Nutrients and Deficiencies Explained
What is the difference between a macronutrient and a micronutrient?
Nutrients are made up of chemical compounds. Some of these are found in nature, and others are synthetically manufactured. No matter the source, there are micronutrients, which plants just need a little of, and macronutrients, which plants can consume large amounts of. In this article, we will break down the nutrient components that are found in fertilizers and talk about signs of nutrient deficiency to beware of.
What is NPK?
Many fertilizers are labeled by nutrient concentration. Nitrogen, phosphorus, and potassium are represented by the letters N, P, and K. Plants take up hydrogen, carbon, and oxygen from air and water which are abundant, but scarcer elemental nutrients essential to growth and metabolism must be scavenged for by the roots. A minimum level of these nutrients is necessary for a plant to stay alive. Without the proper ratios of nutrients, which can change during different growth stages, the plant will show signs of illness and eventually die. Growers often reference NPK tables to help decide which nutrient source is best for their crop.
Iron (Fe) is necessary for photosynthesis. Deficiencies of iron lead to yellowing leaves and browning dead areas on leaves.
Boron (B) is necessary for flowering and fruiting, and some metabolic processes. Deficiencies of boron lead to stunted fruiting and flowering and short, thick roots.
Chlorine (Cl) is important to osmosis (water regulation) and photosynthesis.
Manganese (Mn) is necessary for photosynthesis. Deficiencies of manganese lead to discolored leaves (lighter green).
Zinc (Zn) is important to enzyme activity and DNA production. Deficiencies of zinc lead to stunted leaf growth.
Copper (Cu) is necessary for photosynthesis and enzyme activity. Deficiencies of copper lead to yellowing leaves.
Molybdenum (Mb) is important to enzymes, amino acids, and nitrogen metabolism. Deficiencies of molybdenum lead to reduced nitrogen uptake.
Nickel (Ni) is necessary for nitrogen metabolism and waste detoxification. Deficiencies lead to browning dead areas on leaves.
Carbon, Oxygen, and Hydrogen
Organic molecules produced by plants are composed of carbon, oxygen, and hydrogen. These molecules are important nutrients, energy stores, and structural components such as sugars, starches, and cellulose. Hydrogen is obtained from water and contributes to important metabolic processes like photosynthesis and respiration. Carbon dioxide from the environment is broken down into elemental carbon by plants. Carbon is used in photosynthesis by plants to create cellulose and starches and the oxygen becomes waste. Oxygen diffuses out of stomatal pores and into the air.
Nitrogen (N) is a key component of important plant molecules such as chlorophyll and proteins. Nitrogen needs to be modified into a usable form for the plant by microorganisms in the soil or supplied to it in the form of ammonium (NH4) or nitrate (NO3). In addition to being limited by the need for microorganisms to modify nitrogen, deficiencies in other nutrients such as calcium, potassium, and sulfur can reduce a plant’s ability to process ammonium and nitrate. If a plant is deficient in nitrogen it may have a purple color to its stem and stunted overall growth. Nitrogen-deficient plants may also exhibit slowed growth and yellowing leaves.
Phosphorus (P) is a vital component of DNA, RNA, and ATP. It is needed for photosynthesis, respiration, energy storage, and cell growth and division. Phosphorus is very important to seed germination and plant growth. It most commonly occurs in soil and fertilizers as polyprotic phosphoric acid (H3PO4) or as phosphorus pentoxide (P2O5),. Increased nitrogen levels enhance root growth which increases the ability of a plant to absorb phosphorus13. Nitrogen salts may also aid in phosphorus absorption by making the phosphorus into a more readily absorbed chemical variation. Phosphorus deficient plants may exhibit intensely green or reddish leaves, in some instances, leaves may have a purple tone. Symptoms often become apparent in older leaves first. In some cases, deficient plants may not show any symptoms at all until the deficiency becomes severe.
Potassium (K) regulates the opening and closing of stomatal pores on leaves which are important in regulating moisture and resisting drought conditions. It is also a major component of proteins and carbohydrates and is a major component in photosynthetic reactions. Potassium in fertilizer most commonly occurs in the form of potassium oxide (K2O) or potassium chloride (KCl). Plants will take up more potassium than needed when supply levels are high but when they are deficient they can exhibit a variety of symptoms such as wilting, yellowing leaves, brown spotting, and browning around the edges of the leaf. Deficiency also reduces the ability of a plant to resist pathogens and tolerate frost and heat.
Sulfur (S) is essential for the growth of chloroplast cells and is used by plants to construct amino acids and vitamins. It also plays a role in photosynthesis. Deficiencies of sulfur can be noticed in younger leaves first. The leaves may exhibit stunted growth or yellowing.
Calcium (Ca) plays many roles in plants. It regulates nutrient transport and activates enzymes, it is involved in photosynthesis and is a structural component. Calcium is vital to root growth, cell growth, nitrogen uptake, and detoxification. Calcium combats the build-up of salts in soil that leads to high soil salinity, which is detrimental to plant growth. It helps to mitigate the reduced water usage affect salinity has on plants. Calcium deficiency can cause bloom rot, leaves may curl in or appear blackened. Deficient plants also may exhibit poor root development.
Magnesium (Mg) is an important component of chlorophyll and plays a role in enzyme activation. Phosphorus supply in a plant relies on the activation of these enzymes. Magnesium deficient plants show yellowing, starting in older leaves.