> ## 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.

# Calcium Deficiency in Rubber

> How calcium deficiency and low soil pH affect rubber growth and bark quality, Whorl 2 thresholds, and the liming program for acid Malaysian soils.

Calcium deficiency in rubber is rare as a primary nutrient issue but common as a symptom of soil acidity. Most Malaysian rubber soils are acid (pH 4 to 5), and Ca correction usually happens as a byproduct of liming for pH and Mg management. Ca is essential for cell wall formation and healthy bark, so deficiency affects tapping-panel quality and bark renewal.

## Cause

* **Acid soils** (pH \< 5) with low base saturation
* **Sandy and peat soils** with low Ca reserves
* **Heavy K and Mg fertilization** displacing Ca on the soil exchange
* **No liming** for many years

## Effect

Field signs:

* Young leaves in the top whorl show interveinal chlorosis, green veins on yellow leaf (Ca is immobile, deficiency shows on new growth)
* Distorted new flush, marginal leaf necrosis
* Poor bark renewal on the tapping panel (thin, cracked, slow-regenerating bark)
* Weak root system, elevated root-disease risk

## Leaf-tissue thresholds

Sample **Whorl 2** leaves.

| Ca level (% dry weight) | Interpretation |
| ----------------------- | -------------- |
| \< 0.5                  | Deficient      |
| 0.5 to 0.7              | Marginal       |
| 0.7 to 1.0              | Optimal        |
| > 1.0                   | 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

No direct satellite signal for Ca. Manage via routine soil pH and Whorl 2 tissue tests.

## Action

<Steps>
  <Step title="Test soil pH and base saturation">
    Confirm with soil analysis (target pH 5.0 to 5.5, base saturation > 30%).
  </Step>

  <Step title="Apply ground magnesium limestone (dolomite)">
    Dolomite (\~30% CaO, \~20% MgO) supplies both Ca and Mg and raises pH:

    * Every 3 to 5 years: 500 kg to 1 t/ha broadcast across the block
    * New planting: 250 to 500 g dolomite per planting hole
  </Step>

  <Step title="Alternative: ground limestone (calcite)">
    If Mg is already adequate, use pure ground limestone (\~40% CaO). Common on peat blocks where Mg is separately corrected.
  </Step>

  <Step title="Watch bark renewal on tapped panels">
    Ca-deficient trees have poor bark renewal; the new bark is thin and prone to cracking. This opens the tree to [black stripe](/guides/Crop/Rubber/biotic/diseases/black-stripe) and [pink disease](/guides/Crop/Rubber/biotic/diseases/pink-disease).
  </Step>
</Steps>

## Recommended alert settings

| Trigger         | Condition                                           | Severity  |
| --------------- | --------------------------------------------------- | --------- |
| Leaf tissue Ca  | \< 0.5% on scheduled sample                         | Medium    |
| Soil pH         | \< 4.5                                              | Medium    |
| Bark renewal    | Scout reports thin/cracked new bark on tapped panel | Medium    |
| Liming reminder | 3-year cadence per block                            | Automatic |

## Related

* [Magnesium deficiency](/guides/Crop/Rubber/nutrient/magnesium)
* [Black stripe](/guides/Crop/Rubber/biotic/diseases/black-stripe)
* [Rubber Diagnosis](/guides/Crop/Rubber/rubber-diagnosis)