Essential Plant Micronutrients and Physiological Roles
Out of the 17 essential plant nutrients recognized in agronomy, eight are classified as micronutrients: Zinc (Zn), Iron (Fe), Boron (B), Manganese (Mn), Copper (Cu), Molybdenum (Mo), Chlorine (Cl), and Nickel (Ni). Although required in trace concentrations, their absence arrests crop growth.
Zinc powers tryptophan synthesis (precursor to auxin plant hormone); Iron drives electron transfer and chlorophyll biosynthesis; Boron governs cell wall pectin structure and pollen tube elongation; and Manganese catalyzes photosynthetic water-splitting in Photosystem II.
- Zinc (Zn): Essential for auxin growth hormone production, protein synthesis, and internodal elongation.
- Iron (Fe): Catalyst for chlorophyll synthesis, respiration, and nitrogenase activity in legumes.
- Boron (B): Critical for pollen viability, flowering, fruit setting, and carbohydrate translocation.
- Manganese (Mn) & Copper (Cu): Catalyze enzymatic redox reactions, lignin synthesis, and disease defense.
Visual Deficiency Symptoms Across Field Crops
Because micronutrient mobility varies within plant tissues, deficiency symptoms exhibit characteristic visual spatial patterns. Zinc deficiency appears on middle and lower leaves as bleached bands or 'khaira' rust-brown mottling in rice.
Iron deficiency manifests as severe interveinal chlorosis on the youngest emerging terminal leaves, turning yellow-white while veins stay green. Boron deficiency causes brittle leaves, hollow heart in cauliflower, and fruit cracking in tomato and pomegranate.
- Rice Khaira Disease: Classic zinc deficiency causing rusty brown pigmentation and stunted tillering.
- Iron Chlorosis: Bleaching of youngest leaves in high-pH calcareous soils where iron precipitates into insoluble forms.
- Boron Deficiencies: Internal corking in apples, flower bud abortion in cotton, and grain sterility in wheat.
Soil Application and Chelated Foliar Sprays
Correcting trace mineral shortages requires soil or foliar replenishment using products regulated under the Fertilizer (Control) Order (FCO). Basal soil dressing utilizes inorganic mineral salts like Zinc Sulphate (21% or 33%) and Borax or Disodium Octaborate Tetrahydrate (DOT).
Under high soil pH (alkaline or calcareous conditions) where soil-applied minerals become locked up, foliar spraying of chelated micronutrients (such as Zn-EDTA 12% and Fe-EDTA 12%) provides rapid leaf absorption and greening within 48 to 72 hours.
- Basal Dressing: Incorporate Zinc Sulphate during final land preparation to provide root-zone reserves.
- Chelated Foliar Sprays: Use EDTA-chelated micronutrients for rapid correction without soil fixation.
- Soil Health Card Guidance: Test soil samples to apply only deficient elements, avoiding micronutrient toxicity.
Official source
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Soil Health Card Portal, Ministry of Agriculture & Farmers Welfare ↗Related on KisanPe
Common questions
Which micronutrient deficiency is most widespread in Indian soils?
Zinc (Zn) deficiency is the most widespread trace mineral shortage across Indian agricultural soils, affecting over 40% of tested parcels.
What causes Khaira disease in rice?
Khaira disease is caused by severe zinc deficiency, resulting in stunted seedlings and rusty bronze leaf discoloration.
Why are chelated micronutrients preferred for foliar sprays?
EDTA chelates protect trace metal ions from precipitation and chemical lock-up, ensuring rapid stomatal absorption through crop leaves.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
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