Studies have shown that higher plants require fourteen ‘essential’ mineral nutrients for healthy growth and successful reproduction. There are other minerals which though not essential to all plants, do have some beneficial effects on certain groups of plants.
Of these fourteen, six are termed ‘macronutrients’ and the remaining eight as ‘micronutrients’, or ‘trace elements’. The difference between the two groups is that the macronutrients have been found in plant tissues at levels of at least ten times the levels of micronutrients. Even though they are found at much lower levels, micronutrients are nonetheless essential for healthy growth. In most cases normal soils contain sufficient trace elements or micronutrients already present, so usually there is no need to add them. Only in very sandy soils can they leach away and need to be supplemented. Soil less potting composts and hydroponic solutions also require their addition. It is possible to buy ‘fritted’ trace elements to add to composts.
The Macronutrients are: Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulphur (S).
The Micronutrients are: Iron (Fe), Manganese (Mn), Copper (Cu), Zinc (Zn), Boron (B), Chlorine (Cl), Molybdenum (Mo), and Nickel (Ni).
Beneficial elements include: Sodium (Na), Silicon (Si), and Cobalt (Co).
The macro- and micro – nutrients are all essential, though chlorine and nickel are only known requirements of a relatively few plant species. Some elements are not necessarily essential to all plants but beneficial to some. Cobalt, though it may not be essential to plants directly, it is essential for the biological fixation of nitrogen by bacteria, including those in the nodules of leguminous plants such as peas and beans. Sodium, though not essential, is beneficial to the growth of sugar beet. Silicon is essential for the growth of most grasses (and also for the ‘horsetail’ - Equisetum arvense), but for most plants it is beneficial.
Each nutrient may perform several functions within the plant’s biochemical processes as well as forming part of the organic structure of the plant. Micronutrients mainly assist in activation of enzyme reactions as catalysts or some other manner.
Potassium and chlorine, the only nutrients that don’t form part of the organic structure of the plant, are mainly required for osmotic regulation and electrochemical balance of the cell contents.
Nitrogen is an essential component of many organic compounds, such as proteins, nucleic acids, chlorophyll and hormones.
Phosphorus is present in many organic compounds such as DNA and enzymes in connection with photosynthesis and respiration.
Calcium is required for the production of calcium pectate, an essential constituent of cell walls.
Sulphur is also essential in some proteins and enzymes
Magnesium is required for the production of chlorophyll
Iron acts as catalyst for the processes leading to the formation of chlorophyll, but doesn’t form part of the chlorophyll molecule
Although not classed as nutrients, carbon, from carbon dioxide, oxygen, and hydrogen, from water, are also needed for the production of sugars and other carbohydrates that provide energy and also form the structure of plants.
It can be seen that all these essential nutrients are necessary for plant growth to thrive, and are all interrelated and balanced. Upset that balance, with a shortage or absence of one factor, then the whole plant suffers. Similarly, the supplementing of one factor, without a corresponding attention to any shortcomings in other factors also upsets the balance, again leading to a failure of the plant to thrive.