Fertilisers- CIE iGCSE Chemistry Notes - New Syllabus
Fertilisers for iGCSE Chemistry Notes
Core Syllabus
- State that ammonium salts and nitrates are used as fertilisers
- Describe the use of NPK fertilisers to provide the elements nitrogen, phosphorus and potassium for improved plant growth
Ammonium salts and nitrates as fertilisers
Ammonium salts and nitrates as fertilisers
Plants need essential elements such as nitrogen, phosphorus, and potassium for healthy growth.
Fertilisers are substances added to soil to supply these nutrients. Two of the most important groups of fertilisers are ammonium salts and nitrates.
Ammonium salts as fertilisers:
- Ammonium salts (such as ammonium sulfate, ammonium chloride, ammonium nitrate) contain the ammonium ion (\( \text{NH}_4^+ \)).
- The ammonium ion provides nitrogen in a form that plants can absorb and use directly for making proteins and chlorophyll.
- Ammonium salts are especially important for acidic soils because they slightly acidify the soil, improving nutrient availability.
- Examples include:
- \( \text{(NH}_4\text{)}_2\text{SO}_4 \) (ammonium sulfate)
- \( \text{NH}_4\text{Cl} \) (ammonium chloride)
Nitrates as fertilisers:
- Nitrates (such as sodium nitrate and potassium nitrate) contain the nitrate ion (\( \text{NO}_3^- \)).
- The nitrate ion is highly soluble in water and easily absorbed by plant roots.
- Nitrates are an important source of nitrogen, which plants need to produce amino acids, proteins, enzymes, and nucleic acids (DNA and RNA).
- Examples include:
- \( \text{NaNO}_3 \) (sodium nitrate)
- \( \text{KNO}_3 \) (potassium nitrate)
Importance of ammonium salts and nitrates in agriculture:
- They replenish nitrogen in the soil, which is removed when crops are harvested.
- Without fertilisers, soils become nitrogen-deficient, leading to stunted growth, yellowing leaves, and poor yields.
- By supplying nitrogen, ammonium salts and nitrates help increase crop productivity and ensure healthy plant growth.
Example
Why is nitrogen an essential element for plants?
▶️Answer/Explanation
- Nitrogen is required for the synthesis of amino acids, which are the building blocks of proteins.
- Proteins are needed for enzymes and structural components of the plant.
- Nitrogen is also essential for chlorophyll (needed for photosynthesis) and nucleic acids (DNA, RNA).
Example
Give two examples of ammonium salts and two examples of nitrates used as fertilisers.
▶️Answer/Explanation
- Ammonium salts: ammonium sulfate (\( \text{(NH}_4\text{)}_2\text{SO}_4 \)), ammonium chloride (\( \text{NH}_4\text{Cl} \))
- Nitrates: sodium nitrate (\( \text{NaNO}_3 \)), potassium nitrate (\( \text{KNO}_3 \))
Use of NPK fertilisers
Use of NPK fertilisers
NPK fertilisers are specially formulated fertilisers that contain three essential nutrients: nitrogen (N), phosphorus (P), and potassium (K). Each of these nutrients plays a vital role in plant growth and development, and together they ensure maximum crop yield and soil fertility.
N – Nitrogen:
- Supplied in the form of ammonium salts (\( \text{NH}_4^+ \)) or nitrates (\( \text{NO}_3^- \)).
- Encourages healthy leaf and stem growth by promoting the synthesis of amino acids, proteins, and chlorophyll.
- Deficiency symptoms: yellowing of leaves (chlorosis), stunted growth, and poor crop yield.
P – Phosphorus:
- Supplied in the form of phosphate compounds (e.g., superphosphate, ammonium phosphate).
- Promotes root growth and strengthens plant structure.
- Essential for energy transfer in cells (ATP production) and for DNA and RNA synthesis.
- Deficiency symptoms: poor root development, weak stems, and purple colouring of leaves in some plants.
K – Potassium:
- Supplied in the form of potassium salts (e.g., potassium nitrate, potassium sulfate).
- Important for the opening and closing of stomata, which control water balance and gas exchange in plants.
- Increases resistance to diseases, improves flower and fruit quality, and enhances overall plant vigour.
- Deficiency symptoms: brown edges on leaves, weak stems, and poor fruit/flower development.
Importance of NPK fertilisers in agriculture:
- Provide a balanced supply of the three major nutrients in a single fertiliser.
- Increase crop productivity and ensure consistent soil fertility.
- Reduce the need for separate applications of individual fertilisers, making farming more efficient.
- Ensure that plants grow healthily with strong roots, green leaves, and high-quality flowers/fruits.
Example
Why are NPK fertilisers considered better than using only ammonium salts or nitrates?
▶️Answer/Explanation
- Ammonium salts and nitrates supply only nitrogen, which helps in leaf and stem growth but does not address root or flower/fruit development.
- NPK fertilisers provide a balanced combination of nitrogen, phosphorus, and potassium, ensuring overall plant health.
- This leads to stronger roots, healthier leaves, better resistance to disease, and higher crop yields.
Example
A farmer notices that his plants have poor root development and weak stems. Which nutrient is likely missing, and which fertiliser should he use?
▶️Answer/Explanation
- The missing nutrient is phosphorus, which is essential for root growth and strong stems.
- The farmer should use an NPK fertiliser containing phosphate compounds, such as ammonium phosphate or superphosphate.