○ From living organisms
○ Based on rings and chains of carbon
Mineral soil material - correct-answers-Mineral:
○ "broken-down rocks"
○ Inorganic chemistry
○ Not from living organisms
Organic soil material - correct-answers-Organic:
○ "decomposed life"
,○ Organic chemistry
○ From living organisms
○ Based on rings and chains of carbon
Humus - correct-answers-colloidal (very small), complex organic compounds resistant to
decomposition
Specific Surface area - correct-answers-specific surface area - The surface area relative to the
mass
What fills soil pore space? - correct-answers-● Water and Air
● Dissolved nutrients essential for growth of plants and organisms
How does soil atmosphere compare to above-ground atmosphere? - correct-answers-Higher
CO2 and Lower O2
Where does CO2 come from in the soil? How does it affect soils? - correct-answers-CO 2 comes
from the atmosphere + organisms living in the soil
How does CO2 affect soils? - correct-answers-Strongly influences plant growth, chemical, and
biochemical reactions in soil
Higher levels of CO 2 in soils than in atmosphere
Master horizon A indicates? - correct-answers-Surface horizon darkened by organic matter
Master horizon B indicates? - correct-answers-Subsurface horizon of alteration
, Master horizon C indicates? - correct-answers-Unaltered, but not bedrock materials
Master horizon E indicates? - correct-answers-Horizon of eluviation (strongly leached)
Master horizon O indicates? - correct-answers-Organic Horizon
Master horizon R indicates? - correct-answers-Bedrock
Illuviation: - correct-answers-The process of deposition of soil material removed from one
horizon to another in the soil; Usually from an upper Horizon to a lower horizon.
Eluviation: - correct-answers-The removal of soil material in suspension (or in solution) from a
layer or layers of a soil.
Residual parent material - correct-answers-Soils formed from the breakdown of bedrock *coarse
or rough*
Transported parent material - correct-answers-(Residual) Soils transported from one place to
another *smooth due movement*
Organic parent material - correct-answers-Soils formed from accumulation of organic material in
flooded soils
Alluvium - correct-answers-Deposits of running water, larger particles (sand) settle out of water
first followed by smaller particles (clay) *Organized or well sorted*
glacial till - correct-answers-Glacier deposited materials, very jumbled up (Boulders, rocks, to
clay) *disorganized or poorly sorted*
-Gordon Rees with correct answers
2025
How is soil defined? - correct-answers-"Three dimensional Natural body Composed of mineral
Give the six components of the definition of soil discussed in class. - correct-answers-● Three
Dimensional
● Natural Body
● Composed of mineral and/or Organic Material
● At Earth's Surface
● Vertically differentiated
● Modified by soil-forming Factors
Why do we care about soil? Give several examples of soil functions. - correct-answers-●
Medium for Plant growth
● Systems for water supply and purification
,● Biological habitats
● Nutrient recycling system
● Engineering medium
● Carbon Storage
What is a "typical" soil composition? - correct-answers-● Typical soil composition is 25% air and
25% water in pore space and 45% mineral and 5% organic material for the soil solids
Compare/contrast mineral vs organic soil material - correct-answers-Mineral:
○ "broken-down rocks"
○ Inorganic chemistry
○ Not from living organisms
Organic:
○ "decomposed life"
○ Organic chemistry
○ From living organisms
○ Based on rings and chains of carbon
Mineral soil material - correct-answers-Mineral:
○ "broken-down rocks"
○ Inorganic chemistry
○ Not from living organisms
Organic soil material - correct-answers-Organic:
○ "decomposed life"
,○ Organic chemistry
○ From living organisms
○ Based on rings and chains of carbon
Humus - correct-answers-colloidal (very small), complex organic compounds resistant to
decomposition
Specific Surface area - correct-answers-specific surface area - The surface area relative to the
mass
What fills soil pore space? - correct-answers-● Water and Air
● Dissolved nutrients essential for growth of plants and organisms
How does soil atmosphere compare to above-ground atmosphere? - correct-answers-Higher
CO2 and Lower O2
Where does CO2 come from in the soil? How does it affect soils? - correct-answers-CO 2 comes
from the atmosphere + organisms living in the soil
How does CO2 affect soils? - correct-answers-Strongly influences plant growth, chemical, and
biochemical reactions in soil
Higher levels of CO 2 in soils than in atmosphere
Master horizon A indicates? - correct-answers-Surface horizon darkened by organic matter
Master horizon B indicates? - correct-answers-Subsurface horizon of alteration
, Master horizon C indicates? - correct-answers-Unaltered, but not bedrock materials
Master horizon E indicates? - correct-answers-Horizon of eluviation (strongly leached)
Master horizon O indicates? - correct-answers-Organic Horizon
Master horizon R indicates? - correct-answers-Bedrock
Illuviation: - correct-answers-The process of deposition of soil material removed from one
horizon to another in the soil; Usually from an upper Horizon to a lower horizon.
Eluviation: - correct-answers-The removal of soil material in suspension (or in solution) from a
layer or layers of a soil.
Residual parent material - correct-answers-Soils formed from the breakdown of bedrock *coarse
or rough*
Transported parent material - correct-answers-(Residual) Soils transported from one place to
another *smooth due movement*
Organic parent material - correct-answers-Soils formed from accumulation of organic material in
flooded soils
Alluvium - correct-answers-Deposits of running water, larger particles (sand) settle out of water
first followed by smaller particles (clay) *Organized or well sorted*
glacial till - correct-answers-Glacier deposited materials, very jumbled up (Boulders, rocks, to
clay) *disorganized or poorly sorted*
