Crotalaria juncea (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Forage / feed|
- Protologue: Sp. pl. 2: 714 (1753).
- Family: Papilionaceae (Leguminosae – Papilionoideae, Fabaceae)
- Chromosome number: 2n = 16
- Sunn hemp, Indian hemp, Madras hemp, sann hemp, sun hemp, Bombay hemp, brown hemp (En).
- Chanvre indien, chanvre du Bengale, crotalaire jonciforme, cascavelle (Fr).
- Cânhamo-da-India, cânhamo-de-bengala (Po).
Origin and geographic distribution
Crotalaria juncea is generally considered to be native to Bangladesh, Bhutan and India. It is now widely cultivated in the drier areas of the tropics and subtropics and in many temperate areas with a hot summer. It often escapes from cultivation, naturalizes easily and grows in many areas as a ruderal plant. Crotalaria juncea is recorded in many countries across the African continent from the Atlantic coast to the Red Sea, from Tunisia to South Africa and in the Indian Ocean islands.
The strong bast fibre is used primarily for cordage, twine, fishing nets, cigarette paper, tissue paper, bags, sacks, canvas, soles of shoes and sandals. Other products include carpets, webbing, table and bed linen. With the fibres a potting medium is manufactured.
Crotalaria juncea is one of the most widely grown green manure crops of the tropics, often in rotation or as an intercrop with rice, maize, sorghum, tobacco, cotton, sugarcane, pineapple, coffee and in orchards. It is also grown to suppress weeds, to prevent soil erosion and to reduce nematode numbers. Crotalaria juncea is a good indicator plant for potassium and calcium deficiencies.
The dried stalks and hay are used as forage. Although reported to be poisonous to livestock, seeds are fed to horses in the Soviet Union and to pigs in Zimbabwe. The woody stems remaining after fibre removal are used as fuel. Seeds are used in the production of an adhesive for plywood and as a coffee-substitute. The seeds are used medicinally to purify the blood, to cure impetigo and psoriasis and as an emmenagogue.
Production and international trade
Crotalaria juncea has been grown as a fibre crop in India since 600 BC and is one of the earliest recorded fibre crops in history. The fibre was first introduced into Europe in 1791 by the East India Company, during a period when jute (Corchorus spp.) was considered a fibre plant of less importance. The fibre of Crotalaria juncea proved to be excellent and not inferior to hemp (Cannabis sativa L.). Major producers of Crotalaria juncea include India, Bangladesh, China, Brazil, Korea (DPR), Pakistan, Romania and Russia. Currently China is the main producer of Crotalaria juncea in the world. The fibre is exported mainly to the United States, the United Kingdom, France, Italy, Belgium, Argentina, Greece and Russia. However, the export market has gone down badly due to increased availability of hemp from Italy and Russia in the world market. India grows about 360,000 ha of Crotalaria juncea annually, producing between 80,000 and 100,000 t of fibre, with about 20–30% being exported to the United Kingdom, the United States and Belgium. The imports into the United States and the United Kingdom are mainly used in the manufacture of cigarette and high quality tissue papers.
There are no statistical data on traded volumes in Africa. In Kenya and Uganda the cultivated area is approximately 3000–5000 ha, mainly as a homegarden crop. All trade in tropical Africa is through local or regional markets and international trade is limited to local cross-border trade.
The major significance of Crotalaria juncea lies in its valuable bast fibre, which makes up about 8% of the dry stem weight. The fibre of commerce consists of greyish to pale yellow strands 75–150 cm long. Fibres are entangled in a mesh structure, and single filaments are obtained by combing and splitting the mesh structure. The ultimate fibre cells are (0.5–)6–8(–20) mm long and (10–)25–30(–50) μm wide, with a cell wall thickness of 3–11 μm. The cells often have rounded ends, but these may also be blunt or pointed. They are rounded polygonal or oval in cross-section, with thick walls. Dislocations, cross-markings and longitudinal striations are present. The fibre has a tensile strength of c. 73 kg/mm² and an elongation at break of 5.5%. It is stronger and more durable under exposure than jute (Corchorus spp.), but it is not as strong as hemp (Cannabis sativa L.). The fibre is stronger when wet than when dry, and is fairly resistant to mildew, moisture and microorganisms in salt water, making it particularly suitable for fishing nets and marine cordage. The fibre contains 10% moisture, 67.8% cellulose, 16.6% hemi-celluloses, 3.5% lignin, 0.3% pectin, 1.4% water solubles and 0.4% fat and wax.
The fibre possesses properties that make it an excellent choice for papermaking: good yields of bleachable sulfate pulps; pulp strength properties that are equal to or greater than those of most mixed hardwood pulps; and a fibre length to width ratio that is greater than those of wood fibres. The high cellulose content as well as degree of polymerisation makes this fibre ideal for preparing specialty paper. Prepared pulps are suitable for a wide range of end uses. The fibres are particularly suitable for cigarette paper because of the high cellulose and low ash content.
The stems have the following major constituents: cellulose 78.3%; pentosan 3.6%; urinic anhydrite 1.7%; acetyl content 1.5% and lignin 4.0%. Minor constituents include: fat and wax 0.5%; nitrogenous matter 1.4% and ash 0.3%. Monosaccharide constituents include the following: glucose 80.3%; xylose 5.2%; mannose 11.7%; galactose 2.1%; arabinose 1.7% and rhamnose 0.4%. Dried for cattle feed, the stalks contain 14.4% moisture, 1.1% ether extract, 11.3% albuminoids, 35.8% carbohydrate, 27.4% woody fibre, and 6.4% soluble mineral matter. The hay is mildly toxic, mainly to horses, but cattle can eat it safely when it does not form more than 10% of the total feed intake.
Seeds contain 8.6% moisture, 34.6% crude protein, 4.3% fat, 41.1% starch, 8.1% fibre, and 3.3% ash. Seeds are reported to contain trypsin inhibitors, and are said to be poisonous to cattle. Seeds oil contains 46.8% linoleic acid, 4.6% linolenic acid, and 28.3% oleic acid, and, by difference, 20.3% saturated acids. The seeds contain the toxic pyrrolizidine alkaloids trichodesmine, juncein, senecionine and seneciphylline and 25.6% of the polysaccharide galactomannan.
Adulterations and substitutes
Fibre plants used for the same purpose as Crotalaria juncea include cantala (Agave cantala Roxb.), sisal (Agave sisalana Perrine), hemp (Cannabis sativa) and jute (Corchorus spp.)
Erect laxly branched annual herb up to 1.5(–3.5) m tall; stems ribbed with short appressed hairs. Leaves alternate, simple; stipules 1–2 mm long, slender; petiole 3–5 cm long; leaflets oblong-lanceolate, 5–13(–18) cm × 0.5–3 cm, finely appressed pubescent. Inflorescence a leaf-opposed raceme 10–50 cm long, laxly 6–20-flowered; bracts elliptical, 3–5 mm long. Flowers bisexual, zygomorphic, 5-merous; calyx 1.5–2 cm long, covered in short brown hairs with some longer ones interspersed, lobes 3–4 times as long as the tube; corolla bright yellow, with elliptical standard faintly reddish marked or tinged, wings a little shorter than keel, keel 17–22 mm long, with a long, slightly incurved twisted beak; stamens 10, all joined in a sheath open at base; ovary superior, 1-celled, style curved, stigma small. Fruit a cylindrical pod 30–55 mm × 12–17 mm, short, velvety hairy, 6–12-seeded. Seeds oblique-cordiform, 6–7 mm long, dark brown to black.
Other botanical information
Crotalaria comprises about 600 species and occurs throughout the tropics. Africa is by far richest with approximately 500 species. Crotalaria juncea is the economically most important species of the genus. Crotalaria spectabilis Roth. (‘showy rattlepod’, ‘showy crotalaria’) is another species with simple leaves imported from Asia into West Africa and Madagascar for use as a fibre plant, green manure, and for fodder. In Asia it is planted as an ornamental and for erosion control as well. Further introductions of this species are discouraged as the species is very poisonous due to the presence of the pyrrolizidine alkaloid monocrotaline, and apparently has no advantages over Crotalaria juncea. Also of Indian origin is Crotalaria berteroana DC. (synonym: Crotalaria fulva Roxb.), introduced in Madagascar as a fibre crop and green manure and now widely naturalized. In Madagascar the pulverized grains are used as a plaster to cure scabies. The large amount of scientific papers on the species was triggered by the use in Jamaica in bush tea. This use appeared to be the cause of vascular lesions of the liver described as ‘veno-occlusive disease’ in Jamaica and attributed to the presence of the hepatotoxic pyrrolizidine alkoloid fulvine in the leaves and seeds. Crotalaria xanthoclada Bojer ex Benth. is an endemic of Madagascar; it produces a textile fibre and its seeds are toxic to poultry.
Growth and development
The seeds of Crotalaria juncea normally germinate within about 3 days. Too much moisture is harmful during the first 2 weeks after sowing. Crotalaria juncea is a short-day plant, and long days favour vegetative growth and reduced seed-set. Daylength neutral selections exist. The time from germination to flowering can be as short as 30 days. The lowest flowers of the inflorescence are the first to open and flowers remain open for 2 days. Extensive cross-pollination occurs and self-pollination only takes place after the stigmatic surface is stimulated by an insect or mechanically. Seed set is practically nil when the flowers are kept inside muslin bags. The plant fixes atmospheric nitrogen in a symbiotic relationship with Rhizobium. Nitrogen content of the vegetative parts is highest from the onset of floral initiation to mid bloom, after which it declines as N reserves are allocated to seed production.
Crotalaria juncea is drought resistant and is adapted to hot, semi-arid and arid areas. It tolerates light frost. In India it is grown in areas with 170–200 mm of rain during the growing period, but elsewhere it is often grown in areas with higher rainfall. It is not tolerant to salt or to prolonged waterlogging. It is adapted to a wide range of soil types. It grows on poor soils but growth on these soils is improved by fertilization. A near neutral pH range of 6–7 with an improved phosphate availability is often beneficial to the crop.
Propagation and planting
Crotalaria juncea is propagated by seed. The 1000-seed weight is 30–55 g. Several pre-emergence herbicides (e.g. clomazone at 1.4 kg/ha) have been identified as causing minimal phytotoxicity and providing efficient weed control. The soil moisture should not be below 30% to allow for good germination. Sowing in rows is recommended with a distance between rows of 25–30 cm. Distance within the row should be 5–7 cm and sowing depth 2–3 cm. For fibre production Crotalaria juncea seed is often broadcasted at a rate of c. 100 kg/ha under rainfed conditions and at a lower rate if irrigated. In Pakistan seed is sown broadcast at a rate of 120–240 kg/ha but when planted in rows 30 cm apart, a seed rate of 66 kg/ha can lead to fibre yields 10% higher than when using the higher broadcasting rate. A high seed rate ensures upright erect stems which help to smother weeds, produce a finer fibre and increase the yield. Planting dates differ by location. Adequate soil moisture and frost-free, warm weather conditions will ensure rapid emergence and a high yield.
The land should be well prepared before sowing. It is recommended to apply organic manure at a rate of 3–5 t/ha before land preparation. As a green manure Crotalaria juncea is mainly grown during the rainy season. For fibre, it is grown on fairly light, well-drained, sandy loam or loamy soils that retain sufficient moisture during the growing season. Vigorous growth can also be achieved on clay or low lying soils but the fibres will be coarser and yields lower. Although reports on fertilization requirements vary, additions of phosphorus are generally recommended. The fibre quality is improved by increasing N, P and K levels, the effect being strongest for K. No herbicides other than for pre-emergence use are currently registered for Crotalaria juncea. It is fast growing and generally suppresses weeds by shading but early season weed control has been shown to improve yields when grown for fibre. Where irrigated, furrows are opened in fields dividing them into small plots. If there is no rain after sowing, the field is irrigated along these furrows at intervals of 10–15 days.
As a green manure it is ploughed in as of 2 months after sowing when the plants begin to flower as it decomposes more rapidly and it will have a positive N balance at this stage. Elsewhere it was concluded that green manure fallow duration should be at least 6 months for it to have a positive effect on soil characteristics. A fallow of up to 18 months was found to be beneficial for soil fertility but the economic consequences of such a long fallow should be taken into consideration.
Diseases and pests
Although many diseases and pests have been recorded for Crotalaria juncea from India and the United States, no serious problems are recorded for the species in tropical Africa. If it is to be grown at a larger scale in future, disease and pest problems will undoubtedly arise. It is vulnerable to many diseases and pests that also affect crops like cowpea, soybean, groundnut and pigeon pea. Bemisia tabaci (whitefly) is an important vector for the transfer of virus diseases. Crotalaria juncea is resistant to the nematodes Meloidogyne javanica and Pratylenchus sp. and is succesfully used in rotation to reduce the infestation of the soil by these nematodes. It may however increase the population of the free-living nematodes Xiphimena elongatum and Helicotylenchus sp. It is immune to the parasitic weed Alectra vogelii Benth. and therefore useful in the rotation wherever this weed is a problem.
Most cultivars are ready for harvesting 120–150 days after sowing. Harvesting of the crop at the proper time is very important for ensuring optimal yield as well as optimal fibre quality. Often it is better to harvest the crop at 50% flowering or early pod-stage to compromise between yield and quality. In Zimbabwe the crop is cut when stems have turned yellow along the major portion of their length. If grown for seed, plants are harvested after seeds are well set, and before pods are dry, so that no seed is lost during cutting and bundling prior to threshing. Harvesting at flowering stage gives a finer fibre, but profit obtained from the seed crop is thereby lost.
Harvesting is done manually with the help of sickles and knives at ground level. The stems are sorted for length and thickness and stems of equal sizes are tied in bundles of 20–25 cm diameter and these are kept in the field for 2–3 days for shedding of leaves. The cut stems are graded by pulling out the long and medium stems respectively. Direct chopping with forage harvesters has been successful, but a precise cut is difficult to obtain and the chopped material has proved too bulky to handle. In Europe and the United States Crotalaria juncea is already harvested mechanically by cutting, drying in swathes on the field for a few weeks and subsequently pressing and baling in a single operation.
Dry matter yields vary enormously, depending on factors such as fertilizer application and intensity of weeding, and may be as high as 14 t/ha. Average fibre yields are 560–900 kg/ha, while in Zimbabwe the average yield is about 330 kg fibre per ha. Seed yields are 500–1000(–2500) kg/ha.
Handling after harvest
After the cut stems have dried sufficiently and have shed their leaves, the bundles are retted. The number of days required for retting depends on factors such as temperature, locality, thickness of stems and quantity of stems in relation to the volume of water. In Zimbabwe 10–14 days are required for retting in July, 8–9 days in August and 5–8 in September–October. Cement tanks are preferred for retting, but earth pits, dams, weirs, streams, and backwater pools of rivers are also used. Shallow water 1–1.3 m deep is satisfactory. If more than one ret is to be carried out in a pool, a sufficient flow of water must be maintained to prevent fouling of the water and discolouration of the fibre. Four or five men are required to remove and stack one tonne of straw per day. Bundles are stood on end (15–20 stems placed with butts on ground at a sufficient angle to permit air circulation in all directions). In this way the straw dries in 1–2 weeks. By standing each bundle up and fanning out the butts, drying time is reduced to 4 days. By leaning bundles on each side of a rack, drying time is reduced to 3–4 days. After the fibre is stripped from the stalks by hand, it is washed and hung over bamboo poles to dry in the sun. Cut straw with a yellowish tinge requires 10–21 days to bleach sufficiently so as to have a fibre of a satisfactory colour. Stems cut while green will bleach when exposed directly to the sun but have to be turned at least twice. Precautions must be taken against under-retting or over-retting of fibre. In under-retted condition, removal of fibres will be a difficult task as bark will adhere to the extracted fibre. While in over-retted condition microorganisms will break down the tissues surrounding the fibre and this will result in weakening of the fibre. The fineness of the fibre and cleanness or degree of retting are decisive for processing to ropes and textiles. A better fibre quality can be obtained by cottonization involving the chemical or mechanical rearrangement of the bast fibre. This makes it possible to process the fibres of Crotalaria juncea on cotton spinning machines. By adopting flax spinning machinery, it is possible to produce coarse fabrics for hose pipes, belting and canvas.
If paper companies had suitable cutting devices, binders or hay balers could probably be modified to handle whole stalks. The end-product influences the type of cut that is necessary. For example, board and mechanical pulps require a shorter, more precise cut than a chemical pulp in which a separation of the ultimate fibre occurs.
Crotalaria juncea is distributed widely but is not known from the wild, and genetic diversity depends largely on being preserved in farmers’ fields. Major germplasm collections are maintained by the Institute of Crop Germplasm Resources (CAAS), China, the Vavilov All-Russian Scientific Research Institute of Plant Industry (VSRI), Russia, the Plant Genetic Resources Conservation Unit (PGRCU) in the United States and the Sunnhemp Research Station in India.
Genetic variation is fairly large. In Europe breeding and selection work is aimed at obtaining high quality fibre. Numerous cultivars exist and include the following: ‘Madaripur’, ‘Seraganj’ (Pakistan); ‘Somerset’ (South Africa); KRC-1 (Brazil); ‘Tropical sun’ (Hawaii, United States); ‘Kharif-sunn’, ‘Chindwara’, ‘Bellary, ‘Jabalpur’, ‘Belgoan’ (India).
Worldwide demand for natural fibre is increasing and current fibre supplies cannot continue to meet the market demands. Crotalaria juncea has the potential to be grown on a large commercial scale and can contribute to satisfy the increased demand for natural fibres. It is of economic importance in the tropics and subtropics and great steps have been made in the development of Crotalaria juncea as a fibre crop for the temperate regions. Demand depends on the price of the fibre in relation to that of alternatives and both supply and price have fluctuated considerably in the past. With research to develop new products the demand will increase even more in the future. Compared to other bast fibre plants Crotalaria juncea has the advantages of being able to fix atmospheric nitrogen and being resistant to drought and root-knot nematodes. It is adapted to a range of ecological conditions and can be used for soil rehabilitation and protection. Research should focus on product development, harvesting and processing equipment, and efficient crop management strategies.
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Sources of illustration
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- A. Maroyi, Department of Biodiversity, School of Molecular and Life Sciences, University of Limpopo, Private Bag X 1106, Sovenga 0727, South Africa
Correct citation of this article
Maroyi, A., 2011. Crotalaria juncea L. [Internet] Record from PROTA4U. Brink, M. & Achigan-Dako, E.G. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 11 April 2019.
- See the Prota4U database.