Section A: Short Answer Questions (10 marks each)

1. Define soil pH and explain how it influences nutrient availability for plants.

  • Soil pH measures the acidity or alkalinity of soil on a scale from 0 to 14.
  • Optimal soil pH: 5.5 – 7.5 (most Irish soils are acidic).

    • Effect on nutrients:

  • Low pH (<5.5) reduces availability of phosphorus and essential cations (Ca²?, Mg²?).
  • High pH (>7.5) can cause micronutrient deficiencies (e.g., iron, zinc).

    • 2. List three causes of soil acidity and suggest one method to correct it.

    Causes of soil acidity:

    1. Excessive fertilisation (ammonium-based fertilizers lower pH).

    2. Animal manure (produces organic acids).

    3. Acid rain (sulfur emissions lower pH).

    Correction: Apply lime (CaCO3) to neutralise soil acidity.

    3. What is cation exchange capacity (CEC), and why is it important in soil fertility?

  • CEC is the ability of soil to hold and exchange cations (positively charged nutrients).

    • Importance:

  • Higher CEC means better nutrient retention (more fertile soil).
  • Clay and humus increase CEC, making nutrients more available to plants.

    • 4. Name three major soil cations and describe their role in plant nutrition.

  • Calcium (Ca²?): Strengthens cell walls, improves soil structure.
  • Magnesium (Mg²?): Essential for chlorophyll production (photosynthesis).
  • Potassium (K?): Aids protein synthesis and water regulation.

    • 5. Explain the process of liming and describe two of its benefits for soil health.

    Liming: Adding lime (CaCO3) to increase soil pH.

    Benefits:

    1. Improves nutrient availability (reduces aluminum toxicity).

    2. Enhances microbial activity, increasing organic matter decomposition.

    6. What is flocculation, and why is it important for soil structure?

    Flocculation: The process where soil particles cluster together, forming stable aggregates.

    Importance:

  • Improves aeration and drainage.
  • Increases root penetration and water retention.

    • 7. How does soil texture affect the cation exchange capacity (CEC) of a soil?

  • Clay soils have high CEC (hold more nutrients).
  • Sandy soils have low CEC (leach nutrients quickly).

    • 8. Distinguish between macronutrients and micronutrients, providing one example of each.

  • Macronutrients (needed in large amounts) – e.g., Nitrogen (N) for leaf growth.
  • Micronutrients (needed in small amounts) – e.g., Zinc (Zn) for enzyme function.

    • 9. Describe two symptoms of nitrogen deficiency in plants and explain why nitrogen is essential for plant growth.

    Symptoms:

    1. Chlorosis (yellowing of leaves).

    2. Stunted growth due to lack of proteins.

    Importance of nitrogen: Needed for amino acids, proteins, and chlorophyll production.

    10. What is the Teagasc Soil Index System, and how does it help farmers manage soil fertility?

    Soil Index System (1-4) ranks soil fertility:

  • Index 1: Very low fertility, needs high fertiliser input.
  • Index 4: High fertility, requires little or no fertiliser.

    • Section B: Structured Questions (50 marks each)

    Question 1: Soil pH, Liming & Nutrient Availability

    (a) Define soil pH and explain its effect on plant nutrient uptake.

  • Soil pH is a measure of H+ ion concentration.

    • Affects nutrient solubility:

  • Low pH locks up phosphorus.
  • High pH reduces iron and zinc availability.

    • (b) Describe how liming increases soil pH and improves soil structure.

  • Lime (CaCO3) replaces H+ and Al³? ions with Ca²?, raising pH.
  • Improves soil aggregation by flocculating clay particles.

    • (c) Outline three ways farmers can prevent soil acidification.

    1. Use pH-neutral fertilisers instead of ammonium-based fertilisers.

    2. Apply lime regularly to maintain pH.

    3. Reduce exposure to acid rain by improving soil buffering capacity.

    Question 2: Cation Exchange and Soil Fertility

    (a) What is cation exchange, and how does it affect nutrient availability for plants?

  • Cation exchange is the process of nutrient cations (Ca²?, Mg²?, K?) binding to soil particles.
  • Importance: Ensures nutrient retention and availability for plant uptake.

    • (b) List four factors that affect a soil’s cation exchange capacity (CEC).

    1. Humus content – Highest CEC due to negative charges.

    2. Clay content – More clay = higher nutrient retention.

    3. Soil texture – Fine soils hold more cations.

    4. pH level – Higher pH improves cation retention.

    (c) Compare the CEC of clay soils and sandy soils.

  • Clay soils: High CEC, retain more nutrients.
  • Sandy soils: Low CEC, leach nutrients quickly.

    • Section C: Extended Response Question (50 marks)

    Question 3: Soil Fertility and Sustainable Land Management

    (a) The difference between macronutrients and micronutrients, giving two examples of each.

  • Macronutrients: Needed in large amounts (e.g., Nitrogen, Phosphorus).
  • Micronutrients: Needed in small amounts (e.g., Iron, Zinc).

    • (b) The importance of nitrogen, phosphorus, and potassium (NPK) in plant growth.

  • Nitrogen (N): Promotes leaf and stem growth.
  • Phosphorus (P): Needed for root development and energy transfer.
  • Potassium (K): Helps in water regulation and disease resistance.

    • (c) How improper fertiliser application can lead to soil degradation and water pollution.

  • Excess fertiliser causes soil acidification and nutrient imbalances.
  • Runoff leads to eutrophication (algal blooms in water bodies).

    • (d) Two sustainable farming practices that maintain soil fertility.

    1. Crop rotation: Reduces soil depletion and disease buildup.

    2. Cover cropping: Prevents nutrient leaching and soil erosion.

    (e) The role of soil organic matter in improving soil fertility.

  • Organic matter increases water retention and microbial activity.
  • Improves CEC and nutrient availability.

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