Most oil palm growers are familiar with the primary nutrients nitrogen, phosphorus, and potassium, known collectively as NPK. One nutrient that is sometimes overlooked but is still very important for oil palm and plant growth is magnesium (Mg). Magnesium has a key role in the production of chlorophyll, the green pigment in plants that is responsible for photosynthesis. It also helps plants to absorb and utilize phosphorus. Magnesium also enhances the production of oils and fats, so it has many important functions in plants and especially oil crops like oil palm.

When magnesium nutrition is deficient in oil palm, the most common symptom is orange frond. The pinnae on older fronds turn yellowish-orange and this gradually spreads up to the younger fronds as the symptoms worsen. In more severe deficiencies, the fronds become desiccated, beginning from the pinnae tips.

Magnesium deficiency is commonly observed on roadside palms and palms on hilltops or terraces which receive a lot of sun. These areas are also vulnerable to soil erosion which leads to nutrient runoff losses including magnesium. Soils that are rich in potassium can also trigger magnesium deficiency as high potassium content can leach magnesium from the soil and suppress absorption by the palms.

The common sources of magnesium fertilizers available in Malaysia are water-soluble Kieserite (magnesium sulphate) as well as the less soluble ground magnesium limestone (GML) and dolomite. The typical application rate of Kieserite is 1 – 1.5 kg/palm/year, especially for young and mature palms up to 8 years after planting. In older palms, magnesium fertilization may be done once every 2 years if leaf magnesium levels are good. Some planters use GML or dolomite instead as they are cheaper, but care should be taken because GML and dolomite have a high content of calcium, which can suppress magnesium absorption by the palms if used continuously for many years.

When applying magnesium as a straight fertilizer, it is advisable not to apply it together with potassium (e.g. MOP or SOP), as the potassium can suppress magnesium absorption. It is best to leave at least 4 weeks gap when applying these two fertilizers. Alternatively, planters can use controlled-release fertilizers such as Plantsafe which provides all essential plant nutrients in a balanced and controlled manner to ensure maximum absorption by the palms with minimal losses to the environment. 

Orange frond symptoms on oil palm pinnae due to magnesium deficiency