Term: 2nd Term
Class: Senior Secondary School 1
Age: 15 years
Duration: 40 minutes of 2 periods each
Topic:- Soil formation I
SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to
- Mention and explain the factors that control soil formation
- Discuss the processes of soil formation
INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source
INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures
The teacher reviews the previous lesson on Rock formations
Students pay attention
She mentions and explains the factors that controls soil formation
Students pay attention and participates
She discusses the processes of soil formation
Students pay attention and participate
The teacher writes a summarized note on the board
The students copy the note in their books
FACTORS THAT CONTROL SOIL FORMATION
- CLIMATE: Climate is the average weather condition of a place over long period time. The elements of climate are: temperature, rainfall, wind and pressure.
- PARENT MATERIALS: These are the materials (previously existing rocks) from which the soil is formed. The parent materials are igneous, sedimentary and metamorphic rocks. They determine the type, physical characteristic and chemical composition of the formed.
- TOPOGRAPHY: This is the sharp of the ground in relation to the underlying rock of the earth’s surface. It affects soil formation in the following ways.
- The shape of the land influences the movement and amount of water in the soil.
- Sloppy surfaces support erosion which encourages soil formation.
- More soils are formed in the valleys than on the hills.
- BIOTIC FACTORS: The activities of soil living organisms help to speed up the process of soil formation in the following ways;
- Termites, earthworm and rodents mix with the mineral and organic matter together to form soil.
- They aerate the soil, making air to react with rocks to form soil.
- The activity of man during tillage.
- Microorganism causes decomposition of organic matter to form soil.
- The root of plants penetrates the rocks there by breaking them.
- Organism produces carbon dioxide which promotes weathering of rocks.
- Microbe helps in decomposition of organic matter.
- The leaves which fall from trees decay to increase the humus content of the soil.
- TIME: all the above factors takes a lot of time to finally give rise to soil.
- It takes a long time for small piece of rocks to disintegrate into grains of soil.
- It takes a long time for plants to decay to form soil.
- It takes short time to form immature soil.
PROCESS OF SOIL FORMATION (WEATHERING)
Weathering is defined as the disintegration or breakdown of rocks into tiny particles called soil.
The processes of soil formation include:
- PHYSICAL PROCESS: The agents of physical weathering are temperature, ice, wind, water and pressure
- Temperature: The alternating heating and cooling of rocks produce pressure within the rock which makes them to break into smaller pieces.
- Wind: Solid materials carried by soil surfaces.
- Ice: The conversion of water inside the cracks of rocks into ice results in increase in volume. This results in more pressure on the rocks which eventually break into smaller pieces.
- Water: Running water carries some fragments of rocks in the river bed, thus breaking off small pieces of rocks.
- CHEMICAL PROCESS: Agents of chemical weathering include: solution, carbonation, hydration, hydrolysis and oxidation.
- Hydration: It occurs when water combines with or binds to some minerals e.g.
- Calcium Sulphate changes to gypsum CaSO4+2H20 → CaSO4.H2O
- Red Haematite changes to hydrated yellow Haematite or Limonite Fe203 +3H20 = Fe203.H20
CuS04 + 5H20 = CuS04.5H 20
- Carbonation: The carbondioxide released to the atmosphere combines with acid. This weak acid reacts with rocks to form soil.
- Oxidation/Reduction: When minerals containing iron, manganese and sulphur are exposed to air and water, the famous iron is oxidized to the ferric state.
4F0C03 + O2 = 2FeO3 + 4CO2
(Iron II Carbonate) (Iron Oxide)
- Solution: reaction of water with soluble particles/minerals present in the rock and eventually displacing them given the sloe of the soil.
- Hydrolysis: involves the breaking down of chemical bonds in rock minerals by water.
CaSiO3 + 2H2O → H2SiO3 + Ca(OH)2
Calciumsilicate water silica calcium(Wollastonite) silicate hydroxide
- BIOLOGICAL PROCESS: This involves the activities of plants and animals in the breaking down of rocks to form soil. It can happen in the following ways;
- The root of plants penetrates the rocks to form soil.
- Earthworm and termites burrow into the rocks and break off fragments.
- Activities of man during soil tillage causes the rock to breakdown to form soil.
EVALUATION: 1. Mention and explain the factors that control soil formation
- Discuss the different processes of soil formation
CLASSWORK: As in evaluation
CONCLUSION: The teacher commends the students positively