Lesson Notes By Weeks and Term - Senior Secondary School 1

Date: 6^th -17^th of March 2023

Class: SSS 1

Term: 2nd Term

Week: 9&10

Subject: Agricultural Science

Topic: Soil and Soil Formation

Duration:45 minutes

Teaching Aid: A chart

Reference Book: Essential Agricultural Science for Senior Secondary Schools by O.A Iwena (pg 65-69)

Comprehensive Certificate Agricultural Science for Senior Secondary Schools by L.A et Al (pg 91-93)

Behavioural Objectives: By the end of this topic, students should be able to

1. Define soil
2. Explain the types of soil and their characteristics
3. Discuss soil formation

Presentation I

Step 1: Teacher revises last topic

Step 2: Teacher introduces and explains new topic

Step 3: Teacher writes note on the board

Step 4: Teacher evaluates students

Step 5: Teacher marks students' notes and give assignment

Previous knowledge: Students have been taught rock formation

Content

Soil

Soil can be defined as unconsolidated, weathered materials found in the uppermost area of the earth surface on which plant grows and supports plant growth

Soil Types

Sandy

Clay

Loamy

FACTORS OF SOIL FORMATION

Soil formation is greatly controlled by five major factors which are (i) climate. (ii) parent materials (iii) topography (iv) biotic (living organisms) and (v) time.

Elements of climate such as rainfall, temperature, wind and pressure are all very important in soil formation.

(i)        Temperature: The alternating heating and cooling of rocks result in the continual expansion and contraction which eventually result in cracks in the rocks and its consequent breakdown into small pieces to form the soil.

Temperature affects the rate of chemical weathering of rocks.

(ii)       Rainfall: The action of running water from rainfall causes the gradual wearing away of rocks during erosion to form soil. Rainfall provides water for hydrolysis. Also, rain drops may break down some parent rocks to form soil.

Rainfall enhances vegetative growth of plants whose roots cause further breakdown of rocks, while the rain water transports rock particles after disintegration.

(iii)      Wind: High-wind velocity in deserts carry with it other tiny rocks which collide with one another or other rocks, resulting in the breaking of rocks into tiny pieces to form soil. Wind also removes weathered materials, thereby, exposing parent materials to further breakdown.

(iv)      Pressure: High pressure on a hanging rock may cause such rock to fall down and break into tiny pieces, resulting in the formation of soil.

1. Parent material: Parent materials constitute the major materials from which soil is formed. They are igneous, sedimentary and metamorphic rocks. Parent materials determine the chemical composition of the soil that is formed. It is also contains different minerals which account for differences in the fertility of the soil formed from each of the different types. Parent materials determine the physical characteristics of the soil. Hardness of parent material affects the rate of soil formation.

The shape of the ground in relation to the underlying rock of the earth’s surface is known as topography. Topography affects the rate of run-off and erosion. Steep slopes encourage erosion and retard soil-formation. Soil-formation is faster in the valley than on slopes. Steepness of the slope affects the rate of abrasion of rocks; hence, soil is formed.

The activities of living organisms help to speed up the process of soil formation.

1. Termite, earthworm, rodent mix the mineral and organic matter together, and these results in the formation of soil.
2. They also allow water and air into the soil which eventually react with rocks to cause their break down into soil.

• The activities of man during tillage and other farm operation indirectly help to break rocks into tiny pieces to form soil.

1. The activities of micro-organisms which promote decomposition of organic materials aid soil-formation.
2. The roots of plants penetrate rocks and break them into tiny pieces to form soil.
3. They influence the organic matter content of the soil.

• Organisms produce carbon dioxide which forms carbonic acid with water and enhances the weathering rocks.
• Microbes also improve soil aeration and water percolation. This enhance chemical and physical weathering.

1. Microbes help in the decomposition of organic matter in the soil.
2. The decay of fallen leaves of trees with the aid of bacteria results in the formation of humus, and this is rich in plants food.
3. Time: Time also plays an important role in soil-formation. It takes a long time for mature soil to be formed.
4. It takes a long time for small pieces of rock to disintegrate into grains of soil.
5. It also takes a long time for plants to decay and become part of the soil.

• It also takes time for rainfall to leach chlorides, sulphates and carbonates from the soil.

1. It takes a short time in the formation of immature soil.
2. Time also determines whether or not the soil is well-developed.

Process of soil formation

Physical

Chemical

Biological

Soil properties

1. Soil profile
2. Soil structure
3. Soil texture
4. Soil temperature
5. Soil pH

Evaluation: discuss the formation of soil

Assignment: Discuss soil composition