Soil Formation
Soil forms when weathered parent
material interacts with
environment.
rate of formation
Slow--------------------------------------Fast
~ 1 cm/1000 yr
~ 30cm/50yr
Hans Jenny
• 1941: soil is open system, properties
are functionally related; system changes
when property(ies) change(s).
• Jenny’s CLORPT equation
s = ƒ (cl, o, r, p, t)
1. Climate...
…determines speed, character of soil
development:
a. type and rate of weathering
b. living organisms and plants
found in an area
1. Climate
1. Temperature
-for every 10°C , biochemical rxn rates 2X
2. Effective precipitation
(water that moves through entire soil
column, including regolith)
-depth of water = depth of weathering
-water moves soluble & suspended
materials
• (Fig. 2.15)
Effective
precipitation
p. 42
-seasonal distribution
-temperature, evaporation
-topography
-permeability
Seasonal distribution of precipitation:
Location B
600 mm/yr
Location A
600 mm/yr
50mm
Every month
100mm
6 rainy months only
Temperature and evaporation:
Location A
hot
High
Location B
cool
evapotranspiration
600 mm
Lower effective ppt
Low
evapotranspiration
600 mm
Higher effective ppt
Topography:
level
slope
concave or
bottom of slope
(receiving)
Permeability:
2. Organisms
(Living plants and animals on and in soil)
-type of vegetation influences soil type
-base pumping
-sources of organic matter
-nutrient recycling
-vegetation prevents erosion
Type of vegetation influences soil
type
Base pumping
Deciduous trees are more effective base pumpers than
conifers .
-deciduous litter is easy to break
down
-cations (bases) are released so
surface soils are not acidic
-needles are hard to
break down
-basic cations leach
away: soil is acidic
• Macroanimals (insects, mammals,
gastropods, earthworms)
– mix, bind soil; create channels for air,
water
crotovinas
• Macroanimals (insects, mammals,
gastropods, earthworms)
– mix, bind soil; create channels for air,
water
• Microanimals (nematodes, protozoa)
• Macroanimals (insects, mammals,
gastropods, earthworms)
– mix, bind soil; create channels for air,
water
• Microanimals (nematodes, protozoa)
• Macroplants (the green plants)
– provide organic matter, roots create
channels, adsorb nutrients, release CO2,
stabilize, protect from erosion
• Macroanimals (insects, mammals,
gastropods, earthworms)
– mix, bind soil; create channels for air,
water
• Microanimals (nematodes, protozoa)
• Macroplants (the green plants)
– provide organic matter, roots create
channels, adsorb nutrients, release CO2,
stabilize, protect from erosion
• Micro “plants” (fungi, bacteria,
actinomycetes, algae)
– decomposers
3. Relief/Topography
• important for rate of runoff, erosion,
drainage
Flat valley floors and flat ridge tops: soil accumulates;
(deepening>removal)
Slopes: (removal> deepening)
• Vertical Zonation
– soils, climate, vegetation change with
elevation
4. Parent Material
• Determines texture, types of
weathering, mineral make-up
weathering
• Physical (Mechanical): disintegration of
parent material; increases surface area:
– surface area increases by same factor as
particle size decreases
• Chemical (Biogeochemical) : primary
minerals are broken down and
secondary minerals are formed
• Physical:
1. Freeze/thaw
2. Exfoliation
3. Abrasion
4. Salt wedging
• Chemical (biogeochemical):
1. Hydrolysis: minerals react with H2O
H+ replace soluble parts; OHcombine with mineral cations
2. Hydration: mineral combines with
H2O
3. Oxidation: mineral combines with O2
(lose electron)
Reduction: loss of O2 (gain electron)
4. Carbonation: oxides combine with
acids to make carbonates
5. Complexation: organic acids form
organic complexes with metal cations
Freeze / Thaw
• Physical:
1. Freeze/thaw
2. Exfoliation
3. Abrasion
4. Salt wedging
• Chemical (biogeochemical):
1. Hydrolysis: minerals react with H2O
H+ replace soluble parts; OHcombine with mineral cations
2. Hydration: mineral combines with
H2O
3. Oxidation: mineral combines with O2
(lose electron)
Reduction: loss of O2 (gain electron)
4. Carbonation: oxides combine with
acids to make carbonates
5. Complexation: organic acids form
organic complexes with metal cations
2. Exfoliation
• Physical:
1. Freeze/thaw
2. Exfoliation
3. Abrasion
4. Salt wedging
• Chemical (biogeochemical):
1. Hydrolysis: minerals react with H2O
H+ replace soluble parts; OHcombine with mineral cations
2. Hydration: mineral combines with
H2O
3. Oxidation: mineral combines with O2
(lose electron)
Reduction: loss of O2 (gain electron)
4. Carbonation: oxides combine with
acids to make carbonates
5. Complexation: organic acids form
organic complexes with metal cations
3. Abrasion (wind, water, ice)
wind
water
ice
• Physical:
1. Freeze/thaw
2. Exfoliation
3. Abrasion
4. Salt wedging
• Chemical (biogeochemical):
1. Hydrolysis: minerals react with H2O
H+ replace soluble parts; OHcombine with mineral cations
2. Hydration: mineral combines with
H2O
3. Oxidation: mineral combines with O2
(lose electron)
Reduction: loss of O2 (gain electron)
4. Carbonation: oxides combine with
acids to make carbonates
5. Complexation: organic acids form
organic complexes with metal cations
4. Salt Wedging
hydrolysis
In lab:
Apatite Ca5(PO4)F
Ca5(PO4)F + H2O
Ca(OH)2 + HPO4
basic
BLUE
PINK
carbonation
In lab:
H2O + CO2
RED
H2CO3
YELLOW
5. Time
• Amount of time soil has been exposed
to weathering and soil forming
processes influences soil properties.
– Jenny’s staircase
– Ohio/Ky.
4 soil forming processes:
(pedogenic)
Transformation
4 soil forming processes:
Transformation
Translocation
4 soil forming processes:
Transformation
Translocation
Addition
4 soil forming processes:
Transformation
Translocation
Addition
Loss