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Introductory Soli Science

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Silicon & oxygen are the dominant elements in the earth's crust and soil. ... loess. bedrock. Soil Type. Parent Material. Rock Type ... – PowerPoint PPT presentation

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Title: Introductory Soli Science


1
Introductory Soli Science
  • Formation of Soil

2
Major Ideas
Silicon oxygen are the dominant elements in the
earths crust and soil. Si O combine to form
silicate tetrahedra. Tetrahedra share 1 or more
oxygens to form different silicate minerals
families Clays are sheet-type silicates. Micelles
are clay particles with negative charge - they
attract positively charged particles. The
properties of micelles vary with their
composition.
3
A clay is born
  • silicate clays build little by little about the
    nucleus
  • most clays are crystalline with sheet structures
    like the micas
  • the cations are
  • silicon in the tetrahedral position
  • aluminium in the octahedral position
  • hence they are called aluminosilicates

4
Alumino-silicate structure
Aluminium
Silicon
5
The clay minerals
  • because of the excess oxygen in the sheets their
    charge is negative
  • so they act like large anions
  • they attract cations and the positive ends of
    water molecules
  • these cations may be easily removed and replaced
    by others
  • this is called cation exchange

6
Clay structure
silica sheet

silica sheet
alumina sheet
alumina sheet
silica sheet
- O-OH -
fixed distance
variable distance
- O - O -
silica sheet
silica sheet
alumina sheet
alumina sheet
silica sheet
11 lattice clay
21 lattice clay
7
11 Clay minerals
  • kaolin, halloysite
  • very common in well weathered soils
  • distance between crystal lattice is fixed,
    therefore little expansion occurs on wetting
  • few cations can enter between the lattices, so
    cation exchange capacity (CEC) is low

8
21 Clay minerals
  • montmorillonite or smectite group
  • distance between crystal lattice is variable,
    water may freely enter space therefore expansion
    occurs on wetting
  • cation exchange capacity (CEC) is high

9
Soil Chemistry
The influence of the chemical nature of soil on
its overall appearance and behaviour is
considerable.
  • For example
  • pH
  • Fertility
  • Swelling and shrinking
  • Water retention

10
Soil ChemistrySilicate Clays
  • Different silicate sheets contain different
    elements in different proportions
  • Combination of different sheets will give clays
    with very different properties
  • Two examples follow

11
Soil ChemistrySilicate Clays
12
Soil ChemistrySilicate Clays
  • Because of their different properties
  • Montmorillonite will
  • have good water holding capacity
  • good fertility
  • but will shrink/swell a lot
  • Kaolinite will
  • have lower water holding capacity
  • poorer fertility
  • but will not shrink/swell

13
Soil Chemistry
  • Of course sandy (quartz) soils will have even
    lower water holding capacity fertility

14
Major Ideas
  • Soil chemistry has significant effect on soil
    properties
  • pH
  • water holding capacity
  • nutrient status
  • structure
  • physical movement of the soil mass

15
Major Ideas
  • Soil chemistry has significant effect on soil
    properties
  • pH
  • water holding capacity
  • nutrient status
  • structure
  • physical movement of the soil mass

16
What is soil?
May depend on your view point!! Soil is a
mixture of mineral and organic matter which forms
a thin layer over the underlying bedrock. The
co-evolution of inorganic and organic components
takes place in a seral succession which begins
with exposure of bedrock and progresses towards a
relatively deep and mature soil.
17
What is soil?
  • Soils are composed of
  • an inorganic component
  • an organic component

18
Soil components
  • Inorganic Component
  • Mineral materials
  • they come from weathering of bedrock in situ and
    material that is washed or blown in.
  • Organic Component
  • this comes from material living in or on the soil
  • these change from micro-organisms in bedrock to
    higher plants at the end of the seral succession

19

What is soil?

Soils continue to develop over time and a
vertical differentiation called horizons results
20
The soil profile
21
SOIL FORMATION
  • Charman Murphy pp 3 -12

22
Soil Formation
  • Soil formation involves two parts
  • Soil-forming factors
  • Soil-forming processes
  • We will discuss both-
  • soil-forming factors today
  • soil forming processes tomorrow

23
Soil forming Factors

24
Soil-forming Factors
  • Factors determining soil type
  • parent material
  • climate
  • topography
  • time

25
Soil-forming factors
  • Parent material
  • bedrock materials
  • composition determines soil properties
  • Transported materials
  • gravity colluvial
  • water alluvial
  • wind aeolian
  • ice glacial

26
Soil-forming factors
  • Bedrock is converted to the basic materials
    (minerals) which form the inorganic component of
    soils by the process of weathering

27
Soil Types

28
Soil Types
  • Factors determining soil type
  • parent material
  • climate
  • topography
  • time

29
Soil Type
  • Parent material may be
  • alluvium
  • loess
  • bedrock

30
Soil Type
  • Parent Material
  • Rock Type
  • Some rocks are more susceptible to weathering
    and produce
  • deeper soils
  • more fine particles

31
Particle sizes
  • Sand 2.0 - 0.02 mm (2000 20µm)
  • Silt 0.02 - 0.002 mm (20-2µm)
  • Clay less than 0.002 mm (2 µm)


32
Soil Type
  • Parent material and particle size determine
  • soil texture
  • soil structure
  • soil depth

33
Soil Types
  • Factors determining soil type
  • parent material
  • climate
  • topography
  • time

34
Soil Types
  • Climate
  • Temperature and water have a profound effect on
    weathering

35
Soil Types
Temperature
- - - - -
50 40 30 20
Clay content
l l l l
10 15 20 25
Ave. annual temperature
36
Soil Types
- - - - -
Water
50 40 30 20
Clay content
l l l l
10 20 30 40
Ave. annual rainfall (inches)
37
Soil Types
  • Climate
  • Hot wet climates produce fine textured, deep
    soils
  • Climate also affects soil colour

38
Soil colour
  • Soil colour results from staining of mineral
    grains
  • Humic acid
  • Black
  • brown

39
Soil colour
  • Soil colour results from staining of mineral
    grains
  • Iron oxides
  • Red,
  • yellow or
  • green

40
Soil colour
  • Soil colour results from staining of mineral
    grains
  • Salts
  • White

41
Soil Types
  • Climate and colour
  • hot-wet climate removes organic material leaving
    iron oxides
  • cool dry climate allows humus to build up
  • arid climate are not humus producing and increase
    the potential for salt build-up
  • water-logged soils cause iron oxide build-up

42
Soil Types
  • Factors determining soil type
  • parent material
  • climate
  • topography
  • time

43
Soil Types
  • Topography-slope affects soil depth
  • steep slopes have thin soils
  • colour texture change down slope
  • results in a series of related but different
    soils from top to bottom
  • called a catena

44
Soil Types
  • Factors determining soil type
  • parent material
  • climate
  • topography
  • time

45
Soil Types
  • Time
  • the development of a soil over time is called a
    seral succession
  • mature soils take 100s to 1000s of years to form
  • changes in conditions during the long periods of
    soil development result in polygenetic soils

46
Soil types
  • Organic matter also affects soil development but
    we will deal with this later.
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