What are the Nutrients in Fertilisers For?
The 17 elemental nutrients essential for healthy plant growth are:
Plants get carbon (C), oxygen (O) and hydrogen (H) from water (H2O) and carbon dioxide (CO2) in air. These three elements are the 'backbone' of the organic (carbon) chemistry of all life on Earth and they make up over 95% of the dry matter of plants.
The other essential elements are:
|Element and Use||Usually In the Form||Ion Name|
|N – Nitrogen for proteins, chlorophyll, green growth|| |
NO3-2 or NH4+
|P – Phosphorous for root growth|| |
HPO4-2 or H2PO4-
|K – Potassium for stress tolerance|| |
|S – Sulphur for photosynthesis, protein and oil production|| |
|Mo – Molybdenum aids nitrogen uptake|| |
|Mg – Magnesium for photosynthesis|| |
|Fe – Iron for chlorophyll and strong green foliage|| |
Fe+2 or Fe+3
|Mn – Manganese for chlorophyll production||Mn+||manganous|
|B – Boron for cell development and regulation of metabolism|| |
|Cu – Copper for chlorophyll|| |
|Zn – Zinc for enzymes and plant hormones|| |
|Ca – Calcium for healthy root and shoot development|| |
|Cl – Chlorine for specific enzymes|| |
|Ni – Nickel for specific enzymes|| |
These nutrients are almost always in a compound form, i.e. as part of compounds with other elements. These can be salts in water, gasses in the air, organic materials and others.
Nitrogen (N), Potassium (P) and Phosphorous (K) are the primary macronutrients in many fertilisers (NPK*). Sulphur (S), Calcium (Ca) and Magnesium (Mg) are secondary macronutrients and the others in this list are regarded as micro-nutrients, generally required by plants in smaller amounts. Deficiencies in any of these elements will cause disease and unhealthy growth in plants. Different plants will have different levels of need for each element depending on the species, the plant's growth stage and the environment.
Other elements, not in this list, are found in plants in much smaller amounts and may also have beneficial effects but plants are not likely to be deficient in them. However, in New Zealand, the soil is generally deficient in selenium (Se). Inside cells, selenate (SeO₄⁻²) can influence the production of sulphur compounds that are of vital importance in plant responses to disease and other stress conditions, so selenium at low doses may improve plant productivity and/or enhance photosynthesis, increasing the capacity of plants to tolerate stress.
*The NPK level is often stated on a fertiliser label and the three numbers refer to the percentage of the fertiliser that the element comprises. E.g. PLANThealth Buxus Feed has an NPK of 10:4.3:14.2 so it contains 10% Nitrogen, 4.3 % Potassium and 14.2% Phosphorous.