Prota 14: Vegetable oils/Oléagineux
Select. stirp. amer. hist. : 280 (1763).
2n = 32
Oil palm, African oil palm (En). Palmier à huile (Fr). Dendezeiro, palmeira do azeite, palmeira do dendê, palmeira andim (Po). Mchikichi (Sw).
Origin and geographic distribution
Elaeis guineensis is indigenous to the tropical rainforest belt of West and western Central Africa between Guinea and northern Angola (11°N to 10°S). The greatest genetic variation is found in south-eastern Nigeria and western Cameroon and there is also fossil evidence that the Niger delta is its most likely centre of origin. The abundance of oil palm groves throughout the forest zone is attributed to early domestication. In Nigeria alone, such groves of wild and semi-wild oil palms cover an estimated 2.5 million ha. Isolated groves of semi-wild oil palms are found in Senegal (16°N) and southern Angola (15°S), along the shores of Lake Kivu and Lake Tanganyika, along the coast of East Africa, and even on the west coast of Madagascar (21°S). In West Africa, oil palm has played a major role in the village economy for many centuries and unrefined palm oil is still the preferred cooking oil of the local population.
The semi-wild oil palm groves of north-eastern Brazil have a West-African origin through the slave trade of the 16th–18th centuries. They gradually spread to other regions of tropical America and the original description of the oil palm was based on a specimen growing in Martinique. The introduction of oil palm into South-East Asia started with four seedlings planted in the Botanic Garden of Bogor (Indonesia) in 1848. Offspring of these palms formed the basis for the oil palm plantation industry, which developed gradually from 1911 in Indonesia, initially in the Deli district in Sumatra, and from 1917 in Malaysia.
The 19th century trade in palm oil and kernels between West Africa and Europe depended entirely on the produce of the semi-wild palm groves. In response to demands for more and better quality palm oil, commercial plantations started to be established in Africa after 1920 (e.g. in DR Congo). By 1938 annual world exports were about 0.5 million t palm oil (50% from South-East Asia) and 0.7 million t palm kernels (almost exclusively from Africa). Major new oil palm developments took off during the 1970s in South-East Asia (Malaysia, Indonesia, Thailand and Papua New Guinea), tropical America (e.g. Colombia, Ecuador and Costa Rica) and Africa (e.g. Côte d’Ivoire, Cameroon, Ghana). Smaller oil palm industries are developing in the Philippines, Solomon Islands, China (Hainan), India and Sri Lanka.
Two types of oil are extracted from the fruits of Elaeis guineensis: palm oil from the mesocarp and palm-kernel oil from the endosperm, in a volume ratio of approximately 9 : 1. Palm oil is used for a large variety of edible products, such as cooking oils, margarine, vegetable ghee, shortenings, frying and bakery fats, and for preparing potato crisps, pastry, confectionery, ice-cream and creamers. Unrefined red palm oil is an essential ingredient of the West African diet, while boiled and macerated fruits are used to prepare a nutritious soup, served after removal of the seeds, fibre and part of the oil. About 10% of all palm oil, the inferior grades in particular and also refining residues, is used to manufacture soaps, detergents, candles, resins, lubricating greases, cosmetics, glycerol and fatty acids. Palm oil is employed in the steel industry (tin plating and sheet-steel manufacturing) and epoxidized palm oil is a plasticizer and stabilizer in PVC plastics. Palm oil and more particularly its methyl- or ethyl-ester derivatives have potential as biofuel for diesel engines.
Palm-kernel oil is similar in composition and properties to coconut oil. It may be used as cooking oil, sometimes in blends with coconut oil, or in the manufacture of margarine, edible fats, filled milk, ice-cream and confectioneries. It is also used for industrial purposes, either as an alternative to coconut oil in making high-quality soaps, or as a source of short-chain and medium-chain fatty acids. These acids are chemical intermediates in the production of fatty alcohols, esters, amines, amides and more sophisticated chemicals, which are components of many products such as surface-active agents, plastics, lubricants and cosmetics. The presscake or palm-kernel meal is a valuable protein-rich livestock feed.
In addition to oil, the processing of 1 t of fruit bunches yields about 240 kg empty bunches, 140 kg fibres and 60 kg of shells, which are commonly used as fuel for the boilers of the palm oil mill. The shells are much appreciated by local blacksmiths as high calorific fuel for their furnaces; they are also polished and carved into ornamental rings and beads. The empty bunches, fibre and also the effluent (0.5 t sludge for each t of milled fruit bunches) may also be converted into products such as organic fertilizers.
In West Africa it is common practice to produce palm wine by tapping the unopened male inflorescences, or the stem just below the apex of felled oil palms. In Nigeria in particular, tapping of wine from oil palm is a major industry, as it is also from raffia palm (Raphia hookeri G.Mann & H.Wendl.). The palm heart (soft tissue of undeveloped leaves around the apical bud) is eaten as a vegetable.
Entire palm fronds are less suitable for thatching than those of the coconut palm, because of irregular leaflet insertion. However, the leaflets are woven into baskets and mats; the leaflet midribs are made into brooms and the rachises used for fencing. Young leaflets produce a fine strong fibre for fishing lines, snares and strainers. Palm trunks, available at replanting, provide excellent material for paper and board production, but this has not yet attracted much commercial interest.
Traditional medicinal uses in Africa are numerous. Preparations made from the palm heart are used to treat gonorrhoea, menorrhagia, and perinatal abdominal pain, and are considered laxative, anti-emetic and diuretic. Leaf sap is used in preparations against skin affections, roots as analgesic. The oil is an excipient for herbal ointments.
Oil palm is sometimes planted as a garden ornamental and along avenues.
Production and international trade
World production of palm oil increased from 1.3 million t in 1960 (78% from Africa) to 12.1 million t in 1980 (83% from South-East Asia) and it almost doubled again in the subsequent two decades. It continued to increase substantially, from 25.4 million t (from 10.5 million ha) in 2001 to 34.8 million t (from 12.6 million ha) in 2005, largely as a result of further expansion of oil palm cultivation in South-East Asia. Palm oil is expected to overtake soya bean oil as the most important vegetable oil within the next few years. In 2005, South-East Asia produced 89%, Africa 5% and tropical America 6% of total palm oil supply.
The largest producers of palm oil in 2005 were Indonesia with 15.0 million t (3.6 million ha), Malaysia with 14.8 million t (3.6 million ha), Nigeria with 900,000 t (3.3 million ha), Thailand with 800,000 t (300,000 ha) and Colombia with 700,000 t (200,000 ha). Other African countries with significant palm oil production are Côte d’Ivoire with 360,000 t in 2005 (140,000 ha), DR Congo with 200,000 t (250,000 ha), Cameroon with 150,000 t (57,000 ha), Ghana with 120,000 t (112,000 ha); minor producers are Angola (58,000 t), Guinea (50,000 t), Liberia (42,000 t), Sierra Leone (36,000 t), Benin (35,000 t) and Togo (7000 t).
In Nigeria about 20% of annual palm-oil output is produced by the formal plantation and smallholder sector, which covers only 250,000 ha. The remaining 80% comes from low-yielding semi-wild palm groves, which may explain the very low national average yield figures. On the other hand, actual production may be underestimated, as the considerable trade of palm fruits and oil on local markets probably remains largely unrecorded in formal agricultural statistics.
Palm oil is by far the most important commodity (45%) in the world trade of vegetable oils and fats. World trade in palm oil amounted to 25.7 million t in 2005 or 75% of total production. Malaysia exported about 90% and Indonesia 70% of their production, together 92% of the internationally traded palm oil. About 50% of the internationally traded palm oil is imported by China, India and other Asian countries, another 18% by the 25 countries of the European Union, but only 2% by the United States. Imports of palm oil by countries in tropical Africa amounted to 1.0 million t in 2005, and included palm-oil producing countries such as Nigeria (210,000 t) and Ghana (130,000 t).
In 2005, world palm-kernel oil production was 4.2 million t (Malaysia 1.79 million t, Indonesia 1.75 million t and Nigeria 260,000 t) and palm-kernel meal 5.0 million t, with 47% of the oil and 80% of the meal traded internationally.
Industrially extracted fresh fruit bunches of the most commonly planted oil palm cultivars (‘Dura’ × ‘Pisifera’ hybrids producing thin-shelled ‘Tenera’ fruits) yield per 100 kg 20–28 kg palm oil and 4–8 kg kernels, the latter yielding 2–4 kg palm-kernel oil. Per 100 g, the mesocarp of mature fruits contains: water 30–40 g, oil 40–55 g and fibre (crude fibre and cell walls) 15–18 g. Per 100 g the endosperm of the kernel contains: water 6–8 g, oil 48–52 g, protein 7–9 g, carbohydrate 30–32 g and crude fibre 4–5 g.
Palm oil varies in colour from pale yellow to dark red; its melting point ranges from 25°C to 40°C and it has an energy value of 3700 kJ (884 kcal) per 100 g. It consists of triglycerides with the following fatty acids: myristic acid 1–2%, palmitic acid 43–50%, stearic acid 2–4%, oleic acid 34–41% and linoleic acid 4–9%. Palm olein is produced by subjecting palm oil to a process of ‘winterization’ which involves slow cooling of the oil and removal of solidified fraction by filtration. The process partially removes the saturated fraction, and palm olein contains less palmitic acid (<35%) and more oleic acid (>45%). Palm oil for edible purposes should contain less than 3% free fatty acids (FFA). Crude palm oil also contains nutritionally valuable carotenoids (provitamin A), 800–2000 mg/kg in the orange-red palm oil from West Africa and 400–600 mg/kg in the lighter coloured palm oil from Malaysia and Indonesia. Tocopherol (vitamin E) is present in quantities up to 850 mg/kg. Carotenoid content is reduced to zero and the tocopherol content to half during refining of the oil.
Palm-kernel oil has a pale yellow colour and is almost white when solid. Its melting-point range is 23 to 30°C. The fatty acid composition of palm-kernel oil is similar to coconut oil: caprylic acid 3–4%, capric acid 3–7%, lauric acid 45–52%, myristic acid 15–17%, palmitic acid 6–10%, stearic acid 1–3%, oleic acid 13–19%, and linoleic acid 1–2%. Per 100 g, palm-kernel cake or meal contains: water 8–11 g, crude protein 19–22 g, carbohydrate 42–49 g, crude fibre 11–15 g.
Although crude palm oil contains about 50% saturated fatty acids, it behaves nutritionally much like an unsaturated oil and does not increase LDL-cholesterol levels in the blood. This can be explained by the predominant composition of the triglycerides, with saturated fatty acids on the outer 1- and 3-positions and an unsaturated fatty acid on the 2-position. Hydrolysis during pancreatic digestion leads to free saturated fatty acids and 2-monoglycerides with unsaturated fatty acids, which are easily absorbed by the intestinal wall. Much of the saturated fatty acids give rise to insoluble calcium salts that cannot be absorbed and are excreted.
Unbranched, monoecious tree up to 30 m tall; root system adventitious, forming a dense mat with a radius of 3–5 m in the upper 40–60 cm of the soil, some primary roots directly below the base of the trunk descending for anchorage for more than 1.5 m, roots with pneumatodes under very moist conditions; bole erect, cylindrical, up to 75 cm in diameter, but thicker at the swollen, often inverted cone-like basal part, rough and stout due to adhering petiole bases during the first 12–15 years, slender looking and smooth in older palms; crown with 40–50 leaves. Leaves arranged spirally, pinnately compound, up to 8 m long, sheathing; sheath tubular at first, later disintegrating into an interwoven mass of fibres, those fibres attached to the base of the petiole remaining as regularly spaced, broad, flattened spines; petiole 1–2 m long, channelled above, bearing spines; leaflets 250–350 per leaf, irregularly inserted on the rachis, linear but single fold, 35–65 cm × 2–4 cm, pulvinus at base, with thick wax layer on upper and semi-xeromorphic stomata on lower surface. Inflorescence axillary, short and condensed, unisexual, branching to 1 order; peduncle 30–45 cm long; inflorescence tightly enclosed in spindle-shaped or ovate bracts before anthesis; male inflorescence ovoid, 20–25 cm long, with branches 10–20 cm long, each with 700–1200 closely packed flowers; female inflorescence globose, 25–35 cm long, with thick and fleshy branches, each in the axil of a spiny bract, with 10–25 spirally arranged flowers and a terminal spine. Male flowers 3–4 mm long, perianth consisting of 6 small segments, with 6 stamens and rudimentary pistil; female flowers in shallow cavities accompanied by two rudimentary male flowers and subtended by a spiny bract, with 2 bracteoles, 6 tepals c. 2 cm long, a superior, 3-celled ovary and sessile 3-lobed, creamy-white stigma. Infructescence (fruit bunch) up to 50 cm long and 35 cm wide, weighing 4–60(–90) kg, with 500–3000 tightly packed fruits. Fruit a globose to elongated or ovoid drupe 2–5 cm long, weighing 3–30 g, apex with persistent woody stigma; exocarp smooth, shiny, orange-red when ripe with violet-black pigmented apex, innermost smaller and irregularly shaped fruits often without pigmented apex; mesocarp fibrous, yellow-orange, oily; endocarp (shell) stony, dark brown, with longitudinal fibres drawn out into a tuft at base, and 3 germ pores at apex, usually 1-seeded. Seed (kernel) with dark brown testa, endosperm solid, oily, grey-white, embedding a c. 3 mm long embryo opposite one of three germ pores.
Other botanical information
Elaeis comprises only two species: the African Elaeis guineensis and the tropical American Elaeis oleifera (Kunth) Cortés ex Prain (synonyms: Corozo oleifera (Kunth) L.H.Bailey, Elaeis melanococca Gaertn.), the latter distributed from southern Mexico to the central Amazonian region. Due to low oil yield, Elaeis oleifera is of little economic importance, except in its natural area of distribution. However, it has a range of characters that are potentially useful in oil palm breeding, including resistances to some important pests and diseases, slow stem growth and high unsaturated fatty acid content of the mesocarp oil. Elaeis oleifera and Elaeis guineensis are inter-fertile and hybridization to transfer such characters is in progress. For some time an oil palm with smaller fruits found in Madagascar was considered a separate species (Elaeis madagascariensis Becc.), but is now thought to fall within the normal variability range of Elaeis guineensis.
Classification within Elaeis guineensis is based primarily on variation in fruit characteristics. One with considerable economic consequences is the distinction between 3 types based on shell thickness, which is determined by a single gene: ‘Dura’, homozygous, with a thick endocarp (2–8 mm at cross-section of fruit), ‘Tenera’, heterozygous, with a thin endocarp (0.5–4 mm), and ‘Pisifera’, homozygous, without a lignified endocarp.
Within the ‘Dura’ and ‘Tenera’ types, there is considerable variation in shell thickness which is apparently under polygenic control. ‘Tenera’ is preferred as planting material because it has more oil-bearing mesocarp (60–90% by fruit weight) than ‘Dura’ (20–65% by fruit weight). The original palms introduced in Java (Bogor) in 1848 were of the ‘Dura’ type, and their offspring is generally referred to as ‘Deli Dura’. ‘Pisifera’ is usually unproductive because female inflorescences abort before developing into fruit bunches, but it is used as male parent in crosses with ‘Dura’ palms to produce pure stands of ‘Tenera’ palms.
Other classifications are based on fruit characteristics under monogenic control and include presence or absence of
– anthocyanin in the upper fruit exocarp (absent in the ‘Virescens’ type, present in ‘Nigrescens’; recessive);
– carotene in the mesocarp (absent in the ‘Albescens’ type; recessive);
– additional carpels in the fruit (present in the ‘Poissoni’ (mantled) type; recessive).
The ‘Idolatrica’ oil palm has entire leaves (recessive).
Growth and development
After harvesting oil palm seeds are dormant. Germination starts with the appearance of a white button at one of the germ pores of the endocarp, which develops within 4 weeks into a seedling consisting of a plumule with first green leaf, a radicle and adventitious roots, but still connected to the seed endosperm by a haustorium. Subsequent leaves gradually change from lanceolate to pinnate over a period of 12–14 months, when the seedling may have 18—24 leaves. Leaves on seedlings have no spines and are less xeromorphic than adult leaves. The base of the stem becomes swollen and adventitious primary roots develop from it. In the first 3–4 years, lateral growth of the stem dominates, giving the palm a broad base up to 60 cm in diameter. After that, the stem starts growing in height, 20–75 cm per year, at a somewhat reduced diameter. The rate of height increment and rate of leaf production appear to be independent. A leaf primordium develops about every second week from the single growing point. Succeeding primordia are separated by a divergence angle of 137.5° resulting in a spiral of 8 leaves per full turn. This facilitates identification of leaf 17 (standard leaf sampled for foliar diagnosis of the palm’s nutrient status), as being in a straight line down from the youngest opened and 9th leaves. The rate of leaf production is up to 40 per year in the first 3 years, dropping to 20–24 per year from year 8 onwards. Development from leaf primordium to fully expanded leaf, with a surface area of 2–10 m2, takes some 2 years and a leaf remains photosynthetically active for about 2 years. An adult palm has a crown of 36–48 green leaves, but 40 leaves per palm are usually maintained in plantations. The economic lifespan of oil palm plantations is about 25 years.
All leaf bases contain inflorescence primordia, but the first fully developed inflorescence does not appear before leaf 20 and usually much later, some three years after germination. Differentiation into male or female inflorescence takes place in adult palms at 20–24 months before anthesis, but this can be as short as 12–16 months in young palms. The physiological basis of sex differentiation in oil palm is not well understood, except that there is empirical evidence for drought and other stress conditions to increase maleness. This appears to be an effective mechanism for oil palm to survive under adverse climatic conditions by reducing the load of fruit bunches. Generally, environmental, age and genetic factors determine the ratio of female to total number of inflorescences over time (sex ratio) of individual palms.
The female flower remains receptive for 36–48 hours after initial opening. Pollination is primarily by insects. One of the insect vectors, the African oil palm weevil (Elaeidobius kamerunicus), was successfully introduced from Africa into Malaysia in 1981, and subsequently to Indonesia and Papua New Guinea. Before then, oil palms in South-East Asia required artificial pollination for adequate fruit set, particularly during the first years of production. Male inflorescences spread a strong aniseed fragrance during anthesis. Fruits ripen within 4.5–6 months after pollination. Fruit ripening on the bunch proceeds from top to bottom and from outer to inner fruits. Ripe fruits become detached. Oil formation in the kernel takes place between 2.5 and 3.5 months after pollination, but in the mesocarp it starts only in the 4th month and does not reach its peak until the fruit is fully ripe.
Oil palm is a heliophile plant of the humid tropical lowlands. It is most common at the edges of swamps and along river banks, where competition from faster growing tree species is limited. It reaches its maximum photosynthetic activity only under bright sunshine and unrestricted water availability. Under such conditions palms have a single unopened leaf at any time, while several of such ‘spear leaves’ can be observed on palms suffering from drought or other abiotic stress factors. High correlations have been found between number of hours of effective sunshine (i.e. sunshine hours when the palms are not water stressed) and bunch yields of mature oil palm fields about 2.5 years later. Generally, climatic requirements for high production are: well distributed rainfall of 1800–2000 mm and water deficit of less than 250 mm per year, high air humidity, and at least 1900 hours of sunshine per year. Optimum mean minimum and maximum monthly temperatures are 22–24°C and 29–33°C, respectively. Under conditions of higher annual water deficits (prolonged dry season) or mean minimum monthly temperatures below 18°C (at elevations exceeding 400 m or latitudes above 10°), growth and productivity are severely reduced. Oil palm is also affected by excessively high temperatures, because of progressively lower photochemical efficiency above 35°C.
Oil palm can grow on various soils such as latosols developed over various parent rocks, young volcanic soils, alluvial clays and peat soils, and is tolerant of relatively high soil acidity (pH 4.2—5.5). Major criteria for suitability are soil depth (>1.5 m), soil water availability at field capacity (1–1.5 mm per cm of soil depth), organic carbon (>1.5% in the topsoil) and cation exchange capacity (>100 mmol/kg). Soils should be well drained with no signs of permanent waterlogging, but oil palm is fairly tolerant of short periods of flooding.
Propagation and planting
Freshly harvested, cleaned and dried seeds of oil palm with 14–17% moisture content lose viability within 9–12 months at tropical ambient temperatures (c. 27°C). High seed viability (>85% germination) can be maintained for 24–30 months in air-conditioned stores at 18–20°C and at seed moisture contents of 21–22%. Longer storage of valuable oil palm germplasm by cryopreservation of seeds, kernels, excised embryos or somatic tissues is now also possible. To break dormancy and induce rapid germination, seeds of oil palm require a heat treatment of 39–40°C for 60–80 days, followed by cooling and rehydration. However, in-vitro grown excised embryos start elongating within 24 hours. The 1000-seed weight of ‘Dura’ ( thick-shelled) seed is 4–12 kg and for ‘Tenera’ (thin-shelled) seed 2–3 kg.
Practically all planted oil palms are ‘Dura’ × ‘Pisifera’ hybrids, which are produced by controlled pollination of female inflorescences on selected ‘Dura’ palms with pollen from selected ‘Pisifera’. The fruits are of the ‘Dura’ type, but the palms raised from such seeds will produce thin-shelled ‘Tenera’ fruits. The multiplication factor in oil palm can be in excess of 10,000, since one mature ‘Dura’ seed parent may produce 6–9 hand-pollinated fruit bunches per year each yielding 1000–2500 seeds. Seed production, storage and heat treatment with subsequent flush of germination require considerable technological and logistic expertise and facilities, generally available only in public or private oil palm research centres.
Newly germinated seed can be transported over long distances (300 seeds in a polythene bag and several bags carefully packed in a box) before planting in a pre-nursery in mini polybags (8 cm × 20 cm, 200 gauge black polyethylene). Transplanting into the nursery takes place at the 2-leaf stage and large polybags (40 cm × 60 cm, 500 gauge black polyethylene) are used. Total duration of both nursery stages before transplanting to the field is 10–14 months. Under favourable climatic conditions and ample availability of space and irrigation facilities, a single-stage nursery system can be applied by planting germinated seeds directly in large polybags. Shading has to be provided to young seedlings during the first 2–3 months.
In-vitro methods of clonal propagation of oil palm through somatic embryogenesis, starting from young root or leaf explants, were first developed in the late 1970s. However, the occurrence of epigenetic abnormalities in clonal offsprings, such as various degrees of androgynous inflorescences and mantled fruits, make further research efforts necessary before wide-scale application of clonal propagation in oil palm will become feasible.
Field planting is preceded by land preparation, which may include underbrushing, tree felling and clearing followed by the layout of roads and planting blocks, lining and holing. In non-forest areas, disc ploughing followed by several harrowings can clear the land of strongly growing weeds and other vegetation. Oil palm plantations are usually established on flat or gently undulating land. Where soil permeability is poor, the construction of a drainage system may be necessary. Planting on steep hills requires terracing or construction of individual platforms. A leguminous cover crop is often sown after land preparation or soon after planting to protect the soil, provide humus, add to the nitrogen supply and suppress weeds. The main cover crop species used are Calopogonium mucunoides Desv., Centrosema pubescens Benth. and Pueraria phaseoloides (Roxb.) Benth., often in mixtures of 2 or 3 species, while Calopogonium caeruleum (Benth.) Sauvalle is sometimes planted alone. Except in regions with no distinct dry season, the best time of transplanting into the field is at the beginning of the main rainy season to give the young palm time to form a good root system before the next dry season arrives.
Planting density is a major issue as it determines competition between palms for light in particular, but also for water and minerals. There is experimental evidence for a progressive reduction of dry matter production with higher densities, but also that fruit yield is more affected than vegetative growth. Hence, maximum yields are reached at a planting density that is lower (140–160 per ha) than the density that gives maximum total dry matter production. Oil palm is commonly planted 9 m apart in a triangular pattern giving 143 plants/ha.
The interrows in oil palm fields have to be slashed regularly, especially in fields with young palms. Clean weeding is practised around palms, manually or by applying herbicides to prevent competition from the cover crop. It also facilitates the detection of loose fruits from ripe bunches. Harvesting paths are kept open. During harvesting of bunches, leaves are usually removed as well. If the number of leaves per palm drops below 35, yield declines. Hence the aim is to maintain the number of leaves close to 40. Pruned leaves are generally stacked between palms within or between the rows and provide mulch and ground cover. As the canopies close in mature plantations, the legume cover is gradually replaced by a natural vegetation, often consisting of a mixture dominated by grasses and ferns. Increased use of herbicides instead of hand weeding leads to replacement of the less competitive grass-fern cover by more noxious broad-leaved weeds. Intercropping of oil palm with annual food crops during the first 4 years after planting is common practice among small farmers in West Africa.
Considering the importance of moisture supply, oil palm benefits from irrigation in areas where the dry season is severe or long. Substantial areas of oil palm are under irrigation in southern India and Colombia, where the cost of irrigation is compensated by high yields.
The root system of young palms is not yet sufficiently developed to exploit a large volume of soil. Complete fertilizer applications are beneficial during the first three years after planting to boost vegetative growth and early production. Recommendations in Nigeria are: 0.1–0.6 kg N, 0.3–1.4 kg P and 0.4–1.2 kg K per palm per year, with rates increasing from field planting to 3 years. Nutrient status of adult palms varies considerably with soil and climatic conditions, history of the land before planting, and with the levels and number of years of production. On fertile land cleared from dense secondary forest, oil palm may not show yield responses to fertilizers for several years. The gross annual uptake of nutrients of adult oil palms grown on a marine clay in Malaysia and yielding 25 t of fruit bunches was per palm: 1.4 kg N, 0.2 kg P, 1.8 kg K, 0.6 kg Ca and 0.4 kg Mg. About 30–40% of that is removed by the harvested bunches, 25–35% is returned to the soil as dead leaves and male inflorescences and the rest is immobilized in the trunk. In combination with the results of local fertilizer trials, foliar analysis (sampling a few leaflets from leaf 17) is a reliable diagnostic tool in oil palm to determine types and rates of fertilizer applications for mature oil palms long before deficiency symptoms become apparent. Significant responses to phosphorus and magnesium are less common, but these elements are often included in fertilizer applications as a precautionary measure. The demand for micro-nutrients is less well established for oil palm. Composted waste products from the palm oil mills (empty bunches, fibre and sludge) forms a considerable source of nutrients, which can partly replace inorganic fertilizers, while simultaneously improving physical and biological soil quality.
Oil palm is a fairly labour-intensive crop and optimum plantation management requires about one field worker per 4 ha. The need for increased mechanization of field operations becomes evident in regions with a labour shortage, e.g. in Malaysia. Most field maintenance operations can be mechanized, but economically viable methods for mechanically removing the ripe bunches from the palms have not yet been developed.
Diseases and pests
Nursery seedlings are affected by a number of fungal diseases, which, however, can be controlled by cultural and fungicide treatments. The most important ones are anthracnose (caused by Botryodiplodia spp., Glomerella spp. and Melanconium spp.), seedling blight (caused by Curvularia spp.), Cercospora leaf spot (caused by Cercospora elaeidis) which is restricted to Africa, and blast (a root disease caused by Rhizoctonia lamellifera (synonym: Macrophomina phaseolina) and Pythium spp.). Crown disease is a physiological disorder causing leaf distortion in 2– 4-year old palms, particularly of Deli origin, and having a severe effect on early development and yield. Breeding for crown-disease free oil palm is possible, as susceptibility is inherited by a single recessive gene.
Vascular wilt (caused by Fusarium oxysporum f.sp. elaeidis) occurs only in Africa, mostly in areas marginal to oil palm cultivation. Breeding for resistance has met with some degree of success. The most important disease in adult palms in South-East Asia is basal stem rot (caused by Ganoderma sp.), which may cause high losses, especially when replanting land previously under coconut or oil palm. Infection takes place through root contact with decaying stems and roots. Control is limited to sanitary measures, such as complete removal of all stumps and roots before replanting and removal of diseased palms from plantations. Lethal bud rot (often with little leaf symptoms) and sudden wither are two serious diseases of oil palm in Central and South America. The causes are uncertain, but a promising method of control is planting with resistant Elaeis oleifera × Elaeis guineensis hybrids. Strict plant quarantine measures (e.g. seed treatment) are taken to prevent the inadvertent introduction of diseases such as Fusarium vascular wilt and Cercospora leaf spot into South-East Asia or tropical America.
The leaf miner (Coelaenomenodera lameensis (synonym: Coelaenomenodera elaeidis)) is a serious oil palm pest of West Africa, regularly causing heavy defoliation in Côte d’Ivoire, Ghana, Benin, Nigeria and western Cameroon. Control is effected by a combination of regular monitoring of larvae and adults to determine optimum timing for insecticide spray application (e.g. thiocyclam). Biological control by indigenous or exotic egg and larval parasites is under study. Another important pest in Africa is the palm weevil Rhynchophorus phoenicis often in combination with the rhinoceros beetle (Oryctes monoceros), which burrows into the cluster of central spear leaves and thereby predisposes the palms to a secondary attack by the palm weevil. Pheromone-based mass trapping of Rhynchophorus phoenicis and manual collection of the weevils can be an effective method of pest control. Insects pests causing occasional damage are the African spear borer (the moth Pimelephila ghesquierei) and weevils (Temnoschoita spp.) on young palms in Central and West Africa (e.g. DR Congo) in particular, and leaf-eating nettle and slug caterpillars (Parasa pallida, Parasa viridissima). In South-East Asia, where the range of insect pests differs from that in Africa, techniques of integrated pest management in oil palm plantations are well-advanced. They include close monitoring, biological control and spraying with narrow-spectrum insecticides to prevent major epidemics. Occasional outbreaks of bagworms (Cremastopsyche pendula, Metisa plana, Mahasena corbetti), nettle and slug caterpillars (Darna trima and Setora nitens) occur notably in Sabah and Sumatra. The rhinoceros beetle (Oryctes rhinoceros) of Asia and the Pacific has readily adapted to oil palm. Destruction of breeding sites and good ground cover generally ensure adequate control. Other occasional pests in South-East Asia are the oil palm bunch moth (Tirathaba mundella), root-feeding cockchafers (Adoretus and Apogonia spp.) and grasshoppers (e.g. Valanga nigricornis). In West Africa, young palms need protection by a wire collar against the rodent Thryonomys swinderianus (cutting-grass rat, greater cane rat or agouti) during the first year after field planting. Rats can cause considerable damage on maturing fruit bunches. Control is carried out by baiting. Barn owl (Tyto alba) is also used in Malaysia to prey on rats and nest boxes are placed in the plantation.
Harvesting of bunches generally starts in West Africa 3–3.5 years after planting, in South-East Asia already after 2.5 years. In the estate sector it is common practice to remove the first series of unopened female inflorescences from the young palm, by one round of so-called ablation with a special tool, to promote vegetative growth and because the first bunches have a low oil content. Bunches ripen throughout the year and harvesting rounds are usually made at intervals of 7–10 days. Bunches are cut when they have reached optimum ripeness. A practical indicator of ripeness is the number of loose or detached fruits per bunch, which should be 5 during the first three years of fruiting when bunches are still relatively small, to 10 for older palms. Bunches are cut from the stalk with a chisel in young palms, while in tall palms a ‘Malayan knife’ that consists of a sickle on a long bamboo or aluminium pole is used. In Africa very tall and smooth-stemmed palms are climbed with a climbing rope and the bunches are removed with a cutlass. Loose fruits must be gathered from the ground because they also yield oil. Bunches are transported to collection sites along the road and from there direct to the mill by road or rail track (Asia) for processing.
World average yields per ha in 2005 were 2.8 t palm oil and 0.7 t palm kernels (45% oil and 55% meal). National averages for palm-oil yields per ha are, for example: Nigeria 0.3 t (plantations 1.9 t), DR Congo 0.7 t, Ghana 1.1 t, Côte d’Ivoire and Cameroon 2.6 t, Colombia 3.9 t, Malaysia 4.1 and Indonesia 4.2 t. Oil palm is extremely responsive to environmental conditions and annual yields therefore vary greatly. The course of yield over time, however, shows a clear trend of rising to a maximum in the first four years of production and usually declining slowly thereafter. In well-managed mature plantations in Malaysia, Indonesia and Papua New Guinea annual bunch yields of 24–32 t/ha are common. At factory oil extraction rates of 22% (‘Tenera’ type) this represents palm oil yields of 5.2–7.1 t/ha. In West Africa, where climatic conditions are less favourable (with a substantial dry season), maximum annual bunch yields of 12–16 t are obtained or 2.6–3.5 t of palm oil per ha, which is nevertheless still much higher than for any other oil crop.
Handling after harvest
Palm oil mills, large or small, process fresh fruit bunches (FFB) to oil and kernels through the following stages:
– sterilizing the FFB with steam under pressure to loosen the fruits, destroy the lipolytic enzyme lipase to arrest free fatty acid formation and kill all micro-organisms;
– stripping the fruits from the bunches;
– digesting the fruits and reheating of the macerated mix of pulp and nuts (stones);
– extracting oil by hydraulic or (double) screw presses;
– clarifying to remove water and sludge from the oil in continuous clarification tanks or by centrifugal separation and drying;
– storing of the crude palm oil in tanks before transport for further refining and processing.
Nuts are separated from the presscake, dried, graded and fed into centrifugal crackers to remove the shell. Kernels are extracted for the oil in separate mills, locally or abroad, by methods similar to those used for copra.
On the one hand, there are industrial mills with capacities to process 20–60 t FFB/hour for large oil palm plantations and their smallholder ‘outgrowers’; on the other hand, a range of small plants with oil extraction efficiencies similar to those of large mills (>92%) have been developed over the past 50 years for the smallholder oil palm sector, which operates independently of the estate sector and in West Africa produces mainly for the domestic markets. The capacity varies from 1–2 t FFB/hour in a highly mechanized plant with a double-shafted continuous screw press, to 0.5 t FFB/hour or less by a unit with 1–2 manually operated hydraulic presses with ancillary equipment for sterilization, digestion and clarification.
The traditional method of edible oil extraction in West Africa, still applied in remote villages, includes boiling of the fruits, pounding and boiling again until the floating oil can be skimmed off. Palm oil for soap manufacturing is manually extracted from macerated fruits, which have been allowed to ferment in pits for several days. Oil extraction efficiency of the traditional methods is low (<50%) and free fatty acid content high (6–10%) even in edible palm oil.
Almost all present oil palm planting materials in Malaysia, Indonesia, elsewhere in South-East Asia and tropical America, have been developed from the genetically very narrow ‘Deli Dura’ population and one source of ‘Pisifera’ (the ‘Djongo Tenera’ palm from Yangambi in DR Congo). Oil Palm research centres in West Africa had easier access to germplasm, but except at the Nigerian Institute for Oil Palm Research (NIFOR) most breeding programmes started from genetically restricted base populations. Increasing awareness of the importance of oil palm genetic resources for future breeding progress led NIFOR to mount collecting expeditions in 1956 and 1964 and a very large one in collaboration with the Malaysian Palm Oil Board (MPOB, formerly PORIM and MARDI) in 1973, all in south-eastern Nigeria, the centre of highest genetic diversity. MPOB organized another 9 expeditions in the oil palm belt from Senegal to Angola and even in Tanzania and Madagascar during the period 1984–1994. It also collected Elaeis oleifera germplasm from Central and South America in 1982. The MPOB has the largest oil palm germplasm collection in the world with 1780 accessions (61% from Nigeria and 21% from DR Congo) maintained on 400 ha of field trials at the research station near Kluang, Johore (Malaysia). Another large field collection of more than 1000 accessions is maintained by NIFOR near Benin City (Nigeria). The National Centre for Agricultural Research (CNRA, formerly IRHO) in Côte d’Ivoire maintains a collection of more than 200 accessions. Other public and private oil palm research centres in Asia, Africa and America also try to enlarge their collections of genetic resources.
Oil palm germplasm collected in 1966 in the Bamenda Highlands of Cameroon and in 1977 along Lake Tanganyika, both at altitudes of about 1000 m, are being tested in the cooler uplands of Ethiopia and other countries of East Africa in an effort to extend oil palm cultivation beyond its natural ecosystem of the tropical lowlands. Results are still to be published.
Free exchange of germplasm by seed or pollen is general practice among research centres and strict quarantine rules are followed to avoid inadvertent introduction of new diseases and pests.
Oil palm breeding has progressed from simple mass selection (families and individual palms within the best families) to various forms of (reciprocal) recurrent selection for ‘Dura’ and ‘Pisifera’ trees as parents for higher-yielding ‘Tenera’ planting material. Estimates of selection progress for oil yield in the ‘Deli Dura’ populations of Indonesia and Malaysia are 50–60% over 3–4 generations of mass selection (1910–1960). The change to ‘Tenera’ planting material in the early 1960s resulted in an instant yield increase of another 20% because of the jump in oil extraction rates from 18% in ‘Dura’ to 22% in ‘Tenera’ fruit bunches. Similar developments took place in Africa.
Extensive quantitative genetic studies (1960–1970s) carried out in large breeding programmes of NIFOR in Nigeria and Ghana, CNRA in Côte d’Ivoire and the Oil Palm Genetics Laboratory (OPGL, now MPOB) in Malaysia have confirmed the largely additive inheritance of all yield components. This allows breeders to make estimates of genotypic (breeding) values for these components for a large number of parents by a minimum number of crosses and so reduce the costs of progeny testing. Another observation relevant to selection progress in the oil palm is the moderate to low genotype × environment interaction effects for yield and its components. Selection progress for yield is maximized by combining parents with contrasting yield components, such as the Deli × African ‘interorigin’ crosses, which combine a relatively low number of heavy bunches with a high number of smaller bunches. Further selection progress requires the development of new contrasting subpopulations, more particularly to increase the genetic variability of the ‘Deli Dura’ population and also the source population of ‘Pisifera’ in Asia by introgression with African germplasm. In the Malaysian and some other breeding programmes, considerable selection efforts are being directed to vegetative growth components to improve harvest index and to reduce height increment for the further increase of oil yields and reduction of production costs. Germplasm evaluation in Malaysia has revealed highly productive (up to 10 t/ha of oil) and short stem (height increment of 20–25 cm/year against 45–75 cm/year for present planting material) families of south-east Nigerian origin. The heritability of height increment is high, as is the case with fruit quality components (mesocarp, shell and kernel content) and fatty acid composition of the palm oil, thus allowing effective phenotypic selection of parents for these characters.
Conventional plant breeding that exploits genetic diversity within the genus still offers considerable opportunities for improvement. Further development of high density genetic linkage maps for oil palm, using advanced marker technology (e.g. microsatellites), will enable the identification of significant QTLs (quantitative trait loci) for yield and growth components to increase efficiency of selection, e.g. by preselection at the nursery stage. New complementary biotechnological approaches are being explored. The MPOB in Malaysia has initiated major research projects on genetic transformation in oil palm. Objectives include resistance to herbicides and diseases (e.g. Ganoderma) and changes in the fatty acid composition of palm oil (e.g. high oleic acid content). Increased understanding at the molecular level may help to control flower abnormalities in clonal offspring after in-vitro embryogenesis and so make large-scale clonal propagation possible in oil palm.
World demand for vegetable oils is rising sharply, from 100 million t in 2005 to an estimated 150 million t in 2020, as the world population continues to grow and the standards of living increase in many developing countries. The role of oil palm as a supply of relatively inexpensive and versatile edible oil is, therefore, expected to become ever more prominent. With best practices for cultivation and processing, it can produce 4–6 times more oil/ha than any of the other oil crops, in an economically and environmentally sustainable manner. Extrapolations from crop-growth models suggest that the physiological potential for oil yield of oil palm may well be 12–14 t/ha against present maximum yields of 7 t/ha. The new possibility of clonal propagation is an important factor in this respect. The main drawback of oil palm is the difficulty of cost-effective mechanization of harvesting. Hence, availability and cost of labour may well become limiting factors in producing countries with improving standards of living.
Well-established oil palm plantations provide an ecosystem that has some of the characteristics of humid tropical forests. Recent studies have shown that the net carbon sequestration by a mature oil palm ecosystem is higher than that of humid tropical forests. The negative publicity on palm oil as being an ‘unhealthy tropical vegetable oil’ has been repeatedly proved unjustified by scientific evidence. On the other hand, much needs to be done at national and regional levels, particularly in South-East Asia, to restore the reputation of the oil palm as an ecologically sustainable plantation crop, as this has been severely tarnished in the past decade by poorly controlled expansion causing air pollution and unnecessary destruction of tropical forests. The ‘Roundtable on Sustainable Palm Oil’, initiated by stakeholders of the Malaysian palm oil industry in 2003, appears to be a move in the right direction in this respect.
In West Africa the smallholder sector of palm oil producers, processors and traders is increasingly overtaking the privatized formal plantation sector in becoming the main supplier for the ever-growing domestic markets. Sustainable palm oil production needs to be redefined here, as the best management practices applied in the estate sector may be incompatible with the socio-economic priorities of the smallholders and their families.
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Correct citation of this article:
Ataga, C.D. & van der Vossen, H.A.M., 2007. Elaeis guineensis Jacq. In: van der Vossen, H.A.M. & Mkamilo, G.S. (Editors). PROTA 14: Vegetable oils/Oléagineux. [CD-Rom]. PROTA, Wageningen, Netherlands.
wild and planted
1, tree habit; 2, male inflorescence; 3, infructescence; 4, fruit; 5, fruit in longitudinal section.
Redrawn and adapted by Iskak Syamsudin
oil palm plantation
inflorescence and infructescence
oil palm factory
oil palm fibres