What is Soil?
“a living, dynamic system with organic and inorganic components. Soil is a product of its environment and parent material”.
componentsBy volume:
– 45% mineral– 5% organic material– 50% space (air/water)
By mass?– 0% air– 18% water– 80% mineral– 2% organic material
1. The mineral component• inorganic• “mineral”: definition?
– Primary: original components of earth crust
– Secondary: new minerals made by weathering of earth’s crust
• divided by particle size:– Sand, silt, clay
• mineral make-up due to:
a. Parent Materialb. How resistant minerals arec. Climated. “Age”
a. parent materialmaterial on and in which soil
develops
Examples of soil developing IN rather than ON parent material: 1. Apostle Islands
2. Boundary Waters
• 11 different parent materials …..
Regolith/bedrock:weathered rock
Alluvium:deposits on a flood plain from a river
Marine deposits:shell, reef and other “bits” formerly at
bottom of ocean that have been uplifted
Lacustrine deposits: clay deposits originally laid down at the bottom of a lake; lake is no longer there
Example: glacial lakes in MN
Till:unconsolidated material deposited by
glacial ice
Outwash:unconsolidated, sorted material deposited
by meltwater from a glacier
Organic sediments: peat
Volcanic ash
Loess:deep deposits of silt that have been
deposited by wind
Sand:beach sand, dune sand
Colluvium;material that moved downslope, as in a
landslide
• mineral make-up due to:
a. Parent Materialb. How resistant minerals arec. Climated. Age
b. resistance of minerals• Soluble minerals are readily
LEACHED from soil profile (Ca,Mg,Na)
• Certain minerals tend to accumulate in soil– (oxides of Fe, Al, Si)
• mineral make-up due to:
a. Parent Materialb. How resistant minerals arec. Climated. Age
c. Climate• Amount of leaching
• Rate of weathering
• mineral make-up due to:
a. Parent Materialb. How resistant minerals arec. Climated. Age
d. Age• Parent material is (usually) less
influential in “older” (more highly developed) soil
2. Organic Component• Living (primarily
decomposers)
• Non-living (dead and all in-between stages of decomposition)
…about decomposers:• Nutrient recycling
• Respiration
decomposer activity depends on:
climatesoil moisture conditionsMicro-environmental factors (relief,
drainage)
decomposers and climate:1) climate vegetation, litter
(amount, type)
2) rate of decompositionhot,wet >> cold, dry
soil moisture conditions
• Hot, wet preference of decomposers
micro-environmental factors (relief, drainage)
• Slope aspect affects temperature
• Drainage affects anaerobic/aerobic decomposition
3. The Space component• Soil pores
– filled with air and/or water
A. soil air
O2 CO2 N2 H 2O vapor (per cents by volume)
(rh) Above-ground atm. 20.97 0.03 79.0
<100%
Soil (grassland) atm. 18.4 1.6 79.2 100 %
B. soil water• Functions?• Polar molecule
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