Social and Religious Studies

Key Unit competence: The student-teacher should be able to compare major types of soil in Rwanda and assess their importance.

Introductory Activity 

Soil is very important and a valuable resource for every human being. 

 1. How can you define soil? 

2. Identify different types of soils in Rwanda. 

3. Analyse the causes of soil erosion in Rwanda?

5.1. Definition of soil, types of soils and where they are found

Learning activity 5.1 

The soil types determine how and what we can grow and are the bases for all farming. 

1. Identify any two types of soil found in Rwanda. 

2. Describe any type of soil identified above.

Soil is defined as the thin upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles. 

Types of soils and where they are found 

Generally, there are four different types of soils: clay soils, silty soils, sandy soils and Loam soils. Clay soils, silty soils, and sandy soils are basic while loam soil is a combination of the three: clay, silty, and sandy soils.

In Rwanda, there are also lateritic soils.

In addition to general soil types, soils in Rwanda are also categorized into different classes according to how they are formed and where they occur.

Soil distribution in Rwanda

1. Kaolisols 

This is the dominant soil type in Rwanda. It is specifically common in central part of Rwanda. It is red in colour, thick and is composed of iron oxide. It becomes water logged during the rainy season. It is subdivided into two:

i) Humus-bearing Kaolisols: This forms from parent granitic rocks and metamorphosed basaltic rocks. Is common in low altitudes of the central region and extends to the west. They are covered with humus resulting from plant decomposition. These soils are rich but fragile when exposed to runoff. That’s why it is necessary to protect the humus-bearing layer by planting more plants, use of anti-erosion terracing and maintain its soil fertility by fallow or use of manure and fertilizers. It is commonly found in Gicumbi district.

ii) Xerokaolisols: This is mostly found in the Eastern province especially in Bugesera. It is thin and is covered by aluminium but the top most layer is hard and poor. Therefore, the cultivation on these soils must carefully be carried out in order to avoid the appearance of this sterile (infertile) lateritic layer on the surface.

2. Valley soils

 These are soils which form in valley floors of hills and mountains most especially river valleys. It forms from old alluvial deposits. It is also classified into two groups:

i) Histosoils: This forms from decomposition of organic materials mostly decaying vegetation in valley floors. The soil remains muddy for a bigger period of the year and is covered by swampy vegetation. Example isRugezi Swamps.

 ii) Vertisols: These are light, black and mineral rich soils. These soils however, may lose fertility very easily more especially under dry conditions. They dry up and harden during the dry season and muddy during the wet season. Example is Nyabarongo valley.

3. Altitudinal Soils/ Incept soils 

 This is formed under the influence of low temperatures and high rainfall. The slopes and plateaus covered by mountain forests of the Congo-Nile peak have fertile soils. However, it is necessary to control erosion and preserve the fertility of these soils by the use manure. 

4. Volcanic soils

 These are formed from vulcanicity. They are found in Musanze in Northern province, in Rubavu, Nyabihu, Rusizi and Nyamasheke in Western province. These soils are more fertile for agriculture, but need many attention because they may easily be affected by erosion.

Application activity 5.1 

1. With reference to the map of Rwanda, locate different types of soils in west and eastern part of Rwanda.

 2. Identify soil types that are highly fertile.

5.2. Soil erosion in Rwanda 

 Activity 5.2

 1. Identify any three causes of soil erosion in Rwanda.

 2. Explain how soil erosion affect man and environment.

Soil erosion in Rwanda 

 Soil erosion is a process through which the top soil is removed by running water, wind and animals. In Rwanda, the areas affected by severe soil erosion are the steep slopes of Northern and western Provinces.

5.2.1. Major types of soil erosion in Rwanda. 

There are 4 types of soil erosion. These are: 

• Splash erosion: This is the first stage of the erosion process. It consists of the detachment and airborne movement of small soil particles that is caused by the impact of raindrops on soil. 

 • Sheet erosion: This is the detachment of soil particles by raindrop impact and their removal downslope by water flowing overland as a sheet instead of indefinite channels or rills.

 • Rill erosion: this erosion consists of removal of the soil by concentrated water running through little streamlets, or head cuts. This occurs when several tiny channels, measuring a few centimetres deep are created by water on a piece of land. 

• Gully erosion: this occurs when there is a removal of the top soil along drainage channels by surface water runoff, it is characterized by an open, incised and unstable channel generally more than 30cm deep.

5.2.2. Causes of soil erosion in Rwanda 

 • Removing plant cover by burning pasture or felling trees. 

• Having too many animals on the land in almost dry areas such as Nyagatare. 

• A great increase in population which has led to overuse and misuse of the existing land.

 • Mining and quarrying, these activities expose the soils to erosion. They make the soil particles unstable and when agents of erosion come by, much of the soil is carried away.

• Frequent poor cultivation practices on sloppy areas. 

• Strong wind can carry loose unprotected soil everywhere.

 • Heavy rain and water runoff.

 • Unstable soils coupled with unfavourable climate especially on steep slopes and in valleys

5.2.3. Effects of soil erosion 

 • Area affected by soil erosion suffer much loss of soil fertility 

 • There is decline in crop yields (productivity), soils subjected to erosion lose all nutrients. This lowers their economic value. 

• 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 cover (environmental degradation). 

• In some cases, there is loss of lives due to landslides.

 • It affects transport systems in different ways. 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.

Application activity 5.2 

1. Which regions of our country are more exposed to high effects of soil erosion? 

 2. Suggest measures that should be taken to minimize the strength of soil erosion

5.3. Soil conservation and the management measures in Rwanda 

Learning activity 5.3 

1. What is the difference between soil conservation and soil management? 

2. Identify any 3 examples of soil conservation measures.

Soil conservation refers to the prevention of soils from erosion, degradation or loss of fertility while soil management refers to all the measures put in place to ensure proper use of soils in a sustainable manner.

 Soil erosion and depletion are the major threats to soil as a resource. Therefore, sound farming techniques must be employed to prevent soil erosion and impoverishments and to ensure that agriculture is more profitable in Rwanda, the following should be done:

Mulching: This method consists of covering the bare ground with a layer of organic matter such as straw. This helps to maintain soil moisture and limit rapid evaporation. 

Contour barriers: with this technique, farmers are recommended to use stones, grass, and soil to build barriers along contours. Long narrow holes are dug in front of the barriers to stop and collect water. 

Rock dam: Many stones are collected and piled up to slow down the regular flow of water. This is an efficient technique to prevent gullies and further soil loss.

 Terrace farming: This method is practically used on the steep slopes to avail enough flat land to grow plants. It is a best way to reduce surface run off and soil erosion

Intercropping: This method consists of growing different crops in alternative rows and sown at different periods to protect the soil from rain wash. 

 Contour ploughing: This method prevents excessive soil loss, as gullies are less likely to develop and also reduce run-off so that plants receive more water. Row crops and small grains are often planted in contour pattern so that the plants can absorb much of the rain, and erosion is minimized. 

Rotational Bush Fallowing: Sometimes it is very important to allow a farmland to rest or lie fallow, so that the natural forces can act on the soil. Fallowing also increases the sub-soil moisture and improves the general structure of the soil. 

Zero grazing: (Reducing the number of animals grazed in an area according to the carrying capacity of land.) 

Agro-forestry: This is a land use management system in which trees are grown around or among crops or pastureland.

Application activity 5.3 

1. Why is terracing necessary?

 2. Analyse the importance of zero grazing to farmers. 

3. Explain any three negative effects of soil erosion. 

4. Describe how terraces are used to prevent and control soil erosion in Rwanda.

Skills lab 

Soil degradation is a threat to the society. Discuss the appropriate measures to prevent soil erosion which can be more effective in your area.

End unit assessment

1. Explain the process of soil formation. 

2. Using specific examples, explain the causes of soil erosion in Rwanda.

 3. Soil erosion is one form of soil degradation. Discuss this statement.

 4. Assess the effects of soil erosion on the socio-economic development of Rwanda.