9.3 Fertilisers

9.3 Fertilisers

Importance of Fertilisers

  • Plants require fertilisers to grow effectively.

  • Fertilisers supply essential nutrients when soil lacks them.

  • They enable faster plant growth and increased yields.

Examples of Fertilisers

  • Ammonium salts:

    • Ammonium phosphate: (NH₄)₃PO₄

    • Ammonium nitrate: NH₄NO₃

    • Potassium nitrate: KNO₃

Ammonium Nitrate

  • Considered the most important fertiliser.

  • Provides both:

    • Ammonium ion (NH₄⁺)

    • Nitrate ion (NO₃⁻)

  • Contains 35% nitrogen by mass.

  • Produced from the reaction of ammonia solution with nitric acid:

    • Reaction: NH₃ + HNO₃ → NH₄NO₃

  • Formulated into pellets for easy spreading on land.

  • Soluble in water, which is crucial for plant nutrient uptake through roots.

Compound Fertilisers

  • Ammonium salts can slightly acidify soil.

  • Need to be mixed with chalk (calcium carbonate) to neutralise acidity:

    • Reaction: Ammonium Nitrate + Calcium Carbonate → Calcium Ammonium Nitrate (Nitrochalk)

  • Compound fertilisers: contain multiple compounds to enrich soil with various elements.

NPK Fertilisers

  • N: Nitrogen - essential for protein synthesis and plant growth.

  • P: Phosphorus - vital for healthy root development.

  • K: Potassium - important for flower and fruit production.

Specific Nutrient Needs by Crop

  • Different crops have varied nutrient requirements:

    1. Apples, tomatoes (fruits) - high potassium need.

    2. Cabbage (leafy vegetables) - high nitrogen demand.

    3. Carrots (root crops) - high phosphorus requirement.

  • NPK value: Indicates the concentration of each nutrient in fertilisers.

Fertiliser Factories

  • Modern fertiliser factories produce two types:

    1. Straight N Fertilisers:

      • Solid pellets focused on nitrogen content.

      • Examples:

        • Ammonium sulfate (NH₄)₃SO₄

        • Ammonium nitrate (NH₄NO₃)

        • Urea (CO(NH₂)₂)

    2. NPK Compound Fertilisers:

      • Mixtures of nitrogen, phosphorus, and potassium.

      • Replace lost soil nutrients.

      • Usually contain ammonium nitrate, ammonium phosphate, and potassium chloride in various proportions.

Understanding NPK Fertilisers

  • Nutrient ratio example: 21:8:11

    • Indicates percentage content:

      • 21% nitrogen

      • 8% phosphorus

      • 11% potassium

  • The remaining 60% is typically filler material to aid in chemical dispersion.

  • Note: Nitrogen may leach from fertilisers into water bodies, promoting algal growth.