🍡 Micronutrients: Fe, Mn, Cu, Zn, B, Mo, Cl, Ni & Beneficial Elements

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.

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Micronutrient Concentrations at a Glance

This gallery groups the most tested micronutrient deficiency visuals so symptom-based MCQs can be revised from one place.

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+

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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.