🍡 Micro Nutrients

Iron

• Sources of iron
  • Earth crust contains about 5% Iron.
  • Primary and secondary minerals such as
    • Olivene
    • Pyrite
    • Hematite
    • Goethite
    • Magrulite
    • Limestone

Forms of iron

• There is 10 fold increase of Iron for each unit decreases in pH.
• Over the normal pH range in soils, total solution Fe is not sufficient to meet plant requirements for Fe even in acid soils, where Fe deficiency occur less frequently than in high pH and calcareous soils.

Chelates

• “Is a term derived from a Greek and meaning “Claw”.
• Chelates are soluble organic compounds that bond with metals such as Fe, Mn Cu, and Zn increasing their solubility and their supply to plant roots.
• “Natural organic chelates in soils are products of microbial activity and degradation of soil organic matter and plant residues. Root exudates are capable complexing nutrients substantial quantities of organic completed. Fe can be cycled through crop residue and compounds of citric acid and oxalic acids have chelating properties.”

Functions

• Absorbed mainly in Fe³⁺ (soil availability) but physiologically active in Fe²⁺ (root sites) Fe³⁺ (ferric) is reduced in the plant into Fe²⁺ (ferrous) in presence of Mn.
• Activator in the synthesis of chlorophyll.
• Structural component of porphyrin molecules like cytochromes, hematin, hemes, ferrichrome and leghemoglobin. These substance are involved in oxidation-reduction reactors in respiration and photosynthesis.
• Structural component of non-hemine compounds like ferredoxins (Fe & S-protein).
• Constituent of enzyme systems. Eg. cytochrome oxidase, catalase, nitrogenase reaction in plants.
• Component of flavoprotein like FMN = Flavin mono nucleotides, FAD = Flavin Adinosine Dinudeotide.

Deficiency

• Deficiency symptoms occurs in younger leaves since Fe is immobile element within plant.

• It occurs in soils of calcareous or alkaline soils and poorly drained, H₂O logged soils.

• The principal veins remain conspicuously green and other portions of the leaf turn yellow tending towards whiteness; chlorosis starts from base of leaf.

  

Toxicity

• Fe toxicity causes nutritional disorders in rice grown on poorly drained, submerged soils.
• This condition known as bronzing is associated with Fe levels > 300 ppm in leaf blade of rice at tillering.

Manganese

Sources of Mn

• Earth crust contains 1000 ppm. Various oxides and hydroxides.
• Manganite MnO (OH)
• Braunite Mn₂O₃
• pH: Liming to acid soils decreases solution and exchange Mn²⁺ due to precipitation Mn²⁺ as MnO₂.
• Its content is 25 - 500 mg Mn/Kg.

Functions

• Helps in chlorophyll formation
• Mn 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 evolution.
• It is a constituent of superoxide dismutase (Mn-SOD). Mn SOD, present in mitochondria protects cells against the deleterious effects of superoxide free radicals.
• Mn has a role in TCA cycle (Respiration) in oxidative and non-oxidative decarboxylation reactions with Nicotine Adenine Diamide (NAD)
• Malic dehydrogenase enzyme catalyzing the reaction.

Malate + NADP⁺ → Pyruvate + NADPH + H⁺ + CO₂

Deficiency

• Immobile in plant and deficiency starts in the younger leaves.
• The principal veins as well as the smaller veins are green. Interveinal portion is yellowish not tending towards whiteness; Complete Interveinal chlorosis; chequered appearance to leaf; Oat and Soybean most affected; The minimum level in healthy oat at flowering is 14 ppm; leaf top remains green and base dies.
  • Oats - Gray specks / streaks
  • Peas - Marsh spot
  • Sugarbeet - Speckled yellow
  • Sugarcane - Pahala blight - midrib pale green and white

• The deficiency symptoms looks like those of iron but in case of Mn deficiency sometimes tan, sunken spots appear in the chlorotic areas between the veins.
• Manganese deficiency can occur when the pH of the growing medium exceeds 6.5, because it is tied up and unavailable for uptake.

Toxicity

• Plants are injured by excessive amounts of Mn.
• Crinkle leaf of cotton is a Mn toxicity observed in highly acid red yellow soils.
• Mn toxicity in tobacco, soybeans, tree fruits, and rapeseed is noted on extremely acid soils.

Copper

• pH: The concentration of Cu in soil solution decreases with increase in pH.
• Its content is 5 - 20 mg /kg of dry matter.

Functions

• Essential for the synthesis of vitamin A
• Cu²⁺ is a component of large number of proteins and enzymes like plastocyanin, Diamine oxidase, polyphenol oxidase, Ascorbate oxidase.
• Involved in production of SOD. Location of SOD production is stroma and protects from disintegration of thylakoids
• Constituent of chlorophyll.
• Important in imparting disease resistance.
• Enhances fertility of male flowers.

Deficiency

• Deficiencies of Cu are reported in numerous plants, although they are more prevalent among crops growing in peat and muck soils.
• Chlorosis of the younger shoot tissue, white tips, reclamation disease, necrosis, leaf distortion and Die Back are characteristics of Cu deficiency.
• Guava - cracking of fruits and terminal bud Die Back.
• Citrus – Die Back of new growth/ little leaf & gummosis
• Male flowers’ sterility, delayed flowering and senescence are the most important effects of Cu deficiency.
• Necrosis of apical meristem results in elongation of shoot in cereals and auxiliary shoots in dicots.
• The shoot apex may cease to grow, resulting in the development of several auxiliary bunds (resetting and excess gumming).
• In cereals symptoms appear as bleaching and withering of young leaves.
• Exanthema and dieback in citrus which manifests as dark brown spots on the leaves, terminal twigs and fruits.
• Yellowish brown blotches on the leaf particularly in legumes.
• Tip drying and bluish green leaf tips are the symptoms in rice.
• Empty glumes in wheat.

Zinc

• Soil pH: Avail of Zn decrease with increase soil pH. At high PH, Zn⁺ is converted into negatively charged zincate complex whose availability is reduced in alkaline soil. Calcium Zincate is formed at high pH and thus fixed. Zn def occur in neutral and calcareous soil.
• Zn is present in all parts of the plants. In general root contain more zinc than fruits.
• Its content is 20 - 150 mg Zn/Kg of dry matter

Functions

• Zinc is a constituent of three enzymes viz., Alcoholic Dehydrogenase, Carbonic Anhydrase, Superoxide Dismutase (SOD). ^{UPPSC 2021}
• Zn is involved in the synthesis of Indole Acetic Acid (Auxin), metabolism of Gibberellic Acid and synthesis of RNA.
• Because of preferential binding to sulfhydryl group, zinc plays an important role in the stabilization and structural orientation of the membrane proteins.
• Zn influences translocation and transport of P in plants. Under Zn deficiency, excessive translocation of P occurs resulting in P toxicity.

Deficiency

• Lamina becomes chlorotic and veins remain green; dead spots over leaf including veins, tips and margins; Structural aberrances in root tips; dwarfing of vegetative growth; New leaves emerge white in colour (White bud of maize); In cereals deficiency appears in 2-4 leaves. from top during vegetative stage. Plants bushy due to reduced internodal elongation (malformation).
• Khaira Disease of Rice: The first symptom of zinc deficiency appear in 3 - 4 week old seedlings when the young leaves develop reddish brown pigmentation. The pigmentation appears first in the middle of the leaves, then intensifies and spreads over the entire lamina. The affected tissue becomes papery and necrotic and under conditions of severe deficiency, the entire mass of leaves collapses and further growth of the plant is arrested.
• White bud of Maize: Soon after the emergence of seedlings, areas between the veins of old leaves become light yellow and develop white necrotic spots, which later develop dark brown necrotic areas that enlarge and coalesce, resulting in the necrosis (death of the entire leaf). Leaves that emerge and unroll subsequently appear yellow and white.
• Mottle leaf or Frenching of citrus
• Reduced leaf size and shortening of internodes in brinjal and mango called as Little Leaf.
• Fern Leaf of potato.

  

Boron

• It is absorbed by plants as undissociated boric acid (H₃BO₃).
• Only Nonmetal among micronutrients.
• Its content is 10 - 200 mg B /kg dry matter.
• Source: Tourmaline and borosilicate contains B.

Functions

• Boron is absorbed by plants as boric acid. However, it can also be absorbed in anionic form viz., dihydrogen borate (H₂BO₃^-), mono-hydrogen borate (H₂BO₃^2-) under acidic conditions and borate BO₃^3- under high pH condition.
• New cell development in meristematic tissue.
• Plays a role in pollen germination and pollen tube growth.
• Translocation of sugars, starches, N and P
• Primary role concerned with Ca-metabolism; keeps Ca in soluble form within the cell and acts as a regulator of K/Ca ratio.
• It is responsible for cell wall formation and stabilization, lignification and xylem differentiation. As a consequence, B deficiency causes changes in chemical composition and ultra-structure 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.
• Synthesis of proteins and amino acids.
• Nodule formation in legumes
• Regulation of CHO metabolism.

Deficiencies

• Since it is immobile, deficiency Symptoms occurs in terminal bud growth.
• Boron deficiency symptoms are conspicuous on the terminal buds or the youngest leaves; which become discolored and may die under acute deficiency.
• Internodes become shorter and give appearance of a bush or rosette.
• Specific names given to B deficiency in different crops are
  • Fruit Cracking of Apple
  • Fruit Cracking of Pomegranate
  • Hen & Chicken disease of grape

• Browning or hollow stem of cauliflower
• Hollow heart/heart rot of sugar beet: Break down of internal tissue in root crops given rise to darkened areas referred to Brown heart / black heart.
• Internal Cork of Apple

• Necrosis/black tip in Mango
• Top Sickness of Tobacco
• Citrus Fruit Cracking: B Deficiency ^{AFO 2017}

Molybdenum

• pH: Mo availability increases with increasing pH.
• Liming to correct acidity will increase Mo availability.
• Mo availability decrease with application of acid forming fertilizer (NH₄)₂SO₄
• Its content is 0.2 - 2 mg /kg of dry matter.
• Teast: Soil containing high proportion of Mo.
• Molybdenum is known as nano-nutrient. ^{UPPSC 2021}

Functions

• Essential component of enzyme nitrate (NO₃) reductase, which catalyses NO₃^- to NO₂^-.
• Structural component of nitrogenase enzyme - involved in N fixation.
• Required by N fixing organisms like Azotobacter, Clostridium, Nostoc, Anabaena.
• Involved in carbohydrate metabolism and sugar formation.
• Essential for absorption and translocation of Fe in plant.

Deficiency

• In most plants with reticulate venation, the first effect of Mo deficiency appears as chlorotic mottling between the veins.
• Brassica crops are very susceptible to Mo deficiency, the symptoms developing in 3-4-week-old plants.
• Tomato, lettuce, spinach, beet root and Brassica spices especially cauliflower, broccoli and rape seed are very sensitive to restricted Mo supply.
• Cabbage – Whiptail (leaves get twisted elongated)/ Browning.
• Mo deficiency symptoms markedly evident in Legumes which develop symptoms which resemble N deficiency.
• Imbalances various Amino Acids in plants.

Chlorine

• Normal concentration in plant is about 0.2-2.0%.
• Absorbed by plants as Cl^- through roots and aerial parts.

Functions

• Chlorine has been shown to be involved in the oxygen evolution in photosynthetic reactions.
• In microorganisms, chlorine containing metabolically active compounds like chlorometabolites were found.
• In higher plants, chlorides largely accumulate in free ionic form in cell vacuoles. Creates disease resistant by increase osmotic pressure in cell sap.
• Act as a counter ion during rapid K fluxes.
• Due to Cl^-, tobacco leaf becomes thick, and brittle and don’t burn uniformly whereas proper ‘K’ results shining, luster and proper burning.
• Cl^- interferes in starch formation hence is avoided in rice

Deficiency

• Common symptoms are wilted appearance of the foliage and stuffy roots with laterals showing branching.
• Tomato leaves show chlorotic mottling, bronzing and tissue necrosis.

Toxicity

• Symptoms high level of Cl^- in wheat plants are increase total leaf water potential and cell sap osmotic potential.
• Excess of Cl^- can be harmful, and crops vary widely in their tolerance to this condition.
• Tobacco, legumes are among the most sensitive crops.
• Leaves of tobacco and potatoes thicken and tend to roll.
• The storage quality of potato tubers is adversely affected.

Nickel

• Nickel content in plant is 0.1 - 1.0 ppm dry matter basis. Taken by plant as Ni²⁺
• High levels of Ni may induce Zn or Fe deficiency because of cation competition.
• Ni - metal component of urease that catalyse reaction.

CO (NH₂)₂ + H₂O → 2NH₃ + CO₂

• Essential for N metabolism.
• Stimulates nodule weight and yield of crops.
• It is needed for grain filling & seed vitality.

Beneficial Elements

Silicon 🥽

• Strengthens cell walls, energy transfer & drought resistance
• Reduce water loss & prevent fungal infection.
• Disease resistance, stalk strength, and reduction in lodging.
• Freckling, a necrotic leaf condition is a symptom of low Si in sugarcane receiving direct sunlight due to Ultraviolet radiation. Adequate Si in sugarcane plant filters out harmful ultraviolet radiation.

Cobalt

• Structural component of vitamine ‘B’ which in turn essential for the formation of leghemoglobin needed for N₂ fixation; essential for growth arid metabolism of microorganisms; required by Rhizobia, activator of certain enzymes like orginase, Lecithinase etc.
• Hence, lack of cobalt affects N₂ fixation in soil.

Sodium 🧴

• Na replaces K in certain function in halophytes plants for C4 plants having di-carboxylic photosynthetic pathway.
• Essential for sugarbeets and such crops; influences water relations in sugarbeet and increases their resistance to drought.
• In higher plants, Na is essential and to some extent it can supplement for K.

Vanadium 🏺

• Essential for green algae. Low concentration of Vanadium is beneficial for growth of Microorganisms.
• Vanadium substitute for Mo in N fixation by Rhizobium involves in Biological – Oxidation – Reduction reactions.

Selenium 🪢

• Can be replaced with ‘S’ in the production Methionine, cystein and cystine because it is analogous to ‘S’ (i.e. same function but origin different). (Homologous means same origin).

Aluminium 🍴

• Activator of glandular system but more amount has toxic effect.

- Tisdale, S.L., Nelson, W.L., Beaton, J.D. Havlin, J.L.1997. Soil fertility and Fertilizers. Fifth edition, Prentice hall of India Pvt. Ltd, New Delhi
- Singh, S.S.1995. Soil fertility and Nutrient Management. Kalyani Publishers, Ludhiana
- http://www.ncagr.gov/cyber/kidswrld/plant/nutrient.html
- Mortvedt, J.J. et al.(Eds.). Micronutrients in Agriculture. No.4, Soil Science Society of America, Madison, Wisconsin, USA.