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Magnesium is the central atom of chlorophyll, so Mg deficiency shows as chlorosis on older leaves while young leaves stay green. On pineapple, the classic pattern is interveinal yellowing plus red-purple margins on the lower rosette. Mg deficiency often follows heavy K applications (K induces Mg deficiency by cation competition). Regional priority: High on sandy, BRIS, and leached soils, and on any block with heavy MOP use without matching Mg.

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When pineapple is most vulnerable

From late vegetative (month 8) onward, worsening if not corrected before fruit development.

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How magnesium deficiency shows in satellite data

  • NDVI slightly below phase baseline on affected blocks, but NDRE is more sensitive because chlorophyll is directly depleted.
  • Pattern is block-wide or matches sandy zones within a block.
  • Not detectable at individual-plant scale.

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Field symptoms

  • Interveinal yellow chlorosis on older leaves, veins staying green
  • Red-purple margins on the yellowed leaves
  • Older leaves affected first (Mg is mobile and moves to young growth)
  • Reduced fruit sugar and off-color fruit shells
  • Overlap with K deficiency but Mg shows the vein-band pattern; K shows uniform tip and margin burn

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Reduce the damage by

  • Kieserite (MgSO4) as the standard fast-acting Mg source - 200 to 400 kg/ha per cycle, banded on the mulch.
  • Dolomite (CaMg carbonate) on acid soils - corrects Mg and raises pH at the same time.
  • Foliar MgSO4 (2%) for rapid correction during the season.
  • Balance K:Mg - target K:Mg of 3:1 on mineral, 2:1 on sandy or BRIS soils. High K without Mg induces deficiency.
  • Split kieserite and MOP into separate applications to reduce cation competition at uptake.
  • D-leaf analysis - target 0.3 to 0.4% Mg in the D-leaf. This is a generic target with no site, soil, cultivar or season qualifier, so it supports inside or outside and no finer grade — see Reading a tissue analysis.

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Set an alert for early warning

Turn the diagnosis into a trigger. Mg deficiency is chronic and slow, so schedule sampling and trend alerts rather than event alerts.
Recommended settings for magnesium on pineapple:
  • NDRE trend alert - trigger when 4-week moving NDRE drops 5% or more below phase baseline.
  • D-leaf sampling reminder - month 8 to 10, sample both K and Mg simultaneously.
  • Soil test reminder - every 2 cycles, focused on exchangeable Mg and K:Mg ratio.