Leaving Cert Agricultural Science – Higher Level Sample Answers (Biological Properties of Soil)
Section A: Short Answer Questions (10 marks each)
1. Define the soil microbiome and explain its role in nutrient cycling.
The soil microbiome refers to the community of microorganisms (bacteria, fungi, and actinomycetes) present in soil.It plays a key role in nutrient cycling by:
Breaking down organic matter into humus.Releasing nutrients such as nitrogen, phosphorus, and carbon for plant uptake.Fixing atmospheric nitrogen (e.g., Rhizobium bacteria in clover).2. What is humus, and how does it contribute to soil fertility?
Humus is the fully decomposed organic matter in soil.It improves soil fertility by:
Enhancing soil structure and aeration.Increasing water retention and reducing erosion.Providing nutrients like nitrogen and phosphorus for plant growth.3. List three benefits of organic matter in soil and explain why it is important for plant growth.
1. Improves Soil Structure – Prevents compaction and increases aeration.
2. Enhances Nutrient Retention – Organic matter holds essential nutrients (N, P, K).
3. Increases Microbial Activity – Supports beneficial microorganisms that aid plant growth.
4. Describe the role of earthworms in maintaining soil structure and fertility.
Earthworms improve soil aeration and drainage by burrowing through the soil.Earthworms break down organic matter into humus, enriching soil fertility.Earthworns castings (waste) increase nutrient availability for plants.5. Explain the process of carbon sequestration and its importance in soil management.
Carbon sequestration is the process of storing carbon in soil through organic matter and plant material.Importance in soil management:
Reduces CO2 levels in the atmosphere, helping combat climate change.Improves soil structure and microbial activity.Helps prevent erosion and increase soil fertility.6. What is the rhizosphere, and how does it support plant growth?
The rhizosphere is the soil zone surrounding plant roots, rich in microorganisms.It supports plant growth by:
Facilitating nutrient absorption, particularly phosphorus.Encouraging microbial activity (e.g., Mycorrhizal fungi improve root uptake).Improving soil aggregation and structure.7. Give two examples of biostimulants and describe their effect on crop productivity.
1. Humic Acid – Improves root growth and soil structure.
2. Seaweed Extracts – Enhances plant resistance to stress and boosts germination.
8. How does soil pH affect microbial activity and nutrient availability?
Neutral pH (6-7): Promotes optimal microbial activity.Acidic soils (<5.5): Reduce nitrogen-fixing bacteria efficiency.Alkaline soils (>8): Can cause nutrient deficiencies (e.g., phosphorus lock-up).9. Outline two farming practices that help maintain high levels of organic matter in soil.
1. Crop Rotation: Reduces soil depletion and maintains organic matter.
2. Adding Organic Fertilisers: Farmyard manure, compost, and green manures increase organic matter levels.
10. Describe the role of Rhizobium bacteria in clover and how it benefits soil fertility.
Rhizobium bacteria live in root nodules of clover and fix atmospheric nitrogen into ammonia.Benefits:
Reduces the need for artificial nitrogen fertilisers.Improves soil fertility by increasing nitrogen availability.Section B: Long Questions (50 marks each)
Question 1: The Soil Microbiome & Organic Matter
(a) Define the soil microbiome and describe two ways it benefits soil health.
The soil microbiome consists of bacteria, fungi, and actinomycetes that decompose organic matter and recycle nutrients.Benefits:
1. Enhances soil fertility by making nutrients available for plants.
2. Improves soil structure by forming humus.
(b) Explain the process of humification and how it influences soil structure.
Humification is the breakdown of organic matter into stable humus.Influence on soil structure:Improves aggregation (reduces compaction).Increases water retention and aeration.(c) Discuss three advantages of adding organic matter to agricultural soils.
1. Increases nutrient availability (slow release of nitrogen and phosphorus).
2. Enhances water-holding capacity, reducing drought stress.
3. Boosts microbial activity, supporting a healthy soil ecosystem.
(d) Compare the effects of continuous tillage and permanent grassland on soil organic matter levels.
Continuous tillage: Reduces organic matter due to oxidation and erosion.Permanent grassland: Maintains higher organic matter through plant material decomposition.(e) Describe two methods farmers can use to increase carbon sequestration in soil.
1. Using cover crops: Increases soil carbon content.
2. Reduced tillage: Minimises soil disturbance and retains organic matter.
Question 2: The Role of Earthworms & The Rhizosphere
(a) Explain how earthworms improve soil aeration, drainage, and nutrient cycling.
Earthworms create burrows, improving soil porosity and drainage.Their digestion of organic matter releases nutrients into the soil.(b) What are the optimum conditions for earthworm survival in agricultural soils?
Moist soils with organic matter.pH 6-8 (neutral conditions).Temperature above 12°C.(c) Define the rhizosphere and explain its role in nutrient absorption.
The rhizosphere is the root zone where microorganisms interact with plant roots.It enhances nutrient uptake, especially phosphorus and nitrogen.(d) Describe the symbiotic relationship between mycorrhizal fungi and plant roots.
Fungi absorb nutrients (especially phosphorus) from the soil and transfer them to the plant.In return, the plant provides carbohydrates to the fungi.(e) How can farmers enhance microbial activity in the rhizosphere to improve soil fertility?
Adding organic matter (compost, manure).Using crop rotation to promote microbial diversity.Reducing chemical inputs to preserve beneficial microbes.Section C: Long Question (50 marks)
Question 3: Sustainable Soil Management & Nutrient Cycles
(a) The importance of soil microorganisms in nutrient recycling.
Microorganisms decompose organic matter, releasing nitrogen, phosphorus, and carbon for plant uptake.(b) The role of the nitrogen cycle in maintaining soil fertility.
Nitrifying bacteria convert ammonia into usable nitrates for plants.Denitrifying bacteria return nitrogen to the atmosphere.(c) Farming practices that help reduce soil compaction and erosion.
Reduced tillageCover cropsAdding organic matter.(d) The impact of excessive fertiliser use on soil health and water quality.
Causes soil acidification and eutrophication (water pollution from nitrogen runoff).(e) Strategies to improve soil biodiversity and sustainability.
Planting multi-species swards.Increasing organic matter input.Implementing sustainable grazing systems.
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Leaving Cert Agricultural Science – Higher Level Sample Answers (Biological Properties of Soil)
Section A: Short Answer Questions (10 marks each)
1. Define the soil microbiome and explain its role in nutrient cycling.
The soil microbiome refers to the community of microorganisms (bacteria, fungi, and actinomycetes) present in soil.It plays a key role in nutrient cycling by:
Breaking down organic matter into humus.Releasing nutrients such as nitrogen, phosphorus, and carbon for plant uptake.Fixing atmospheric nitrogen (e.g., Rhizobium bacteria in clover).2. What is humus, and how does it contribute to soil fertility?
Humus is the fully decomposed organic matter in soil.It improves soil fertility by:
Enhancing soil structure and aeration.Increasing water retention and reducing erosion.Providing nutrients like nitrogen and phosphorus for plant growth.3. List three benefits of organic matter in soil and explain why it is important for plant growth.
1. Improves Soil Structure – Prevents compaction and increases aeration.
2. Enhances Nutrient Retention – Organic matter holds essential nutrients (N, P, K).
3. Increases Microbial Activity – Supports beneficial microorganisms that aid plant growth.
4. Describe the role of earthworms in maintaining soil structure and fertility.
Earthworms improve soil aeration and drainage by burrowing through the soil.Earthworms break down organic matter into humus, enriching soil fertility.Earthworns castings (waste) increase nutrient availability for plants.5. Explain the process of carbon sequestration and its importance in soil management.
Carbon sequestration is the process of storing carbon in soil through organic matter and plant material.Importance in soil management:
Reduces CO2 levels in the atmosphere, helping combat climate change.Improves soil structure and microbial activity.Helps prevent erosion and increase soil fertility.6. What is the rhizosphere, and how does it support plant growth?
The rhizosphere is the soil zone surrounding plant roots, rich in microorganisms.It supports plant growth by:
Facilitating nutrient absorption, particularly phosphorus.Encouraging microbial activity (e.g., Mycorrhizal fungi improve root uptake).Improving soil aggregation and structure.7. Give two examples of biostimulants and describe their effect on crop productivity.
1. Humic Acid – Improves root growth and soil structure.
2. Seaweed Extracts – Enhances plant resistance to stress and boosts germination.
8. How does soil pH affect microbial activity and nutrient availability?
Neutral pH (6-7): Promotes optimal microbial activity.Acidic soils (<5.5): Reduce nitrogen-fixing bacteria efficiency.Alkaline soils (>8): Can cause nutrient deficiencies (e.g., phosphorus lock-up).9. Outline two farming practices that help maintain high levels of organic matter in soil.
1. Crop Rotation: Reduces soil depletion and maintains organic matter.
2. Adding Organic Fertilisers: Farmyard manure, compost, and green manures increase organic matter levels.
10. Describe the role of Rhizobium bacteria in clover and how it benefits soil fertility.
Rhizobium bacteria live in root nodules of clover and fix atmospheric nitrogen into ammonia.Benefits:
Reduces the need for artificial nitrogen fertilisers.Improves soil fertility by increasing nitrogen availability.Section B: Long Questions (50 marks each)
Question 1: The Soil Microbiome & Organic Matter
(a) Define the soil microbiome and describe two ways it benefits soil health.
The soil microbiome consists of bacteria, fungi, and actinomycetes that decompose organic matter and recycle nutrients.Benefits:
1. Enhances soil fertility by making nutrients available for plants.
2. Improves soil structure by forming humus.
(b) Explain the process of humification and how it influences soil structure.
Humification is the breakdown of organic matter into stable humus.Influence on soil structure:Improves aggregation (reduces compaction).Increases water retention and aeration.(c) Discuss three advantages of adding organic matter to agricultural soils.
1. Increases nutrient availability (slow release of nitrogen and phosphorus).
2. Enhances water-holding capacity, reducing drought stress.
3. Boosts microbial activity, supporting a healthy soil ecosystem.
(d) Compare the effects of continuous tillage and permanent grassland on soil organic matter levels.
Continuous tillage: Reduces organic matter due to oxidation and erosion.Permanent grassland: Maintains higher organic matter through plant material decomposition.(e) Describe two methods farmers can use to increase carbon sequestration in soil.
1. Using cover crops: Increases soil carbon content.
2. Reduced tillage: Minimises soil disturbance and retains organic matter.
Question 2: The Role of Earthworms & The Rhizosphere
(a) Explain how earthworms improve soil aeration, drainage, and nutrient cycling.
Earthworms create burrows, improving soil porosity and drainage.Their digestion of organic matter releases nutrients into the soil.(b) What are the optimum conditions for earthworm survival in agricultural soils?
Moist soils with organic matter.pH 6-8 (neutral conditions).Temperature above 12°C.(c) Define the rhizosphere and explain its role in nutrient absorption.
The rhizosphere is the root zone where microorganisms interact with plant roots.It enhances nutrient uptake, especially phosphorus and nitrogen.(d) Describe the symbiotic relationship between mycorrhizal fungi and plant roots.
Fungi absorb nutrients (especially phosphorus) from the soil and transfer them to the plant.In return, the plant provides carbohydrates to the fungi.(e) How can farmers enhance microbial activity in the rhizosphere to improve soil fertility?
Adding organic matter (compost, manure).Using crop rotation to promote microbial diversity.Reducing chemical inputs to preserve beneficial microbes.Section C: Long Question (50 marks)
Question 3: Sustainable Soil Management & Nutrient Cycles
(a) The importance of soil microorganisms in nutrient recycling.
Microorganisms decompose organic matter, releasing nitrogen, phosphorus, and carbon for plant uptake.(b) The role of the nitrogen cycle in maintaining soil fertility.
Nitrifying bacteria convert ammonia into usable nitrates for plants.Denitrifying bacteria return nitrogen to the atmosphere.(c) Farming practices that help reduce soil compaction and erosion.
Reduced tillageCover cropsAdding organic matter.(d) The impact of excessive fertiliser use on soil health and water quality.
Causes soil acidification and eutrophication (water pollution from nitrogen runoff).(e) Strategies to improve soil biodiversity and sustainability.
Planting multi-species swards.Increasing organic matter input.Implementing sustainable grazing systems.
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