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Environmental processes and systems, LEC 103 > Soil components, Lecture 28 > Flashcards

Soil components, Lecture 28 Flashcards

1
Q

Soil is a three phase system, made up of

A

solid, liquid and gas

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2
Q

Pore space if made up of

and what does this depend on?

A

made up of water or air

and this depends on climate

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3
Q

What is soil made up of which isn’t pore space?

2

A

minerals and organic

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4
Q

Ideal percentage of organic matter in soil for crops?

A

5%

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5
Q

Which size pores are better for water?

A

smaller

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6
Q

Soil physical properties

7

A
  1. soil colour
  2. soil texture
  3. structure of mineral soils
  4. soil density
  5. pore space of mineral soils
  6. soil aggregates
  7. engineering properties
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7
Q

Three main factors determing soil colour

A
  1. carbon content, levels of organic matter
  2. water content, levels of moisture
  3. chemical makeup, oxygen levels
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8
Q

Inorganic components of soil

A

Sand/silt/clay,
minerals particles
primary minerals
secondary minerals

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9
Q

Inorganic components of soil

mineral particles

A

wide size and composition range

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10
Q

Inorganic components of soil

primary minerals

A

little changed from orginal rock

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11
Q

Inorganic components of soil

secondary minerals

A

altered by interacttion with air and water

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12
Q

Organic components of soil

3

A

living organisms
dead and decaying plant and animal remains
humus - humic and non-humic substances (OM)

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13
Q

Functions of organic matter in soil

5

A
  1. Supply of nutrients (release Ca, K, S, N, P)
  2. Maintaining structure (soil aggregation)
  3. Water storage (absorb water)
  4. Heat absorption (dark colour)
  5. Deactivation of chemicals (bind herbicides)
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14
Q

Decomposition in soil is a …

A

continuous process

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15
Q

Soil respiration is by

A

microbes

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16
Q

Importance of soil organic matter

2

A
  • main source of energy for soil organisms, without this there would be no biochemical activity
  • useful source of plant nutrients, helps to maintain soil fertility
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17
Q

Soil organic matter is comprised of

A

Partially decomposed plant and animal residues and organic compounds synthesised by soil microbes as the decomposition occurs.

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18
Q

Organic matter content of mineral soils percentage

A

0-10%

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19
Q

What does organic matter content of mineral soils depend on?

2

A

land use and climate

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20
Q

Organic matter content of organic soils percentage?

A

50% (on a volume basis)

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21
Q

Organic matter has a great influence on soil properties and therefore influences…

A

plant growth

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22
Q

Ways organic matter influences soil properties

4

A
  1. binds mineral particles into granules
  2. improves soil aeration
  3. increases soil capacity to hold water
  4. increases nutroent supplying capacity
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23
Q

Where is water found in soil?

A

pores

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24
Q

Soil solution

made up of

A

Water and soluble constituents, inc. nutrients

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25
Q

Soil solution

role

A

A critical medium for supplying nutrients and water to growing plants

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26
Q

How water transported through the soil?
2
(in lateral response to plants)

A
  1. upwards - evaporation

2. downwards - gravity

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27
Q

What is air in a given soil regulated by?

A

moisture content

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28
Q

Oxygen in soil needed for?

2

A
  1. respiration by plant roots

2. decomposition of organic matter by micro-organisms

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29
Q

Lack of oxygen in soils…

A
  • will affect a number of biochemical reactionsm resulting in:
    1. loss of certain nutrients, such as N and S
    2. possible reduction in nutrient solubility
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30
Q

What characterises a well-aerated soil?

A

Rapid exchange between soil air and atmospheric air

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31
Q

A well-aerated soil is ideal for what?

A

plant growth

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32
Q

Soil horizons rich in organic matter colour/shade

A

darker

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33
Q

Water content affect on soil colour

A

moisture darkens colours

34
Q

Colour of well-drained soil where oxygen levels are high?

why?

A

red,

presence of highly oxidised Fe - rust

35
Q

Poorly drained soil colour with low oxygen levels

A

grey/blue

36
Q

Soil texture

A

Combination of inorganic material in the soil.

Knowledge of the proportions of different-sized particles in a soil

37
Q

What indicates soil texture?

A

sand, silt, clay

38
Q

Which soil properties depend on soil clay content?

5

A
  1. shrink - swell capability
  2. plasticity
  3. water - holding capacity
  4. strength
  5. chemical adsorption
39
Q

Types of sand

soil texture

A

fine and coarse

40
Q

Clay in soil

A

Very high capacity to hold water and other substances and large specific surface area

41
Q

Shape/form of clay particles

A

flakes or plates

42
Q

AIr and water movement in clay

A

very slow due to tiny pores

43
Q

Specific surface area

A

Total surface area of a material per unit mass (solids)

googled

44
Q

Influence of soil tecture on soil properties (related to specific surface area (SSA))
5

A
  1. greater SSA means greater ability to retain water on the surface of soil particles
  2. greater SSA, greater capacity to retain nutrients and pollutants
  3. greater SSA, fast rate of weathering
  4. greater SSA, greater likelihood of forming a cohesive soil
  5. larger SSA, more microbial activity on particle surfaces
45
Q

As particle size decreases, what happens to SSA?

A

it increases

46
Q

Major soil textural classes are defined by

A

percentage sand, silt and clay

47
Q

Determing the texture of a soil test

A

(like on 166 module)
form a ball, sausage, horseshoe
the more tests completed, the higher the clay content of the soil, therefore the smaller soil particles.

48
Q 
Granular soil
(type of soil structure)
A

Looks like crumbs.

Soil found where roots have permeated the soil.

49
Q 
Crumb soil
(type of soil structure)
A

very porous, the individual particles don’t fit together

50
Q

What determines soil structure?

A

How individual soil granules clump or bind together and aggregate, and therefore, the arrangement of soil pores between them.

51
Q

What does soil structure have a major influence on?

4

A
  1. water and air movement
  2. biological activity
  3. root growth
  4. seedling emergence
52
Q 
Soil struture
(definition)
A

The arrangement of the solid parts of the soil and of the pores space located between them

53
Q

What is soil structure dependent on?

5

A
  1. parent material
  2. environmental conditions during soil formation
  3. clay present
  4. organic materials present
  5. recent history of soil management
54
Q

Most forms of cultivation will cause a decline in…

A

soil structure

55
Q

What helps retain soil structure?

A

returns of organic matter

56
Q 
Platy soil
(soil structure)
A

Form thin layers or horziontal planes

57
Q 
Blocky soil
(soil structure)
A

Soil particles that cling together in nearly square or angular blocks having more or less sharp edges.

58
Q

Soil particle density (Dp)

A

Mass per unit volume of soil solids

59
Q

What determine the particle density of a mineral?

A

chemical composition and crystal structure

60
Q

Does pore space affect particle density?

A

no,

61
Q

Bulk density of soil (Db)

A

Weight of soil in a given volume

62
Q

What affects bulk density of soil?

A

the packing arrangement of sand grains

63
Q

Bulk density is generally lower if

A

the grains are mostly of one class size (well-sorted sand)

64
Q

Characteristics of the highest density soils?

3

A

poor organic content, wide size range, tight packing of grains

65
Q

Factors affecting bulk density

1 with 4 parts

A

Human activity

  1. agriculture
  2. forestry
  3. construction
  4. leisure
66
Q

Where does the movement of fluids occur in soils?

A

through the pore spaces, in between the solid soil grains

67
Q

Which two measurement help find total porosity of soil?

A

bulk denisty and particle densities

68
Q

Are soil pores interconnected?

why?

A

They can be, it depends!

soil pores have a variety of shapes and sizes

69
Q

What plays a large role in pore formation?

A

biota

70
Q

Macropores of soil

A

large soil pores, greater than 0.08 mm in diameter

71
Q

Biopores

A

Macropores which are created by earthworms, roots, moles, badgers, etc.

72
Q

Which soil texture type is dominated by macropores?

A

sandy soils

73
Q

Macropores, fluid movement

A

allows ready movement of fluids = air and water with associated dissolved substances

74
Q

Micropores

A

Small soil pores,

Less than 0.08mm in diameter

75
Q

Are macropores or micropores usually air filled?

A

macropores are usually air filled

76
Q

Are macropores or micropores usually water filled?

A

micropores are usually water filled

77
Q

Gas movement within micropores?

A

too small to allow significant gas movement

78
Q

Water movement within micropores?

A

slow, not available to plants

79
Q

Which soil texture type is mainly made up of micropores?

A

fine-textured soils, low organic content

80
Q

Root development and microbial activity in soils which dominated by micropores?
why?

A

low levels,

due to poor aeration

81
Q

What are vital for soil biota?

A

macropores

Environmental processes and systems, LEC 103 (10 decks)

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