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:

Every month 6 rainy months only

Location A600 mm/yr

Location B600 mm/yr

50mm 100mm

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. 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 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

hydrolysisIn lab:Apatite Ca5(PO4)F

Ca5(PO4)F + H2O Ca(OH)2 + HPO4

basic BLUE PINK

carbonationIn lab:

H2O + CO2 H2CO3

RED 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