Short answer. Magnesium (Mg) deficiency shows on the older fronds: leaflets in full sun turn olive-green to orange-yellow from the tip, while leaflets shaded by the fronds above stay green. Potassium deficiency looks different — it starts as spots, not an even colour. Confirm with a leaf test before you buy, then choose between fast-acting kieserite and slower, cheaper dolomite based on your soil, rainfall and pH.
Start with the older fronds lower in the crown. Magnesium moves inside the palm, so when supply runs short the palm draws it out of old fronds to feed new growth — and the old fronds show it first.
These descriptions come from the SNV and Wageningen University smallholder oil palm handbook, which draws on standard oil palm nutrition references.
| What you see | Where on the palm | Most likely cause |
|---|---|---|
| Even olive to orange-yellow colour on sunlit leaflets; shaded parts stay green | Older fronds | Magnesium |
| Irregular yellow or orange spots that let light through when you hold the leaflet up to the sun; spots later merge | Older fronds | Potassium |
| Whole leaflets pale green or yellow, often in low-lying or waterlogged areas | Older fronds first | Nitrogen |
| Crinkled, dark-green leaves, sharply hooked leaflet tips, a flattened crown | New fronds | Boron |
Deficiencies often overlap. On palms short of both nutrients, the oldest fronds can show potassium symptoms while the mid-crown fronds show magnesium symptoms. Treating the wrong nutrient wastes a fertiliser round, which is why a leaf test is worth the cost.
Visual symptoms point you in the right direction; a leaf and soil test confirms it. Oil palm leaf samples are normally taken from frond 17 on mature palms (frond 9 on young palms), and the results are read against optimal ranges rather than a single cut-off value. A soil test adds exchangeable magnesium, potassium and pH — which also tells you whether a liming material makes sense on your block. Book a soil lab test.
Both work. In a five-year trial on sandy soil in Malaysia, ground magnesium limestone (GML) and kieserite both corrected magnesium deficiency and raised fresh fruit bunch (FFB) yield by an average of 11%. Kieserite supplied magnesium more efficiently — GML reached 83% of its agronomic efficiency — but GML was about 1.5 times more economical because it cost less. GML also lowered leaf potassium slightly, although yield was not affected (Goh, Chew and Teoh, 1998).
| Kieserite | Dolomite / GML | |
|---|---|---|
| Form of magnesium | Magnesium sulphate — dissolves in water | Carbonate — dissolves slowly |
| Speed | Fast; the usual choice for acute deficiency | Slower; suited to maintaining levels |
| Effect on soil pH | No liming effect | Raises pH on acid soils and supplies calcium |
| Watch out for | Higher losses on sandy, hilly or very wet sites | Keep potassium supply adequate |
| Our product | NEXGROW Kieserite — MgO 27% min | NEXGROW Dolomite — CaO 30% min, MgO 20% min |
As a general guide only, the SNV and Wageningen handbook lists 0.5–1.0 kg of kieserite, or 1.0–1.5 kg of dolomite, per mature palm per year for palms yielding 18–24 t FFB a year, rising for higher yields. Magnesium on peat is usually needed only when symptoms appear. These are not NEXGROW label rates: we set the rate for your block from your leaf and soil results.
Related guides and products: NEXGROW Kieserite · NEXGROW Dolomite · Fertilising young oil palm · Soil pH management · Oil palm programme · Estate quotation
See the dedicated fertiliser programme for this crop — application timing, key challenges and soil lab testing (a minimum charge applies).
Soil Testing & Lab Analysis — texture, pH, nutrients and organic matter, with a written programme.
NEXGROW Kieserite (MgO 27% min) for fast correction, NEXGROW Dolomite for acid soils. Send us your leaf or soil results and we will recommend a rate and quote.
See NEXGROW Kieserite →