Yield
In India, green biomass production from Crotalaria juncea sown in the pre-monsoon period ranged between 22 and 27 t/ha (Tripathi et al., 2013). In Cuba, it was possible to get 3.4 t DM/ha in 2 cuts (Machado et al., 1994). Worldwide, green matter yield averages 18-27 t/ha and forage yield is about 5-19 t/ha (Sarkar et al., 2015). In Thailand, when cultivated as a green manure after rice, sunn hemp yielded 2 t/ha of high quality DM in 6-8 weeks (FAO, 2017).
Establishment
Crotalaria juncea is propagated by seeds under moist and frost-free conditions, sowing periods varying upon location and final use of sunn hemp. As a green manure, sunn hemp is mainly grown during the rainy season. Sunn hemp should be preferably sown in a well-prepared, fertilized, weeded, seedbed to a depth of 2-3 cm. Seeds can be broadcast or sown in rows. They germinate within 3 days under favourable conditions. Sunn hemp is a fast growing species that suppresses weeds by shading them out once sufficient height is reached (FAO, 2017). Density of sowing depends on which use sunn hemp is intended for, and on the place where it is grown. When grown for fibre, sunn hemp should be sown at higher seed rate in order to promote erect growth, stem elongation and high quality fibre. Under rainfed conditions, seed rates ranging from 100 to 240 kg/ha were recommended for broadcasting while only 66 kg were enough for plantation in rows, and resulted in higher yields (Maroyi, 2011). Where irrigation is possible, sunn hemp is sown in small plots surrounded by furrows in which water is distributed at intervals of 10-15 days.
Rotations
Sunn hemp can be used for rotation with many cash crops. In India, recommended crop successions are sunn hemp-wheat, sunn hemp-potato, sunn hemp-mustard, sunn hemp-paddy-wheat, sunn hemp-mustard-wheat. The highest performing rotation was the sunn hemp-wheat rotation in which the yield of wheat was found to increase by 10-15% (Chaudhury et al., 1997). In Brazil, sunn hemp is intercropped with wheat, sorghum, sugarcane and beans (Cook et al., 1996). It is intercropped with cotton in the USA and with kenaf in Cuba (Chaudhury et al., 1997).
Harvest
Fibre
Harvesting should be done at the flowering stage (60-90 days after sowing) since the fibre is thinner at this stage. Harvesting can be done by hand or with a mechanical harvester. The top portion of the plants are chopped off soon after harvesting for use as cattle fodder (Sarkar et al., 2015). The main portion of the stem is left to dry on the ground during 1 to 6 days, depending on places, so that it shed its leaves and becomes ready for retting. In some areas, stems are left up to 15 days on the ground and retting occurs naturally thanks to morning dew (Sarkar et al., 2015).
Green manure
As green manure, sunn hemp should be ploughed in 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. It was recommended that green manure fallow lasts at least 6 months for a positive effect on soil characteristics. A fallow of up to 18 months was found beneficial for soil fertility but could have economic consequences (Maroyi, 2011).
Forage
Sunn hemp intended for forage can be harvested 4 times, starting 6-8 weeks after sowing and then every 4 weeks (Orwa et al., 2009). Sunn hemp should be cut for hay in the early flowering stage, 1.5-2.5 months after planting (FAO, 2017).
It has been recommended to sun-dry sunn hemp foliage prior to feeding animals as they do not eat fresh sunn hemp (FAO, 2017). However, Indian farmers have been reported to feed it green to cattle (Sarkar et al., 2015). When sunn hemp has been harvested for fibre, the top portion of the stem is used for fodder or hay after mixing with paddy straw (Sarkar et al., 2015).
In Brazil, a mixture of maize and sunn hemp (in a 6:20 seed ratio) grown for silage production yielded 16.2 t/ha while it only yielded 12.9 t/ha when grown alone. The protein yielded by the mixture was 1.30-1.45 t vs. 0.69 t in pure maize stand. In the silage, DM content was between 30.6 and 32.4%. Protein content was higher for the mixture and silage carbohydrates were not affected. In vitro digestibility, Ca, P and ammonium-N contents, and pH were unaffected (Obeid et al., 1992).