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Agricultural Science

ROCK WEATHERING

The process of soil formation is referred to as weathering. Weathering is defined as the disintegration of rocks into smaller particles to form soil.

 

PROCESSES OF ROCK WEATHERING

The processes of soil formation (rock weathering) include:

  1. Physical process
  2. Chemical process
  3. Biological process

 

PHYSICAL PROCESS OF ROCK WEATHERING

Agents of physical weathering include temperature, ice, rainfall, wind and pressure.

  1. Temperature: The rise and fall of temperature brings about the expansion and contraction in rocks respectively. After a long time, rocks begin to crack and break down which later give rise to soil.
  2. Ice: When rivers overflow their banks or when it rains, water collects in the openings. At a cool temperature or freezing point, the water in the openings freezes and increases in volume, the force of expansion makes the rock to expand thereby cracking them to particles. As the temperature rises, ice melts and carries the rock particles away from their origin to a different place to form soil.
  3. Rainfall /water:The splash of rainfall exerts force on the rock surfaces. Flowing water also carries and hits rock particles against one another turning them into fragments.
  4. Wind: heavy winds carry particles of rock, hitting them against one another or against hard surfaces to form smaller fragments.
  5. Pressure: high pressure on hanging rock may cause such rocks to fall and the process break into smaller particles to form soil.

 

EVALUATION

  1. Define rock weathering.
  2. What are the processes of rock weathering?
  3. List three agents of physical weathering.
  4. Describe two of the agents of physical weathering.

 

CHEMICAL PROCESS OF WEATHERING

Agents of chemical weathering include solution, hydration, hydrolysis, carbonation and oxidation.

  1. Solution:This is when water dissolves soluble minerals present in the rock and the minerals taken from one place to another while flowing.
  2. Carbonation: Carbon (iv) oxide reacts with water to form trioxocarbonate (iv) acid, a weak acid which weakens and dissolves rock minerals.
  3. Hydration:This is the reaction of water with rock minerals which result in chemical alteration of the mineral. Example is the conversion of iron (ii) rocks to hydrated rocks.
  4. Hydrolysis: This is the reaction of water with rock minerals to produce a rock that is different from the original one.
  5. Oxidation: This is the reaction of rocks with oxygen from the atmosphere which then weakens the rocks.

 

EVALUATION

  1. List five agents of chemical weathering
  2. Explain two of the processes mentioned above

 

BIOLOGICAL PROCESS OF WEATHERING

This is the activities of plants and animals in the breaking down of rocks to form soil.

  1. The action can be brought about by some animals such as termites, earthworms, millipedes and other soil organisms.
  2. Movement of some organisms /heavy animals like cattle can cause small fragments of rocks to disintegrate.
  3. The roots of some crops penetrate through cracks in rocks making them to expand and break to form soil
  4. Activities of man during tillage can break small rocks into tiny pieces.

 

EVALUATION

  1. Outline four biotic factors of rock weathering
  2. What are the processes of rock formation?
  3. State three agents of physical weathering.

 

GENERAL EVALUATION

  1. What is rock weathering?
  2. What are the processes of rock formation?
  3. State three agents of physical weathering
  4. Describe five agents of chemical weathering.
  5. List five factors of soil formation.

 

BOOK REVIEW

Essential Agricultural science by O. A. Iwena chapter 11, page 65 – 68

 

READING ASSIGNMENT

Answer question 1 and 2a from Essential Agricultural science by O.A. Iwena chapter 11, page 86

 

WEEKEND ASSIGNMENT

  1. The attachment of water to rock minerals resulting in chemical alternation of the minerals is termed A.carbonation hydration  C. hydrolysis  D. solution
  2. The reaction of rock with oxygen from the atmosphere which eventually weakens the soil is carbonation  B. oxidation  C. hydrolysis  D. solution
  3. Which of these is not an agent of physical weathering ice  B. water  C. animal
  4. temperature
  5. Which of the following is not a soil organism that disintegrates rock particlesA. termite earthworm  C. cattle  D. millipede
  6. ____ is defined as the disintegration of rocks into smaller particles to form soil.
  7. Chemical reaction B. Weather C. Weathering D. Breaking down

 

THEORY

  1. What is rock weathering?
  2. Mention three processes of rock weathering.
  3. List and discuss three agents of one of the processes mentioned above.

See also

ROCK FORMATION AND TYPES

AGRICULTURAL ECOLOGY

HUSBANDRY AND CULTIVATION OF SOME SELECTED CROPS

POST – PLANTING OPERATIONS

PLANTING OPERATIONS – DISTANCE, DATE, SEED RATE, NURSERY AND NURSERY PRACTICE

 

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