Role of Iron in Crops and Chlorosis Identification
Iron is an indispensable micronutrient required for chlorophyll biosynthesis, enzymatic electron transfer during photosynthesis, and respiration in plant cells. Because iron is immobile within plant vascular systems, deficiency symptoms manifest first on the youngest expanding leaves.
Iron chlorosis is characterized by distinct interveinal yellowing: the veins remain visibly green while the intervening leaf lamina turns pale yellow, ivory, or completely bleached white. Severe deficiency leads to leaf necrosis, stunted shoot extension, flower drop, and drastic yield losses.
- Key Symptom: Interveinal chlorosis on youngest leaves, where veins stay dark green against yellow leaf tissue.
- High-Risk Soils: Calcareous soils with high calcium carbonate, alkaline soils with pH above 7.5, and compacted or waterlogged soils.
- Crop Susceptibility: Highly susceptible crops include groundnut, sugarcane, citrus, grapes, apples, pulses, and paddy nurseries.
Soil Application and Foliar Correction Techniques
In alkaline and calcareous soils, direct soil application of unchelated ferrous sulfate is often inefficient because soluble ferrous ions (Fe2+) rapidly oxidize and precipitate into insoluble ferric hydroxides inaccessible to roots. To improve soil uptake, farmers mix ferrous sulfate with well-rotted farmyard manure (FYM) or compost before basal banding.
For rapid rescue of standing crops suffering from iron chlorosis, foliar spraying of diluted ferrous sulfate (commonly at 0.5 percent concentration with a small quantity of citric acid to maintain acidic solution pH) delivers direct uptake through leaf stomata, restoring chlorophyll within 5 to 7 days.
- Foliar Rescue Spray: Dissolve ferrous sulfate in clean water with citric acid or lime to buffer pH and prevent leaf scorch.
- Enriched Compost Application: Blend ferrous sulfate with organic manure or vermicompost prior to soil application to improve iron availability.
- Multiple Foliar Passes: Repeat foliar sprays 2 to 3 times at 10-day intervals for severe deficiency symptoms.
- Timing: Apply foliar treatments during early morning or late afternoon to maximize absorption and avoid evaporation.
Fertilizer Standards and Application Precautions
Under the Fertilizer (Inorganic, Organic or Mixed) (Control) Order (FCO), agricultural-grade ferrous sulfate heptahydrate must contain a minimum of 19 percent water-soluble iron and conform to strict moisture and heavy metal limits.
Do not mix ferrous sulfate with phosphatic fertilizers or strongly alkaline crop protection chemicals in spray tanks, as this causes chemical precipitation and clogged spray nozzles. Store bags in a dry, shaded warehouse to prevent oxidation and caking.
- FCO Compliance: Confirm certified nutrient purity (19% Fe) under official Fertilizer Control Order specifications.
- Incompatibility: Avoid tank-mixing with phosphatic fertilizers (DAP, SSP) or alkaline pesticides that precipitate iron.
- Storage Care: Keep containers airtight to protect ferrous crystals from atmospheric oxidation into insoluble ferric iron.
Official source
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Department of Agriculture and Farmers Welfare (FCO) ↗Related on KisanPe
Common questions
What causes iron deficiency in Indian agricultural soils?
Iron deficiency commonly occurs in alkaline and calcareous soils where high pH (above 7.5) and abundant calcium carbonate convert soluble iron into insoluble chemical forms that plant roots cannot absorb.
How can a farmer distinguish iron deficiency from magnesium deficiency?
Iron is immobile and shows interveinal chlorosis on the youngest upper leaves first, whereas magnesium is mobile and shows chlorosis on the oldest lower leaves first.
Why is foliar spray often preferred over soil application for ferrous sulfate?
In alkaline soils, soil-applied ferrous sulfate quickly precipitates into unavailable forms; foliar spraying bypasses soil lockup, supplying iron directly through leaf tissues for rapid greening.
Why is citric acid added when preparing a ferrous sulfate foliar spray?
Adding a small quantity of citric acid keeps the spray water slightly acidic, chelating the iron ions and preventing ferrous iron from oxidizing into insoluble ferric precipitates.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
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