Meaning of Soil | Factors of Soil Formation | Soil Formation Process | Soil Profile Development SSS 1 – Agricultural Science

AGRICULTURAL SCIENCE

AGRICULTURE ECOLOGY 

SENIOR SECONDARY SCHOOL (SSS 1)

THEME: AGRICULTURE ECOLOGY 

PREVIOUS LESSON – Agricultural Science Plan Lesson Notes for Senior Secondary Schools – SSS 1

TOPIC – SOIL FORMATION AND PROFILE DEVELOPMENT

LEARNING AREA

1. Meaning of Soil

2. Soil Formation and Profile Development

3. Principles of Soil Classification

PERFORMANCE OBJECTIVES 

By the end of the lesson, most of the students should have attained the following objectives –

1. List factors of soil formation.

2. Make a sketch of a soil profile.

3. Discuss the basic principles of soil classification.

 

ENTRY BEHAVIOUR

INSTRUCTIONAL MATERIALS

The teacher will teach the lesson with the aid of:

1. Diagram of soil profile.

2. Dug or existing soil profile.

METHOD OF TEACHING

Choose a suitable and appropriate methods for the lessons.

Note – Irrespective of choosing methods of teaching, always introduce an activities that will arouse pupil’s interest or lead them to the lessons. 

REFERENCE MATERIALS

1. Scheme of Work

2. National Curriculum SSS Classes

3. Course Book

4. All Relevant Material

5. Online Information

CONTENT OF THE LESSON

MEANING OF SOIL

Soil is the top layer of the earth’s surface which made up of living and non living things such as water, leaf litters, rocks, humus, dead animals, living animals, air, soil particles – sand, loam and clay.

FACTORS OF SOIL FORMATION

1. PARENT ROCK

Soil minerals form the basis of soil. They are produced from rocks (parent material) through the processes of weathering and natural erosion.

2. ORGANISMS

Soil formation is influenced by organisms (such as plants), micro-organisms (such as bacteria or fungi), burrowing insects, animals and humans.

3. CLIMATE

Temperature affects the rate of weathering and organic decomposition. With a colder and drier climate, these processes can be slow but, with heat and moisture, they are relatively rapid.

4. TOPOGRAPHY

The shape, length and grade of a slope affects drainage. The aspect of a slope determines the type of vegetation and indicates the amount of rainfall received. These factors change the way soils form.

5. TIME

Soil properties may vary depending on how long the soil has been weathered.

Source materials – How soil is formed?

SOIL FORMATION PROCESS

1. WEATHERING

This is the process of breaking down of rock (parent material) into smaller particles to form soil. Water, wind, temperature change, gravity, chemical interaction, living organisms and pressure differences all help break down parent material.

2. ACCUMULATION OF MATERIALS 

Materials such as organic matter and decomposing materials or new mineral materials are added to the soil by the forces of ice, water, or wind and they accumulate over time.

3. LEACHING

Leaching is the removal of soluble components of the soil column by water.

4. TRANSFORMATION

Transformation is the chemical weathering of soil particles, including silt, sand, and clay minerals as well as the change of organic materials into degradation-resistant organic matter.

5. CLASSIFICATION

Calcification occurs when the removal of water via evapotranspiration exceeds precipitation causing the upward movement of dissolved alkaline salts from the groundwater.

Source materials – Process of Soil Formation – Mcrobenotes.com

SOIL PROFILE DEVELOPMENT

Soil profile is defined as the vertical section of the soil from the ground surface downwards to where the soil meets the underlying rock.

The soil is arranged in layers or horizons during its formation. These layers or horizons are known as the soil profile. It is the vertical section of the soil that is exposed by a soil pit.

The layers of soil can easily be identified by the soil colour and size of soil particles. The different layers of soil are:

• Topsoil

• Subsoil

• Parent rock

Each layer of soil has distinct characteristics.

Soil profile helps in determining the role of the soil as well. It helps one to differentiate the given sample of soil from other soil samples based on factors like its colour, texture, structure, and thickness, as well as its chemical composition.

In mineral horizons (A, B, and C-horizons) and parent rock or R-horizon.

1. O – Horizon (Organic) 

The O horizon is the upper layer of the topsoil which is mainly composed of organic materials such as dried leaves, grasses, dead leaves, small rocks, twigs, surface organisms, fallen trees, and other decomposed organic matter.

2. A – Horizon (Topsoil) 

This layer is rich in organic material and is known as the humus layer. This layer consists of both organic matter and other decomposed materials. The topsoil is soft and porous to hold enough air and water.

3. B – Horizon (Subsoil) 

It is the subsurface horizon, present just below the topsoil and above the bedrock.

This layer holds enough water than the topsoil and is lighter brown due to the presence of clay soil. The soil of horizon-A and horizon-B is often mixed while ploughing the fields.

4. C – Horizon (Bedrock) 

It is a compacted and cemented layer. Different types of rocks such as granite, basalt and limestone are found here.

Apart from the rocks, minerals, and layers, soil profile also consists of a water content, which is referred to as soil moisture.

PRESENTATION

To deliver the lesson, the teacher adopts the following steps:

1. To introduce the lesson, the teacher revises the previous lesson. Based on this, he/she asks the students some questions; then, the teacher –

2. Displays soil profile diagram, conduct students to existing soil profile and discuss.

Student’s Activities – Examine soil and Soil profile.

3. Summarizes the lesson on the board.

Student’s Activities – Copy as the teacher writes.

CONCLUSION

To conclude the lesson for the week, the teacher revises the entire lesson and links it to the following week’s lesson.

LESSON EVALUATION 

Ask students to:

1. Mention different types of rocks.

2. Describe the processes of rock formation.