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Potassium is the most critical nutrient for latex synthesis. Mature tapped rubber is a heavy K user: latex export removes 40 to 60 kg K/ha/year. K deficiency causes tip die-back on older leaves, reduced latex flow, and elevated TPD incidence. It is the second most common nutrient issue in Malaysian rubber after N.

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Cause

  • Heavy tapping without K replacement (K export in latex is significant)
  • Sandy soils with low K reserves and high leaching
  • Coastal lowland with K leaching after heavy rain
  • Peat soils with low K
  • Erosion on hilly blocks

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Effect

Field signs:
  • Older leaves yellow-orange with tip die-back and marginal necrosis (classic K deficiency signature)
  • Younger leaves normal, deficiency concentrated on lower whorl
  • Reduced latex flow, watery latex
  • Elevated TPD incidence
  • Bark cracking on tapping panel

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Leaf-tissue thresholds

Sample Whorl 2 leaves.
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.

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Satellite signals

K deficiency is easily confused with over-tapping or TPD; tissue analysis is essential.

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Action

1

Confirm with tissue

Whorl 2 K < 1.1% confirms deficiency. If borderline (1.1 to 1.3%) combined with heavy tapping, treat as deficient.
2

Apply muriate of potash (KCl, 60% K2O)

Split into 2 to 3 applications per year:
  • Immature: 100 to 200 g KCl/tree/year
  • Mature tapped: 300 to 500 g KCl/tree/year, split
Apply after main rains, worked into the top 5 cm around the drip zone.
3

Reduce tapping intensity on deficient blocks

Switch to d/3 or d/4 until K status is restored. Continued heavy tapping on K-deficient trees is the top nutrient cause of TPD.
4

Follow up

Re-sample Whorl 2 leaves 3 months after application. Latex flow response takes 3 to 6 months.