THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil ©2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458 Chapter 2 Formation

THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Chapter 2 Formation of Soils from Parent Materials

Sampling moon “soil.” (NASA, Apollo 14)



Figure 2.1

(a) (b)



Figure 2.2



Figure 2.3







Physical Weathering Processes

• Unloading• Temperature

– Thermal Expansion

– Freeze-Thaw

– Frost Wedging

• Abrasion– Water, Ice, Wind

• Biological Activity– Burrows

– Root Wedging



Biogeochemical Weathering Processes• Hydration

– Intact water molecules combine with a mineral5Fe2O3 + 9H2O Fe10O15(9H2O)

• Hydrolysis– Water Molecule splits into hydrogen and a hydroxyl and the hydrogen

replaces a cation from the mineral structureKAlSi3O8 + H2O HAlSi3O8 + K+ + OH-

• Dissolution– Aided by small amounts of acid in the water

– Soluble ions are retained in the underground water supply CaCO3 + 2[H+(H2)O] Ca2+ + CO2 + 3H2O

ORCaSO4(2H2O) + 2H2O Ca2+ + SO4

2- + 4H2O



Biogeochemical Weathering Processes

• Carbonation– Weathering is accelerated by the presence of weak acids

CO2 + H2O H2CO3 (Carbonic Acid) Then

H2CO3 + CaCO3 Ca2+ + 2HCO3-

• Oxidation-Reduction– Any chemical reaction in which a compound or radical loses

electrons

– Important in decomposing ferromagnesian minerals 4Fe + 3O2 2Fe2O3

Or4Fe(2-)O + O2 + 2H2O 4Fe(3-)OOH (Goethite)



Figure 2.5

(a) (b)



Figure 2.6

(a) (b)



Development of Clays

• The breakdown of parent rock results in the development of clays



Factors Influencing Soil FormationCLORPT

• Climate– Primarily precipitation and temperature

• Organisms– Especially vegetation, microbes, and soil animals

• Relief– Slope, aspect, and landscape position

• Parent Material– Geological or organic precursors to the soil

• Time



Effects of Parent Material

• The parent material is what the soil and the nutrients ultimately come from– Examples

• Colluvium

• Alluvium

• Floodplain

• Glacial

• Marine Sediments

• Loess

• Organic Bogs



Figure 2.11



Figure 2.12

A productive soil in the Appalachian Mountains formed on colluvium



Figure 2.14 Alluvial fans merging into a Bajada in Alaska,

which will form well-drained soils



Figure 2.13



Figure 2.15



Glacial Erosion



Glacial Erosion



Figure 2.17



Figure 2.16

1. Till deposits of various kinds2. Glacial-lacustrine deposits3. The Loessial blanket4. Area that escaped glaciation but has loess



Figure 2.18



Figure 2.19

GlacialTill

GlacialOutwash



Figure 2.20

Distribution of Dune Sands and Loess Deposits



Homes carved from Loess deposits in China



Figure 2.22 Development of a peat bog resulting in Histosols



Effects of Climate

• Effective Precipitation– Depends on timing, topography, and soil type

• Temperature– Effects the rate of weathering

• Climate also affects vegetation



Box 2.1

a. Seasonal Distribution, b. Temperature and Evaporation, c. Topography, d Permeability



Figure 2.23

Temperature and Precipitation work together to affect depth of regolith weathered from bedrock



Figure 2.24 Climate and Vegetation are interconnected



Effects of Organisms

• Flora– Lichen, Moss, Trees

• Fauna– Mites, Nematodes, Springtales, Earthworms



Figure 2.8 The effect of lichen etching bedrock



Figure 2.25

Difference in the soil profile under grassland versus forest vegetation



Change in soil Ph because of forest type



Semiarid rangeland vegetation will locally enhance fertility, photos from Patagonia Argentina



Figure 2.28

Prairie dog burrows help to mix the soil (called crotovinas), photo taken in Illinois



Effects of Topography

• Slope and Aspect– Determines amount of solar radiation absorbed

• Parent Material Interactions– Affects the distribution of colluvium and alluvium

• Salt Buildup– Arid areas slats are leached from relatively higher areas to lower

areas

• Interaction With Vegetation– Moisture regime is affected by microtopographic changes which in

turn controls vegetation distributions



Figure 2.29

(a) (b)

Topographic influence on soil depth



Figure 2.30



Effects of Time

• All soil forming processes occur over a very long period of time

• The time it takes to develop a soil is relative, dependent upon– Climate

– Vegetation

– Human Interaction



Figure 2.31



When Everything Else Is Held Equal (Sequences)

• Catenas – When soils are developed on the same parent material and the soils

only differ on the basis of drainage due to variations in relief

• Chronosequence – A sequence of related soils that differ in certain properties

primarily as a result of time as a soil-forming process

• Lithosequence – A group of related soils that differ as a result of parent material

• Climosequence – A sequence of soils that differ as a result of changes in climatic

regimes (temperature and precipitation)

• Biosequence – A group of related soils that differ primarily due to variation in

kinds and numbers of plants and soil organisms



Four Basic Processes of Soil Formation • Transformation

– When soil constituents are chemically or physically modified or destroyed and others are synthesized from precursor materials

• Translocation– The movement of organic and inorganic materials horizontally or

vertically across a pedon

• Additions– Inputs of materials from outside sources (i.e. plant litter)

• Losses– Materials that are removed from the soil profile by leaching or

erosion



Figure 2.32



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THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil ©2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458 Chapter 2 Formation