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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.

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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

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Effect

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)

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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

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.

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Action

1

Confirm with tissue and soil test

P deficiency is confirmed by Whorl 2 tissue < 0.20% combined with soil P (Bray-1) < 15 ppm.
2

Apply rock phosphate at planting

Best practice: 250 to 500 g rock phosphate per planting hole, mixed with topsoil.
3

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)
4

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.