By the end of this unit, a learner should be able to: State the different types of soil in Rwanda Identify the causes and effects of soil erosion in Rwanda Identify the importance of soils in Rwanda.

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Unit 5: Soils in
Rwanda

2. Soils in Rwanda
Soil is the upper layer of the Earth in which plants grow. It is
made up of a mixture of:
Rock particles,
Organic matter,
Minerals,
Gases, liquids,
Air and living organisms
that support life.
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45%
25%
25%
5%
Components of soil
Minerals
Water filled pores
Air filled pores
Organic Matter

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Silt
Clay
Loam
Generally, there are
four different types
of soils. Three are
basic while the
fourth one is a
combination of the
three.
Clay
Silt
Sand
Loam

4. A
C
B
D

5. Loam soils
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• These are very fertile soils.
• They have the ability to support
the growth of crops.
• They have a high content of
humus, salt, sand and sometimes
clay.
• They are well drained and rarely
become waterlogged.
• They have high levels of water
moisture which is maintained for a
long period of time.
• They are found in the Northern
and Western Provinces of Rwanda.

6. Clay soils
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• They have limited humus.
• They have large quantities of
nutrients.
• They have the ability to retain water
for a long time
• Their acidic level is high. Therefore,
they only support specific types of
crops such as rice.
• They are associated with limited
decomposition due to the absence
of bacteria.
• They are common along the rivers,
valleys and swamps such as the
Akanyaru swamp in Gisagara
district

7. Sandy soils
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• They are described by their
large particles, which allow
the presence of huge pore
spaces
• They have a high level of
percolation i.e. they are
easily infiltrated by surface
run-off.
• They are common in
Umutara and Bugesera.

8. Lateritic soils
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• They are formed when rock
fragments bond together to form a
very hard substance known as
laterite or murram.
• They are formed as a result of
leaching.
• They lack humus and are therefore
infertile.
• They are found in the Rusumo
region of Eastern Province.

9. Types of soil in Rwanda
There are 5 main types of soils depending on the mode of
formation and their location:
1. Valley soils
• Histosols
• Vertisols
2. Altitudinal soils or inceptisols.
3. Kaolisols
4. Xerokaolisols
5. Antisols
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10. Kaolisols
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• They are found in the Central plateau
and extend to the Western region of
Rwanda.
• They are formed from the
disintegration of granitic rocks that
were being metamorphosed.
• These soils are enriched with humus
hence have a dark colour.
• They are found in the upper horizons
(A) and (O).
• The humus found in this section
comes from the decaying vegetation
and animals.
• This soil is found in Gicumbi district

11. Xerokaolisols/Xeroferr
al
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• This soil is commonly found
in the Eastern Province
especially in Bugesera.
• It is characterised by a hard
and poor top layer that is
dry. This is due to high
evaporation, evapo-
transpiration and
unreliability of rainfall.
• The most common mineral
contained in this soil is
aluminium.

12. Altitudinal
soils/Inceptisols
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• They are found along the heavily
forested areas that experience low
temperatures and heavy rainfall.
• These soils are easily eroded into the
valleys.
• These soils are common in the
Northern and Western Provinces.
• The dense vegetation cover supplies
dead organic matter that decays
hence forming humus. The humus is
reflected by the black colour of the
top most layers.
• They are fertile and support
agriculture.

13. Volcanic soils/Antisols
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• These are soils that are found in the
volcanic regions of Rwanda.
• They are young soils, formed from
recent volcanic rocks.
• They have a black colour.
• They have high levels of soil
nutrients and a great humus
content.
• They are very fertile and support
plant growth.
• These soils are common in both the
Northern and Western Provinces of
Rwanda.

14. Valley soils
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• These soils are formed through deposition of sediments into the valleys hence the
name valley soils.
• They are found in valley floors of hilly and mountainous areas such as in river
valleys. These soils are further subdivided into:
Vertisoils
• These are valley soils which have a black colour and a high mineral content.
• They lose their fertility during seasons of unreliable rainfall. When the wet season
sets in, they become muddy.
Histosoils
• These are soils that are associated with the decomposition of vegetation that
occupy the valleys.
• The poor drainage characterised by waterlogging within the valley floors slows
down the decomposition of organic matter. This makes the soils to stay muddy for
longer periods.
• In areas where such soils are found, they support plant growth.
• They are found in Bugesera swamp.

15. Factors influencing soil formation of
Rwanda
• The nature of the parent rock: The soils of Rwanda have got an
influence from volcanic, metamorphic and sedimentary rocks.
• Climate: Lateritic soils dominate in Rwanda because of influence of
equatorial climate. Soils of northern and western provinces of Rwanda
where rainfall is high are deep and well evolved. Soils of the eastern
province are thin and less evolved due to low rainfall and high
temperature.
• Relief or topography: On the steep slopes of highlands, soils are very
thin, easily eroded and become less fertile. In lowlands (valleys and
depressions), soils are deeper and fertile due to the deposition of soils
especially when in valleys there is little water.
• Influence of living organisms: Living organisms such as plants and
animals (bacteria, moles, snakes, etc.) contribute to decay organic
matter and rocks to evolve the soil. Man brings fertilizers in the soils
and protects them against erosion
• Time: It is the duration of the operation of soil formation. Most of
soils in Rwanda are mature because they have had a sufficient time to
form. Entisoils are young thin soils, having short time of formation.
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16. Importance of soils
• Development of agriculture
• They support settlement and the growth of vegetation
• Tourism attraction sites
• Scientific research
• Used in tile and brick making
• Raw materials in craft industry especially for pottery
• They favor mining
• They may be used in building (mud, white clay…)
• Source of revenue for the government through taxation
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17. Soil erosion in Rwanda
This is a process by which the top most layers is removed by
running water, wind and glaciers. In Rwanda, the areas affected
by severe soil erosion are the steep slopes of northern and
western regions. They include the following.
• Gicumbi district
• Burera district
• Musanze district
• Rubavu district
• Muhanga district
• Nyabihu district
• Rusizi district
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Soil erosion is of 4 main
types:
1. Rill erosion
2. Sheet erosion
3. Splash erosion
4. Gulley erosion

18. Types of Erosion
1. Rill Erosion: Rill erosion is removal of soil by concentrated
water flow, and it occurs when the water forms small channels
in the soil as it flows off site
2. Sheet erosion: Sheet erosion occurs as a shallow 'sheet' of
water flowing over the ground surface, resulting in the
removal of a uniform layer of soil from the soil surface.
3. Splash Erosion: This is the first stage of the erosion process. It
occurs when raindrops hit bare soil. The explosive impact
breaks up soil aggregates so that individual soil particles are
'splashed' onto the soil surface.
4. Gulley erosion: Gully erosion is the removal of soil along
drainage lines by surface water runoff. Unless steps are taken
to stabilise the disturbance, gullies will continue to move by
headward erosion or by slumping of the side walls
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20. Causes of soil erosion in Rwanda.
• Relief: Rwanda is mountainous country especially in Northern
and western parts. This causes the run-off to flow at high speeds
hence quickly eroding and transporting the soils.
• Climate: In Rwanda, rainfall is the most active agent of erosion.
In areas where heavy rainfall is received the surface runoff
present washes away large quantities of the top-soils. Wind
erosion is dominant in eastern province. There is also seasonal
glacier erosion on the top of Mt. Kalisimbi during the wet
season.
• Vegetation: Areas with less vegetation or bare soils are
subjected to agents of erosion and evidently eastern province of
Rwanda.
• Soil erodibility: Rwandan soils is dominated by the permeable
soil which makes it easy for the water to infiltrate and makes
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21. • Poor methods of farming: Farming methods such as
monoculture and ploughing of land along slopes of Rwanda
speed up erosion. They subject the soils to erosion especially by
water
• Mining and quarrying: methods like open cast mining expose the
soils to erosion. They make the soil particles unstable and when
agents of erosion come by, much of the soils are carried away.
• Overgrazing: In some parts of Rwanda where animals are still
communally grazed, much of the soils remain bare due to the
clearance of the vegetation by animals. This exposes the land to
agents of erosion.
• Bush burning: The pastoral communities of eastern and north
western part of Rwanda have a tendency of burning grass or
pasture lands during the dry season in preparation for the rainy
season. The burning of vegetation leaves a given area bare and
totally exposed to agents of erosion
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22. Cause of soil erosion in Rwanda
(Summary)
1. A great increase in population which has led to overuse and
misuse of the existing land
2. The steep slopes which are easily eroded by running water
especially after heavy rainfall.
3. Poor methods of farming especially on steep and gentle slopes
4. Cutting of trees on slopes.
5. Uncontrolled grazing (overstocking) in almost dry areas such
as Mutara
6. Unstable soils coupled with unfavorable climate especially
on steep slopes.
7. Bush fires
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23. Effects of soil erosion in Rwanda
• Low soil productivity: Soils subjected to erosion lose all nutrients and
lowers their economic value because they can hardly support crop
production due to their infertility.
• Low soil moisture: Areas affected by erosion experience loss of
moisture. This further reduces the permeability, porosity, and
biological activity of soils hence rendering them unproductive.
• Destruction of crops: Wind erosion destroys young seedlings which
costs the farmers more costs via replanting. Sometimes, the
sediments being transported are deposited in farms where they end
up burying germinating seeds to deeper depths preventing them
from reaching the surface.
• Affects underground water: Soil erosion sometimes involves run-off
which percolates and dissolves soluble minerals. Some of the minerals
pollute the underground water.
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24. • Affects transport systems: Many roads in Rwanda especially up
country and feeder roads are affected by gullies created by
continuous surface run-off. This hinders the movement of goods
and services and increases the government’s expenditure due to
frequent rehabilitations
• Flooding: Through soil erosion, sediments are deposited into
lakes, rivers and streams. When there is too much deposition in a
river or lake, its carrying capacity reduces and becomes shallow.
As a result, water starts overflowing hence flooding the
surrounding areas.
• Silting: Closely related to the flooding, the silting problem comes
along with increased expenses of dredging, resettling people and
total disruption of the eco-system.
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Soil conservation methods in Rwanda

26. Soil conservation methods in Rwanda
• Proper soil management and application of fertilizers on poor
soils
• Better farming methods such as contour ploughing, strip
cropping, terracing, etc.
• Afforestation and re-afforestation in grazing and mountainous
areas.
• Reducing the number of animals grazing in an area
according to the carrying capacity of land.
• Planting of cover crops in areas.
• Practicing Agro-forestry especially in eastern parts of the
country.
• Mulching of the cultivated farmlands.
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27. Effects of soil erosion in Rwanda
• Loss of soil fertility
• There is decline in crop yields (productivity)
• Famine is always rampant among the local people
where there has been severe erosion.
• Over flooding of the river valley may occur as a result of
eroded materials blocking the flow of a river.
• Destruction of natural vegetation covers (environmental
degradation).
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