Soil Science 120 Final Study Guide -Gordon Rees
Exam With Complete Solutions
How is soil defined? - ANSWER "Three dimensional Natural body Composed of mineral
Give the six components of the definition of soil discussed in class. - ANSWER ● 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. - ANSWER ● 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? - ANSWER ● 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 - ANSWER 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 - ANSWER Mineral:
○ "broken-down rocks"
○ Inorganic chemistry
○ Not from living organisms
Organic soil material - ANSWER Organic:
○ "decomposed life"
,○ Organic chemistry
○ From living organisms
○ Based on rings and chains of carbon
Humus - ANSWER colloidal (very small), complex organic compounds resistant to
decomposition
Specific Surface area - ANSWER specific surface area - The surface area relative to the mass
What fills soil pore space? - ANSWER ● Water and Air
● Dissolved nutrients essential for growth of plants and organisms
How does soil atmosphere compare to above-ground atmosphere? - ANSWER Higher CO2
and Lower O2
Where does CO2 come from in the soil? How does it affect soils? - ANSWER CO 2 comes from
the atmosphere + organisms living in the soil
How does CO2 affect soils? - ANSWER Strongly influences plant growth, chemical, and
biochemical reactions in soil
Higher levels of CO 2 in soils than in atmosphere
, Master horizon A indicates? - ANSWER Surface horizon darkened by organic matter
Master horizon B indicates? - ANSWER Subsurface horizon of alteration
Master horizon C indicates? - ANSWER Unaltered, but not bedrock materials
Master horizon E indicates? - ANSWER Horizon of eluviation (strongly leached)
Master horizon O indicates? - ANSWER Organic Horizon
Master horizon R indicates? - ANSWER Bedrock
Illuviation: - ANSWER 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: - ANSWER The removal of soil material in suspension (or in solution) from a layer
or layers of a soil.
Residual parent material - ANSWER Soils formed from the breakdown of bedrock *coarse or
rough*
Transported parent material - ANSWER (Residual) Soils transported from one place to another
Exam With Complete Solutions
How is soil defined? - ANSWER "Three dimensional Natural body Composed of mineral
Give the six components of the definition of soil discussed in class. - ANSWER ● 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. - ANSWER ● 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? - ANSWER ● 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 - ANSWER 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 - ANSWER Mineral:
○ "broken-down rocks"
○ Inorganic chemistry
○ Not from living organisms
Organic soil material - ANSWER Organic:
○ "decomposed life"
,○ Organic chemistry
○ From living organisms
○ Based on rings and chains of carbon
Humus - ANSWER colloidal (very small), complex organic compounds resistant to
decomposition
Specific Surface area - ANSWER specific surface area - The surface area relative to the mass
What fills soil pore space? - ANSWER ● Water and Air
● Dissolved nutrients essential for growth of plants and organisms
How does soil atmosphere compare to above-ground atmosphere? - ANSWER Higher CO2
and Lower O2
Where does CO2 come from in the soil? How does it affect soils? - ANSWER CO 2 comes from
the atmosphere + organisms living in the soil
How does CO2 affect soils? - ANSWER Strongly influences plant growth, chemical, and
biochemical reactions in soil
Higher levels of CO 2 in soils than in atmosphere
, Master horizon A indicates? - ANSWER Surface horizon darkened by organic matter
Master horizon B indicates? - ANSWER Subsurface horizon of alteration
Master horizon C indicates? - ANSWER Unaltered, but not bedrock materials
Master horizon E indicates? - ANSWER Horizon of eluviation (strongly leached)
Master horizon O indicates? - ANSWER Organic Horizon
Master horizon R indicates? - ANSWER Bedrock
Illuviation: - ANSWER 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: - ANSWER The removal of soil material in suspension (or in solution) from a layer
or layers of a soil.
Residual parent material - ANSWER Soils formed from the breakdown of bedrock *coarse or
rough*
Transported parent material - ANSWER (Residual) Soils transported from one place to another
