Seed Production of Sunnhemp

Sunnhemp (Crotalaria juncea L.) also known as brown hemp, Indian hemp or Madras hemp, is a tropical Asian plant that belongs to the family leguminoaceae. Crotalaria juncea is generally considered to have been originated in India (Montgomery, 1954). The genus name ‘crotalria’ means rattle and is indicative of the noise made by the seeds shaken in the matured pods (White and Haun, 1965). The crop is known by various names like 'Sonai' or 'San' (Hindi), 'Sanpat' (Bengali & Oriya), 'Tag' (Marathi), 'Vakku' (Malayalam), 'Janumu' (Telegu), 'Saab' (Kannada) in India. It is an important multipurpose fabaceous crop grown all-over India for fibre, green manure and fodder purposes.

Botanical Description

Sunnhemp is a short-day, erect shrubby annual, generally 1 to 4 m in height. The simple, elliptic to oblong shaped leaves, are spirally arranged on the stem. The root system is characterized by a long, strong taproot; well-developed lateral roots and much branched with lobed nodules, up to 2.5 cm in length. The inflorescence is a terminal open raceme with deep yellow flowers. Flowering is indeterminate. Seeds are small, flattened, kidney-shaped and contain approximately 35% protein. Due to cultivars and environments, seed weight is highly variable, ranging from 18,000 to 30,000 seeds per kg (Dempsey, 1975). 'Tropic Sun', a Hawaiian cultivar was reported to have 30,000 to 35,000 seeds per kg (Rotar and Joy, 1983). Sunnhemp is a diploid plant with 16 somatic chromosomes (n=8).

Production scenario in India

Sunnhemp is mostly cultivated in India as a fibre crop followed by China and Bangladesh. In India, the area under this fibre crop is around 45000 ha and the annual production of fibre is 0.102 million bales (1 bales=180 kg) with average annual productivity of 409 kg ha^-1. The maximum area in sunnhemp is in Maharashtra (11,900 ha) followed by Odisha (9,800 ha), Uttar Pradesh (6,600 ha), and Bihar (3,300 ha).

Importance of Sunnhemp

N-fixing legume and soil improver

Sunnhemp can fix about 50-60 kg N ha^-1 within 60-90 days of cultivation. When it is used as green manure, it provides 60 kg N ha^-1 to the soil. Sunnhemp has the potential to improve soil properties, to build up organic matter and sequester carbon in the soil. Soil reclamation can be done by adopting this crop (Sarkar et al., 2015).

Sunnhemp Leaf

The leaves of sunnhemp contain 25.30 percent crude protein and if not utilized as fertilizer or forage would provide excellent material as dehydrated leaf meal for livestock and poultry meal supplement.

Sunnhemp Seed

The seeds of sunnhemp are a secondary source of income. It contains 30-35 percent proteins and can be used for making adhesive for plywood industries. Besides this, the seeds also have some medicinal values. It is used as a blood purifier, in impetigo, psoriasis, urinary crystalluria and as an emmenagogue. Seeds of ‘Crotalaria juncea’ contain 'Trypsin inhibitor'- a very mysterious substance and an alkaloid like - 'Retusamine - N-oxide'. Sunnhemp seeds are characterized by a high percentage of water soluble proteins and all others by a high percentage of albumin and globulin.

Sunnhemp seed contain

Nutritive value of Sunnhemp dry matter as fodder

Sunnhemp Stalk contains

Raw Sunnhemp plant contains

Usages:

Sunnhemp as Green Manure

The whole green plant of Crotalaria juncea is widely grown throughout the world as an excellent cover crop or green manure. It possesses certain characteristics which contribute to its usefulness as a green manure-

(i) Root can fix nitrogen to the tune of 60 to 80 kg or more per hectare as it nodulates freely (ii) Plants are erect, fast growing and compete effectively with weeds and need no further care until ploughed down after 45 - 60 days (iii) Plants are generally drought resistant and high yielder (iv) The crop can be grown on infertile soil (v) It can be grown in rotation with potato, tobacco, sugarcane, tea, coffee and other crops which are subjected to damages by nematodes.

Sunnhemp as Forage Crop

The whole plant could be harvested prior to seed maturation and can be fed with less or no harm to livestock.

Sunnhemp as Fibre Crop

Sunnhemp retted fibre can be used for rope, string and fishing nets. Cordage made from sunnhemp is considerably stronger than that of jute. It is also resistant to salt water. The tow from retted fibre is used for marine caulking. By adopting flax spinning machinery for sunnhemp, Belgium twines cords, matting, sacking, tarpaulins, soles of shoes, sandals and marine cordage are produced. The other products include rugs, carpets, webbing, table and bed linen (Wealth of India).

Sunnhemp for Paper Making

For paper industries, the whole dry stems of sunnhemp may provide a new economic crop. USDA Research at the Northern Regional Research Laboratories, Peoria, Illinois showed that the whole stem possesses good pulping characteristics with a high macerate yield pulp that appears suitable for a wide range of uses. As a raw material for paper, sunnhemp stems rated second next to mesta. For paper making purpose, the highest yield of dry stems occurs in a later stage, but this does not affect the quality of paper. Thus it is recommended to harvest the crop at the mature seed pod stage, which would be about 180 days after planting.

Sunnhemp against Root-Knot Nematode and Weed

Sunnhemp has been reported to be effective in preventing a build-up of root-knot nematodes when grown in rotation with cotton and many other crops. Good weather condition and heavy seedling rates enable to smoother the weeds. It is also valuable for controlling Kans grass (Saccharum spontaneum).

Minor usage of Sunnhemp

Some other uses are (i) After washing and extraction of fibres, woody stems can be used for fuel purposes and (ii) it can be used as an indicator plant to denote potassium and calcium deficiency in loose sandy and sandy loam soil.

Need for Sunnhemp seed production

Sunnhemp is highly cross pollinated and due care is taken to maintain its genetic purity. The seed production of sunnhemp is yet to be organized. By tradition, the farmer sows a few lines of sunnhemp on the borders of pearl millet, ragi and sorghum or on the bunds of rice fields for obtaining seed. Nowadays, more focus is giving on organic farming, to avoid the use of chemical fertilizers; use of green manure is the obvious alternative. We all know that sunnhemp is the outstanding green manure crop and a massive quantity of seeds is required for green manuring. So, it is necessary to grow sunnhemp for the production of quality seed to supply the increasing demands so that farmers can go for green manuring as well as they can get quality fibres.

Seed production

Package of practices

Climate

The crop grows best in tropical and sub-tropical climates. It thrives well within a temperature range of 23-30°C but not less than 10°C and rainfall variation of 40 to 50cm. It needs good sunshine hours with no rainfall during the seed setting stage.

Land preparation

To get well pulverized soil, 2 to 3 ploughings with cultivator followed by laddering should be done. For suitable germination of seed, the moisture content of soil at the time of sowing is 25 to 30% soil moisture is necessary for better germination of the seed.

Sowing Time

The seed crop is raised late in the kharif season, i. e. the end of July to the first fortnight of August in the sunnhemp growing districts of the northern states of India but it is ideal to grow a seed crop in the rabi season in a zone where winter is not severe. The best sowing time in such areas is September to October.

Seed rate

For seed crops, sowing of 20 to 25 kg ha^-1 seed is sufficient. Seed should be treated with Mancozeb 50 WP @ 0.2% for better stand and vigour.

Spacing

The crop is generally grown with the spacing of 25 to 30 cm × 5 to 10 cm but it does not produce sufficient seed. Wider spacing i. e. 40 × 20 cm was found suitable to produce more seeds.

Irrigation

Sunnhemp seed crop is mostly cultivated as a rainfed crop so enough soil moisture is available at the time of sowing and no irrigation is required at the early growth stages of the crop. But two to three light irrigations are recommended at seed setting and pod maturation stages that result in more seed yield.

Fertilizer

Application of fertilizer N:P₂O₅:K₂O @ 20:40:40 kg ha^-1 is essential to increase seed yield. Total amount of nitrogen, phosphorus and potash are to be added during final land preparation.

Harvesting and Threshing

The crop should be harvested at 150 to 160 days after sowing with the help of a sickle when the seed inside the pod has started rattling.

Threshing can be done by tractor or by beating pods against a hard surface. After threshing and winnowing, the seeds should be dried for 3 to 4 days under the sun until the moisture content of the seed reached to an extent of 10% for better storage.

Seed yield

Seed yield depends on the climatic condition of the area where it is cultivated. The average seed yield varies from 16 to 20 q ha^-1.

Pests and diseases

Major diseases of sunnhemp include Fusarium wilt (Fusarium udum var. crotalariae), Antharacnose etc. and major pests include sunnhemp pod borer, sunnhemp moth (Utetheisa pulchella), stink bug (Nezara viridula). To avoid outbreaks of pests and diseases, the field should be rotated at least every three years.

Seed quality and standard

Field standards

Isolation distance of foundation and certified fields of other varieties and also same variety not conforming to varietal purity should be maintained at 250 m and 100 m respectively. For checking the field standards, minimum two inspections shall be made, the first at the flowering stage and the second before harvest.

Seed standards

After harvesting and completion of all the postharvest operations of certification. The certifying agency collects the seed samples and arranges laboratory tests. After laboratory test, it is recommended for use with a certification tag and standard packaging if the seed lot confirms the prescribed standards as per the following table:

Minimum seed certification standards for sunnhemp

Source: Indian Minimum Seed Certification Standards

Conclusion

The importance of sunnhemp is regaining due to its biodegradable fibres as well as green manuring properties. Non-availability of quality seeds is a major limiting factor for the expansion of this crop.

Reference:

Dempsey, J. M. 1975. Fiber Crops. The University Presses of Florida, Gainesville, Florida.

Montgomery, B. 1954. Sunn fiber. In: H. R. Mauersberger (edition), Mathew's textile fibers. 6^th edition. Wiley, New York. pp.323-327.

Rotar, P. P. and Joy, R. J. 1983. `Tropic Sun' Sunnhemp (Crotalaria juncea L.). University of Hawaii, College of Tropical Agriculture and Human Resources, Institute of Tropical Agriculture and Human Resources Research Extension Series 36.

Sarkar, S. K., Hazra, S. K., Sen, H. S. Karmakar, P. G. and Tripathi, M. K. 2015. Sunnhemp in India. ICAR-Central Research Institute for Jute and Allied Fibres (ICAR), Barrackpore, West Bengal. pp.140.

Wealth of India, pp. 377-378

White, G. A. and Haun, J. R. 1965. Growing Crotalaria juncea, a multi-purpose fiber legume, for paper pulp Economic Botany. 19:175-183.

Bijan Behari Barick¹, Debarati Seal², Kabita Mishra³, Sabuj Pati⁴ & Bikas Chandra Patra⁵

(1, 2, 3 & 4 Research Scholar and 5 Professor)

Department of Agronomy, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal-741252, India