> ## Documentation Index
> Fetch the complete documentation index at: https://badixth-dc85e378.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Diagnose and Respond to Phosphorus Deficiency in Rice

> Identify phosphorus deficiency in paddy from dark-green stunted plants with reddish-purple older leaves, and correct it with basal P placement and lime on acid soils.

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.

## When rice is most vulnerable

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

## 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](/guides/Crop/Rice/rice-ecosystems).
* 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.

## 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

## 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.

## Set an alert for early warning

<Tip>
  Turn the diagnosis into a trigger. Go to the [Alerts](/guides/alerts-notifications) page and configure a rule so weak establishment on P-limited zones is flagged in time to intervene at tillering.
</Tip>

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](/guides/Crop/Rice/rice-ecosystems#main-season-and-off-season-are-not-the-same-crop).

## Related

* [Rice Diagnosis](/guides/Crop/Rice/rice-abiotic-stress)
* [Rice: Poor Soil](/guides/Crop/Rice/rice-abiotic-stress/rice-poor-soil) - overlapping signature and often overlapping cause.
* [Set up automated crop alerts](/guides/alerts-notifications)