WEEK 5

SUBJECT: BASIC SCIENCE

TERM: 1ST TERM

CLASS: PRIMARY 5

TOPIC: CHANGE AROUND US�

INSTRUCTIONAL MATERIALS:

A chart showing different types of erosion

REFERENCE MATERIALS

Scheme of work

All relevant materials �� �

9-Years Basic Education Curriculum

Online information

BUILDING BACKGROUND/CONNECTION TO PRIOR KNOWLEDGE:

Pupils are familiar with the topic in their previous classes.

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CONTENT

EROSION

The wearing away of the surface soil by water or wind is called erosion. Wind and water, which cause erosion, are called agents of erosion.

Effects of erosion

Erosion has several effects on human beings. The following are some of them:

1. Crops grow in the soil. Yam, maize, potato, guinea corn, cassava, millet, soya beans and other crops absorb chemical substances from the soil. These chemical substances help the crops to remain healthy, grow and produce a high yield. Human beings need a high yield of crops so as to be adequately fed. Erosion washes away the top soil, and with it the chemical substances that crops require for a good yield. Erosion, therefore, makes the soil poor and reduces the yields of crops.
2. Erosion may make the land unusable. In certain parts of Nigeria, erosion is a serious problem. Large areas of land have been destroyed by erosion. The surface of the land in such a place is no more even, but is full of deep gulleys. Such a piece of land cannot be used for agriculture or for anything else.
3. Erosion can cause landslides. In the worst cases of erosion, gulleys, which are many metres deep, develop. Near a very deep gulley, a large area of land may suddenly collapse and fall into the gulley. This is called a landslide. When a landslide occurs, nearby houses may also fall into the gulley, leading to loss of lives and property.

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Control of erosion

Erosion may be prevented or controlled in several ways. Some of the ways are:

1. planting of grasses e.g. Bahama grass or carpet grass:

Grasses are planted on playing fields, roadsides and lawns in residential areas to prevent or control erosion. The roots of the grasses bind soil particles together and prevent them from being easily washed away by flowing water or wind.

2. Planting of trees e.g. bamboo or cashew: Trees used in checking erosion are those that have spreading root systems, such as bamboo and cashew. The root systems of the trees bind soil particles together and protect them from being washed or carried away.

3. Planting of cover crops: Cover crops are plants of the beans family, which are planted on land that has been allowed to fallow in a particular year.

Examples are Centrosema, Calapogonium and Styloxanthes gracilis.

A cover crop has at least three advantages. Firstly, its leaves protect the soil from the force of raindrops. Secondly, its roots hold soil particles together so that they are not washed away by rain. Thirdly, root nodules in the root system of a cover crop fix nitrogen, thus making the soil more fertile than before.

4. Making ridges at right angles to the slope of the land: In a farm, ridges are made at right angles to the slope of the land. This prevents run-off water from flowing freely through the farm.

5. Making crossbars across water channels: In a farm, crossbars are made at intervals between two neighbouring ridges. This checks the free or fast flow of water through the farm.

6. Avoidance of bush burning: Bush burning exposes the surface of the soil to erosion. By avoiding bush burning, we prevent or control erosion.

ASSESSMENT AND EVALUATION

1. What is erosion?
2. Name two agents of erosion.
3. Explain the harmful effects of erosion on human beings.
4. Describe four ways of controlling erosion.

WRAP-UP (CONCLUSION)

Teacher goes over the topic once again to enhance better understanding.

Answer these questions

1. What is erosion?

2. Name two agents of erosion.

3. Explain the harmful effects of erosion on human beings.

4. Describe four ways of controlling erosion.