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2. (a) Explain how the weathering of rocks contributes to soil formation - Leaving Cert Agricultural Science - Question 2 - 2008
Question 2
2. (a) Explain how the weathering of rocks contributes to soil formation. (b) Explain the following terms as used in the context of plant growth in soil: 1. ... show full transcript
Worked Solution & Example Answer:2. (a) Explain how the weathering of rocks contributes to soil formation - Leaving Cert Agricultural Science - Question 2 - 2008
Step 1
Explain how the weathering of rocks contributes to soil formation.
Answer
Weathering of rocks is a critical process in forming soil. It involves the physical and chemical breakdown of rocks into smaller particles, which become the basis of soil.
Some examples of how weathering contributes to soil formation include:
- Physical Weathering: Processes such as freeze-thaw cycles, where water infiltrates cracks in rocks and expands when frozen, leading to the disintegration of rock materials.
- Chemical Weathering: Rainwater can interact with minerals in rocks, leading to chemical reactions that further break down these materials.
- Biological Weathering: Plants and animals contribute to weathering; roots can penetrate rocks, and organisms can produce acids that enhance rock decay.
Overall, the accumulation of these weathered particles over time results in mature soil layers rich in minerals and organic matter.
Step 2
Explain the following terms as used in the context of plant growth in soil:
Answer
1. Field capacity
Field capacity refers to the amount of water retained in the soil after excess water has drained away and gravity has done its work. This is the optimal moisture level for plant growth, as it allows for maximum water availability without waterlogging.
2. Permanent wilting point
The permanent wilting point is the minimum soil moisture level at which plants can no longer extract water efficiently. At this point, the remaining water is held too tightly by soil particles, making it unavailable for plant uptake, causing the plants to wilt and potentially die.
3. Available water
Available water is the amount of water in the soil that can be utilized by plants. It represents the difference between field capacity and the permanent wilting point.
Step 3
What is the percentage of available water in sample A?
Answer
To calculate the percentage of available water in sample A, we can use the formula:
Substituting the values from the table for sample A:
ext{Available Water} = 6 ext{%} - 2 ext{%} = 4 ext{%}
Therefore, the percentage of available water in sample A is 4%.
Step 4
Which sample would be the most suitable for a crop suffering a drought during the growing season?
Answer
For a drought situation, we need a soil sample that retains a higher percentage of available water. Referring to the provided table:
- Sample A: 4% available water
- Sample B: 12% available water
- Sample C: 8% available water
Sample B is the most suitable for crops suffering from drought, as it has the highest percentage of available water at 12%.
Step 5
Which sample would be the most suitable for a crop growing during a wet spring?
Answer
In wet conditions, the ideal soil sample should have good drainage while retaining enough moisture. Reviewing the samples:
- Sample A: 6% water at field capacity
- Sample B: 24% water at field capacity
- Sample C: 30% water at field capacity
Sample C, with 30% water at field capacity, is the most suitable for crops during a wet spring as it can accommodate wet conditions effectively.
Step 6
Describe an experiment to compare the capillarity of two contrasting soils.
Answer
To compare the capillarity of two contrasting soils, conduct the following experiment:
- Materials: Choose two contrasting soil samples (e.g., sandy soil and clayey soil), two transparent containers of equal size, water, and a ruler.
- Procedure: Fill each container with one type of soil up to the same height.
- Water Application: Pour equal amounts of water into each container until the soil is saturated.
- Measurement: After allowing the water to percolate for a specified time, measure the height of the water level in each container using the ruler.
- Observation: Record the rise or fall of the water level in each soil type over time.
- Conclusion: Compare the water retention ability of the two soils based on the measurements taken, observing which soil retained more water and displayed better capillarity.