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9.03 Fertilisers

Posted02/01/2025
Updated10/01/2025
ByBMF
Views57

1. Introduction to Fertilisers

a. Importance of Fertilisers:

  • Role in Agriculture:
    • Plants require essential nutrients to grow, develop healthy leaves, roots, flowers, and fruits.
    • While plants perform photosynthesis using carbon dioxide and water, they rely on minerals from the soil for additional nutrients.
  • Nutrient Depletion:
    • Intensive farming depletes soil minerals, necessitating the replenishment of these nutrients through artificial fertilisers.
  • Global Food Supply:
    • Fertilisers enable faster plant growth and larger crop yields, crucial for feeding the world’s growing population.

b. Types of Fertilisers:

  • Straight N Fertilisers:
    • Contain only nitrogen (N) compounds.
    • Examples: Ammonium nitrate (NH₄NO₃), Ammonium sulfate ((NH₄)₂SO₄), Urea (CO(NH₂)₂).
  • Compound Fertilisers (NPK Fertilisers):
    • Contain a mixture of nitrogen (N), phosphorus (P), and potassium (K).
    • Examples: NPK 21:8:11 (21% N, 8% P, 11% K).

2. Nitrogenous Fertilisers

a. Ammonium Salts:

  • Ammonium Nitrate (NH₄NO₃):
    • Composition: Contains both NH₄⁺ (ammonium) and NO₃⁻ (nitrate) ions.
    • Production Reaction:
  • Properties:
    • Solubility: Highly soluble in water, allowing plants to uptake nitrogen easily.
    • Mass Composition: Contains 35% nitrogen by mass.
    • Uses: Widely used as a nitrogenous fertiliser and in the production of explosives.
  • Ammonium Sulfate ((NH₄)₂SO₄):
    • Production Reaction:
  • Properties:
    • Solubility: Soluble in water.
    • Effect on Soil: Makes soil slightly acidic; often mixed with chalk (calcium carbonate) to neutralize acidity.
  • Urea (CO(NH₂)₂):
    • Production Reaction:
  • Properties:
    • Solubility: Highly soluble in water.
    • Uses: Major nitrogenous fertiliser due to high nitrogen content (46% N).

b. Nitrates:

  • Potassium Nitrate (KNO₃):
    • Composition: Contains K⁺ (potassium) and NO₃⁻ (nitrate) ions.
    • Properties:
      • Solubility: Soluble in water.
      • Uses: Provides both nitrogen and potassium, essential for plant growth.

3. Compound Fertilisers (NPK Fertilisers)

a. Definition:

  • Compound Fertilisers: Mixtures that supply multiple essential nutrients (nitrogen, phosphorus, potassium) in balanced proportions tailored to specific plant needs.

b. NPK Values:

  • Understanding NPK Numbers:
    • Example: NPK 21:8:11
      • 21% Nitrogen (N): Promotes leafy growth.
      • 8% Phosphorus (P): Enhances root development.
      • 11% Potassium (K): Aids in flower and fruit production.
    • Usage: Different crops require different NPK ratios. For instance:
      • Fruits (e.g., apples, tomatoes): Higher potassium content.
      • Leafy Vegetables (e.g., cabbage): Higher nitrogen content.
      • Root Crops (e.g., carrots): Higher phosphorus content.

c. Examples of Compound Fertilisers:

  • Calcium Ammonium Nitrate (CAN):
    • Composition: Contains calcium carbonate (chalk) mixed with ammonium nitrate.
    • Formula: Ca(NO₃)₂·CaCO₃
    • Benefits: Neutralizes soil acidity caused by ammonium salts.

4. Chemical Reactions in Fertiliser Production

a. Synthesis of Ammonium Nitrate:

  • Process: Ammonia solution reacts with nitric acid to produce ammonium nitrate, which can be crystallised into pellet form for easy application.

b. Solubility and Plant Uptake:

  • Ammonium Nitrate and Ammonium Salts:
    • Highly Soluble: Ensures that nitrogen is readily available for plant uptake through roots.
    • Importance: Soluble nitrogen compounds are essential for effective fertilisation.

c. Neutralizing Soil Acidity:

  • Explanation: Calcium carbonate (chalk) neutralizes the acidity from ammonium salts, maintaining optimal soil pH for plant growth.

5. Environmental Considerations

a. Pollution from Excessive Fertilisers:

  • Eutrophication: Excess nitrates and phosphates run off into water bodies, causing excessive algal growth that depletes oxygen and harms aquatic life.
  • Soil Acidification: Overuse of ammonium salts can make soil overly acidic, negatively impacting plant health and soil microorganisms.
  • Greenhouse Gas Emissions: Production and application of fertilisers can contribute to greenhouse gas emissions, exacerbating climate change.

b. Sustainable Practices:

  • Balanced Application: Using appropriate NPK ratios tailored to specific crops to minimize excess.
  • Buffering Soil Acidity: Incorporating calcium carbonate or other neutralizing agents to maintain soil pH.
  • Precision Agriculture: Employing technologies to apply fertilisers more efficiently and reduce runoff.

6. Key Terminology

  • Fertilisers: Substances added to soil to supply essential nutrients for plant growth.
  • Ammonium Salts: Fertilisers containing the ammonium ion (NH₄⁺), such as ammonium nitrate and ammonium sulfate.
  • Nitrates: Fertilisers containing the nitrate ion (NO₃⁻), such as potassium nitrate.
  • Compound Fertilisers (NPK): Mixtures providing nitrogen (N), phosphorus (P), and potassium (K).
  • Ammonium Nitrate (NH₄NO₃): A nitrogenous fertiliser providing both NH₄⁺ and NO₃⁻ ions.
  • Calcium Ammonium Nitrate (CAN): A compound fertiliser that neutralizes soil acidity.
  • NPK Values: Numbers indicating the percentage composition of nitrogen, phosphorus, and potassium in fertilisers.
  • Eutrophication: Over-enrichment of water bodies with nutrients, leading to excessive plant growth and oxygen depletion.
  • Soil Acidification: Decrease in soil pH due to excessive use of certain fertilisers, harming plant growth.
  • Precision Agriculture: Farming management concept using technology to optimize field-level management regarding crop farming.

Examples:

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