We all need proper nutrition to be healthy. Proper nutrients allow our bodies and minds to function at their optimum levels, our bodies immune systems to fight off disease and heal from injury and encourage healthy rates of growth. The same is true for plants. NPK are the macronutrients that are most desired.
Nutrients play an essential role in the health, growth and reproduction of plants in the garden. Understanding how plants use essential nutrients can help us manage deficiencies that could have a harmful effect on the garden. There are no less than 14 essential macro- and micronutrients that aid in proper plant health and development. Aside from Oxygen, Carbon and Hydrogen (the three essential macronutrients derived from air and water) there are three soil-based primary macronutrients that play vital and pivotal roles in the health of our plants: Nitrogen, Phosphorus and Potassium.
How Plants Use Nitrogen, Phosphorus and Potassium (NPK)
The growth of all organisms depends on the availability of mineral nutrients, and none is more important than nitrogen. Nitrogen is required in large amounts as an essential component of proteins, nucleic acids, enzymes and other cellular compounds. It is an essential part of chlorophyll, but it influences growth and utilization of sugars more than it influences photosynthesis.
There is an abundant supply of nitrogen in the earth’s atmosphere—nearly 79% in the form of N2 gas. However, N2 is unavailable for use by most organisms. In order for nitrogen to be used for growth in plants it must be “fixed” (combined) in the form of ammonium (NH4) or nitrate (NO3) ions. Various plants and microorganisms play a vital role in the bioavailability of Nitrogen through various metabolic processes that perform this conversion.
The presence of fixed Nitrogen alone is not enough for our plants to flourish. Nitrogen must be available for use in combination with important micronutrients like Calcium, Potassium and Sulfur which affect the conversion of organic Nitrogen into protein.
Nitrogen deficient plants may exhibit a purple appearance on the stems, petioles and underside of leaves.
Like Nitrogen, Phosphorus is involved with many vital plant processes. Within a plant, it is present mainly as a structural component of the nucleic acids, DNA and RNA, and is important in cell membrane development and function. All energy transfers in the cell are critically dependent on phosphorus which can also be used to modify the activity of various enzymes.
Phosphorus is concentrated at the most actively growing points of a plant and stored within seeds in anticipation of their germination. It is useful to apply a high phosphorus content fertilizer, such as bone meal, to perennials to help with successful root formation.
A Phosphorus deficiency in plants is characterized by an intense green coloration or reddening in leaves due to lack of chlorophyll. If the plant is experiencing high phosphorus deficiencies the leaves may become denatured and show signs of death, starting in the older leaves first.
Though Potassium is does not play a role in the metabolic processes of plants, it does occur in all parts of plants in substantial amounts. It seems to be of particular importance in leaves and at growing points. Potassium is outstanding among the nutrient elements for its mobility and solubility within plant tissues. Processes involving potassium include the formation of carbohydrates and proteins, the regulation of internal plant moisture, as a catalyst and condensing agent of complex substances, as an accelerator of enzyme action, and as contributor to respiration and photosynthesis.
Potassium regulates the opening and closing of the stomata by a potassium ion pump. Since stomata are important in water regulation, potassium reduces water loss from the leaves and increases drought tolerance.
When potassium is moderately deficient, the effects first appear in the older tissues, and from there progress towards the growing points. Acute deficiency severely affects growing points, and die-back commonly occurs.
Other Macronutrients and Micronutrients of Importance
Macronutrients (secondary and tertiary)