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PRY 5 IST TERM AGRICULTURAL SCIENCE
FIRST TERM LESSON NOTE
WEEK 2&3
TOPIC: SOIL FORMATION
BEHAVIOURAL OBJECTIVES: At the end of the lesson, pupils should be able to:
- Describe how the action of wind helps in soil formation.
- Describe each of these activities.
- Name four activities of man that help in soil formation.
- Name six agents of soil formation.
Instructional Materials:
A chart showing all farm tools
Reference Materials
- Lagos state scheme of work
- Online information
- Relevant materials
- Pupils textbook
Behavioral Objectives: pupils are familiar with the topic in their previous classes.
CONTENT
MEANING OF SOIL FORMATION
Soil formation
Soil is basically formed from rocks through a process called weathering. Weathering is the breaking down of rocks by such agents as water and wind to form soil.
Agents of Soil Formation
Rain
The rock particles, which are dark in color, mix with organic matter to form humus. This type of soil is very fertile and is good for growing crops. Rain also falls on dead plants and animals, and helps in their decay to form soil.
Rain is water that falls in drops from (rain-making) clouds in the sky. When rain falls on mountains and hills, it washes downhill the broken rock particles, which help to form soil at their bases. It also breaks them down into rock particles.
Rainfall causes leaching, which dissolves minerals such as carbonates in the soil. The rain then washes them deeper into the soil. Other things that affect soil formation include parent material, living organisms, topography and time.
Rain effects:
- Increased moisture means more plant growth.
- Rainwater washes materials off slopes.
- Rain dissolves minerals and leaches them deeper into the soil
Temperature
When the atmosphere is hot, hills and rocks expand. When the atmosphere is cold, hills and rocks shrink or contract. Those changes create cracks on the surface of hills, rocks and mountains. In the process, small particles fall from the surfaces of the hills, rocks and mountains to form soil.
Temperature is the measure of how hot or cold the atmosphere is at a particular time of the day or night.
Rocks expand and contract as they heat up or cool, breaking them apart.
Temperature controls the rates of chemical weathering (when water interacts with minerals in the rocks to create chemical reactions). Chemical weathering happens much faster in warm places.
Warmer temperatures may also mean more plant growth, soil organisms and litter decomposition.
Wind
Wind blows on surfaces of hills and mountains. The force of the wind makes particles fall off the hills and mountains to form soil elsewhere
The wind is also able to move surprisingly large quantities of soil. On occasions fine soil deposits can be seen which have been blown all the way from North African deserts.
Man
Man can also aid in formation. This happens when we break parent rocks which will in time form soils
Man breaks up rocks with pickaxes or hammers. The small pieces of the rocks collect to form soil. Man also uses heavy machines to crack rocks into small pieces which form soil.
Animals and Plants
These animals may carry some dead leaves and grasses into the holes as beddings. When rain falls on them, these dead materials decay to form soil.
Some animals dig holes in the ground and live there. When animals dig holes in the ground, they cause physical damage to rocks to form soil. Examples of such animals are the rat, cricket and the earthworm.
Living things influence soil formation in many ways. Plants, microorganisms, animals and even humans can make a difference. Once a plant community becomes established, it has a big effect on soil development. Tree roots penetrate deeply into soils, bringing up minerals and incorporating them into organic matter. Grasses penetrate less deeply but have increased biological activity and more rapid nutrient cycling.
Some trees grow in-between rocks. Their roots help to break up rocks into particles that form soil.
Plants grow in the soil. They drop their leaves, including dead ones, on the ground. When rain falls, the leaves decay to form soil. Plants also die and decay to form soil.
Earthworms and other animals tunnel through and mix the soil. They aerate the soil and allow water to penetrate more deeply. Humans also influence soil formation.
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