Why plants need nutrients
Green plants make their own food by photosynthesis, but they still need mineral nutrients absorbed from the soil to grow healthily. These nutrients are the raw materials for building proteins, chlorophyll and other important substances. Nutrients are divided into macronutrients, needed in large amounts, and micronutrients, needed only in tiny amounts.
The main macronutrients
- Nitrogen (N) is used to make proteins and chlorophyll; it promotes healthy leaf and stem growth. A shortage causes yellowing leaves and stunted plants.
- Phosphorus (P) encourages strong root growth and the development of flowers and fruits.
- Potassium (K) helps flowering and fruiting and improves the plant's resistance to disease.
- Magnesium (Mg) is a component of chlorophyll, the green pigment needed for photosynthesis.
Key idea
Remember the trio in most fertilisers — N, P and K: Nitrogen for leaves, Phosphorus for roots, and potassium (K) for flowers and fruits.
Micronutrients and fertilisers
Micronutrients such as iron, zinc and boron are needed only in very small amounts, but a plant still becomes unhealthy without them; a shortage of iron, for instance, also leads to pale, yellow leaves because the plant cannot make chlorophyll properly. Every time a crop is harvested, nutrients are removed with it, so the soil slowly becomes poorer. Farmers replace these lost nutrients using fertilisers. Organic fertilisers such as compost and animal manure release nutrients slowly and improve the structure of the soil, while inorganic (chemical) fertilisers such as NPK act quickly but must be used with care to avoid polluting rivers.
Example
On an oil palm estate in Malaysia, NPK fertiliser is added around the base of each palm. The nitrogen keeps the fronds green, while phosphorus and potassium support strong roots and heavy bunches of fruit.