Some elements in relatively large amounts, the soil supplies to the plants are often called the macronutrients for plants. We are hereby going to discuss about the important Micronutrients for plants as follows:
Nitrogen is taken by plants usually in the form of NO2 and NO3 from the soil. Most soils are deficient in nitrogen since this element is easily lost through leaching of nitrate ions or conversion of nitrate ions to volatile N2 by micro-organisms. Nitrogen is essential to plants because it is a part of several organic compounds like amino acids, proteins, coenzymes, nucleic acids, vitamins, alkaloids and chlorophyll. . It plays an important role in protein synthesis, photosynthesis, respiration, growth and other metabolic processes. So nitrogen is the important Macronutrients for Plants.
Nitrogen deficiency symptoms include general yellowing or chlorosis, especially in mature leaves. Young leaves remain green longer because of soluble forms of nitrogen are transported to them from the older leaves. Some plants like tomato show a purplish coloration on stems, petioles and the lower surface of leaves due to accumulation of anthocyanin pigments. Deficiency of nitrogen also causes stunting of plants, dormancy of lateral buds, late flowering, wrinkling of cereal grains and inhibition of cell division. However, plants grown in excess of nitrogen are usually dark green in colour with dense foliage and poorly developed root system. Excess nitrogen retards flowering and seed formation in several agricultural crops. So over dose of macronutrients for plants is not suggested.
Potassium, another macronutrients for plants, does not form a stable structural part of any molecule inside plant cells, yet large amounts of this element are required for proper growth and development of the plant. It acts as a coenzyme or activator for many enzymes. It helps in influential anion-cation balance, and turgidity in cells and is concerned in protein synthesis. It is also concerned in the formation of cell membranes and in opening and closing of stomata.
Deficiency symptoms of potassium include scorched leaf tips, shorter internodes, die back, chlorosis in interveinal areas, loss of apical supremacy, bushy habit, and loss of cambial activity, disintegration and increase in rate of respiration.
Potassium is the other of the important macronutrients for plants. Although potassium does not form a stable structural part of any molecule inside plant cells, yet large amounts of this element are required for proper growth and development of the plant. It acts as a coenzyme or activator for many enzymes. It is also involved in the formation of cell membranes and in opening and closing of stomata.
Deficiency symptoms of potassium include scorched leaf tips, shorter internodes, die back, chlorosis in interveinal areas, loss of apical dominance, bushy habit, loss of cambial activity, disintegration and increase in rate of respiration.
Another of the macronutrients for plants is sulphur. Sulphur is absorbed as SO4- - ions. Most of the absorbed sulphate is translocated as such to the shoot where it is incorporated into organic compounds like sulphur containing amino acids. Since sulphur is a constituent of some amino acids, it has indirect role in protein synthesis. Ferredoxin plays a vital role in photosynthesis, thereby sulphur plays indirect role in photosynthesis too.
Sulphur deficiency leads to breakdown of protein synthesis. Sulphur deficient plants show general yellowing of leaves, first noticed in younger leaves.
Magnesium also has its importance as one of the macronutrients for plants. It is present in the soil in water soluble, exchangeable, and fixed forms. It plays important role in photosynthesis and carbohydrate metabolism. It is an essential part of chlorophyll molecule. Roots and micro-organisms which lack chlorophyll require magnesium for the activation of many essential enzymes. Those enzymes which are known to utilize energy in ATP are activated by magnesium.
Magnesium deficiency induces extensive interveinal chlorosis and necrotic or purple spots on mature leaves.
Major portion of calcium in the soil occurs in a non-exchangeable form. It is found in mostly inside cell vacuoles as crystals of calcium oxalate. Calcium pectases of the middle lamella prop up the primary walls together so that cells of a tissue remain bound to one another. As a macronutrients for plants calcium performs essential function in the synthesis and stability of pectic substances. In higher plants, calcium is needed in low concentrations in membranes to maintain its structure and characteristics of differential permeability. It promotes translocation of carbohydrates, amino acids and root development.
Calcium deficiency results into premature falling of flowers, thus reserve of seed formation.
The other macronutrients for plants, iron is a relatively immobile ion and is absorbed both in ferrous (Fe++) and ferric (Fe+++) forms. It has a number of important functions in the overall metabolism of plants. It acts as an activator for enzymes catalyzing reactions of chlorophyll synthesis. Iron is also found in enzymes like peroxidases and catalases.
Iron-deficient plants develop pronounced interveinal chlorosis on younger leaves; Iron deficiency also induces chloroplast disintegration, death of root tips, reduce in respiratory rate, etc.