Crotalaria juncea

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Photography courtesy of Western Weeds CD-ROM. A guide to the weeds of Western Australia by B.M.J. Hussey, G.J. Keighery, R.D. Cousens, J. Dodd and S.G. Lloyd. Web version by R. Randall.
© Western Weeds

Local names:
Bengali (shonpat,shon,ghore sun), English (brown hemp,sunn hemp,sunhemp,Bengal hemp,Bombay hemp,madras hemp,benares hemp,Indian hemp,jubbalpore hemp), Filipino (karay-kagay,putokputukan), French (chenvre indien), Hindi (kharif,sannai sunn), Indonesian (o

Crotalaria juncea is an erect, herbaceous, laxly branched annual, 1-3.5 m tall. The stems are cylindrical and ribbed, pubescent, up to 2 cm in diameter; vegetative parts covered with short, downy hairs. Long, strong taproot, well-developed lateral roots, and multibranched and lobed nodules, up to 2.5 cm in length.

Leaves simple with minute, pointed stipules; petiole entire, short, about 5 mm long with pulvinus blade, linear elliptic to oblong, 4-12 x 0.5-3, bright green.

Inflorescence a lax, terminal raceme, up to 25 cm long; flowers conspicuous, small with 5 hairy sepals, shortly united at base, lobes pointed, with 3 lower sepals united at tips, separating in fruit; petals deep yellow, standard erect, about 2.5 cm in diameter, rounded, sometimes streaked purple on dorsal surface, wings shorter and keel twisted.

Pods cylindrical, 3-6 x 1-2 cm, tomentose, light brown, containing about 6 seeds. Seed heart-shaped, with narrow end strongly incurved, up to 6 mm long, dark brown to black.

The genus name ‘Crotalaria’, meaning rattle, is indicative of the noise made by the seeds shaken in the mature pods. The species name was given by Linnaeus because the plant’s green, rushlike, scantily leaved branches resemble Spartium junceaum L., the Spanish broom of the Mediterranean region.


Although generally considered a tropical or subtropical crop, sunn hemp is drought resistant and is widely adaptable to different soil types. Its tolerance to salt and frost is low.

Native range
Australia, India

Tree management

When grown for fibre, the plants are usually harvested at the flowering stage or when the stems turn yellow. For seed production, the crop is harvested when the seeds are ripe; fibre is extracted from the stems afterwards. There are no significant differences in strength and quality of fibre obtained from plants retted at flowering time and those retted when seeds are fully mature. The retting period depends on water temperature, locality, time of year, weather conditions, depth and source of water, thickness of stalks, and quantity of straw in relation to volume of water. Cut straw with a yellowish tinge requires 10 days to 3 weeks to bleach out sufficiently to have fibre of a satisfactory colour. Stems cut while green will bleach out when exposed directly to the sun but have to be turned at least twice.

Land should be prepared well before planting for fibre production. Although C. juncea generally suppresses weed populations due to the dense shade of its canopy, early-season weed control improves fibre yield. Reports on fertilization requirements vary, but addition of phosphorus is generally recommended for soils low in phosphorus.

When grown for forage, C. juncea can be harvested 4 times, starting 6-8 weeks after sowing and then every 4 weeks. It should be cut for hay or ploughed in for green manure in the early flowering stage when it is 1.5-2.5 months old.

Seed weight is highly variable, depending on cultivar and environment; it can range from 18 000 to 33 000 seeds/kg.

Although generally considered a tropical or subtropical crop, sunn hemp is drought resistant and is widely adaptable to different soil types. Its tolerance to salt and frost is low.

Seeds are ready for harvest when pods begin to turn yellow and seeds rattle in them. C. juncea is propagated by direct seeding. General sowing rates are 40-45 kg/ha; when it is sown for fibre, the rate is 100-240 kg/ha. It nodulates readily with native cowpea-type rhizobia. Germination is rapid and seedlings emerge 3 days after sowing, soon producing a thick ground cover that smothers weeds.

Recommendations for seeding rates vary greatly among production areas. Planting dates also differ among locations; however, adequate soil moisture and frost-free warm weather bring about rapid emergence and provide the highest yields.

If irrigated, furrows should be opened, separating the fields into small plots. Irrigate lightly compared with crops such as tobacco and chillies, only once in 10-15 days. Too much moisture is harmful during the 1st 2 weeks after germination.

Poison: The seeds of many Crotalaria species contain toxic pyrrolizidine alkaloids. Trichodesmine is the principal toxic alkaloid in C. juncea. The seeds are reported to contain trypsin inhibitors; they are said to be poisonous to cattle, and they can poison both horses and pigs. 

Fodder: C. juncea is widely used as forage in Sri Lanka and southern Africa. The presence of compounds that cause unpalatability, which are poisonous under some conditions, is typical of the genus Crotalaria. Seeds may contain about 35-40% protein; stems are about 40% fibre. Leaves and stems are dried, as animals do not eat C. juncea when it is green. Sheep will not suffer any adverse effects if forced to eat dried forage, but they will suffer from toxicity if fed large quantities of seed. C. juncea should not be fed to horses, and intake of hay by cattle should be restricted to about 10% of their diet.

Fibre:  The major significance of sunn hemp lies in its valuable fibre, which is extracted from the bark and used to make twine and cord, canvas and fishing nets, and paper and pulp. Sunn hemp fibre has greater tensile strength and is more durable under exposure than jute. It is not as strong as hemp (Cannabis sativa). The 3 main properties that make sunn hemp an excellent candidate for paper-making are 1) good yields of bleachable sulphate pulps, 2) pulp strength properties that are equal to or greater than those of mixed southern hardwood pulp, and 3) length-to-width ratio of bast fibre that is greater than that of wood fibres. Stems are composed of 2 fibres--the bast and the woody core. Bast fibres, located in the outer bark, are much longer than the core fibres, but the 2 fibre widths are similar. The proportion of bark in the total stalk by dry weight ranges from 15% to 20%. Sunn hemp fibre is used in twine, rug yarn, cigarette and tissue papers, fishnets, sacking, canvas and cordage. Fibre is stronger when wet; it is fairly resistant to mildew, moisture and microorganisms in salt water.

Medicine: The seeds are said to purify the blood and are used to treat impetigo and psoriasis.

Nitrogen fixing: C. juncea is capable of fixing atmospheric nitrogen.

Soil improver: C. juncea is widely grown in the tropics as a green manure. Total green matter yield averages 18-27 t/ha; forage yield, 5-19 t/ha. As well as producing high organic-matter yields, it can reduce the build-up of root-knot nematode populations.

Intercropping:  Often grown as a cover crop and in rotation with tobacco, vegetables, dry grains, rice, corn, cotton, sugarcane, pineapples, coffee, and orchard crops.