> ## 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.

# Magnesium Deficiency in Rubber

> How magnesium deficiency shows on older rubber leaves, Whorl 2 tissue thresholds, and the kieserite / dolomite program for acid tropical soils.

Magnesium is the central atom of chlorophyll. Deficiency shows first on older leaves (Mg is mobile, remobilized to new growth) as yellowing with characteristic red-purple margins. Common on very acid soils (pH \< 4.5), sandy soils, and blocks with heavy K fertilization (K and Mg compete for uptake).

## Cause

* **Very acid soils** (pH \< 4.5)
* **Sandy soils** with low Mg reserves
* **Heavy K fertilization** without Mg balance (K:Mg ratio > 3:1 in soil)
* **Coastal lowland** and peat soils
* **Erosion** on hilly blocks

## Effect

Field signs:

* Older leaves in the lower whorl yellow first (Mg is mobile)
* Yellowing progresses to red-purple **leaf margins** (classic signature)
* Interveinal chlorosis: yellow between veins, veins stay green
* Newer whorls stay normal until deficiency is severe
* Premature leaf drop in extreme cases

## Leaf-tissue thresholds

Sample **Whorl 2** leaves.

| Mg level (% dry weight) | Interpretation |
| ----------------------- | -------------- |
| \< 0.20                 | Deficient      |
| 0.20 to 0.24            | Marginal       |
| 0.24 to 0.30            | Optimal        |
| > 0.30                  | 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>

Also check K:Mg ratio in soil; should be 2:1 to 3:1.

## Satellite signals

Mg deficiency is patchy across the canopy (lower whorl only) and does not have a strong satellite signature until severe. Rely on ground scouting and tissue analysis.

## Action

<Steps>
  <Step title="Confirm with tissue and soil test">
    Whorl 2 Mg \< 0.20% and soil Mg \< 0.5 me/100g confirms deficiency.
  </Step>

  <Step title="Apply kieserite or magnesium sulphate">
    Kieserite (27% MgO, 22% S) is the standard fast-acting Mg source:

    * Immature: 100 to 200 g kieserite/tree/year
    * Mature: 200 to 300 g kieserite/tree/year
  </Step>

  <Step title="Long-term correction with dolomite">
    Ground magnesium limestone (dolomite, \~20% MgO, \~30% CaO) raises pH and supplies Mg. Apply 500 kg to 1 t/ha every 3 to 5 years on acid soils.
  </Step>

  <Step title="Rebalance K:Mg">
    If heavy KCl programs are causing induced Mg deficiency, split K applications more finely and interleave with Mg.
  </Step>

  <Step title="Follow up">
    Re-sample Whorl 2 leaves 4 months after correction. New whorls should be normal green; older leaves may not recover.
  </Step>
</Steps>

## Recommended alert settings

| Trigger         | Condition                                | Severity |
| --------------- | ---------------------------------------- | -------- |
| Leaf tissue Mg  | \< 0.20% on scheduled sample             | Medium   |
| Soil pH         | \< 4.5 on scheduled soil test            | Medium   |
| Soil K:Mg ratio | > 4:1                                    | Medium   |
| Scout report    | Red-purple margins on lower-whorl leaves | Medium   |

## Related

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