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Iron toxicity is common on acid sulfate soils, low-lying valley bottoms, and inland valleys with prolonged flooding. Under strong soil reduction, iron becomes soluble at concentrations that damage rice roots and leaves. It is a toxicity, not a deficiency, and it responds to water and pH management more than to fertilizer.

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When rice is most vulnerable

From seedling establishment through early tillering. Severe iron toxicity can kill young plants; moderate cases stunt tillering and cap final yield.

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How iron toxicity shows in satellite data

  • Low, patchy NDVI in low-lying zones and toe-slopes where water accumulates and stays reduced.
  • Same zones affected season after season, closely correlated with elevation and drainage.
  • Signature overlaps with poor soil, submergence, and salinity - use soil pH, standing water depth, and the bronze leaf color on the ground to separate them.

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Field symptoms

  • Tiny brown to bronze-orange stipples on lower leaves, spreading and coalescing into a bronzed appearance
  • Purplish-brown streaks along the leaf blade in some cultivars
  • Stunted plants with limited tillering and dark, blackened, sparse root system
  • Yellow-orange discoloration in severe cases, mistaken for tungro or N deficiency
  • Affected patches follow topography (low spots, water-collecting zones)

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Reduce the damage by

  • Improve drainage - alternate wetting and drying reduces soil reduction and iron solubility.
  • Delay transplanting by a few weeks on affected fields to let reduction subside after initial flooding.
  • Apply lime on acid soils (pH below 5.0) to precipitate iron.
  • Use iron-toxicity-tolerant cultivars such as those released from Africa Rice and IRRI screening for iron-toxic environments.
  • Balance nutrients - adequate P, K, and Zn reduce the severity of iron toxicity symptoms.
  • Do not confuse with brown spot or tungro - confirm with soil pH and water history.

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Set an alert for early warning

Turn the diagnosis into a trigger. Go to the Alerts page and configure a rule so low-lying iron-toxic zones are flagged within weeks of transplanting.
Recommended settings for iron toxicity on rice:
  • NDVI threshold alert on flagged low-lying zones at 14 to 30 days after transplanting.
  • Seasonal review - iron toxicity is chronic and zone-specific; combine alert data with a prescription map for zone-specific drainage and cultivar planning.