Hibiscus cannabinus (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Hibiscus cannabinus L.

Protologue: Syst. nat. ed. 10: 1149 (1759).

Family: Malvaceae

Chromosome number: 2n= 36

Hibiscus sabdariffa L. var. δ (1753), H. sabdariffa L. subsp. cannabinus (L.) G. Panigrahi & S.K. Murti (1989).

• Kenaf, Deccan hemp, Bimlipatam jute (En). Kénaf, chanvre de Bombay, chanvre de Guinée (Fr)
• Indonesia: kenaf, Java jute
• Thailand: po kaeo (central), po daai (northern).

Kenaf is of African origin; in most countries south of the Sahara H. cannabinus is a very common wild plant and it is also widely grown as a vegetable or fibre crop. Angola may have been a primary centre of origin, but greatest morphological diversity is found in East Africa. Both kenaf and roselle ( H. sabdariffa L.) may have been domesticated as early as 4000 BC in Sudan. The date of initial introduction into India is unknown. References to kenaf cultivation started to be published around 1800 and it first appeared on the London market as "Bimlipatam jute" in 1901. India has remained the largest kenaf-producing country with concentrations of cultivation in West Bengal and in coastal areas around Visakhapatnam (Andhra Pradesh) and Madras (Tamil Nadu). Kenaf was introduced into Indonesia from India in 1904. An extensive programme of kenaf cultivation was initiated in the 1920s in the Caucasus region of the Russian Federation (former USSR) and from there it was introduced into China in 1935. Kenaf production was also initiated after 1945 in e.g. the United States, Cuba and South America. Kenaf is now widespread in the tropics and subtropics, often cultivated as a fibre plant. In Malesia it is cultivated but does not grow wild.

Dry retted kenaf fibre is used in the manufacture of coarse textiles, such as sacking and hessian cloth for the packaging of agricultural and industrial commodities, and is also made into twine, rope and rope-soled shoes. In some countries the fibre is converted into carpets and rugs. Directly scraped and dried bast ribbons are also used by local artisans in Asia and Africa to make cordage and sleeping mats. Blends of cotton and kenaf fibres can be made into apparel and upholstery quality yarns and fabrics. The bast can be processed into high-quality long-fibre pulps, e.g for cigarette paper. It can be used in blends with short-fibred pulps (e.g. from hardwood) to impart high tearing strength to specialty papers. The stripped woody core material of the stem ("sticks") provides fuel, fences, cattle sheds, a substitute for cork stoppers (Taiwan), raw material for particle board and laminated sheets for panelling, packing materials, animal bedding, mulch, potting media and absorbents. Whole stems are suitable raw material for the pulp and paper industry, and the use of whole stems is often a more economical option than separating the bast and core.

In Africa kenaf is mainly grown for its leaves, which are eaten as a vegetable. The flowers and young fruits are sometimes eaten as well. Whole young kenaf plants are an excellent fodder for cattle. The seeds are also an animal feed. The seed oil can be used in the production of linoleum, paints and varnishes. Sometimes it is used as a lubricant. The seed cake is edible and suitable for use as livestock feed or fertilizer. Various plant parts have medicinal uses: old leaves are used as a laxative and the juice from the flowers is taken against biliousness in India, where the seeds are considered stomachic, appetizing and aphrodisiac; they are employed externally as a poultice for pains and bruises. Experiments indicate that kenaf is suitable for use in plant bed filters to remove nitrogen and phosphorus from wastewater.

The average annual world production in 1997-2001 of jute-like fibres, a group consisting of kenaf, roselle, Congo jute (Urena lobata L.), Abutilon theophrasti Medik. and other Malvaceae, and sunn hemp (Crotalaria juncea L.), was about 450 000 t, harvested from 335 000 ha. Separate statistics are not available, but kenaf is estimated to make up about 90% of the total. Important kenaf fibre producing countries are India, China and the Russian Federation. In South-East Asia sizeable quantities of kenaf fibre are produced in Indonesia and Thailand. Almost all kenaf fibre is processed domestically and there is very little international trade. The fibre is traded under the name kenaf, but sometimes this name is also used for roselle fibre.

Kenaf is growing in importance as a raw material for paper making in a number of areas, including South-East Asia, India, China, Africa, the Caribbean and the southern part of the United States.

Kenaf produces a bast fibre similar to jute (Corchorus spp.), except that it has a greater tensile strength and is somewhat coarser and more brittle. Kenaf fibre can be spun alone, or in admixture with jute, on machinery for jute spinning. The raw (retted and dried) bast fibre makes up 5-7% and the wood 15-21% of the freshly harvested and defoliated green stems. On a dry weight basis the bast fibre content of the stem ranges from 21% in wild accessions to 36% in modern cultivars. The ultimate bast fibres are (1.5-)2-3(-12) mm long and (7-)15-25(-41) μm wide, with an average cell wall thickness of 4-9 μm and lumen width of 7-13 μm. In cross-section they are polygonal to round or oval, with a varying lumen width and cell wall thickness. In longitudinal section the fibre cells are cylindrical. The fibre ends show great variation, but most often they taper into a blunt point. The fibre cells in the woody core are (0.4-)0.5-0.9(-2.4) mm long and 18-33(-37) μm in diameter, with an average cell wall thickness of 4-8 μm and a lumen width of 16-23 μm. The length of both bast and core fibre cells increases from the base to the top of the stem. The fibre strands of commerce, consisting of fibre cells cemented together by pectin and hemicelluloses, are 1.5-3.0 m long. Kenaf fibre contains 44-62% α-cellulose, 14-20% hemicelluloses, 4-5% pectin, 6-19% lignin and 0-3% ash.

Whole stems contain 77-79% holocellulose, 37-50% α-cellulose, 16-20% lignin and 2-4% ash. The bark fraction (depending on cultivar, but normally 31-39% of the stem) contains 62-81% holocellulose, 37-57% α-cellulose, 21-26% hemicelluloses, 6-12% lignin and 3-9% ash. The core fraction (61-69% of the stem) contains 65-72% holocellulose, 34-39% α-cellulose, 24-29% hemicelluloses, 14-20% lignin and 2-6% ash. In general, kenaf bast chemical pulps are stronger than softwood pulps; whole stalk chemical pulps have strength properties between those of softwood and hardwood pulps; and core chemical pulps have lower tear strength but higher tensile and burst strength than hardwood pulps. Paper made from whole kenaf stems is relatively tight and nonporous compared to that of wood.

Seeds contain up to 22(-26)% oil, with an average fatty acid composition of palmitic acid (14-20%), stearic acid (3-7%), oleic acid (28-51%) and linoleic acid (23-46%). The press cake contains 9% moisture, 32% crude protein, 8% oil, 8% crude fibre and practically no antinutritional components.

The 1000-seed weight of most cultivars is 25-27 g, but for some semi-wild accessions of African origin it is only 9-12 g.

For many purposes, such as coarse packaging fibres and cordage, jute, kenaf and roselle may be substituted for each other. However, as kenaf and roselle are coarser and therefore cheaper than jute, they are considered more as a substitute of jute than the other way round. Other bast fibres that can serve as substitutes for jute, kenaf and roselle include those of Abroma augusta (L.) L.f., Helicteres isora L., Malachra capitata (L.) L. and Urena lobata L. For sack-making kenaf also has to compete with synthetic fibres such as polypropylene.

• An erect annual herb, up to 2 m tall in the wild, up to 5 m in cultivars. Taproot well developed, up to 25 cm deep with lateral roots spreading horizontally to 1 m and adventitious roots on lowest stem section.
• Stem slender, cylindrical, in cultivation unbranched and glabrous, prickly on wild accessions, entirely green, green with red or purple pigmentation, or red, sometimes lower half green and upper half pigmented.
• Leaves alternate; stipules filiform, 5-8 mm long, pubescent; petiole 3-30 cm long, finely pubescent on the adaxial surface and bristled on the abaxial surface, green to red; blade 1-19 cm × 0.1-20 cm, very shallowly to very deeply palmately 3-7-lobed on lower stem, often unlobed on upper stem or even bract-like near the apex, base cuneate to cordate, margins serrate or dentate, apex acuminate, upper surface glabrous but with a prominent, 3 mm long nectary at the base of the midrib, lower surface hairy along the veins.
• Flowers axillary, solitary or sometimes clustered near the apex, bisexual, 5-merous, 7.5-10 cm in diameter; pedicel 2-6 mm long, articulated at the base; epicalyx of 7-8 linear bracteoles, 7-18 mm long, persistent; calyx campanulate with 5 acuminate to subcaudate lobes 1-2.5 cm long (up to 3.5 cm in cultivars), persistent, green, bristly and with a characteristic white, woolly, arachnoid tomentum especially near the base and margins, with a prominent nectary gland on each midrib; corolla large and showy, usually cream to yellow with red inner base, sometimes blue or purple; petals free, usually spreading, twisted clockwise or anticlockwise, obovate, 4-6 cm × 3-5 cm, outer side stellate-pubescent; staminal column epipetalous and surrounding the style, 17-23 mm long, dark red, with numerous 1-2 mm long filaments and 1-celled yellow or red anthers; pollen spiny, spherical; pistil with superior, 5-locular, ovoid, pointed, villose ovary, each locule containing many ovules arranged in 2 vertical rows, a single red style, branching into 3-5, hairy arms 2-4 mm long, each branch ending in a capitate stigma.
• Fruit an ovoid, beaked capsule, 12-20 mm × 11-15 mm, densely appressed pubescent, the beak 1 mm long, containing 20-25(-35) seeds.
• Seed subreniform to triangular with acute angles, 3-4 mm × 2-3 mm, ash grey or brown-black with light yellowish spots, hilum brown.
• Seedling with epigeal germination.

Kenaf seeds have no dormancy and will germinate within 2-3 days after sowing in moist and warm soil. Growth rate increases gradually and is at its maximum, 7-8 cm of stem length per day, between 2 and 3 months after germination. Maturing time, defined as the period between seedling emergence and flowering under normal growing conditions, may vary from 80 days for very early cultivars to 120 days for medium ones and 140 days for late ones. Early cultivars may have a plant height of only 2.5 m at maturity versus 4.5 m for late types. Flowering in most cultivars lasts about 4 weeks with maximum flush in the second week. In some African accessions, the period of flowering may be more than 8 weeks. Flowers of kenaf are short-lived, opening before sunrise and closing by noon of the same day. The pistil is already receptive before anther dehiscence starts shortly after sunrise. The stigmatic lobes hang down initially, almost touching the unopened anthers, but become turgid later in the day and soon stand out above the anthers. Kenaf is mainly self-pollinated, but up to 12% cross-pollination has been recorded. Cross-pollination is mainly effected by bees and other insects. Seeds are mature within 32-35 days after anthesis. Under normal weather conditions most kenaf cultivars have indehiscent fruits, but in many African accessions the fruit wall bursts and the seeds are shattered.

Hibiscus L. comprises 200-300 species, found mainly in the tropics and subtropics, many of which are grown as ornamentals. The estimated number of species varies because opinions differ about inclusion or exclusion of several related groups of species in the genus. In a recent revision (2001), for instance, 22 Hibiscus spp., formerly grouped under Hibiscus sect. Azanzae DC., have been excluded from Hibiscus and placed in the segregate genus Talipariti Fryxell. These include some trees of which the bark is made into good-quality rope and other cordage items in South-East Asia, such as T. macrophyllum (Roxb. ex Hornem.) Fryxell (synonym: H. macrophyllus Roxb. ex Hornem.) and T. tiliaceum (L.) Fryxell (synonym: H. tiliaceus L.), both treated in PROSEA 5 "Timber trees". H. floccosus Mast., the bast of which is made into rope in Peninsular Malaysia, has not been removed from Hibiscus.

Kenaf belongs to Hibiscus section Furcaria, a group of about 100 species which have in common a pergamentaceous calyx (rarely fleshy) with 10 strongly prominent veins, 5 running to the apices of the segments and bearing a nectary, and 5 to the sinuses. The section Furcaria has x = 18 as basic chromosome number. Interspecific hybridization has been attempted with varying success between H. cannabinus and other species within the same section, e.g. H. acetosella Welw. ex Hiern, H. diversifolius Jacq., H. radiatus Cav., and H. sabdariffa. H. cannabinus can easily be distinguished from the related species H. radiatus and H. sabdariffa by the white, arachnoid tomentum on the calyx. In the Philippines, H. cannabinus as listed by Merrill has to be referred to H. radiatus, since the specimens quoted belong to that species.

H. cannabinus is highly variable and various subclassifications have been proposed, but none is generally accepted. Best known are the so-called 5 botanical varieties that have been distinguished in India, but which are in fact cv. groups:

• Purpureus: stem purple, leaves palmate with purple petiole;

• Ruber: stem red below and greenish above, leaves palmate with green petiole;

• Simplex: purple stem, entire leaves with purple petiole;

• Viridis: green stem, entire leaves with green petiole;

• Vulgaris: stem green, leaves palmate with green petiole.

The majority of kenaf cultivars belong to the cv. groups Viridis and Vulgaris.

H. radiatus, possibly an allotetraploid of H. cannabinus and H. surattensis is grown as an ornamental, vegetable and medicinal herb in South-East Asia and as a fibre plant in Brazil. H. surattensis L. is sometimes grown for its fibre.

Kenaf has a wide range of adaptation to climate and soil, and is grown between 45°N and 30°S. Kenaf plants are tolerant of daily temperature variation between 10°C and 50°C, but are killed by frost. It grows best where mean daily temperatures during the growing season are higher than 20°C and average monthly rainfall is 100-125 mm during the growing season. These conditions are met during the rainy season in the tropics and the wet summer season of the subtropics. Kenaf is a short-day plant: regardless of the time of planting, most cultivars remain vegetative until the daylight period falls below 12.5 hours. Cultivars planted at a latitude of 20°N will, therefore, not start flowering before early September. At higher latitudes flowering commences progressively later, whereas at the equator plants flower early and attain insufficient height, except when the grown cultivar is photo-insensitive. Kenaf can be grown on a wide range of soils, but thrives best on free-draining sandy loams of alluvial or colluvial origin, with pH 6-6.8. It is salt-tolerant, but sensitive to waterlogging.

Kenaf is normally propagated by seed. It may also be propagated from stem cuttings, especially for the production of breeder and basic seed. Kenaf seeds deteriorate quickly under humid conditions, but high viability can be maintained for more than one year by storing dry seeds (< 10% moisture content) in airtight containers and for several years by storing at sub-zero temperatures (-10°C). The optimum temperature for germination of kenaf seeds is 35°C, with a base temperature of 10°C and a maximum temperature of 46°C.

Kenaf is mostly a rain-fed crop sown directly in the field at the start of the rainy season. Time of planting is very important, as the crop should grow during long days. The longer the period of vegetative growth before first flowering, the higher the yield of biomass and fibre and also the better the fibre quality. In Java, Indonesia (8°S) kenaf is sown during October-November with the onset of the rainy season and flowers in March-April, while in north Thailand (18°N) the cropping season is between April and September. A deep cross-ploughing is usually desirable for thorough tillage, followed by harrowing to subdue weeds and to obtain a fine state of tilth. Most kenaf is grown by smallholders, who plant by broadcasting at seed rates of 15-25 kg/ha, followed by harrowing or laddering to cover the seed with 1-2 cm soil. Such plots require thinning by hand to reduce plant density to about 400 000 plants per ha. Row plantings require less seed and result in more uniformity and higher yields at lower establishing and maintenance costs (e.g. by mechanical drilling and weeding). Recommended spacings for row planting vary between countries. They are generally similar to those for jute, i.e. 20-30 cm between and 5-10 cm within rows, when grown for fibre, but a somewhat wider spacing to produce pulp for paper making. Seeds can be produced on plants left in the field after harvesting the main crop. However, the amount and quality of seeds is much higher on special seed plots sown late in the season, as profuse flowering is induced by declining daylengths.

Kenaf grows rapidly and requires little additional weeding after a few rounds of thinning and weeding during the first month after sowing. Nutrient requirements depend on soil type, initial soil fertility and yield levels. The uptake of major nutrients by one ha of kenaf producing 36 t green plants (1.7 t dry retted fibre) is estimated at about 94 kg N, 26 kg P, 121 kg K, 138 kg Ca and 29 kg Mg. Part of this is usually returned to the soil when stems are left to defoliate on the field after harvesting. In field trials kenaf often shows large yield responses to N fertilizers, sometimes significant responses to P and K and almost never to Ca fertilizers. Smallholders seldom apply fertilizers to a kenaf crop, but still get a reasonable yield due to residual fertility from a previous food crop or inherent fertility of the soil (e.g. alluvial flood plains). Kenaf is a rain-fed crop, but receives supplementary irrigation in some countries to boost yields. Out-of-season seed plots may require irrigation for proper seed set and quality.

The economic importance of kenaf diseases varies among countries. Stem and seedling rots caused by Macrophomina phaseolina and leaf spot by Cercospora hibisci-cannabini are serious kenaf diseases in several Asian countries. Fusarium sp. is a major disease in Indonesia causing damping-off in young seedlings and black or brown stem lesions resulting in lodging and death of older plants. Collar-rot caused by Phytophthora nicotianae var. parasitica is the most serious soil-borne disease of kenaf in Thailand, in particular during the peak growing period. Other diseases in kenaf in Asia are a leaf spot caused by Phoma sp., anthracnose (Colletotrichum spp.), virus A (leaf curl) and virus B (mosaic).

Kenaf harbours numerous insects, but only a few cause serious damage to the crop. Flea beetles (Podagrica spp.) and the jassid leaf hopper (Amrasca biguttula) are among the most important insect pests in Asia. Other insect pests of kenaf in Asia include the spiral borer (Agrilus acutus), cotton bollworm (Helicoverpa armigera), black cutworm (Agrotis ipsilon ), the cotton stainer (Dysdercus spp.) and stink bug (Tectocoris spp.).

Kenaf is particularly susceptible to root-knot nematodes (Meloidogyne spp.), which may cause severe damage, especially in light-textured soils. Flooding of the land prior to kenaf cultivation and regular crop rotation help to reduce nematode attacks. Some difference in tolerance to nematodes exists among kenaf cultivars.

In kenaf the quantity and quality of fibre depend very much on the time of harvesting. Harvesting at the flower bud stage produces the best quality but less fibre, whereas at the pod (immature capsules) stage fibre yield will be higher but of poor quality. Thus, the recommended time to harvest for an optimum balance in fibre yield and quality is when about 50% of the plants are flowering. In Asia, kenaf is generally harvested by hand, cutting the stem close to the surface of the soil with a sickle. On sandy soils whole plants may be pulled up, and the lower end with roots cut off. The plants are then tied into loose bundles, which are placed upright against each other for 2-3 days in the field to induce defoliation and desiccation. After shaking off all remaining leaves the stems are first graded before assembling bundles of about 10 kg each, containing stems of uniform thickness. These are tied with bark strips and transported to the nearby retting pool.

World yield of kenaf is about 1.2 t dry fibre per ha, averaged over the period 1997-2001. Average yields per country are: Indonesia 1.4 t/ha, Thailand 1.6 t/ha, India 1.7 t/ha and China 2.4 t/ha. The potential yield of kenaf, as obtained in experimental fields with improved cultivars, is 3-5 t dry fibre per ha. Seed yields of 1-1.5 t/ha can be obtained from late-sown kenaf plots.

Kenaf stems are usually retted in water for a period of 10-15 days at warm (>30°C) temperatures to liberate the fibres from the bark tissues by enzymatic action of micro-organisms. The bundles are steeped in shallow water in 2-3 layers, which are kept submerged by the weight of bundles of water hyacinth (Eichhornia crassipes (Martius) Solms) or rice straw, bricks or concrete slabs. The retting progress is monitored towards the end of the process by testing a few stems removed from the centre of the bundles. Retting efficiency depends on factors such as cultivar, maturity, water quality, microbial activity, and day and night temperatures. Retting should be carried out in clear and slow moving water at the optimal proportion of 1:20 for plant biomass to water quantity. In case of stagnant water, addition of urea (0.01% of the green weight of kenaf plants) may enhance the retting process and removal of brown colour. When retting is complete, the fibres are stripped manually from the stem, washed thoroughly in clean water and dried well in dust- and sand-free conditions. As in jute, the fibre quality is very much determined by correct retting, cleaning and drying. Ribbon retting, whereby the bark is stripped from freshly harvested stems by manual or machine decorticators ("ribboning") and only the ribbons are steeped in water, requires much less water and reduces the retting time by half. It is a method generally applied in areas with chronic water shortage during the harvesting season, but it also reduces handling and transport costs from the field to the retting pools and tends to produce fibre of more uniform and higher quality. The dried fibres are transported in crude bales to local centres for initial grading and packing in low compression bales of 60-150 kg before transportation to the spinning mills. Whole kenaf stems may also be transported directly from the field to pulp- and paper-making factories.

Kenaf has been successfully pulped with a range of chemical, semi-chemical and mechanical processes. The choice of the pulping process depends mainly on the plant part used (bark, core or whole stems) and the type of paper to be produced. Kenaf kraft (sulphate) and soda pulps have similar yields and strength properties, but soda pulps have better initial drainage characteristics (freeness). Kenaf bark fibres pulped with the kraft, kraft-anthraquinone, soda and soda-anthraquinone processes give pulp yields of 51-63%, and kenaf core fibres give yields of 40-54% with the same processes. With the cold soda and alkaline sulphite processes kenaf bark gives high pulp yields (72-88%) with satisfactory strength properties, brightness and opacity. The alkaline sulphite-anthraquinone process is well suited for kenaf bark and whole stems, giving better yield, strength, viscosity and brightness than soda and soda-anthraquinone pulping. The alkaline sulphite-anthraquinone-methanol process gives even better results. For the production of high-quality newsprint chemi-thermo-mechanical pulping of whole stems is effective. Nonchlorine bleaching processes have been successfully applied on kenaf pulps, e.g. using ozone and peroxide.

The existing kenaf cultivars are based on a narrow range of genetic variability and are constrained by low adaptability to agro-ecological conditions and susceptibility to several diseases and insect pests. The former International Jute Organization (IJO) has therefore mandated the genebank of the Bangladesh Jute Research Institute (BJRI) in Dhaka, Bangladesh, to become also the world germplasm repository for kenaf. The present collection consists of some 920 accessions, including old and new cultivars, landraces, wild and semi-wild accessions of kenaf and related species from Africa. The wild accessions of kenaf and other Hibiscus species from East Africa appear to be especially promising sources of genetic variation, as these were collected from a diverse range of habitats and soil types. A duplicate set of seed samples for all accessions is stored at the Commonwealth Scientific Industrial Research Organization (CSIRO) in Canberra, Australia. Research centres in India, China, Thailand, Indonesia and other kenaf-producing countries have unrestricted access to genetic resources present in the genebank of the BJRI.

Methods of selection and breeding common to self-pollinating crops are applied to kenaf, mostly line selection within landraces or after intervarietal crosses and backcrosses. Higher yield is an important breeding objective in kenaf, but in South and South-East Asia the on-farm yields of improved cultivars are often less than half the on-station (potential) yields. This gap is caused partly by inadequate cultural practices and low inputs at farm level, but also by the fact that the available cultivars are often inherently poor achievers in marginal ecosystems. Breeding for new cultivars with the potential of high yields under suboptimal conditions is all the more urgent because the kenaf crop is being pushed increasingly into marginal environments due to pressure from food and other crops. Earlier maturing and photo-insensitive kenaf cultivars also fit better in systems of multiple cropping. Other breeding objectives are plants without prickly stems and bristly capsules to facilitate manual harvesting, and host resistance to diseases, insect pests and nematodes. Resistance to diseases such as anthracnose (Colletotrichum spp.) and stem rot (Macrophomina phaseolina) is available from H. cannabibus accessions, but adequate levels of resistance to root-knot nematodes (Meloidogyne spp.) are mostly restricted to related species, such as H. acetosella, H. rostellatus Guill. & Perr., H. sabdarrifa, and H. surattensis. Introgression of target characters into kenaf from these species is being attempted by conventional as well as advanced techniques (e.g. protoplast fusion) of interspecific hybridization.

Despite the fact that kenaf, like jute, is being pushed onto marginal land under pressure from food and other crops, and is also under strong competition from synthetic fibres, prospects for increased production of both fibre and whole stems are promising in view of growing concerns about environmental pollution and dwindling forest resources. Kenaf fibre is biodegradable and an environment-friendly raw material suitable for many applications, such as specialty paper (either alone or in blends with hardwood), non-woven fabrics, geotextiles and semi-rigid and laminated sheets for packaging and panelling. Furthermore, whole kenaf stems are an excellent substitute for softwood as raw material for paper making. It is therefore likely that the importance of kenaf as a raw material for paper making will continue to increase.

• Cook, C.G., Chow, P., Meimban, R.J., Lambert, R.J., Bajwa, D. & Nelson, L.R., 1998. Influence of cultivars, years, environment, and stem location on kenaf fibre properties. TAPPI (Technical Association of the Pulp and Paper Industry) Journal 81(10): 135-140.
• Dempsey, J.M., 1975. Fiber crops. University Presses of Florida, Gainesville, Florida, United States. pp. 203-304.
• Dulyaphat, C., 2000. JAF based cropping patterns and their importance (Thailand). In: Proceedings of the Workshop and third and final meeting of the Project Coordination Committee. International Jute Organization, Dhaka, Bangladesh. pp. 185-188.
• Khristova, P., Kordsachia, O., Patt, R., Khider, T. & Karrar, I., 2002. Alkaline pulping with additives of kenaf from Sudan. Industrial Crops and Products 15(3): 229-235.
• Pande, H. & Roy, D.N., 1996. Delignification kinetics of soda pulping of kenaf. Journal of Wood Chemistry and Technology 16(3): 311-325.
• Sastrosupadi, A., 2000. JAF cropping patterns and their importance (Indonesia). In: Proceedings of the Workshop and third and final meeting of the Project Coordination Committee. International Jute Organization, Dhaka, Bangladesh. pp. 168-178.
• van Borssum Waalkes, J., 1966. Malesian Malvaceae revised. Blumea 14(1): 1-213.
• Webber III, C.L., 1992. Varietal differences in kenaf yield components. TAPPI (Technical Association of the Pulp and Paper Industry) Journal 75(8): 153-155.
• Wilson, F.D., 1999. Revision of Hibiscus section Furcaria (Malvaceae) in Africa and Asia. Bulletin of the Natural History Museum, Botany Series 29(1): 47-79.
• Wilson, F.D. & Menzel, M.Y., 1964. Kenaf (Hibiscus cannabinus), roselle (Hibiscus sabdariffa). Economic Botany 18(1): 80-91.

Shamsuddin Ahmad & H.A.M. van der Vossen