Fertilisers
Section: 10. Chemistry of the Environment | Syllabus: Cambridge AS Level Physics 9702
Fertilisers Fertilisers Substances added to soil to provide essential nutrients that promote plant growth. They replace nutrients removed by crops or lost through leaching. Why Plants Need Fertilisers Plants require three main elements for healthy growth: Nitrogen (N): For leaf and stem growth, protein synthesis Phosphorus (P): For root development and energy transfer Potassium (K): For flower and fruit development, disease resistance NPK Fertilisers Fertilisers that contain compounds of all three essential elements: Nitrogen, Phosphorus, and Potassium.
The NPK ratio on fertiliser packaging indicates the relative proportions of these elements. Common Nitrogen Sources in Fertilisers Ammonium salts: Ammonium nitrate (NH₄NO₃), ammonium sulfate ((NH₄)₂SO₄) Nitrates: Potassium nitrate (KNO₃), calcium nitrate (Ca(NO₃)₂) These compounds are highly soluble in water, making nitrogen readily available to plant roots.
Element Chemical Form in Fertiliser Function in Plants Nitrogen (N) Ammonium salts (NH₄⁺), Nitrates (NO₃⁻) Leaf growth, chlorophyll production, protein synthesis Phosphorus (P) Phosphates (PO₄³⁻) Root development, DNA/RNA, energy transfer (ATP) Potassium (K) Potassium compounds (K⁺) Flower/fruit formation, enzyme activation, disease resistance Environmental Concerns While fertilisers boost crop yields, overuse can lead to environmental problems: Eutrophication: Excess nitrates and phosphates run off into waterways, causing algal blooms Water pollution: Fertilisers leach through soil into groundwater Oxygen depletion: Decomposing algae consume dissolved oxygen, harming aquatic life
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