Micronutrients are essential nutrients that are required in small quantities for the normal growth and development of plants. Micronutrients play a supporting role in overall plant health and development. Micronutrients promote essential plant processes and growth, which translates into nutrient-rich food for animals and humans. Micronutrients include boron, chlorine, copper, iron, manganese, molybdenum and zinc, which are often in short supply for growing crops.
- Iron is a constituent of two groups of proteins, viz.
- It activates a number of enzymes, including aminolevolinic acid synthetase and coproporphyrinogen oxidase.
- It plays an essential role in the nucleic acid metabolism.
- It is necessary for synthesis and maintenance of chlorophyll in plants.
- Interveinal chlorosis of young leaves. Veins remain green except in severe cases.
- Twig dieback.
Iron-containing Commercial Fertilizers:
- Ferrous ammonium phosphate – Fe(NH4)PO4.H2O – 29%
- Ferrous ammonium sulphate – NH4SO4.FeSO4.6H2O -14%
- NaFeEDTA – 5 – 11 %
- NaFeHPDTA – 5 – 9%
- Zinc is involved in many enzymatic activities such as dehydrogenase, proteinase. peptidase etc.
- Zinc is involved in the synthesis of indole acetic acid, metabolism of gibberellic acid and synthesis of RNA .
- Zn plays an important role in the stabilization and structural orientation of the membrane proteins.
- Zinc influences translocation and transport of P in plants. Under Zn-deficiency, excessive translocation of P occurs resulting in P-toxicity.
- Decrease in stem length and shortening of internodes, resetting of terminal leaves.
- Reduced fruit bud formation.
- Mottled leaves, interveinal chlorosis. Sometimes, a red. spot-like discoloration (caused
- by anthocyanins) on the leaves often occurs. Symptoms of chlorosis and necrosis on
- older leaves of zinc-deficient plants are most likely the result of phosphorus toxicity.
- Dieback of twigs after the first year.
- Striping or banding on corn leaves.
Zinc-containing Commercial Fertilizers:
- Zinc sulphate – (ZnSO4 7H2O) –36 %
- Zinc Oxide – ZnO -60 – 78%
- Zinc oxysulphate – 18 – 50%
- NaZnTA – 13%
- Molybdenum is a component of nitrate reductase. nitrogenase, xanthine oxidase/dehydrogenase and sulphite oxidase.
- Biological nitrogen fixation (BNF) is catalysed by the Mo- containing enzyme. nitrogenase (essentially comprising of Mo-Fe-S protein and a Fe-S cluster protein) which directly transfers electrons to N2. Because of its involvement in BNF.
- Interveinal chlorosis. Veins remain green producing a mottled appearance.
- Stunting and lack of vigour. This is similar to nitrogen deficiency due to the key role of
- molybdenum in nitrogen utilization by plants.
- Marginal scorching and cupping or rolling of leaves.
Molybdenum-containing Commercial Fertilizers:
- Ammonium molybdate- (NH4)6Mo7O26– 53 %
- Molybdenum trioxide – MnO3– 66%
- Molybdenum dioxide- MnO2 -75%
- It is responsible for the cell wall formation and stabilization, lignification and xylem differentiation. As a consequence. B-deficiency causes changes in chemical composition and ultrastructure of cell wall, accumulation of toxic phenols. inhibition of lignin synthesis and a decrease in the production of indole acetic acid (IAA).
- Decrease in IAA is responsible for the induction of Ca-deficiency.
- It imparts drought tolerance to the crops. Regular boric acid sprays help in mitigating harmful effects of drought.
- Boron plays a role in pollen germination and pollen tube growth.
- It facilitates transport of K in guard cells as well as stomatal opening.
- Boron deficiency in the shoots are noticeable at the terminal buds or youngestleaves, which become discoloured and may die.
- Internodes are shorter, giving the plants abushy or rosette appearance.
- Deficiency is found mainly in the youngest plant tissues.
- Interveinal chlorosis on mature leaves may occur, as might misshapen leaf blades.
- Drop ofbuds, flowers, and developing fruits is also a typical symptom of boron deficiency.
- Boron also apparently regulates plant metabolism of carbohydrates.
- Boron isnon-mobile in plants, and a continuous supply is necessary at all growing points.
List of Boron-containing Commercial Fertilizers:
- Borax -Na2B4O7.10H2O –11%
- Boric Acid – H3BO3 – 16%
- It plays a major role in osmoregulation (cell elongation, stomatal opening) and charge compensation in higher plants.
- It acts as a co factor in Mn-containing water splitting enzyme of photosystem II.
- Chlorine in abundance suppresses the plant diseases, viz. grey leaf spot in coconut palms, take-all and common root rot in wheat, common root rot and Fusarium root rot in barley, stalk rot in corn, stem rot and sheath blight in rice, hollow heart and brown centre in potatoes, Fusarium yellows in celery, and downy mildew in millet.
- Chlorine supply improves the nutritional quality of vegetables by preferentially lowering the NO3– -N concentration in tissues.
- A blue-green shiny appearance of young leaves.
- Wilting, followed by chlorosis.
- Excessive branching of lateral roots.
- Bronzing of leaves.
- Chlorosis and necrosis in tomatoes and barley.
List of Chloride-containing Commercial Fertilizers:
- Calcium chloride -CaCl2-50%
- Potassium chloride – KCl– 48%
- Manganese is an integral component of the water-splitting enzyme associated with photosystem II. Because of this role. Mn-deficiency is associated with adverse effects on photosynthesis and O2
- It is a constituent of superoxide dismutase (Mn-SOD).
- Role of Mn assumes criticality because Mn-SOD (present in mitochondria. peroxisomes, and glyoxysomes) protects cells against the deleterious effects of superoxide free radicals.
- Manganese has a role in tricarboxylic acid cycle (TCA) in oxidative and non-oxidative decarboxylation reactions.
- Interveinal chlorosis of young leaves. Gradation of pale green coloration with darker
- colour next to veins. No sharp distinction between veins and Interveinal areas as with
- iron deficiency.
- Development of gray specks (oats), interveinal white streaks (wheat), or interveinal
- brown spots and streaks.
Manganese-containing Commercial Fertilizers:
- Manganese chelate – MnEDTA – 5 – 12%
- Manganese oxide -MnO -53%
- Manganese oxysulphate- 30 – 50%
- Manganese sulphate – MnSO4.4H2O -24%
- Copper is a constituent of number of enzymes.
- Copper is important in imparting disease resistance to the plants.
- It enhances the fertility of male flowers.
- Leaves may be chlorotic or deep blue-green with margins rolled up.
- The bark of trees is often rough and blistered, and gum may exude from fissures in the
- Young shoots die back.
- Flowering and fruiting may fail to develop in annual plants and they may die in the
- seedling stage.
- Stunted growth.
- Formation of gum pockets around central pith in oranges.
Copper-containing Commercial Fertilizers:
- Copper sulphate (monodydrate) -CuSO4.H2O – 35%
- Cupric ammonium phosphate – Cu(NH4)PO4.H2O – 32%
- Cupric chloride – CuCl2 – 17%
- Cupric oxide – CuO- 75%
- Cuprous oxide – Cu2O -89%
Article written By:
Prof. S. B. Dahiphale
Department of Soil Science &Agril. Chemistry
College of Agriculture, Bhanashiware.
Senior Research Assistant