Palm oil BMP: Reduced fertilizer use

Oil palm trees require some form of fertilization to produce yields that are viable economically. A number of options are available, however, to reduce the amount of fertilizer applied.

Well-rounded assessment before use

Palm oil producers should be encouraged to evaluate the types of fertilizers used in order to assess ways to increase the efficiency and reduce the environmental impacts of their use.

This would allow for the identification of specific application practices or the timing of applications that should be encouraged, as well as those that should be discouraged or even banned.

For example, any techniques that reduce surface runoff will reduce leaching of nutrients, which in turn minimizes contamination of surface and groundwater with nitrogen and phosphorus. To complement this, nitrogen-fixing legumes should be included in cover crops to reduce the need for purchased nitrogen fertilizers.

Ideally, added fertilizers should never exceed the amounts of nutrients exported in the harvested product plus what erodes, leaches, or volatilizes annually or when replanted.

Nutrient recycling

Another way to greatly reduce the use of nutrient inputs is through nutrient recycling, particularly from production of waste and/or by-products. One of the main categories of waste on oil palm plantations is the empty fruit bunches remaining after processing.

Every 25 metric tonnes of full fruit bunches yield 16 metric tonnes of empty fruit branches. This can be returned to the fields. If applied at 6 metric tonnes per hectare per year, given average yields, eventually it can return half of the nutrients originally harvested in the bunches once it decomposes.

To the extent that it is feasible financially, this waste should be spread around the trees throughout the plantation. One of the larger plantations focuses this material on the 2-metre radius around the trees. A problem with recycling this material is that many of the mills return it to their own land rather than to the lands of those who sell seed to them. Thus, this is an issue of cost and ownership.

Recycling palm oil effluent

The other main waste product that should be recycled is the palm oil effluent. This is one of the most difficult wastes to handle as it is in liquid form and the temptation is simply to release it into the environment. It too should be applied back to the fields, as it makes an excellent soil additive.

Using mature tree trunks

Trunks of mature trees that have been cut to allow replanting should be recycled more effectively. They contain up to 1,000 kilograms per hectare of potassium. Windrowing the trunks gives a slow breakdown of the material. This is the best way to release the nutrients.

Chipping or shredding releases all the nutrients within 2-3 years, and unless the chips are spread over a much larger area than the replanted area, the nutrients released would exceed the uptake capacity of the new trees. One other important factor that has to do with the best way to recycle trunks is whether they are diseased or whether there is disease in the area. If pests are a problem in the area, then it may be best to chip, pulverise or grind the trunks to reduce the time over which the nutrients are available to pests.

Fruit branches & trunks: good source of mulch

Empty fruit branches and trunks can be chipped and used as mulch if they are free of diseases. When used in circles around mature trees, the mulch can reduce herbicide requirements, but it may be a less efficient way to recycle nutrients than when spread over a larger area. For young trees, biodegradable mulch sheets can also reduce herbicide use.

There are 3 areas where improvements could reduce fertilizer use. First, to avoid over application of potassium, palm oil mill effluent and empty fruit branches should not be applied to the same areas. Second, there is evidence that nitrogen may be lost if palm oil mill effluent is stored for long periods in effluent ponds.

If so, the raw effluent should be recycled directly on the fields as soon as possible after processing. In any case, the sludge from effluent ponds should be applied to fields that are low in organic matter. And third, increased monitoring is needed to understand better nutrient use, storage, and loss.

Numerous options at hand

Composting residues from oil mills and using them as mulch are seen as effective ways to maintain or build soil nutrients. Empty fruit bunches have also been used successfully in a joint Finnish/Indonesian project to produce paper. These efforts should be evaluated and, to the extent that they are appropriate, should be encouraged. Studies have shown the production of edible mushrooms is also a financially viable possibility.

Oil palm trees regularly lose branches as they grow, which creates waste on the ground beneath the trees. In addition, empty fruit bunches from oil palm mills must be disposed of; they are generally burned or converted into mulch.

All in all, the weight and volume of waste far exceeds the commercially viable products produced from oil palm seeds. In addition, overly mature trees (25 years or older) are felled and either left lying on the ground or gathered and burned or chipped.

The trunks of trees can also be used for lumber or made into fibreboard. Palm kernel waste is a major raw material, and is processed into cake for animal feed such as food for pigs. Many plantation owners now put most of the processing waste back onto the farm as mulch. There is still considerable potential for preparations of other by-products such as fertilizers.

Source: Adapted from "World Agriculture & Environment" Clay (2004)

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