🍡Micronutrients: Fe, Mn, Cu, Zn, B, Mo, Cl, Ni & Beneficial Elements
Complete guide to all 8 micronutrients and 6 beneficial elements — functions, deficiency diseases (Khaira, White Bud, Whiptail, Hollow Heart), toxicity, and diagnostic terms for competitive exams
Why Micronutrients Matter: A Farmer’s Perspective
A rice farmer in eastern UP sees reddish-brown spots on 3-4 week old seedlings — Khaira disease, caused by zinc deficiency. A cauliflower grower in Punjab gets hollow stems — boron deficiency. An apple orchardist in Kashmir finds internal cork in his fruits — again boron. Despite using adequate NPK, these farmers lose 20-40% of their potential yield because they ignored trace elements. Micronutrients are needed in tiny amounts, but their absence causes devastating crop losses.
Micronutrient Concentrations at a Glance
NOTE
These are average plant concentrations. Despite being needed in tiny amounts (ppm), each is absolutely essential.
| Micronutrient | Symbol | Average Plant Concentration | Uptake Form |
|---|---|---|---|
| Chlorine | Cl | 100 ppm (0.01%) | Cl- |
| Iron | Fe | 100 ppm | Fe2+, Fe3+ |
| Manganese | Mn | 50 ppm | Mn2+ |
| Boron | B | 20 ppm | H3BO3, BO3- |
| Zinc | Zn | 20 ppm | Zn2+ |
| Copper | Cu | 6 ppm | Cu2+ |
| Molybdenum | Mo | 0.1 ppm | MoO42- |
| Nickel | Ni | 0.1-1.0 ppm | Ni2+ |
Iron (Fe)
Key Facts
| Property | Details |
|---|---|
| Earth crust | 5% Iron |
| Primary minerals | Olivine, Pyrite, Hematite, Goethite |
| pH relationship | 10-fold increase in Fe availability for each unit decrease in pH |
| Mobility in plant | Immobile — deficiency on younger leaves |
| Content in plants | 100 ppm |
Functions of Iron
| Function | Agricultural Significance |
|---|---|
| Biosynthesis of chlorophyll | Fe is not a part of chlorophyll but is essential for making it |
| Oxidation-reduction reactions | Regulates respiration, photosynthesis, nitrate and sulphate reduction |
| Component of porphyrin molecules | Cytochromes, hematin, hemes, ferrichrome, leghemoglobin |
| Component of ferredoxins (Fe-S proteins) | Non-heme iron compounds |
| Constituent of enzymes | Cytochrome oxidase, catalase, nitrogenase |
| Component of flavoproteins | FMN, FAD |
Chelates
- From Greek meaning “claw” — chelate molecules wrap around and grip metal ions
- Soluble organic compounds that keep Fe, Mn, Cu, Zn in soluble form, preventing fixation
- Natural chelates: products of microbial activity and organic matter degradation
- Citric acid and oxalic acid from root exudates have chelating properties
Deficiency of Iron
| Symptom | Details |
|---|---|
| Interveinal chlorosis of younger leaves | Principal veins remain conspicuously green; other portions turn yellow to white |
| Called “Iron chlorosis” or “Lime-induced chlorosis” ARS Mains-2017 | Common in calcareous/alkaline soils |
| Severe deficiency — leaves become “pale white” | Sharp distinction between veins and chlorotic areas |
| Brassica — necrotic terminal buds at early seedling stage | Growing point damage |
| Reddish-brown necrotic spots along leaf margins in tree crops | Young shoot damage |
Agricultural example: In the calcareous soils of Gujarat (pH > 8), sorghum and groundnut commonly show lime-induced iron chlorosis. Foliar spray of 0.5% FeSO4 + 0.25% citric acid provides quick correction.
Toxicity of Iron
| Condition | Details |
|---|---|
| Bronzing in rice | Fe levels > 300 ppm in leaf blade at tillering |
| Mechanism | Under waterlogging, Fe3+ reduces to highly soluble Fe2+ → excessive uptake |
| Akiochi disease in rice | Caused by both H2S toxicity and Fe deficiency |
Manganese (Mn)
Key Facts
| Property | Details |
|---|---|
| Earth crust | 1000 ppm |
| Primary minerals | Manganite MnO(OH), Braunite Mn2O3 |
| pH effect | Liming decreases Mn availability (precipitates as MnO2) |
| Content in plants | 25-500 mg/kg |
| Mobility in plant | Immobile — deficiency on younger leaves |
Functions of Manganese
| Function | Details |
|---|---|
| Water-splitting enzyme in Photosystem II | Without Mn, light reactions cannot proceed |
| Helps in chlorophyll formation | Essential for photosynthesis |
| Helps movement of Iron within plant | Fe translocation |
| Constituent of Mn-SOD (superoxide dismutase) | Protects cells against superoxide free radicals in mitochondria |
| Role in TCA cycle (respiration) | Oxidative and non-oxidative decarboxylation with NAD |
Deficiency of Manganese
| Symptom | Details |
|---|---|
| Interveinal chlorosis of young leaves | Chlorotic and necrotic spots between veins |
| Greyish areas near base of younger leaves | Become yellowish to yellow-orange |
| Chequered appearance of leaf | Principal and smaller veins stay green |
| Deficiency occurs when pH exceeds 6.5 | Mn tied up and unavailable |
Crop-specific Mn deficiency diseases:
| Crop | Disease Name |
|---|---|
| Oats | Gray Specks / Streaks |
| Peas | Marsh Spot |
| Sugarbeet | Speckled Yellow |
| Sugarcane | Pahala Blight / Streak Disease |
| Apple | Little Leaf (due to Mn, not Zn in apple) |
| Wheat | More susceptible to root rot disease |
TIP
Distinguishing Fe vs. Mn deficiency: Both cause interveinal chlorosis on young leaves. But Mn deficiency shows tan, sunken spots in chlorotic areas and a chequered pattern. Fe deficiency shows a sharper vein-interveinal contrast without sunken spots.
Toxicity of Manganese
- Crinkle Leaf of cotton — Mn toxicity in highly acid red-yellow soils
- Also affects tobacco, soybeans, tree fruits, rapeseed on extremely acid soils
Copper (Cu)
Key Facts
| Property | Details |
|---|---|
| pH effect | Cu availability decreases with increasing pH |
| Content in plants | 5-20 mg/kg |
| Uptake form | Cu2+ (cupric ion) |
| Poisonous | Even in very small excess concentrations |
Functions of Copper
| Function | Details |
|---|---|
| Essential for synthesis of Vitamin A | |
| Component of plastocyanin | Essential for electron transport in photosynthesis |
| Electron carrier in oxidation-reduction | Similar functions to Fe |
| Helps in chlorophyll synthesis | Via iron utilisation |
| Involved in SOD production (in stroma) | Protects thylakoids |
| Disease resistance | Strengthens cell walls |
| Pollen formation and fertilisation | Enhances male flower fertility |
| Ethylene biosynthesis | Fruit ripening |
| Indirectly affects nodule formation ICAR JRF 2016 | In legumes |
Deficiency of Copper
More prevalent in crops on peat and muck (organic) soils — these soils bind Cu strongly, leaving little available.
| Symptom | Details |
|---|---|
| White tips, narrow twisted leaves | Interveinal chlorotic mottling |
| Die-back of new growth | Necrosis of apical meristems |
| Pollen sterility | Critical stage: microsporogenesis — poor fruit set |
| Empty glumes in wheat | No grain formation |
| Tip drying and bluish-green leaf tips in rice |
Crop-specific Cu deficiency diseases:
| Crop | Disease Name |
|---|---|
| Citrus | Die Back, Exanthema, Gummosis, Little Leaf |
| Guava | Fruit cracking, terminal bud Die Back |
| Cereals | Reclamation disease, bleaching and withering of young leaves |
Agricultural example: In the newly reclaimed peat soils of Kerala’s Kuttanad region, copper deficiency is common in rice. Application of copper sulphate at 5-10 kg/ha corrects the problem.
Zinc (Zn)
NOTE
Zinc deficiency diseases are high-frequency exam topics: Rice (Khaira), Maize (White Bud), Citrus (Frenching/Mottle Leaf), Brinjal/Mango (Little Leaf), Potato (Fern Leaf).
Key Facts
| Property | Details |
|---|---|
| pH effect | Zn availability decreases with increasing pH; forms calcium zincate at high pH |
| Content in plants | 20-150 mg/kg; roots contain more Zn than fruits |
| Mobility | Limited mobility in plant; immobile in soil |
| Most common deficiency | In neutral and calcareous soils |
Functions of Zinc
| Function | Details |
|---|---|
| Constituent of 3 enzymes: Alcohol Dehydrogenase, Carbonic Anhydrase, SOD UPPSC 2021 | Regulates various metabolic reactions |
| Synthesis of IAA (Auxin) | Explains why Zn deficiency causes stunted growth and small leaves |
| Gibberellic acid metabolism and RNA synthesis | Growth hormone regulation |
| Photosynthesis, chlorophyll synthesis, protein synthesis | Broad metabolic role |
| Membrane protein stabilisation | Via sulfhydryl group binding |
| Influences P translocation | Zn deficiency → excessive P translocation → P toxicity |
Deficiency of Zinc
General symptoms: interveinal chlorosis, dead spots, dwarfing, rosetting (reduced internodes), chlorotic/brown rusty spots, lower auxin level.
Crop-specific Zn deficiency diseases:
| Crop | Disease Name | Key Symptom |
|---|---|---|
| Rice | Khaira Disease | Reddish-brown pigmentation on 3-4 week seedlings; papery necrotic tissue |
| Maize | White Bud | Light yellow areas between veins; white necrotic spots; emerging leaves yellow-white |
| Citrus | Mottle Leaf / Frenching | Mottled chlorosis |
| Brinjal, Mango, Cotton | Little Leaf | Reduced leaf size, shortened internodes |
| Potato | Fern Leaf | Fern-like leaf deformation |
| Fruit trees | Rosette | Clustering of small leaves at shoot tips |
Agricultural example: Khaira disease is one of the most widespread nutritional disorders of rice in India, especially in the alkaline soils of UP and Bihar. Basal application of ZnSO4 at 25 kg/ha prevents it effectively.
Toxicity of Zinc
- Excess Zn causes Fe deficiency due to cation competition
Boron (B)
NOTE
Boron deficiency diseases are among the most frequently asked topics: Apple (Fruit Cracking, Internal Cork), Cauliflower (Hollow Stem), Sugarbeet (Hollow Heart), Mango (Black Tip), Grape (Hen & Chicken).
Key Facts
| Property | Details |
|---|---|
| Only non-metal among micronutrients | |
| Content in plants | 10-200 mg/kg |
| Primary mineral | Tourmaline and borosilicates |
| Absorption form | H3BO3 (boric acid — neutral molecule, unlike other nutrients) |
| Mobility | Immobile in plants — deficiency on terminal buds/youngest leaves |
Functions of Boron
| Function | Agricultural Significance |
|---|---|
| New cell development in meristematic tissue | Essential for cell division |
| Cell wall formation and stabilisation, lignification, xylem differentiation | Structural role |
| Pollen germination and pollen tube growth | Without B, pollination fails → poor fruit/seed set |
| Translocation of sugars through cellular membranes | Prevents sugar polymerisation |
| Ca metabolism — keeps Ca soluble in cells | Regulator of K/Ca ratio |
| N and carbohydrate metabolism | Broad metabolic role |
| Water relations — prevents hydration of root tips | Strengthens roots |
| Disease resistance | Against virus, fungi, insects |
| Nodule formation in legumes | Important for N fixation |
Deficiency of Boron
General symptoms: terminal bud death/discolouration, rosetting, cracking/cork formation, shortened internodes.
Crop-specific B deficiency diseases:
| Crop | Disease Name |
|---|---|
| Apple | Fruit Cracking, Internal Cork IBPS AFO 2016 |
| Pomegranate | Fruit Cracking |
| Grape | Hen & Chicken Disease (small and large berries mixed) |
| Cauliflower | Browning / Hollow Stem |
| Sugarbeet | Hollow Heart / Heart Rot / Brown Heart |
| Mango | Necrosis / Black Tip |
| Tobacco | Top Sickness |
| Citrus | Fruit Cracking AFO 2017 |
| Orange | Bitter fruits with thickened peels, blackish discolouration |
| Papaya | Deformed fruits |
| Flowers | ”Blossom Blast” — flowers wilt, die, persist on tree |
Agricultural example: In apple orchards of Kashmir, internal cork causes unmarketable fruits. Foliar spray of 0.2% borax at pink bud stage prevents the problem.
Toxicity of Boron
- Yellowing of leaf tips and margins → scorching → early leaf drop
Molybdenum (Mo)
Key Facts
| Property | Details |
|---|---|
| Unique pH behaviour | Mo availability increases with increasing pH — only micronutrient that becomes more available as pH rises |
| Content in plants | 0.2-2 mg/kg |
| Called “Nano-nutrient” UPPSC 2021 | Needed in extremely small quantities |
| Liming | Increases Mo availability |
Functions of Molybdenum
| Function | Details |
|---|---|
| Component of nitrate reductase | Catalyses NO3- → NO2-; essential for N utilisation |
| Component of nitrogenase | Essential for N fixation in legumes |
| Required by N-fixing organisms | Azotobacter, Clostridium, Nostoc, Anabaena |
| Iron absorption and translocation | Essential for Fe metabolism |
| Phosphate system and ascorbic acid synthesis | Metabolic roles |
Deficiency of Molybdenum
| Symptom | Details |
|---|---|
| Chlorotic mottling between veins | Reddish/purplish discolouration, marginal necrosis |
| Brassica crops very susceptible | Symptoms develop in 3-4 week old plants |
| Cabbage/Cauliflower — Whiptail | Leaves twisted, elongated, browning |
| Citrus — Yellow Spot | Leaf yellowing |
| Legumes — symptoms resemble N deficiency | Because Mo is needed for N fixation in nodules |
| NO3 accumulation in plants | Inhibits N utilisation for protein synthesis |
Agricultural example: Cauliflower in the acidic soils of Jharkhand develops Whiptail because low pH reduces Mo availability. Liming the soil (not just applying Mo) is the long-term solution.
Chlorine (Cl)
Key Facts
| Property | Details |
|---|---|
| Plant concentration | 0.2-2.0% (100 ppm average) |
| Uptake form | Cl- through roots and aerial parts |
Functions of Chlorine
| Function | Details |
|---|---|
| O2 evolution in Photosystem II | Works alongside Mn in water-splitting |
| Stomata regulation | Counter ion for K+ fluxes in guard cells |
| Disease resistance | Increases osmotic pressure in cell sap |
| Turgor production in guard cells | Via osmotic pressure |
WARNING
Cl- makes tobacco leaves thick, brittle, and burn unevenly — so KCl (MOP) is avoided for tobacco; K2SO4 (SOP) is preferred. Cl- also interferes with starch formation, so is avoided in rice and potato.
Deficiency of Chlorine
- Wilted appearance, chlorotic mottling, bronzing, tissue necrosis in tomato
- Burning of tips and margins, over-wilting, leaf fall
Toxicity of Chlorine
- Bronze or yellow leaves with scorched margins
- Most sensitive crops: tobacco, legumes, potato, sugarcane
- Leaves thicken and roll; storage quality of potato tubers affected
Nickel (Ni)
Key Facts
| Property | Details |
|---|---|
| Plant concentration | 0.1-1.0 ppm |
| Most recently recognised | Essential micronutrient (added 1987) |
| Toxicity risk | High Ni from sewage sludge may induce Zn or Fe deficiency |
Functions of Nickel
| Function | Details |
|---|---|
| Metal component of urease enzyme | Without Ni, urease cannot function → toxic urea accumulates in leaf tips |
| Essential for N metabolism | |
| Stimulates nodule weight and crop yield | |
| Needed for grain filling and seed vitality |
Beneficial Elements
These are not essential for all plants but significantly boost growth or stress tolerance in specific crops.
| Element | Key Functions | Important Crops |
|---|---|---|
| Silicon (Si) | Strengthens cell walls, disease/pest resistance, reduces lodging, drought resistance. Si needed when rice straw < 11% Si | Rice, Sugarcane, Maize. Freckling in sugarcane = low Si symptom |
| Cobalt (Co) | Component of Vitamin B12; essential for leghemoglobin formation and N2 fixation by Rhizobium | Legumes (not essential for the plant itself, but for its N-fixing bacteria) |
| Sodium (Na) | Replaces K in C4/CAM plants; PEP regeneration; osmo-regulation; drought resistance | Sugarbeet, Turnip, C4 plants |
| Vanadium (V) | Substitutes for Mo in N fixation; beneficial for microorganism growth | Green algae, N-fixing bacteria |
| Selenium (Se) | Analogous to S; can replace S in methionine, cysteine, cystine synthesis; antioxidant | Important for animal nutrition via forages |
| Aluminium (Al) | Activator of glandular system at low concentration; toxic at higher amounts (damages root tips in acid soils) | Tea (stimulated by low Al) |
Nutrient Mobility and Absorption Summary
Absorption Speed
| Speed | Nutrients |
|---|---|
| Rapid | Urea Nitrogen, Potassium, Zinc |
| Moderate | Calcium, Sulfate, Manganese, Boron |
| Slow | Magnesium, Copper, Iron, Molybdenum |
Mobility in Soil
| Mobility | Nutrients |
|---|---|
| Highly mobile (prone to leaching) | NO3-, SO42-, Cl-, H2BO32-, Mn2+ |
| Moderately mobile | NH4+, K, Ca, Mg, Mo |
| Immobile | Organic N, P, Cu, Fe, Mn, Zn (chelated forms are mobile) |
Mobility in Plant
| Mobility | Nutrients | Deficiency Appears On |
|---|---|---|
| Highly mobile | N, P, K, Cl, Mo, Mg | Older leaves first |
| Moderately mobile | S, Cu, Fe, Mn, Zn | New growth |
| Immobile | B, Ca | Growing tips / youngest leaves |
Key Diagnostic Terms
| Term | Meaning | Caused by Deficiency of |
|---|---|---|
| Chlorosis | Yellowing of leaves | N, K, Fe, Mg, Mn, Zn, S |
| Mottled | Coloured spots (anthocyanin) on leaf surface | N, Mg, P, S |
| Necrosis | Patches of dead tissue | Mg, K, Zn, Ca, Mo |
Summary Table: Micronutrient Deficiency Diseases
| Crop | Disease | Nutrient Deficiency |
|---|---|---|
| Rice | Khaira Disease | Zn |
| Rice | Bronzing | Fe toxicity |
| Rice | Akiochi | H2S toxicity + Fe deficiency |
| Maize | White Bud | Zn |
| Oats | Gray Specks | Mn |
| Peas | Marsh Spot | Mn |
| Sugarbeet | Speckled Yellow | Mn |
| Sugarbeet | Hollow Heart | B |
| Sugarcane | Pahala Blight | Mn |
| Apple | Fruit Cracking / Internal Cork | B |
| Cauliflower | Hollow Stem / Browning | B |
| Cauliflower/Cabbage | Whiptail | Mo |
| Mango | Black Tip | B |
| Grape | Hen & Chicken | B |
| Citrus | Die Back / Exanthema | Cu |
| Citrus | Mottle Leaf / Frenching | Zn |
| Citrus | Yellow Spot | Mo |
| Potato | Fern Leaf | Zn |
| Tobacco | Top Sickness | B |
| Cotton | Crinkle Leaf | Mn toxicity |
| Wheat | Empty Glumes | Cu |
| Tea | Tea Yellows | S or Fe |
| Tobacco | Sand Drown | Mg |
TIP
Mnemonic for Boron deficiency crops: “Apple Cauliflower Sugarbeet Mango Grape Tobacco Citrus” — “A Careful Student Must Get Top Class” = all Boron deficiency!
References
- Tisdale, S.L., Nelson, W.L., Beaton, J.D., Havlin, J.L. 1997. Soil Fertility and Fertilizers. 5th ed. Prentice Hall of India, New Delhi.
- Singh, S.S. 1995. Soil Fertility and Nutrient Management. Kalyani Publishers, Ludhiana.
- Mortvedt, J.J. et al. (Eds.). Micronutrients in Agriculture. No.4, SSSA, Madison, Wisconsin, USA.
- IARI Toppers Soil Science Part-9 (6th Edition 2025).Pro Content Locked
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Why Micronutrients Matter: A Farmer’s Perspective
A rice farmer in eastern UP sees reddish-brown spots on 3-4 week old seedlings — Khaira disease, caused by zinc deficiency. A cauliflower grower in Punjab gets hollow stems — boron deficiency. An apple orchardist in Kashmir finds internal cork in his fruits — again boron. Despite using adequate NPK, these farmers lose 20-40% of their potential yield because they ignored trace elements. Micronutrients are needed in tiny amounts, but their absence causes devastating crop losses.
Micronutrient Concentrations at a Glance
NOTE
These are average plant concentrations. Despite being needed in tiny amounts (ppm), each is absolutely essential.
| Micronutrient | Symbol | Average Plant Concentration | Uptake Form |
|---|---|---|---|
| Chlorine | Cl | 100 ppm (0.01%) | Cl- |
| Iron | Fe | 100 ppm | Fe2+, Fe3+ |
| Manganese | Mn | 50 ppm | Mn2+ |
| Boron | B | 20 ppm | H3BO3, BO3- |
| Zinc | Zn | 20 ppm | Zn2+ |
| Copper | Cu | 6 ppm | Cu2+ |
| Molybdenum | Mo | 0.1 ppm | MoO42- |
| Nickel | Ni | 0.1-1.0 ppm | Ni2+ |
Iron (Fe)
Key Facts
| Property | Details |
|---|---|
| Earth crust | 5% Iron |
| Primary minerals | Olivine, Pyrite, Hematite, Goethite |
| pH relationship | 10-fold increase in Fe availability for each unit decrease in pH |
| Mobility in plant | Immobile — deficiency on younger leaves |
| Content in plants | 100 ppm |
Functions of Iron
| Function | Agricultural Significance |
|---|---|
| Biosynthesis of chlorophyll | Fe is not a part of chlorophyll but is essential for making it |
| Oxidation-reduction reactions | Regulates respiration, photosynthesis, nitrate and sulphate reduction |
| Component of porphyrin molecules | Cytochromes, hematin, hemes, ferrichrome, leghemoglobin |
| Component of ferredoxins (Fe-S proteins) | Non-heme iron compounds |
| Constituent of enzymes | Cytochrome oxidase, catalase, nitrogenase |
| Component of flavoproteins | FMN, FAD |
Chelates
- From Greek meaning “claw” — chelate molecules wrap around and grip metal ions
- Soluble organic compounds that keep Fe, Mn, Cu, Zn in soluble form, preventing fixation
- Natural chelates: products of microbial activity and organic matter degradation
- Citric acid and oxalic acid from root exudates have chelating properties
Deficiency of Iron
| Symptom | Details |
|---|---|
| Interveinal chlorosis of younger leaves | Principal veins remain conspicuously green; other portions turn yellow to white |
| Called “Iron chlorosis” or “Lime-induced chlorosis” ARS Mains-2017 | Common in calcareous/alkaline soils |
| Severe deficiency — leaves become “pale white” | Sharp distinction between veins and chlorotic areas |
| Brassica — necrotic terminal buds at early seedling stage | Growing point damage |
| Reddish-brown necrotic spots along leaf margins in tree crops | Young shoot damage |
Agricultural example: In the calcareous soils of Gujarat (pH > 8), sorghum and groundnut commonly show lime-induced iron chlorosis. Foliar spray of 0.5% FeSO4 + 0.25% citric acid provides quick correction.
Toxicity of Iron
| Condition | Details |
|---|---|
| Bronzing in rice | Fe levels > 300 ppm in leaf blade at tillering |
| Mechanism | Under waterlogging, Fe3+ reduces to highly soluble Fe2+ → excessive uptake |
| Akiochi disease in rice | Caused by both H2S toxicity and Fe deficiency |
Manganese (Mn)
Key Facts
| Property | Details |
|---|---|
| Earth crust | 1000 ppm |
| Primary minerals | Manganite MnO(OH), Braunite Mn2O3 |
| pH effect | Liming decreases Mn availability (precipitates as MnO2) |
| Content in plants | 25-500 mg/kg |
| Mobility in plant | Immobile — deficiency on younger leaves |
Functions of Manganese
| Function | Details |
|---|---|
| Water-splitting enzyme in Photosystem II | Without Mn, light reactions cannot proceed |
| Helps in chlorophyll formation | Essential for photosynthesis |
| Helps movement of Iron within plant | Fe translocation |
| Constituent of Mn-SOD (superoxide dismutase) | Protects cells against superoxide free radicals in mitochondria |
| Role in TCA cycle (respiration) | Oxidative and non-oxidative decarboxylation with NAD |
Deficiency of Manganese
| Symptom | Details |
|---|---|
| Interveinal chlorosis of young leaves | Chlorotic and necrotic spots between veins |
| Greyish areas near base of younger leaves | Become yellowish to yellow-orange |
| Chequered appearance of leaf | Principal and smaller veins stay green |
| Deficiency occurs when pH exceeds 6.5 | Mn tied up and unavailable |
Crop-specific Mn deficiency diseases:
| Crop | Disease Name |
|---|---|
| Oats | Gray Specks / Streaks |
| Peas | Marsh Spot |
| Sugarbeet | Speckled Yellow |
| Sugarcane | Pahala Blight / Streak Disease |
| Apple | Little Leaf (due to Mn, not Zn in apple) |
| Wheat | More susceptible to root rot disease |
TIP
Distinguishing Fe vs. Mn deficiency: Both cause interveinal chlorosis on young leaves. But Mn deficiency shows tan, sunken spots in chlorotic areas and a chequered pattern. Fe deficiency shows a sharper vein-interveinal contrast without sunken spots.
Toxicity of Manganese
- Crinkle Leaf of cotton — Mn toxicity in highly acid red-yellow soils
- Also affects tobacco, soybeans, tree fruits, rapeseed on extremely acid soils
Copper (Cu)
Key Facts
| Property | Details |
|---|---|
| pH effect | Cu availability decreases with increasing pH |
| Content in plants | 5-20 mg/kg |
| Uptake form | Cu2+ (cupric ion) |
| Poisonous | Even in very small excess concentrations |
Functions of Copper
| Function | Details |
|---|---|
| Essential for synthesis of Vitamin A | |
| Component of plastocyanin | Essential for electron transport in photosynthesis |
| Electron carrier in oxidation-reduction | Similar functions to Fe |
| Helps in chlorophyll synthesis | Via iron utilisation |
| Involved in SOD production (in stroma) | Protects thylakoids |
| Disease resistance | Strengthens cell walls |
| Pollen formation and fertilisation | Enhances male flower fertility |
| Ethylene biosynthesis | Fruit ripening |
| Indirectly affects nodule formation ICAR JRF 2016 | In legumes |
Deficiency of Copper
More prevalent in crops on peat and muck (organic) soils — these soils bind Cu strongly, leaving little available.
| Symptom | Details |
|---|---|
| White tips, narrow twisted leaves | Interveinal chlorotic mottling |
| Die-back of new growth | Necrosis of apical meristems |
| Pollen sterility | Critical stage: microsporogenesis — poor fruit set |
| Empty glumes in wheat | No grain formation |
| Tip drying and bluish-green leaf tips in rice |
Crop-specific Cu deficiency diseases:
| Crop | Disease Name |
|---|---|
| Citrus | Die Back, Exanthema, Gummosis, Little Leaf |
| Guava | Fruit cracking, terminal bud Die Back |
| Cereals | Reclamation disease, bleaching and withering of young leaves |
Agricultural example: In the newly reclaimed peat soils of Kerala’s Kuttanad region, copper deficiency is common in rice. Application of copper sulphate at 5-10 kg/ha corrects the problem.
Zinc (Zn)
NOTE
Zinc deficiency diseases are high-frequency exam topics: Rice (Khaira), Maize (White Bud), Citrus (Frenching/Mottle Leaf), Brinjal/Mango (Little Leaf), Potato (Fern Leaf).
Key Facts
| Property | Details |
|---|---|
| pH effect | Zn availability decreases with increasing pH; forms calcium zincate at high pH |
| Content in plants | 20-150 mg/kg; roots contain more Zn than fruits |
| Mobility | Limited mobility in plant; immobile in soil |
| Most common deficiency | In neutral and calcareous soils |
Functions of Zinc
| Function | Details |
|---|---|
| Constituent of 3 enzymes: Alcohol Dehydrogenase, Carbonic Anhydrase, SOD UPPSC 2021 | Regulates various metabolic reactions |
| Synthesis of IAA (Auxin) | Explains why Zn deficiency causes stunted growth and small leaves |
| Gibberellic acid metabolism and RNA synthesis | Growth hormone regulation |
| Photosynthesis, chlorophyll synthesis, protein synthesis | Broad metabolic role |
| Membrane protein stabilisation | Via sulfhydryl group binding |
| Influences P translocation | Zn deficiency → excessive P translocation → P toxicity |
Deficiency of Zinc
General symptoms: interveinal chlorosis, dead spots, dwarfing, rosetting (reduced internodes), chlorotic/brown rusty spots, lower auxin level.
Crop-specific Zn deficiency diseases:
| Crop | Disease Name | Key Symptom |
|---|---|---|
| Rice | Khaira Disease | Reddish-brown pigmentation on 3-4 week seedlings; papery necrotic tissue |
| Maize | White Bud | Light yellow areas between veins; white necrotic spots; emerging leaves yellow-white |
| Citrus | Mottle Leaf / Frenching | Mottled chlorosis |
| Brinjal, Mango, Cotton | Little Leaf | Reduced leaf size, shortened internodes |
| Potato | Fern Leaf | Fern-like leaf deformation |
| Fruit trees | Rosette | Clustering of small leaves at shoot tips |
Agricultural example: Khaira disease is one of the most widespread nutritional disorders of rice in India, especially in the alkaline soils of UP and Bihar. Basal application of ZnSO4 at 25 kg/ha prevents it effectively.
Toxicity of Zinc
- Excess Zn causes Fe deficiency due to cation competition
Boron (B)
NOTE
Boron deficiency diseases are among the most frequently asked topics: Apple (Fruit Cracking, Internal Cork), Cauliflower (Hollow Stem), Sugarbeet (Hollow Heart), Mango (Black Tip), Grape (Hen & Chicken).
Key Facts
| Property | Details |
|---|---|
| Only non-metal among micronutrients | |
| Content in plants | 10-200 mg/kg |
| Primary mineral | Tourmaline and borosilicates |
| Absorption form | H3BO3 (boric acid — neutral molecule, unlike other nutrients) |
| Mobility | Immobile in plants — deficiency on terminal buds/youngest leaves |
Functions of Boron
| Function | Agricultural Significance |
|---|---|
| New cell development in meristematic tissue | Essential for cell division |
| Cell wall formation and stabilisation, lignification, xylem differentiation | Structural role |
| Pollen germination and pollen tube growth | Without B, pollination fails → poor fruit/seed set |
| Translocation of sugars through cellular membranes | Prevents sugar polymerisation |
| Ca metabolism — keeps Ca soluble in cells | Regulator of K/Ca ratio |
| N and carbohydrate metabolism | Broad metabolic role |
| Water relations — prevents hydration of root tips | Strengthens roots |
| Disease resistance | Against virus, fungi, insects |
| Nodule formation in legumes | Important for N fixation |
Deficiency of Boron
General symptoms: terminal bud death/discolouration, rosetting, cracking/cork formation, shortened internodes.
Crop-specific B deficiency diseases:
| Crop | Disease Name |
|---|---|
| Apple | Fruit Cracking, Internal Cork IBPS AFO 2016 |
| Pomegranate | Fruit Cracking |
| Grape | Hen & Chicken Disease (small and large berries mixed) |
| Cauliflower | Browning / Hollow Stem |
| Sugarbeet | Hollow Heart / Heart Rot / Brown Heart |
| Mango | Necrosis / Black Tip |
| Tobacco | Top Sickness |
| Citrus | Fruit Cracking AFO 2017 |
| Orange | Bitter fruits with thickened peels, blackish discolouration |
| Papaya | Deformed fruits |
| Flowers | ”Blossom Blast” — flowers wilt, die, persist on tree |
Agricultural example: In apple orchards of Kashmir, internal cork causes unmarketable fruits. Foliar spray of 0.2% borax at pink bud stage prevents the problem.
Toxicity of Boron
- Yellowing of leaf tips and margins → scorching → early leaf drop
Molybdenum (Mo)
Key Facts
| Property | Details |
|---|---|
| Unique pH behaviour | Mo availability increases with increasing pH — only micronutrient that becomes more available as pH rises |
| Content in plants | 0.2-2 mg/kg |
| Called “Nano-nutrient” UPPSC 2021 | Needed in extremely small quantities |
| Liming | Increases Mo availability |
Functions of Molybdenum
| Function | Details |
|---|---|
| Component of nitrate reductase | Catalyses NO3- → NO2-; essential for N utilisation |
| Component of nitrogenase | Essential for N fixation in legumes |
| Required by N-fixing organisms | Azotobacter, Clostridium, Nostoc, Anabaena |
| Iron absorption and translocation | Essential for Fe metabolism |
| Phosphate system and ascorbic acid synthesis | Metabolic roles |
Deficiency of Molybdenum
| Symptom | Details |
|---|---|
| Chlorotic mottling between veins | Reddish/purplish discolouration, marginal necrosis |
| Brassica crops very susceptible | Symptoms develop in 3-4 week old plants |
| Cabbage/Cauliflower — Whiptail | Leaves twisted, elongated, browning |
| Citrus — Yellow Spot | Leaf yellowing |
| Legumes — symptoms resemble N deficiency | Because Mo is needed for N fixation in nodules |
| NO3 accumulation in plants | Inhibits N utilisation for protein synthesis |
Agricultural example: Cauliflower in the acidic soils of Jharkhand develops Whiptail because low pH reduces Mo availability. Liming the soil (not just applying Mo) is the long-term solution.
Chlorine (Cl)
Key Facts
| Property | Details |
|---|---|
| Plant concentration | 0.2-2.0% (100 ppm average) |
| Uptake form | Cl- through roots and aerial parts |
Functions of Chlorine
| Function | Details |
|---|---|
| O2 evolution in Photosystem II | Works alongside Mn in water-splitting |
| Stomata regulation | Counter ion for K+ fluxes in guard cells |
| Disease resistance | Increases osmotic pressure in cell sap |
| Turgor production in guard cells | Via osmotic pressure |
WARNING
Cl- makes tobacco leaves thick, brittle, and burn unevenly — so KCl (MOP) is avoided for tobacco; K2SO4 (SOP) is preferred. Cl- also interferes with starch formation, so is avoided in rice and potato.
Deficiency of Chlorine
- Wilted appearance, chlorotic mottling, bronzing, tissue necrosis in tomato
- Burning of tips and margins, over-wilting, leaf fall
Toxicity of Chlorine
- Bronze or yellow leaves with scorched margins
- Most sensitive crops: tobacco, legumes, potato, sugarcane
- Leaves thicken and roll; storage quality of potato tubers affected
Nickel (Ni)
Key Facts
| Property | Details |
|---|---|
| Plant concentration | 0.1-1.0 ppm |
| Most recently recognised | Essential micronutrient (added 1987) |
| Toxicity risk | High Ni from sewage sludge may induce Zn or Fe deficiency |
Functions of Nickel
| Function | Details |
|---|---|
| Metal component of urease enzyme | Without Ni, urease cannot function → toxic urea accumulates in leaf tips |
| Essential for N metabolism | |
| Stimulates nodule weight and crop yield | |
| Needed for grain filling and seed vitality |
Beneficial Elements
These are not essential for all plants but significantly boost growth or stress tolerance in specific crops.
| Element | Key Functions | Important Crops |
|---|---|---|
| Silicon (Si) | Strengthens cell walls, disease/pest resistance, reduces lodging, drought resistance. Si needed when rice straw < 11% Si | Rice, Sugarcane, Maize. Freckling in sugarcane = low Si symptom |
| Cobalt (Co) | Component of Vitamin B12; essential for leghemoglobin formation and N2 fixation by Rhizobium | Legumes (not essential for the plant itself, but for its N-fixing bacteria) |
| Sodium (Na) | Replaces K in C4/CAM plants; PEP regeneration; osmo-regulation; drought resistance | Sugarbeet, Turnip, C4 plants |
| Vanadium (V) | Substitutes for Mo in N fixation; beneficial for microorganism growth | Green algae, N-fixing bacteria |
| Selenium (Se) | Analogous to S; can replace S in methionine, cysteine, cystine synthesis; antioxidant | Important for animal nutrition via forages |
| Aluminium (Al) | Activator of glandular system at low concentration; toxic at higher amounts (damages root tips in acid soils) | Tea (stimulated by low Al) |
Nutrient Mobility and Absorption Summary
Absorption Speed
| Speed | Nutrients |
|---|---|
| Rapid | Urea Nitrogen, Potassium, Zinc |
| Moderate | Calcium, Sulfate, Manganese, Boron |
| Slow | Magnesium, Copper, Iron, Molybdenum |
Mobility in Soil
| Mobility | Nutrients |
|---|---|
| Highly mobile (prone to leaching) | NO3-, SO42-, Cl-, H2BO32-, Mn2+ |
| Moderately mobile | NH4+, K, Ca, Mg, Mo |
| Immobile | Organic N, P, Cu, Fe, Mn, Zn (chelated forms are mobile) |
Mobility in Plant
| Mobility | Nutrients | Deficiency Appears On |
|---|---|---|
| Highly mobile | N, P, K, Cl, Mo, Mg | Older leaves first |
| Moderately mobile | S, Cu, Fe, Mn, Zn | New growth |
| Immobile | B, Ca | Growing tips / youngest leaves |
Key Diagnostic Terms
| Term | Meaning | Caused by Deficiency of |
|---|---|---|
| Chlorosis | Yellowing of leaves | N, K, Fe, Mg, Mn, Zn, S |
| Mottled | Coloured spots (anthocyanin) on leaf surface | N, Mg, P, S |
| Necrosis | Patches of dead tissue | Mg, K, Zn, Ca, Mo |
Summary Table: Micronutrient Deficiency Diseases
| Crop | Disease | Nutrient Deficiency |
|---|---|---|
| Rice | Khaira Disease | Zn |
| Rice | Bronzing | Fe toxicity |
| Rice | Akiochi | H2S toxicity + Fe deficiency |
| Maize | White Bud | Zn |
| Oats | Gray Specks | Mn |
| Peas | Marsh Spot | Mn |
| Sugarbeet | Speckled Yellow | Mn |
| Sugarbeet | Hollow Heart | B |
| Sugarcane | Pahala Blight | Mn |
| Apple | Fruit Cracking / Internal Cork | B |
| Cauliflower | Hollow Stem / Browning | B |
| Cauliflower/Cabbage | Whiptail | Mo |
| Mango | Black Tip | B |
| Grape | Hen & Chicken | B |
| Citrus | Die Back / Exanthema | Cu |
| Citrus | Mottle Leaf / Frenching | Zn |
| Citrus | Yellow Spot | Mo |
| Potato | Fern Leaf | Zn |
| Tobacco | Top Sickness | B |
| Cotton | Crinkle Leaf | Mn toxicity |
| Wheat | Empty Glumes | Cu |
| Tea | Tea Yellows | S or Fe |
| Tobacco | Sand Drown | Mg |
TIP
Mnemonic for Boron deficiency crops: “Apple Cauliflower Sugarbeet Mango Grape Tobacco Citrus” — “A Careful Student Must Get Top Class” = all Boron deficiency!
References
- Tisdale, S.L., Nelson, W.L., Beaton, J.D., Havlin, J.L. 1997. Soil Fertility and Fertilizers. 5th ed. Prentice Hall of India, New Delhi.
- Singh, S.S. 1995. Soil Fertility and Nutrient Management. Kalyani Publishers, Ludhiana.
- Mortvedt, J.J. et al. (Eds.). Micronutrients in Agriculture. No.4, SSSA, Madison, Wisconsin, USA.
- IARI Toppers Soil Science Part-9 (6th Edition 2025).Knowledge Check
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