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Phosphorus deficiency limits root development, tillering, and early crop vigor. It is common on acid upland soils, weathered soils, and cold-water-fed paddies. P is immobile in soil, so early basal placement matters more than for any other nutrient.

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When rice is most vulnerable

Early - from seedling through active tillering. Correction after panicle initiation has almost no yield benefit.

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How phosphorus deficiency shows in satellite data

  • Persistently low NDVI at establishment on affected zones - the field never reaches the expected early-season NDVI band for its ecosystem.
  • Tillering is reduced, so canopy closure is delayed - visible as low ground cover in mid-season imagery.
  • Signature overlaps with poor soil and cold stress; separate them using soil map, water source, and the reddish leaf color on the ground.

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Field symptoms

  • Dark-green, narrow, erect leaves (the classic P-deficient look)
  • Stunted plants with very few tillers
  • Older leaves develop reddish-purple discoloration on cultivars able to produce anthocyanin
  • Delayed maturity
  • Small panicles and poor grain filling

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Reduce the damage by

  • Basal placement of P fertilizer at or before transplanting - P does not move in soil.
  • Apply lime on acid soils (pH below 5.5) to raise P availability.
  • Use P-tolerant cultivars where soil P is chronically low.
  • Add organic amendments (compost, farmyard manure) to slowly build available P and reduce P fixation on iron and aluminum oxides.
  • Do not skip starter P even when soil test values look adequate on newly cleared or long-fallowed land.

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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 weak establishment on P-limited zones is flagged in time to intervene at tillering.
Recommended settings for phosphorus on rice:
  • NDVI threshold alert at 21 to 30 days after transplanting - trigger when NDVI stays below your ecosystem baseline for two consecutive passes.
  • Seasonal review of zones that consistently underperform at establishment - correct with basal P next season, not with rescue applications this one. Compare like season with like: main against main, off against off.