Sun Hemp
Crotalaria juncea

Family: Fabaceae

What it is like

Crotalaria juncea or commonly known as Sun Hemp is an evergreen shrub that reaches up to 2.5 m in height and 2 m in width. Its stem is erect with silky hairs on the branches. It has a strong taproot and the roots have root nodules. The leaves are spirally arranged, narrow, and simple. The pea-shaped flowers are yellow in colour. The fruit is a pod that is covered with soft hairs, short, inflated and light yellow in colour. The seeds are believed to purify the blood and are used in the treatment of impetigo and psoriasis. The leaves and flowers are edible. The plant is widely grown in the tropics as a green manure, often as a cover crop. The bark yields fibre used in making twine and cord, canvas and fishing nets, and paper and pulp. The fibre is stronger when wet and is resistant to mildew, moisture and microorganisms in salt water.

Crotalaria juncea is a ANNUAL growing to 1.6 m (5ft) by 0.4 m (1ft 4in) at a fast rate. See above for USDA hardiness. It is hardy to UK zone 10 and is frost tender. The flowers are pollinated by Bees, Insects. The plant is not self-fertile. It can fix Nitrogen. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils and prefers well-drained soil. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils and can grow in very acid and very alkaline soils. It cannot grow in the shade. It prefers moist soil and can tolerate drought.

Height (m): 1.6

Where it is found

A tropical plant growing in open sunny positions.

E. Asia - India.

Conservation Status: This taxon has not yet been assessed

Countries/locations it is found in

Africa, Asia, Australia, Bhutan, Burkina Faso, Cambodia, China, East Africa, Guianas, Guyana, Haiti, Hawaii, India, Indochina, Indonesia, Laos, Malawi, Malaysia, Mozambique, Myanmar, Nepal, Northeastern India, Pacific, Pakistan, Papua New Guinea, Russia, SE Asia, South Africa, Southern Africa, South America, Suriname, Swaziland, Thailand, USA, Vietnam, Zambia, Zimbabwe.

How it is used

Food

Rating: 1

The leaves have been recorded as being eaten. The flowers are pickled. They are also cooked with meat and fish.

Condiment: the various plants that are used as flavourings, either as herbs, spices or condiments.

Medicine

Rating: 1

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

Blood purifier: Purifies the blood.

Skin: Plants used in miscellaneous treatments for the skin.

Other

Rating: 4

Agroforestry Uses: 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. It is often grown as a cover crop and in rotation with tobacco, vegetables, dry grains, rice, corn, cotton, sugarcane, pineapples, coffee, and orchard crops. Other Uses A valuable fibre is extracted from the bark. It is used to make twine and cord; canvas and fishing nets; and paper and pulp. Sun hemp fibre has greater tensile strength and is more durable under exposure than jute (Corchorus spp), though it is not as strong as hemp (Cannabis sativa). The 3 main properties that make sun 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 two types of fibre - the bast and the woody core. Bast fibres, located in the outer bark, are much longer than the core fibres, but the widths of both fibres 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. Crotalaria juncea holds a relatively high fuel value and possible could be a good bio-fuel. Chemical composition (g/100g of seed powder): Moisture = 10.2. Ash = 4.0. Ether extractives = 3.9. Nitrogen-free extract = 59.6. Protein (crude) (N x 6.25) = 30.1. Fibre (crude) = 8.7. Calcium (mg/100 g) = 20. Phosphorus (mg/100 g) = 371.0. Iron (mg/100g) = 28.9. Nacin (mg/100g) = 2.95. Ascorbic acid (mg/100 g) = 1.39. Total soluble carbohydrates and total reducing substances (27 deg. (+/-3 deg. C ): total water soluble carbohydrates = 14.9. Total benzoic acid soluble carbohydrates = 18.1. Total 5% TCA soluble carbohydrates = 26.7. Total reducing substances = 0.13. (100o C): total water soluble carbohydrates = 17.2. Total benzoic acid soluble carbohydrates = 23.8. Total 5% TCA soluble carbohydrates = 31.5. Total reducing substances = - . A new amino acid - strongly nihydrin positive - has also been found in the seeds.

Biomass: Provides a large quantity of plant material that can be converted into fuel etc.

Fibre: Used for making cloth, rope, paper etc.

Fuel: Usually wood, plant materials that have been mentioned as being a good fuel.

Green manure: Fast-growing plants that can be used to increase the fertility of the soil.

Insecticide: Kills insects.

Paper: Related to the entry for Fibre, these plants have been specifically mentioned for paper making.

String: Plants that can be used for string or can be easily made into a string. See also Fibre. Plants for ropes may be included.

Food Forest: Plants for Edible Forest Gardens and Food Forests.

Nitrogen Fixer: Plants that fix nitrogen in the soil

How it is grown

Often cultivated in the dry to moist tropics and subtropics, where it can be grown at elevations up to 1,500 metres. It grows best in areas where annual daytime temperatures are within the range 20 - 30c, but can tolerate 4 - 40c. Mature plants can be killed by temperatures of -2c or lower, whilst young growth will be severely damaged at -1c. It prefers a mean annual rainfall in the range 500 - 1,500mm, but tolerates 200 - 4,300mm. Sun hemp is generally sensitive to photoperiod. Long day lengths favour vegetative growth and reduce seed set, although selections exist that are neutral to day length. Widely adaptable to different soil types. For fibre production, a light, loamy well-drained soil is preferred; on low-lying or clay soils plants achieve vigorous growth, but the bast fibre is coarser and yields are lower. Plants are not very tolerant of salty conditions. Prefers a pH in the range 6 - 7, tolerating 5 - 8.4. Established plants are drought resistant. When grown as a fibre crop, the plants are usually harvested at the flowering stage or when the stems turn yellow. When the main priority is seed production, the crop is harvested when the seeds are ripe; the fibre is extracted from the stems afterwards. The production of green plants is normally 40 - 60 tonnes/ha yielding 2.5 - 4.5 tonnes/ha of dry fibre. 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 - 21 days 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. This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby. Soybean soils must contain the proper nitrogen-fixing bacteria. When grown on the same land for 2 - 3 successive years, increasing yields are obtained year after year. Seed can be purchased that has been treated with this rhizobium, it is unnecessary on soils with a pH below 5.5 but can be helpful on other soils. When removing plant remains at the end of the growing season, it is best to only remove the aerial parts of the plant, leaving the roots in the ground to decay and release their nitrogen.

Propagating it: Seed - sown in situ. Germination is rapid and seedlings emerge 3 days after sowing, soon producing a thick ground cover that smothers weeds. Too much moisture is harmful during the first 2 weeks after germination. Seeds are ready for harvest when pods begin to turn yellow and seeds rattle in them.

Best place to grow:

Habit: Annual

Hardiness: 10-12

Growth: Fast

Soil: Light (sandy), medium, heavy (clay)

Shade: No shade

Moisture: Moist

Things to keep in mind

The seeds of many Crotalaria species contain toxic pyrrolizidine alkaloids. Trichodesmine is the principal toxic alkaloid in Crotalaria 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.

It can be an invasive weed and has been listed as a noxious weed in Arkansas, USA. Crotalaria juncea, reduced both the germination and seedlings of various crop species including bell pepper, tomato, onion, and others.

Its other names

Local names

Crotalaria juncea or commonly known as Sun Hemp, brown hemp, Indian hemp, Madras hemp, and sunn hemp. Also known as: brown hemp, Bumpo, Ghore sun, Indian hemp, Janumu, Madras hemp, Oohawaimaton, San, Sana, Sanabu, Sanai, Sanal, Sann hemp, Sannai sunn, Sannappu, Saun, Senabina soppu, Shon, Shonpat, Sunn hemp, Tag, Tum-thang, Wuckoo nar.

Synonyms

Crotalaria benghalensis Lam. Crotalaria fenestrata Sims Crotalaria porrecta Wall. Crotalaria sericea