Topic 8: Soil Erosion

Question 1

What is soil erosion?

Answer 1

A natural process where soil particles are removed by wind or water

Question 2

What is the rate of soil erosion like in sois that haven’t been affected by human activity?

Answer 2

The same as the rate of soil formation

Question 3

When is soil erosion an issue?

Answer 3

When the rate is faster than that of soil formation

Question 4

Name the 2 types of soil erosion

Answer 4

Wind erosion
Water erosion

Question 5

When is soil most vulnerable to wind erosion?

Answer 5

When it is a dry soil or has a low clay content
This is because they are likely to be loose and there is little cohesion between the particles that would hold the soil together
So the soil blows away

Question 6

Where is wind erosion a problem?

Answer 6

In the area where the soil has been removed
In the area where the soil is deposited- it may cover crops or land in urban areas

Question 7

Name the types of water erosion

Answer 7

Rain splash erosion
Surface runoff erosion
Slumping and landslides

Question 8

What increases all forms of water erosion?

Answer 8

Steeper gradients

Question 9

Rain splash erosion

Answer 9

When soil particles are dislodged by a rain droplet
Soil particles are dispersed in different directions
Those going downhill are more likely to go further

Question 10

Surface runoff erosion

Answer 10

Caused when the infiltration capacity of the soil has been exceeded
Can occur in heavy or prolonged rainfall or if soil is impermeable
Leads water to flow over the ground surface

Question 11

Slumping and landslides

Answer 11

When soil on slopes becomes wet, increased mass and lubrication of water makes it more likely that large amounts of soil will move downwards
Often occurs when deep soil on slopes becomes less stable because of deforestation

Question 12

Why are landslides more common because of deforestation?

Answer 12

The roots of trees that held the soil together decompose
The soil isnt held together as strong
Landslides are more likely after heavy rain

Question 13

What areas are susceptible to both types of soil erosion?

Answer 13

Areas with seasonal rainfall, like Sub-Saharan Africa

Question 14

Why may areas like sub-Saharan Africa suffer from both types of soil erosion?

Answer 14

Wind erosion in the dry season
Rainfall erosion in the wet season

Question 15

How does vegetation reduce the rate of soil erosion?

Answer 15

-it acts as a natural windbreak, reduces wind velocity/kinetic energy that could carry away soil particles
-that and leaf litter reduce the impact of raindrops-soil particles are less likely to be dislodged
-soil organic matter helps to bind soil particles together
-plant roots hold the soil together
-plants held infiltration of water into soil high reduces the rate of runoff, reducing water erosion

Question 16

What human activities increase the rate of soil erosion?

Answer 16

Vegetation removal
Ploughing vulnerable soils
Overgrazing
Reducing soil biota
Soil compaction
Cultivating steep slopes

Question 17

How can vegetation removal increase soil erosion?

Answer 17

Removes protection from erosion

Question 18

How can ploughing vulnerable soils increase soil erosion?

Answer 18

It breaks up soil structure
Soil particle are exposed to erosion as a result of

Question 19

how can overgrazing increase soil erosion?

Answer 19

Vegetation eaten faster than it can grow
Soil is exposed to erosion
Disturbance & root damage by hooves can increase erosion risk

Question 20

How can reducing soil biota increase soil erosion?

Answer 20

Less dead organic matter is broken down

Question 21

How does soil compaction increase soil erosion?

Answer 21

Use of heavy machinery
Reduction in soil detrivores
Makes smaller interstitial spaces which reduces the infiltration rate

Question 22

How does cultivating steep slopes increase soil erosion?

Answer 22

Surface runoff water flows more rapidly down steeper slopes
More kinetic energy to pick up more soil particles
Ploughing e.g. adds to erosion risk

Question 23

What are the affects of accelerated soil erosion?

Answer 23

Reduced productivity
Sedimentation in rivers & reservoirs
Increased atmospheric particulates
Desertification

Question 24

How is productivity reduced because of accelerated soil erosion?

Answer 24

Fertile top soil is usually what is eroded
Remaining soil will be less fertile
Plant growth is reduced
Smaller harvests
Shallower soil may also make root penetration difficult

Question 25

How is sedimentation in river and reservoirs an affect of accelerated soil erosion?

Answer 25

Soil particles in water may be deposited if they slow down-less kinetic energy
Sediments in rivers reduces flow capacity so river is more likely to overflow and cause flooding after heavy rain

Question 26

How is increased atmospheric particulates an effect of accelerated soil erosion ?

Answer 26

Wind erosion increases the amount of atmospheric particulates
Can make health problems like asthma worse

Question 27

Explain desertification as an affect of accelerated soil erosion

Answer 27

Soil erosion makes it more difficult for vegetation to grow
Contributing to further soil erosion and reduced rainfall
Leading to the expansion of deserts

Question 28

What are the methods of reducing soil erosion?

Answer 28

Long term crops, zero-tillage cultivation, contour ploughing, tied ridging, terracing, rows of stones, windbreaks, multi cropping,increased soil organic matter, livestock management

Question 29

How are long term crops a method of reducing soil erosion?

Answer 29

The growth of crops that dont need frequent replanting reduces soil disturbance and erosion rate
E.g. permanent grassland or bush
Tree crops like fruit,tea,coffee,cotton

Question 30

Explain zero-tillage cultivation as a method of reducing soil erosion

Answer 30

Cultivation that reduces soil disturbance and therefore erosion
Direct drilling of seeds into the ground- reduces ploughing- reduces disturbance

Question 31

Explain contour ploughing as a method of reducing soil erosion

Answer 31

Ploughing on contours at a 90 degree angle to the slope reduces erosion as the water flow is stopped by ploughed furrows and loses its kinetic energy so it cant carry particles
Works until the rainfall is so heavy that the furrow overflows

Question 32

Explain tied ridging as a method of reducing soil erosion

Answer 32

Used on almost flat land
Divide a field into crisscross sections for intersecting ridges
They retain water when it rains and increase filtration and reduce runoff

Question 33

Explain terracing as a method of reducing soil erosion?

Answer 33

Sloping land is cultivated into a series of narrow fields
Soil is held in place by retaking walls along the contours
Water flowing over the walls is quick but slows down
Most water will infiltrate the soil as a result

Question 34

Explain rows of stones as a method of reducing soil erosion

Answer 34

Used if there’s a gentle gradient
Laid along contours to slow runoff and reduce erosion
Any disturbed soil will be deposited

Question 35

Explain how windbreaks can be used as a method of reducing soil erosion

Answer 35

Growing crop reduces wind velocity and wind erosion
Field will be exposed when crops re,over
Protection maintained by hedgerows or trees around a field
Hedgerows will reduce the wind velocity for a distance of 30 x its height

Question 36

Explain multi cropping as a method of reducing soil erosion

Answer 36

Can redice exposure to wind if they are harvested at different times
Done by human labour rather than machinery

Question 37

Explain increasing soil organic matter as a method of reducing soil erosion

Answer 37

Anything that adds organic matter
Will protect soil from wind and rain impact
As it decomposes it will help soil particle adhesion

Question 38

How will livestock management reduce soil erosion?

Answer 38

Reduce trampling damage
Reduce livestock near a riverbank where it is more likely to cause erosion into the river
Remove livestock at high-risk times like heavy rain

Question 39

What does the USLE do?

Answer 39

Estimate soil loss rates and assess the impact of changes to farming techniques

Question 40

USLE formula

Answer 40

A=R x K x L x S x C x P

Question 41

A in the soil loss equation

Answer 41

Rate of soil erosion

Question 42

R in the soil loss equation

Answer 42

Rainfall erosivity
(The potential ability of soil to be eroded by rain)

Question 43

K in soil loss equation

Answer 43

Soil erodability

Question 44

L in soil loss equation

Answer 44

Slope length

Question 45

S in the soil loss equation

Answer 45

Slope gradient

Question 46

C in the soil loss equation

Answer 46

Cropping management
(Impact of vegetation)

Question 47

P in the soil loss equation

Answer 47

Erosion control
(Effect of type of ploughing)

Question 48

Under what value will soil loss be considered sustainable ?

Answer 48

9 t ha-1 year-1
Which is the natural rate of soil formation