Functions and sources of the primary mineral nutrients

1. The Role of Primary Nutrients

Plants require three primary nutrients for growth and development:

1. Nitrogen $(N)$ – Promotes leaf growth and is essential for chlorophyll production (photosynthesis).
2. Phosphorus $(P)$ – Stimulates root and seed development, aids in flowering and fruit production.
3. Potassium $(K)$ – Improves fruit quality, enhances disease resistance, and strengthens cell walls.

2. Sources of Primary Nutrients

Nutrient	Natural Sources	Fertiliser Sources
Nitrogen $(N)$	Guano (bird droppings), compost, manure	Nitrate salts $(NO₃⁻)$, ammonium salts $(NH₄⁺)$ from the Haber Process
Phosphorus $(P)$	Bone meal, rock phosphate	Superphosphates: Single Superphosphate $(SSP),$ Triple Superphosphate $(TSP)$
Potassium $(K)$	Wood ash, kelp (seaweed)	Potassium chloride $(KCl),$ potassium nitrate $(KNO₃),$ potassium sulphate $(K₂SO₄)$

3. The Nitrogen Cycle and Fixation

• Atmospheric nitrogen $(N₂)$ cannot be used by plants directly and must be fixed into usable forms:
  • Biological fixation: Bacteria in soil and plant roots (e.g., legumes).
  • Atmospheric fixation: Lightning converts $N₂$ into nitrates.
  • Industrial fixation: Haber Process produces ammonia $(NH₃)$ for fertilisers.

4. Industrial Production of Fertiliser Nutrients

The Haber Process (Nitrogen Fixation)

• Reaction: $N_2 + 3H_2 \xrightarrow{\text{Fe catalyst}} 2NH_3$

• Used to produce ammonium salts $(NH₄⁺)$ and nitrate salts $(NO₃⁻).$

The Contact Process (Sulphuric Acid for Phosphates)

• Produces $H₂SO₄,$ which reacts with rock phosphate to make superphosphates.

Potassium Fertilisers

• Mined as potassium chloride $(KCl)$ or potassium sulphate $(K₂SO₄).$

5. Key Takeaways

• Nitrogen, phosphorus, and potassium are the three primary nutrients needed for plant growth.
• Fertilisers replenish soil nutrients and improve crop production.
• The Haber, Contact, and other industrial processes produce essential fertiliser compounds.