> ## 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.

# Phosphorus Deficiency in Rubber

> How phosphorus deficiency limits rubber girth increment and root development, Whorl 2 tissue thresholds, and the fertilizer program for acid tropical soils.

Phosphorus is the key nutrient for root development and girth increment in immature rubber. Most Malaysian tropical soils are P-fixing (acid, high in Fe/Al oxides), so P is often the limiting factor on new plantings, even where total soil P is adequate.

## Cause

* **Acid soils** (pH \< 5) with high P fixation by Fe and Al oxides
* **Peat soils** with P bound in organic form
* **No P fertilizer** at planting (rock phosphate application missed)
* **Erosion** on hilly blocks removing topsoil

## Effect

| Stand age    | Symptom                                                           |
| ------------ | ----------------------------------------------------------------- |
| 0 to 3 years | Slow girth increment, poor root development, delayed canopy build |
| 3 to 5 years | Delayed opening for tapping (year 7-8 instead of year 5-6)        |
| 5+ years     | Chronically low yield, thin canopy                                |

Field signs:

* Small dark-green leaves (as opposed to N deficiency which is pale green)
* Reduced leaf size on new flush
* Purple-red tint on older leaves in severe cases
* Poor root development visible at collar scraping
* Slow girth increment (measure at 150 cm; \< 5 cm/year on immature blocks flags P deficiency)

## Leaf-tissue thresholds

Sample **Whorl 2** leaves.

| P level (% dry weight) | Interpretation |
| ---------------------- | -------------- |
| \< 0.20                | Deficient      |
| 0.20 to 0.23           | Marginal       |
| 0.23 to 0.28           | Optimal        |
| > 0.28                 | High           |

<Warning>
  This is a **generic band for the crop**, with no site, soil, clone, age or season qualifier. `Deficient` and `Optimal` resolve. **`Marginal` does not** — that tier exists because the transition is not sharp. **`High` does not either**, because no page states what High means or what to do about it. And where more than one nutrient reads deficient, **only the most deficient rating is valid.** See [Reading a tissue analysis](/snippets/tissue-diagnosis).
</Warning>

## Satellite signals

P deficiency has no strong satellite signal. Diagnosis is by tissue analysis and girth measurement. Slow canopy build on immature blocks is the main indirect signal.

| Index              | What to watch                  | Threshold      |
| ------------------ | ------------------------------ | -------------- |
| NDVI (immature)    | Slow rise vs age-band baseline | -0.05 for age  |
| Canopy closure age | > 6 years vs expected 5        | Direct measure |

## Action

<Steps>
  <Step title="Confirm with tissue and soil test">
    P deficiency is confirmed by Whorl 2 tissue \< 0.20% combined with soil P (Bray-1) \< 15 ppm.
  </Step>

  <Step title="Apply rock phosphate at planting">
    Best practice: 250 to 500 g rock phosphate per planting hole, mixed with topsoil.
  </Step>

  <Step title="Corrective application on established blocks">
    Triple super phosphate (TSP) or Christmas Island rock phosphate:

    * Immature: 100 to 200 g TSP/tree/year
    * Mature: 100 to 150 g TSP/tree/year (P demand is low once canopy is established)
  </Step>

  <Step title="Address soil acidity">
    Lime application (500 kg to 1 t/ha ground magnesium limestone) raises pH and reduces P fixation. Especially important on peat and very acid mineral soils.
  </Step>
</Steps>

## Recommended alert settings

| Trigger                | Condition                                       | Severity |
| ---------------------- | ----------------------------------------------- | -------- |
| Leaf tissue P          | \< 0.20% on scheduled sample                    | Medium   |
| Girth increment        | \< 5 cm/year on year 2-4 block                  | Medium   |
| Soil pH                | \< 4.5 on scheduled soil test                   | Medium   |
| Canopy closure delayed | Year 6+ without closure on mineral upland block | Medium   |

## Related

* [Rubber Diagnosis](/guides/Crop/Rubber/rubber-diagnosis)
* [Field Walk Protocol](/guides/Crop/Rubber/field-walk-protocol)