Soil Formation

1
Soil Formation
2
Types of Soil Parent Materials
3
Organic Parent Materials
4
Igneous Rocks
5
Sedimentary and Metamorphic Rocks
6
Geographical Distribution of Parent Materials
7
Wind Deposited Parent Materials
8
Climate
9
Effect of Biota on Nutrient Cycling and Retention
10
Role of Earthworms (and animals in general)

• Darwins last paragraph
• When we behold a wide turf covered expanse, we
  should remember that its smoothness, on which so
  much of its beauty depends, is mainly due to all
  the inequalities having been slowly leveled by
  worms.It may be doubted whether there are many
  other animals which have played so important a
  part in the history of the world

11
A Biomantle in California
12
Mima Mounds in California
13
Topography
14
Geological Time Scale
15
Relative Geological Time

• One of great intellectual developments of last
  millennium
• 4 Eras of time related to major biological events
  or changes
• - Precambrian
• Nearly 4 billion years of time
• Evolution of bacteria and simple forms of life
  that still dominate our planet
• Paleozoic
• Cambrian explosion of life
• Evolution of land plants
• Ended with large extinction
• Mesozoic
• Age of dinosaurs
• Ended with extinction
• Cenozoic
• Age of mammals
• Tertiary vs. Quaternary
• Now experiencing great extinction event

16
Relative Geological Time Scale
17
The Significance of Humans in Relative Time
18
Processes of Soil Formation
19
Dust on Earth
20
Wind Erosion, Atacama Desert, Chile
21
Salt Weathering, Atacama Desert
22
Chemical Weathering of Minerals
23
The Silica Tetrahedron

• 1 Si, 4 O -4 net charge
• Tetrahedra can be linked by sharing O, thereby
  reducing net negative charge.
• Class of silicate is determined by number of
  shared O, and need for cations to neutralize net
  negative charge

24
Nesosilicates Singe Tetrahedra Linked with
Cations

• Foresterite
• Single tetra linked with Mg2
• Other minerals in group have all Fe2
• Highly susceptable to chemical weathering via
  ejection of cations by acid (H)
• Products then form secondary silicates and oxides

25
Inosilicates Chains

• Diopside
• Single chains

• Tremolite
• Double chains

26
Phyllosilicates Sheets

• Phlogopite
• trioctahedral w/ Mg2
• K strongly adsorbed in cavities

• Muscovite
• dioctahedral w/ Al3

27
Tectosilicates Framework

• Anorthite (Ca)
• 50 Al for Si substition

• Albite (Na)
• 25 Al substition

• Quartz
• No substition/O charge

28
11 phyllosilicates kaolinite

• One layer of Si tetrahedra
• One layer of Al octahedra
• Individual minerals are held to another via H
  bonds

29
Chemical Weathering of Minerals
30
(No Transcript)
31
Chemical Weathering of Minerals
32
Field Observable Properties of Soils

• Major terms and concepts
• Soil profile 2d vertical exposure of soil vs.
  depth (pedon)
• Soil horizons roughly horizontal bands of soil
  that form from soil forming processes

33
Processes of Soil Formation
CO2 flux

• Additions
• Organic C
• Dust
• Removals
• CO2
• Weathering products
• Transfers
• Clay
• Organic matter
• Carbonate
• Transformations
• Plants to SOM
• Primary silicates to secondary silicates,
  carbonates

OM additions, OM transformations, weathering
Clay transfers
Clay and carbonate transfers
Leaching
34
Soil Horizon Nomenclature

• Based on interpretation of dominant soil forming
  processes affecting that horizons
• Names based on presumed changes relative to
  parent material (t0)
• Universal with some variance
• Originated by Russians in 19th Century

35
Master Horizon Nomenclature
36
Upcoming Field Trip
A
Bt
Btqm
BC
37
Master Horizon Subdivisions
38
(No Transcript)