Elaeis guineensis (PROSEA)
Elaeis guineensis Jacq.
- Protologue: Select. stirp. amer. hist.: 280 (1763).
- Family: Palmae
- Chromosome number: 2n= 32
- Oil palm, African oil palm (En). Palmier à huile (Fr)
- Indonesia: kelapa sawit (general), kalapa ciung, kalapa minyak (Sundanese)
- Malaysia: kelapa sawit. Burma (Myanmar): si-ohn, si-htan
- Cambodia: dôong preeng
- Thailand: paam namman, ma phraao hua ling (central), maak man (peninsular)
- Vietnam:cọdầu, dừa dầu.
Origin and geographic distribution
E. guineensis is indigenous to the tropical rain-forest belt of West and Central Africa between Senegal and North Angola (12°N-10°S latitudes). There is fossil evidence for the Niger delta as a possible centre of origin. The natural habitat of this heliophile palm is assumed to be at the edges of swamps and along river banks, where there is little competition from the faster growing tree species. The abundance of oil-palm groves throughout the forest zone is attributed to early domestication by man, who in ancient times started to open up patches of primary forest for habitation and cultivation. 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 populations.
The semi-wild oil-palm groves of north-eastern Brazil have a West African origin through the 17th Century slave trade. It gradually spread to other regions of tropical America and the original description of E. guineensis by Jacquin in 1763 was based on a specimen growing in Martinique. The introduction of the oil palm into South-East Asia started with four seedlings planted in the Bogor Botanic Gardens (Indonesia) in 1848. Offspring of these palms formed the basis for the oil-palm plantation industry, which started to develop from 1911 in Indonesia, mainly in Sumatra, and from 1917 in Malaysia.
The 19th Century trade in palm oil and kernels between West Africa and Europe was entirely dependent on the produce of the semi-wild palm groves. In response to increasing demands for more and better quality palm oil, commercial plantations also started to be established in Africa after 1920 (e.g. 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 started in 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. Ivory Coast, Cameroon, Ghana). Smaller oil-palm industries are also developing in the Philippines, Solomon Islands, China (Hainan), India and Sri Lanka. World palm oil production increased from 1.3 million t in 1960 (78% from Africa) to 12.1 million t in 1980 (83% from South-East Asia).
Two types of oil are extracted from the fruit of E. guineensis : palm oil from the mesocarp and palm-kernel oil from the endosperm, in the volume ratio of approximately 9:1. Palm oil is used in many edible products, such as cooking oils, margarine, vegetable ghee ("vanaspati"), shortenings, frying fats, bakery and biscuit fats, potato crisps, pastry, confectionery, ice-cream and creamers. While red crude palm oil is an essential ingredient of the West African diet, the clear olein fraction is preferred as cooking oil in South-East Asia. About 10% of all palm oil, the inferior grades in particular and also refining residues, is used to manufacture soaps, detergents, cosmetics, candles, resins, lubricating greases, glycerol and fatty acids. Palm oil is also employed in the steel industry’s tin plating and sheet steel manufacturing. Epoxidized palm oil is a plasticizer and stabilizer in PVC plastics. Crude oil and its methyl esters can be used as bio-fuel 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 as done in Indonesia, 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 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 like surface-active agents, plastics, lubricants and cosmetics. The presscake or palm-kernel meal is a valuable protein-rich livestock feed.
The empty bunch stalks, mesocarp fibres after oil extraction and the shells from the cracked nuts are used as fuel for the boilers of the palm-oil mill. Various other wastes from the palm-oil mill may be converted into fertilizers and other valuable products.
The popular African practice of producing palm wine by tapping the unopened male inflorescences, or the stem just below the apex of standing or felled oil palms, has not been adopted in South-East Asia. The palm heart consisting of the soft tissues 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 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 materials for paper and board production, but this has not yet attracted much commercial interest.
Oil palm is sometimes planted as a garden ornamental and along avenues.
Production and international trade
Between 1996 and 2000, annual world production of palm oil increased from 16.2 to 21.8 million t and the total area from 5.3 to 6.6 million ha. South-East Asia produced 86%, West Africa 7% and tropical America 6% of total palm oil supply. The largest producers of palm oil in 2000 were Malaysia with 10.70 million t, Indonesia with 6.65 million t, Nigeria with 0.74 million t, Colombia with 0.52 million t and Thailand with 0.44 million t. Papua New Guinea produced 285 000 t and the Philippines 54 000 t palm oil. Areas planted to oil palm in South-East Asia are: Malaysia 2.91 million ha, Indonesia 2.01 million ha, Thailand 0.17 million ha, Papua New Guinea 70 000 ha and the Philippines 20 000 ha. World trade in palm oil amounted to 14.6 million t in 2000 or 70% of the total production. Malaysia and Papua New Guinea exported more than 90% of their production, Indonesia 50%, Colombia and Thailand each about 20%, while practically all of Nigeria’s palm oil was consumed domestically. Oil palm still takes second place in world production after soya bean (24% against 28%), but in 2000 palm oil was the most important commodity (42%) in the world trade of vegetable oils and fats.
In 2000, world palm-kernel oil production was 2.6 million t with Malaysia (1.42 million t), Indonesia (0.67 million t) and Nigeria (0.18 million t) being the leading producers. Palm-kernel meal production in 2000 was 3.2 million t and Malaysia was the biggest producer (1.72 million t) followed by Indonesia with 0.83 million t and Nigeria with 0.21 million t. Fifty percent of the oil and 85% of the meal were traded internationally.
Industrially extracted fresh fruit bunches of the most commonly planted E. guineensis cultivars (Dura × Pisifera hybrids producing thin-shelled Tenera fruits) yield per 100 kg: palm oil 20-28 kg and kernels 4-8 kg (2-4 kg kernel oil). Per 100 g, the mesocarp of mature fruit 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, protein 7-9 g, oil 48-52 g, carbohydrates 32-30 g and crude fibre 4-5 g.
Palm oil varies in colour from pale yellow to dark red; its melting point ranges from 25-40°C and it has an energy value of 3700 kJ per 100 g. It consists of triglycerides with the following fatty acids: myristic acid 1-2%, palmitic acid 45-52%, stearic acid 2-4%, oleic acid 34-41% and linoleic acid 4-9%. Palm oil for edible purposes should contain less than 3% free fatty acids. 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 of up to 850 mg/kg. Carotenoid content is reduced to zero and the tocopherol content to half during the refining of the oil. High quality palm oil should have the following characteristics: <2% free fatty acid (FFA), <0.1% moisture and <0.002% dirt content; iodine value of >53; carotene 500 ppm; tocopherol 800 ppm; good bleachability and consistency of all other properties.
Kernel oil is light yellow, but almost white when solid. Its melting point range is 23-30°C. The fatty acid composition of palm-kernel oil is similar to that of coconut oil: 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%. However, there is less caprylic acid (3-4%) and capric acid (3-7%). Per 100 g palm-kernel cake contains: water 8-11 g, crude protein 19-22 g, carbohydrates 42-49 g, crude fibre 11-15 g and some other minor components such as calcium, phosphorous and iron.
The weight of 1000 "seeds" (kernel with endocarp) is 4-12 kg for Dura (thick shelled) and 2-3 kg for Tenera (thin shelled).
An armed, unbranched, pleonanthic, monoecious palm up to 15-30 m tall, with a terminal crown of 40-50 leaves. 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 vertically for anchorage for more than 1.5 m; the roots also develop pneumatodes, particularly under very moist conditions. Stem erect, cylindrical, 30-75 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 and smooth in older palms. Leaves spirally arranged, 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 conspicuous, adaxially channeled, abaxially angled, 1-2 m long, bearing spines, upper spines are modified small pinnae; juvenile leaves lanceolate, entire to gradually becoming pinnate; mature leaf paripinnate, up to 8 m long; leaflets 250-350 per leaf, irregularly inserted on the rachis and giving the oil-palm crown a shaggy appearance, linear but single fold, 35-65 cm × 2-4 cm, pulvinus at base, with thick cuticular wax layer on upper surface and semi-xeromorphic stomata on lower side. Inflorescence axillary, solitary, looking like a short and condensed compound spike or spadix, unisexual, several adjacent axils producing inflorescences of one sex followed by several producing the other sex, branching to 1 order; peduncle 30-45 cm long; inflorescence tightly enclosed in 2 fusiform or ovate spathes before anthesis; central rachis with 100-200 spirally arranged spikes; male inflorescence ovoid, 20-25 cm long and spineless, with cylindrical spikes 10-20 cm long, each with 700-1200 closely packed flowers; male flower 3-4 mm long, perianth consists of 6 small segments, androecium tubular with 6 anthers and rudimentary gynoecium; female inflorescence subglobose, 25-35 cm long, with thick rachis, spikes thick and fleshy, each in the axil of a spiny bract, with 10-25 spirally arranged flowers and a terminal spine; female flower in shallow cavity accompanied by two rudimentary male flowers and subtended by a spiny bract, with 2 bracteoles, 6 sepaloid tepals 2 cm long, a rudimentary androecium, a tricarpellate ovary and a sessile, 3-lobed, creamy-white stigma. Infructescence with 500-3000 fruits together in tightly packed subspherical bunches up to 50 cm long and 35 cm wide, weighing 4-60(-90) kg; fruit a globose to elongated or ovoid, sessile drupe, 2-5 cm long, weighing 3-30 g, apex with persistent woody stigma and usually violet-black pigmented; exocarp smooth, shiny, orange-red when ripe; mesocarp fibrous, yellow-orange, oleiferous, comprising 20-90% of the fruit; endocarp (shell) stony, dark brown, very variable in thickness, with longitudinal fibres drawn out into a tuft at base and 3 germ pores at apex; innermost fruits are smaller, irregularly shaped and have a less pigmented apex. Seed (kernel) usually 1, sometimes 2 or 3, with dark brown testa; endosperm solid, oleiferous, grey-white, embedding an embryo opposite one of the endocarp germ pores. Embryo about 3 mm long.
Growth and development
After harvesting, oil-palm seeds are dormant. Germination starts with the appearance of a white button, 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 petioled haustorium. Subsequent leaves gradually change from lanceolate to pinnate over a period of 12-14 months, when the seedling has 18-24 leaves. Pinnate leaves on seedlings have no spines and are less xeromorphic than adult leaves. The base of the stem becomes like a swollen bulb from where adventitious primary roots develop. In the first 3-4 years, lateral growth of the stem dominates, giving a broad base up to 60 cm in diameter. After that, the stem starts growing in height, 20-75 cm per year, at 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°, causing leaf bases to be arranged in apparent spirals, of which a spiral of 8 leaves per tour is the most obvious one. 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 leaf and 9th leaf. 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 (2-10 m2) takes 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 lifetime 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 on 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 this sex differentiation is not yet 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 the oil palm to survive under adverse climatic conditions by reducing the crop 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, 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-like fragrance during anthesis. Fruits ripen within 4.5-6 months after anthesis. Fruit ripening on the bunch proceeds simultaneously from top to bottom and from outer to inner fruits. Ripe fruits become detached. Oil formation in the seed takes place from 2.5-3.5 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.
Other botanical information
Elaeis Jacq. comprises only two species: the African E. guineensis and the tropical American E. oleifera (Kunth) Cortes (synonyms Corozo oleifera (Kunth) L. H. Bailey, E. melanococca Gaertn.). E. oleifera is distributed from southern Mexico to the central Amazonian region (Brazil, Colombia and Ecuador) and grows in poorly drained, sandy, often open habitats along river banks, in swamps and fresh-water mangrove communities. Due to low oil yield, E. oleifera is of little economic importance, except in its natural area of distribution. However, it has a range of other characters that are potentially useful in oil-palm breeding, including resistance to some important pests and diseases, slow stem growth and high unsaturated fatty acid content of the mesocarp oil. E. oleifera and E. guineensis are inter-fertile and hybridization to transfer such characters is in progress.
Barcella odora (Trail) Trail ex Drude (syn. Elaeis odora Trail), is another palm closely related to the oil palm. It occurs along the Rio Negro in Brazil, has no petiole spines, a long peduncle and male and female flowers in the same inflorescence.
E. guineensis is very variable and many classifications exist to describe the variation, but no classification into cultivars and cultivar groups exists. Agricultural classifications are primarily based on variation in fruit characteristics. One with considerable economic consequences is the distinction between three forms based on shell thickness, which is determined by a single major gene:
- Dura: homozygous (sh+sh+) for the presence of a relatively thick endocarp (2-8 mm at cross-section of fruit);
- Tenera: heterozygous (sh+ sh-) with a relatively thin endocarp (0.5-4 mm);
- Pisifera: homozygous (sh-sh-) for the absence of a lignified endocarp.
Within the Dura and Tenera forms, 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% per fruit weight) than Dura (20-65% per fruit weight). The original Bogor oil palms and the material derived from them were of the Dura form and as a population, it is generally referred to as Deli Dura. Pisifera is usually unproductive because the female inflorescences abort before developing fruit bunches, but it is used as male parent in crosses with Duras to produce pure stands of Tenera palms.
Other classifications based on fruit characteristics (also controlled by one gene) are:
- anthocyanin in the upper fruit exocarp: absent in virescens form, present in nigrescens form (recessive);
- carotene in the mesocarp: absent in albescens form (recessive);
- additional carpels in the fruit: present in poissoni (mantled) form (recessive).
The so called "idolatrica" oil palm has entire leaves because the leaflets do not separate (recessive character).
For some time an oil palm with smaller fruits found in Madagascar was considered a separate species ( E. madagascariensis Becc.), but is now thought to fall within the normal variability range of E. guineensis . In Madagascar E. guineensis has probably been introduced.
Oil palm is a heliophile crop of the humid tropical lowlands, with maximum photosynthetic activity only under bright sunshine and unrestricted water availability. Such palms show one unopened leaf at any time, while several 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 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 (in elevations exceeding 400 m or latitudes above 10°), growth and productivity are severely reduced. The oil palm is also affected by excessively high temperatures, as photochemical efficiency becomes progressively lower above 35°C.
Oil palm can grow on various soils like latosols developed over different 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/cm 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 the oil palm is fairly tolerant of short periods of water stagnation.
Propagation and planting
Freshly harvested, cleaned and dried (14-17% moisture content) "seeds" of oil palm lose viability within 9-12 months at tropical ambient temperatures (27°C). High seed viability (>85% germination) can be maintained for about 24-30 months in air-conditioned stores at 18-20°C and seed moisture content of 21-22%. Longer storage of valuable oil-palm germplasm by cryopreservation of seeds, excised embryos or somatic tissues is now also possible. Seeds of the oil palm require a heat treatment at 39-40°C for 60-80 days, followed by cooling and rehydration, to break dormancy and induce rapid germination, but in vitro grown excised embryos start elongating within 24 hours.
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 Pisiferas. The fruits are of the Dura type, but the palms raised from them 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 seeds can be transported over long distances (300 in a polythene bag and several bags carefully packed in a box) before planting in a mini polybag (8 cm × 20 cm lay-flat, 200 gauge, black polythene) pre-nursery. Transplanting takes place at the 2-leaf stage into a large polybag (40 cm × 60 cm lay-flat, 500 gauge, black polythene) nursery. 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 in the oil palm through somatic embryogenesis, starting from young root or leaf explants, were first developed in the late 1970s. Vegetative reproduction offers by far the quickest and most efficient means of fixing genetic improvements in a cross-pollinated species. 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 widespread application of clonal propagation in the oil palm can 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 strong 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 crops used are Calopogonium muconoides Desv., Centrosema pubescens Benth. and Pueraria phaseoloides (Roxb.) Benth., often in a mixture of two or all three. Except in regions with no distinct dry season, the best time for 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 nutrients. There is experimental evidence for a progressive reduction of dry matter production with higher density, but also that fruit yield is more affected than vegetative growth. Hence, maximum plant densities for oil yield (140-160 palms per ha) are lower than those for maximum total dry matter production. Planting palms 9 m apart in a triangular pattern gives 143 plants/ha.
The inter-rows in oil-palm fields have to be slashed regularly, especially in fields with young palms. Weeding is practised around palms, manually or by applying herbicides, to prevent competition from the cover crop. Clean ring-weeding 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 together with ground cover. As the canopies close in mature plantations, the legume cover is gradually replaced by natural vegetation, often consisting of a mixture dominated by various 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 ( Asystasia spp. , Diodia spp., Mikania spp.). Intercropping oil palms with annual food crops during the first few years after planting is a common practice among small farmers, mainly in Africa.
Considering the importance of moisture supply, oil palms will undoubtedly benefit from irrigation, depending on the severity and length of dry periods. Substantial areas of oil palm are under irrigation in southern India and Colombia where water deficits during the dry period are compensated for by high numbers of sunshine hours and good yield results.
The root system of young palms is not sufficiently developed to exploit a large volume of soil. Regular complete (NPKMg) fertilizer applications are therefore recommended during the first three years after planting to boost vegetative growth. Nutrient requirements of adult palms vary considerably with soil and climatic conditions, as well as with yield levels. The gross annual uptake of nutrients by adult oil palms grown on a marine clay in Malaysia and yielding 25 t/ha of fruit bunches was: 1.4 kg N, 0.2 kg P, 1.8 kg K, 0.4 kg Mg and 0.6 kg Ca per palm. 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. Foliar analysis (sampling a few leaflets from leaf 17) in oil palm in combination with the results of local fertilizer trials, is a reliable diagnostic tool to determine types and rates of fertilizer applications for mature oil palms long before deficiency symptoms on leaves become apparent. Generally nitrogen and potassium are the most important nutrients for maintaining growth and yield. Significant responses to phosphorus and magnesium are less common, but these are often included in fertilizer application as a precautionary measure. In plantations in Malaysia, 2-4 kg N fertilizer and 1.5-3 kg K fertilizer per palm are commonly applied annually. On the other hand, fertilizer requirements of palms on the nutrient-rich volcanic soils in parts of Sumatra are much lower. The need for micro-nutrients is less well established for oil palm. Well-documented cases of boron deficiency and suspected incidents of copper deficiency on peat soils have been reported.
The oil palm is a fairly labour-intensive crop. Optimum management requires about one field worker per 4 ha, but in Malaysia this has been decreased to approximately one per 10-12 ha. The need for increased mechanization of field operations becomes evident in a number of regions with a labour shortage. Most field maintenance operations can be mechanized, but there are no economically viable methods available for mechanically removing the ripe bunches from the palms.
Diseases and pests
In the nursery, oil palm seedlings are affected by a number of fungal diseases, which however can be controlled by cultural and fungicidal treatments. The most important 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 and Pythium spp.). Crown disease is a physiological disorder causing leaf distortion in 2-4-year old palms, particularly of the Deli origin, and having a severe effect on early development and yield. Breeding for crown disease-free palms is possible, as susceptibility is inherited by a single recessive gene.
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 on land previously under coconut, but also after 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 new planting and removal of diseased palms in plantations.
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 resulted in some degree of success. Lethal bud rot (often with few leaf symptoms) and sudden wither are two serious diseases of oil palms in Central and South America. The causes are unknown or uncertain. A promising method of control is planting resistant E. oleifera × E. guineensis hybrids.
Strict plant quarantine measures (e.g. seed treatment) are taken to prevent the inadvertent introduction of such diseases as Fusarium wilt and Cercospora leaf spot into South-East Asia.
Most insect pests in South-East Asia are controlled by integrated pest management. Techniques include close monitoring, biological control and spraying with narrow-spectrum insecticides to prevent major epidemics. Occasional outbreaks of bagworms ( Psychidae , e.g. Cremastopsyche pendula, Mahasena corbetti and Metisa plana ), nettle and slug caterpillars ( Limacodidae , e.g. Darna trima and Setora nitens ) occur notably in Sabah and Sumatra. The rhinoceros beetle ( Oryctes rhinoceros ) has readily adapted to the oil palm. Good ground cover and the destruction of breeding sites generally ensure adequate control. Other insects occasionally cause some damage like oil-palm bunch moth ( Tirathaba mundella ), root-feeding cockchafers ( Adoretes and Apogonia spp.) and grasshoppers (e.g. Valanga nigricornis ). The leaf miner ( Coelaenomenodera elaeidis ) and the weevil Rhynchophorus phoenicis are serious oil-palm pests of West Africa, while leaf eating caterpillars (e.g. Darna metaleuca and Sibine fusca ), root miner caterpillars ( Sagalassa valida ) and the beetle Strategus aloeus are damaging insect pests in the American continent.
Rats are sources of problems in many plantations. Control is carried out by rat baiting. The barn owl ( Tyto alba) is also used to prey on rats and nest boxes are placed in the plantation.
Under normal plantation conditions, harvesting of bunches of oil palm starts about 2.5 years after field planting in South-East Asia and after 3-3.5 years in West Africa. 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. The first bunches are small and have a low oil content anyway. Bunches ripen throughout the year and harvesting rounds are usually made at intervals of 7-10 days when they reach the optimum degree of 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. In young oil palms bunches are cut from the stalk with a chisel; in old palms with a Malayan knife that consists of a sickle attached to a long bamboo or aluminium pole. Loose fruits must be gathered from the ground because they also yield oil. So far, high costs have discouraged the use of mechanized forms of harvesting. Bunches are transported to collection sites along the road and from there, direct to the mill by road or rail track.
World average yields per ha in the year 2000 were 3.3 t palm oil and 0.8 t palm kernels (45% oil and 55% meal). National averages for palm-oil yields per ha are 4.1 t in Papua New Guinea, 3.8 t in Colombia and Malaysia, 3.3 t in Indonesia, 2.9 t in Ivory Coast and 1.3 t in the Democratic Republic of Congo. Oil palm is extremely responsive to environmental conditions and yields therefore vary greatly. Over time, however, yields show 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 a factory oil extraction rate of 22% (Tenera fruit type), this represents palm-oil yields of 5.3-7.01 t/ha. In West Africa with less favourable climatic conditions (substantial dry season), annual bunch yields of 12-16 t are obtained or 2.6-3.5 t of oil per ha, which is nevertheless still much higher than for any other vegetable oil crop.
Handling after harvest
Palm-oil mills process fruit bunches to oil and kernels through the following stages:
- sterilizing bunches 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 of the fruits from the bunches;
- digesting the fruits and reheating the macerated mix of pulp and nuts;
- 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 large tanks before transport for further processing.
Nuts are separated from the presscake, dried, graded and fed into centrifugal crackers to remove the shell. Kernels are extracted for oil in separate mills, locally or abroad, by methods similar to that for copra.
Almost all present oil-palm planting materials in Malaysia, Indonesia and elsewhere in South-East Asia have been developed from the genetically very narrow Deli Dura population and one source of Pisifera (the Djongo Tenera palm from Yangambi in the Democratic Republic of 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 Angola to Senegal and even in Tanzania and Madagascar during the period 1984-1994. It also collected E. 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 the Democratic Republic of Congo maintained on 400 ha of field trials at the research station near Kluang, Johore. Another large field collection of more than 1000 accessions is maintained by NIFOR near Benin city, Nigeria. The National Centre for Agricultural Research (CNRA) in Ivory Coast 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 genetic resources. 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 palms 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 in the 1960s and 1970s carried out in large breeding programmes of NIFOR in Nigeria and Ghana, CNRA (formerly IRHO) in Ivory Coast and the Oil Palm Genetics Laboratory (OPGL, now MPOB) in Malaysia 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 generally insignificant 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 Pisiferas in Asia) by introgression with other "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-stemmed (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 that of fruit quality components (mesocarp, shell and kernel content) and fatty acid composition of the palm oil, thus allowing effective phenotypic selection of parents.
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 the 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, such as preselection at the nursery stage. The Malaysian Oil Palm Board has initiated research projects on genetic transformation in the oil palm. Objectives include resistance to herbicides and diseases (e.g. Ganoderma ) and changing the fatty acid composition of the 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 the oil palm.
The prospects for the oil palm appear bright. The demand for vegetable oils is rising as the standard of living increases in parts of the Third World. As a crop, it is better suited than annual food crops to most soils in the humid tropics, which are prone to leaching. It provides continuous ground cover and ecological conditions similar to the original forest vegetation. Further increases in yield may also be expected. Extrapolations from crop-growth models suggest that the physiological potential for oil yield of the 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.
In most countries with a suitable climate, oil-palm cultivation is expanding. The main drawback of the oil palm is the difficulty of cost-effective mechanization, notably of harvesting operations. Hence, availability and cost of labour may well become the main limiting factors in countries with improving standards of living.
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J.J. Hardon, N. Rajanaidu & H.A.M. van der Vossen