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Soil Formation
Soil forms when weathered parent material interacts with
environment.
• Soil environment includes:
– Climate and weather– Animals– Microbes– Human use– Hazards ( natural and unnatural )– Topographical relief
rates of soil 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. CLIMATE2. ORGANISMS3. RELIEF4. PARENT MATERIAL5. TIME
1. CLIMATE
…determines speed, character of soil development:
type and rate of weathering
living organisms and plants found in an area
components of 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
-a) seasonal distribution
-b) temperature, evaporation
-c) topography
-d)permeability
a) Seasonal distribution of precipitation:
Every month 6 rainy months only
Location A600 mm/yr
Location B600 mm/yr
50mm 100mm
b) Temperature and evaporation:
Location Ahot
Location Bcool
600 mm600 mm
High evapotranspiration
Low evapotranspiration
Higher effective pptLower effective ppt
Topography:
level slope
concave or bottom of slope(receiving)
Permeability:
2. Organismsplant and animal
(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 pumpingDeciduous 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/thaw2. Exfoliation3. Abrasion4. Salt wedging
• Chemical (biogeochemical):1. Hydrolysis: minerals react with
H2O
H+ replace soluble parts; OH- combine 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/thaw2. Exfoliation3. Abrasion4. Salt wedging
• Chemical (biogeochemical):1. Hydrolysis: minerals react with
H2O
H+ replace soluble parts; OH- combine 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/thaw2. Exfoliation3. Abrasion4. Salt wedging
• Chemical (biogeochemical):1. Hydrolysis: minerals react with
H2O
H+ replace soluble parts; OH- combine 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/thaw2. Exfoliation3. Abrasion4. Salt wedging
• Chemical (biogeochemical):1. Hydrolysis: minerals react with
H2O
H+ replace soluble parts; OH- combine 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
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