Formation & importance of soils, lecture 27 Flashcards
1
Q
Soil
A
The outermost layer of the Earth
2
Q
How is soil formed?
A
Weathering of rocks
3
Q
Phrase to describe soil
A
‘living mantle of the Earth’
4
Q
Is soil a renewable or non-renewable resource?
A
non-renewable resource
5
Q
Rough soil formation time
A
thousands of years to form
6
Q
Soils are at the interfere of
4
A
- Lithosphere
- Atmosphere
- Hydrosphere
- Biosphere
7
Q
Soils at the interface of
the Lithosphere
A
Soils formed from rock constituents.
8
Q
Soils formed from rock constituents.
the atmosphere
A
Air overlies and intermingles with soil.
9
Q
Soils are at the interface of
the hydrosphere
A
Water flows through soil.
10
Q
Soils are at the interface of
the biosphere
A
Biota live in and on soil.
11
Q
Soil science is…
A
interdisciplinary
12
Q
Key functions of soil
6
(according to DEFRA)
A
- Food and Fibre Production
- Environmental Interaction
- Support of Ecological Habitat and Biodiversity
- Protection of Cultural Heritage
- Providing a platform for construction
- Providing Raw Materials
13
Q
There is unlocked potential in soil resources for…
A
biological and medical resources
14
Q
Regulation of water by soil,
Soil misuse or over-exploitation can have significant consequences for…
example?
A
groundwater, rivers, estuaries and coastal waters
eg: overuse of fertilisers
15
Q
Link of soil to history
A
Dominant nations had good soil,
facilitates productive agriculture
16
Q
Soils quality reflects
3 aspects
A
all chemical physical biological properties
17
Q
Main threats to soil function and quality
5
A
- Erosion
- Compaction and sealing
- Contamination
- loss of SOM (Soil organic matter)
- Salinisation
18
Q
Threats to soil function and quality
Erosion
A
(landslides)
loss of productivity and biodiversity
used linked to overuse
19
Q
Threats to soil function and quality
Compaction and sealing
A
intensive use of heavy equipment or grazing whilst the soil is saturated
(loss of biodiversity, flooding)
20
Q
Threats to soil function and quality
contamination
A
Metals and organic contaminants could degrade soil quality and functions, implications for the wider environment
21
Q
Threats to soil function and quality
loss of SOM
A
Loss of SOM, loss of fertility, increased risk of erosion, also reduces water retention capacity, linked to climate change
22
Q
Threats to soil function and quality
Salinisation
A
- Excess accumulation of soluble salts due to saline water use in farming or irrigation practices
- generally in hotter countries, Middle East
23
Q
Percentage of the World’s freshwater stored in soil for plant use
A
66%
24
Q
How should soil be viewed?
A
as a finite resource
25
Weathering
Physical and chemical breakdown of rocks and other materials
26
Soils relate to what
the rock they originate from
27
Factors controlling soil formation
| 5
1. parent material
2. climate
3. biota
4. topography
5. time
28
Factors affecting soil formation
| parent material
unconsolidated material or rock in which soil development occurs
29
2 examples of parent material deposits
organic deposits - peat
| glacial ice transport - glacial till
30
Example of parent material
| organic deposits - peat
Organic material deposited when accumulation exceeds decomposition: stratified deposit of peat.
31
Example of parent material
| glacial ice transport - glacial till
Glacial till, material deposited directly by ice, is a heterogeneous (unstratified) mixture of rounded boulders, stones, sand, silt, and clay.
32
Factors affecting soil formation
| climate
Temperature and precipitation (rainfall, snowfall)
33
Which is the most influential of the four factors acting on parent material?
climate
34
Which two climatic factors have major effects on physical and chemical weathering and biological processes
precipitation and temp.
35
What allows carbonates to accumulate at shallow depths?
low rainfall
36
Why do acidic soils form in humid areas?
intense weathering and leaching of basic cations - Ca, K, Mg
37
Effect of water induced soil erosion on sloping land?
constant removal of developing layers
38
When developing soil layers eroded from slopes due to erosion by water, what is the effect on soil downslope?
Deposition of soil materials downslope covers developing soil layers
39
Weathering, leaching and erosion in warm and humid regions
more intense and occur for a longer period of time
40
Why does rapid weathering not occur in cold areas such as Alaska?
soil is too cold
41
Factors affecting soil formation
| Biota
Living organisms, plants, organic residue, microbes, soil animals
42
Soil in humid forest vegetation
soils are leached but have many layers of slowly decomposing organic matter
43
Grassland soils
generally rich in well decomposed organic matter
44
Arable soils
generally have low content of organic matter
45
Soils that harbour many burrowing animals have...
fewer but deeper soil horizons.
46
How do micro-organisms help soil formation?
by decomposing organic matter and forming weak acids
47
Role of worms in soil
| factors affecting soil formation - biota
important for mixing of soil
48
Factors affecting soil formation
| Topography
The Earth's surface contour.
| Slope, aspect, elevation and landscape position
49
Horizons of soils on steep hillsides
thin
50
Landlocked depressions
| runoff, productivity, decomposition rates
receive more runoff, greater production of vegetation, but slower decomposition.
51
Waterlogged, and high productivity of vegetation and low rate of decomposition results in...
organic (peat and muck) soils
52
Slopes facing sun are...
warmer and drier than those not; water limitation may affect vegetation cover and warmer temperature can affect the breakdown of organic matter.
53
Slopes tend to
| - soil depth, drainage, erosion
decreased soil depth,
better drainage,
increased wind and water erosion
54
What is relief vs topography?
```
Relief = height difference between a high and low point (measured by contours on a map not elevation)
Topography = What the land looks like based on elevation
```
55
Factors affecting soil formation
| Time
Tine since parent materials were exposed
56
What soil maturity based on?
development stage rather than age
57
Is younger or older soil generally more fertile?
| why?
younger soil is, as it had more minerals
58
Which factors determine the length pf time for soil formation?
4
- climate
- the nature of the parent material
- the organisms
- topography
59
What type of climate is soil formation faster in?
warm, humid climates
60
Time periods of glacial till and sediments
short, <200 years
61
Weathering of rock time period
varies, but can take thousands/millions of years
62
Processes during soil formation (genesis)
| 5
1. additions
2. removals
3. mixing
4. translocation
5. transformation
63
Soil Horizons
Different layers of soil
64
Soil profile
A section through soil horizons
65
How many soil horizons are there?
six
66
What are the six soil horizons?
| in order
```
O - horizon
A - horizon
E - horizon
B - horizon
C - horizon
R - horizon
```
67
O - horizon of soil
A thin layer which is at the top of the soil and is composed of leaf litter and organic matter
68
A - horizon of soil
The soil layer below the top layer (o-horizon) which is composed of the most humus so is the darkest generally.
69
E - horizon of soil
The layer below A - horizon with a high clay content and insoluble minerals such as quartz, soluble materials will have leached from this layer.
70
B - horizon
The layer below the E - horizon where there is little organic matter content, yet soluble minerals and iron oxides build up here.
71
C - horizon
Bedrock which is mixed with clay and is broken, decayed and slightly altered.
72
R - horizon
The bottom soil horizon which made up of unaltered bedrock.
73
Processions during soil formation (genesis)
Additions
9
Water (from the surface, and by ground water discharge)
Suspended and dissolved materials carried by water
Solids transported by wind
Gases from the air
Energy from the sun
Organic carbon by plants in the form of roots and root-derived material
Organic carbon by photoautotrophic bacteria
Organic nitrogen by nitrogen-fixing bacteria
Plant and animal remains on and in the soil
74
Processes during soil formation (genesis)
Removals
7
Material removed by wind erosion
Material removed by water erosion
Dissolved and suspended material leached out
Uptake of nutrients from the soil by plants
Carbon dioxide gas produced by plant root, microbial and faunal respiration
Other gases such as nitric oxide, nitrous oxide and nitrogen produced by denitrifying bacteria
Other gases such as methane which are produced under anaerobic conditions
75
Processes during soil formation (genesis)
Mixing
4
Soil animals
Tree fall and gravity
Shrinking and swelling due to water content changes
Freezing and thawing
76
Processes during soil fomation (genesis)
Translocation
3
Gradients in water potential and chemical concentrations within the soil pores
Soluble minerals, colloidal material, organic compounds, and iron may move up or down the profile, between horizons, with water movement.
Biological activity may cause gradients in the chemical composition of the water and air-filled pores of the soil.
77
In the formation of soils, translocation means...
vertical movement of materials
78
Processes during soil transformation (genesis)
Transformation
3
Soil components are transformed by chemical and biological reactions.
Organic compounds decay, some minerals dissolve, other minerals precipitate.
These transformations result in the development of soil structure, and in changes in colour, relative to the parent material.
