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A Level Environmental Science > Soils > Flashcards

Soils Flashcards

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1
Q

Why is soil important?

A
  • Plant growth
  • Habitat for soil biota
  • Nutrients for plant uptake
  • Earth’s natural cycles (e.g. N)
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2
Q

What is soil fertility?

A

The ability of soil to sustain plant growth and optimise crop yield

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3
Q

What are the 5 components of soil?

A
  • Mineral particles
  • DOM
  • Water
  • Air
  • Soil biota
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4
Q

What are the 3 types of soil minerals?

A
  • Sand
  • Silt
  • Clay
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5
Q

Why is soil water content important for fertility?

A
  • Essential for soil biota and plants
  • Nutrients are dissolved within it for plant uptake
  • Waterlogged soils are anaerobic
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6
Q

What nutrients do fertile soils contain?

A
  • NPK in ionic form
  • Iron and magnesium
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7
Q

Why is air content important for soil fertility?

A
  • Aerobic soils increase the rate of decomposition
  • Organisms and processes are mostly aerobic
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8
Q

Why is DOM content important for soil fertility?

A
  • Provides nutrients through decomposition
  • Increases soil water retention
  • Binds the soil
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9
Q

Why is pH important for soil fertility?

A

Soils with a pH between 5.5 and 7.0 are in the range of tolerance for most plant species

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10
Q

What can acidic soils cause?

A
  • Nutrient leaching
  • Root hair cell damage
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11
Q

What can alkaline soils cause?

A

Phosphates become insoluble

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12
Q

Why are soil biota important for soil fertility?

A
  • Detritivores break up DOM and release nutrients
  • Increased drainage
  • Nitrification and nitrogen fixation
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13
Q

What does soil texture refer to?

A

The proportions of sand, silt and clay

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14
Q

Which of the mineral particles are largest?

A

Sand (L)
Silt
Clay (S)

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15
Q

What is a loam soil?

A

A soil with a relatively even mix of mineral particles

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16
Q

What determines soil structure?

A

Soil particles form aggregates (peds) which are bound together

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17
Q

What are crumb peds?

A

Small and round aggregates which provide good drainage and aeration

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18
Q

What are platy peds?

A

Large and flat aggregates which provide poor drainage and aeration

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19
Q

Why is soil depth important for soil fertility?

A
  • Deeper soils are less likely to become waterlogged
  • Deeper soils provide anchorage for large root systems
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20
Q

How is drainage impacted by soil texture?

A

Large, spherical particles increase drainage as there are more pore spaces (sand)

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21
Q

How is water content impacted by soil texture?

A

Water stays closer to the surface in clay soils (capillary action)

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22
Q

How is aeration impacted by soil texture?

A

Large, spherical particles increase aeration are there are more pore spaces (sand)

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23
Q

How are nutrient levels impacted by soil texture?

A

Clay soils have higher nutrient levels as water remains close to the surface (ionic form)

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24
Q

How is root penetration impacted by soil texture?

A

Greater penetration in sandy soils

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25
Q

How is ease of cultivation impacted by soil texture?

A

Sandy soils are easier to turn and plough

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26
Q

Which type of soil is optimal for agriculture?

A

Loam

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27
Q

Which 5 human activities impact soil fertility?

A
  • Aeration by ploughing and drainage
  • Changing nutrient levels
  • Irrigation
  • Soil compaction
  • pH control
28
Q

How does aeration by ploughing and drainage impact soil fertility?

A

Creates aerobic conditions which increases N fixation, nitrification and decomposition

29
Q

How can soil nutrient levels be increased?

A
  • Inorganic NPK fertilisers
  • Organic matter (mulch)
  • Planting legumes to encourage N fixation
30
Q

How can soil nutrient levels be decreased?

A
  • Soil erosion
  • Removal of biomass
  • Increased nutrient leaching
  • Aerobic soils encourage denitrification
31
Q

How does irrigation impact soil fertility?

A
  • Increases fertility where water is a limiting factor of growth
  • Keeps stomata open for efficient gas exchange
  • Water dissolves nutrients
32
Q

How does compaction impact soil fertility?

A
  • Heavy machinery and livestock farming compact the soil
  • Reduced aeration creates anaerobic conditions and encourages denitrification
  • Waterlogging is more likely
33
Q

How can soil pH be controlled?

A
  • Sulfur can be used to acidify soils (H2SO4)
  • Agricultural limestone can be used to decrease acidity
34
Q

What is wind erosion?

A

Wind energy lifts and moves soil particles to new locations (mostly impacts loose, sandy soils)

35
Q

What are the 3 types of water erosion?

A
  • Rainsplash
  • Surface runoff
  • Slumping
36
Q

What is rainsplash erosion?

A

Soil particles are dislodged by raindrops

37
Q

What is surface runoff erosion?

A

Soil particles are carried overland in runoff

38
Q

What is slumping?

A

Soil becomes saturated which leads to reduced friction and mass movement such as landslides

39
Q

How does vegetation reduce soil erosion?

A
  • Roots have a binding effect
  • Increased interception
  • Dropped leaves provide a protective cover
  • Increased OM binds the soil
  • Root uptake reduces soil saturation
  • Acts as a windbreak
40
Q

How can agriculture accelerate soil erosion?

A
  • Ploughing loosens soil
  • Over-saturation from irrigation
  • Harvesting leaves soil bare
  • Overgrazing
  • Compaction
  • Agri-chemicals reduce biota
  • Steep-slope cultivation
41
Q

What are the 4 main problems caused by soil erosion?

A
  • Reduced productivity
  • Sedimentation
  • Increased atmospheric particulates
  • Desertification
42
Q

What is accelerated soil erosion?

A

When the natural dynamic equilibrium between soil formation and erosion is disrupted

43
Q

What are long-term crops?

A

Planting crops with longer growing periods to avoid frequent replanting and soil disturbance (e.g. permanent grassland, tea)

44
Q

What is terracing?

A

Constructing retaining walls along contours of a slope to increase infiltration and reduce runoff

45
Q

What is zero-tillage cultivation?

A

Drilling seeds directly into the ground to reduce soil disturbance and erosion

46
Q

What is contour ploughing?

A

Ploughing along the contours of a field (soil particles are deposited in furrows as runoff speed is reduced)

47
Q

What is tied ridging?

A

Dividing fields using intersecting ridges to increase water retention during heavy rainfall (used on flat fields)

48
Q

What are rows of stones?

A

Laying stones along contours to reduce runoff speed on gentle gradients (disturbed soil is deposited)

49
Q

What are windbreaks?

A

Construction hedgerows or rows of trees to reduce wind velocity and erosion

50
Q

What is multi-cropping?

A

Harvesting and re-sowing different crops at different times to retain protection from the wind (can be strip cropping)

51
Q

How can soil OM be increased?

A

Add a layer of mulch to protect from wind and rain splash erosion

52
Q

What is livestock management?

A

Control of the stocking density of livestock to reduce soil compaction

53
Q

What is an example of livestock management?

A

Controlling the movement of livestock (e.g. away from riverbanks to reduce sedimentation)

54
Q

How can you determine soil texture?

A

Sedimentation method
- Separate soil particles
- Place in a container and shake
- Invert to mix
- Leave for at least two days to settle

55
Q

How long does it take each of the mineral particles to settle?

A

Sand - 2 minutes
Silt - 2 hours
Clay - 2 days

56
Q

Why does clay stay in suspension for longer?

A

Particles are charged

57
Q

What is another method of determining soil texture?

A

Soil sieve method
- Separate dry soil particles
- Place in the stacked sieves and shake
- Smallest particles are collected in the last collection tray

58
Q

How can you determine soil water content?

A
  • Add soil to a pre-weighed crucible
  • Heat at 100C
  • Repeat heating and weighing until constant mass is reached
59
Q

How can you determine soil air content?

A
  • Add 250ml of soil to a 500ml container
  • Add 250ml of water and stir
  • Calculate loss of expected volume
60
Q

How can you determine soil OM content?

A
  • Add dry soil to a pre-weighed crucible
  • Heat at 450C
  • Repeat heating and weighing until contant mass is reached
61
Q

Why does the temperature need to be below 550C when determining OM content?

A

Mass would be lost as mineral particles breakdown due to the extremely high temperature

62
Q

How can you determine soil pH?

A

Use an electronic pH probe that has been calibrated using a buffer solution (of a known pH)

63
Q

What is the optimum pH range for most plants?

A

5.5-7.0

64
Q

What are 2 methods of sampling soil organisms?

A
  • Soil flooding
  • Soil pit extraction
65
Q

What can be used to flood soil for earthworm extraction?

A

Water mixed with mustard powder

66
Q

What are 3 methods of determining turbidity?

A
  • Secchi disc
  • Light penetration meter
  • Turbidity bottle

A Level Environmental Science (23 decks)

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