Fertilisation provides the plant nutrients that the soil does not supply. Here are macro- and micronutrients, NPK figures and how to read them, the difference between organic, mineral and slow-release fertiliser, dosing based on soil analysis and the most important deficiency symptoms.
Introduction
Plants get most of their mass from air and water, but they need a range of nutrients from the soil to grow. If the soil can't supply enough, you fertilise. Fertilisation is about giving the right material in the right amount at the right time — neither too little (deficiency) nor too much (waste and leaching).
Macro- and micronutrients
Nutrients are divided according to how much the plant uses. Macronutrients are used in large quantities, micronutrients in small — but the lack of a micronutrient can be just as harmful as the lack of a macronutrient.
- 01Macronutrients (macro): nitrogen (N), phosphorus (P) and potassium (K) — the three that the NPK number indicates.
- 02Secondary macronutrients: calcium (Ca), magnesium (Mg) and sulphur (S).
- 03Micronutrients (trace minerals): iron (Fe), manganese (Mn), boron (B), zinc (Zn), copper (Cu) and molybdenum (Mo).
- 04N drives leaf growth and green colour; P root growth and establishment; K strength, winter hardiness and disease resistance.
NPK values — how they are read
A commercial fertilizer is marked with three numbers, e.g. 16-2-7. The numbers are weight percentages of nitrogen (N), phosphorus (P) and potassium (K) respectively. A 16-2-7 thus contains 16 % N, 2 % P and 7 % K; the rest is filler, sulphur, magnesium and any micronutrients. The higher the N number, the more nitrogen per kg of fertilizer.
Organic, mineral and long-acting
| Fertiliser type | Effect | Application |
|---|---|---|
| Organic (compost, farmyard manure, horn shavings) | Slow; also improves soil structure and humus | Soil improvement and sustainable fertilisation |
| Mineral (NPK commercial fertiliser) | Quick and precisely dosable | Starter fertiliser and targeted nutrition |
| Long-acting (coated/depot) | Released gradually over weeks to months | Lawn and beds — fewer applications, less leaching |
Dosing based on soil analysis and crop
The dose is determined by what the plant requires and what the soil already has. A soil analysis provides reaction value (Rt/pH), phosphorus value (Pt) and potassium value (Kt); if Pt or Kt is low, extra fertiliser is applied with that substance while a high value means you can save (see »Soil and growing layer« for interpretation). For new establishments a starter fertiliser is often given and a lawn is maintained with repeated smaller fertilisations over the season (see »Lawn from scratch«). Always follow the analysis recommendation and the product's dosage guidance.
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