Understanding Role of Specific Nutrient for Oil Palm
Most required nutrients have specific roles to play in improving yield and crop quality:
• Nitrogen is important to build the palm and maintain frond productivity increasing FFB and oil yields. Oversupply though, can be counterproductive as it promotes excessive vegetative growth and encourages pest and disease attack.
• Phosphorus is particularly important for root growth and flower initiation, increasing fruit number, bunch
weight and yield.
• Potassium, like nitrogen, also boosts crop development, increasing bunch size and FFB yield. Large amounts are utilized by the palm, but supplies need to be balanced alongside those of nitrogen and other cations such as magnesium and calcium.
• Magnesium is needed in relatively large quantities to maintain photosynthesis, frond development and bunch number and fruit weight. It also plays a role in improving bunch oil content.
• Calcium is important for palm health.
• Sulfur is required for high yield alongside nitrogen.
• Boron is important for root development and also for fruit set.
• Zinc - especially on peat soils - helps support new tissue development.
• Copper - especially on peat soils - plus manganese and iron will also help maintain growth.
A large amount of nutrients are taken up by oil palm – more than most tropical crops – and with the crop now increasingly being grown on soils with a low fertility, fertilizers are a key input.
Uptake varies widely according to the crop’s stage of development and target yield, the soil type, fertility and climate.
A significant proportion of nutrients are removed in the harvested bunch and fertilizer rates need to take this into account.
At the same time, fertilizer programmes need to support the large amount of nutrients required to support palm growth and which are stored in the palm root, bole, trunk and fronds. Equally, fertilizer application must be balanced against the amount of nutrients released and recycled from pruned fronds and male flowers or availability from recycled crop components such as empty fruit bunches (EFB) and palm oil mill effluent (POME).
With many crops grown in association with a leguminous ground cover during the immature phase, fertilizer use should also take into account these needs and the nitrogen fixed and released by this crop, which is subsequently available to the palm.
At the seedling stage, the oil palm requires a balance of nutrients, and fertilizer use should aim to supply all major, secondary, and micro nutrients.
Once the seedling is ready for transplant – at a weight of around 1.4 kg shoot DM – it has taken up around 20g of N and K2O plus significant levels of other nutrients, notably phosphorus and key micronutrients (Table 6).
As the palm develops, nitrogen and potassium uptake reaches a plateau at around 4-5 years after transplanting (Figure 22), 4-5 years before the crop delivers its highest oil yields.
The level of this uptake varies according to site and if potential is low – e.g. in regions where rainfall and solar radiation are not as high – then nutrient uptake is consequently lower.
Nitrogen is a key nutrient for leaf production and net assimilation in the palm. For a FFB production of 25t/ha around 1400g/palm is required (Table 7).
A relatively high proportion of this – 59% - is found in the fronds and vegetative DM, with 36% in the fruit
bunch. Offtake in the fresh fruit bunch is around 3kg/t.
Some common nutrient application rates/ha are given in Table 9. Rates should be adjusted according to local trials, crop age/offtake and nutrient returns from other sources.
Nitrate-N is immediately available to the palm and is the preferred form of nitrogen which is taken into the plant. Ammonium-N is mainly converted to nitrate-N and so is slightly slower to become available.
While low rates of ammonium can be taken up, its use can have adverse effects on the soil and palm. This includes the release of protons (H+) which acidify the rhizosphere. In addition, the consequent increase of
aluminum in the soil and the reduction of nutrient and water uptake can have a
major impact on palm productivity.
This acidification of the rhizosphere and increase of aluminum activity is particularly detrimental to seedling growth (Figures 40 and 41) and nutrient uptake (Figure 42). Root growth is also significantly impaired (see photo).
Once the pH drops to 4.5 the mineralization of the ammonium is slower and nitrate availability reduced,
restricting oil yields (Figure 43). In this study, after 3 weeks of incubation, only 0.2% and 0.8% of nitrogen applied as urea and ammonium sulfate respectively was found in the nitrate form. Almost all available nitrogen was present in the ammonium form and only 53.5 to 55% of total nitrogen applied as urea or ammonium sulfate was recovered in an instantly available form. However, where ammonium nitrate was used, 46% out of 50% nitrate was recovered as nitrate and 28% out of 50% as ammonium.
The nitrogen fertilizer with the greatest effect on soil acidity is ammonium sulphate; it will acidify the soil at three times the rate of urea, the next most acidifying nitrogen fertilizer.
In contrast, the YaraMila ammonium nitrate based NPK combination has little effect on soil acidity. This gives it a major advantage over ammonium sulfate. The photo below shows this effect on root mass.
While ammonium sulfate is better than urea as a nitrogen source, ammonium nitrate is the best most consistent source, leading to the highest yields
Ammonium based product