Crotalaria juncea can fix about 50-60 kg N/ha within 60-90 days of cultivation. It provides 60 kg N/ha to the soil when it is used as green manure. Sunn hemp has the potential to improve soil properties, to build organic matter and sequester carbon in the soil. It can be used for soil reclamation (Sarkar et al., 2015).
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).
Crotalaria juncea is commonly grown for fodder. It can be used as fresh forage or made into hay. In Andhra Pradesh, India, it is stacked in alternate layers with rice straw to increase the value of the straw (Göhl, 1982).
Weed and nematode control
Crotalaria juncea does well on a wide range of soils provided they are well-drained. It does not withstand waterlogging. When it is grown for fibre, sunn hemp does better on fairly light textured soil (sandy loam or loam) of moderate or good fertility. For other purposes, it is possible to grow it on clayey soils of low fertility, provided they are well-drained. A neutral range of pH is preferred but sunn hemp can grow on soils with pH ranging from 5 to 8.4 where phosphorus is available. Sunn hemp tolerance of salinity is generally low but there have been reports of moderate tolerance (Orwa et al., 2009; Cook et al., 2005).
In Bangladesh, in sacco protein disappearance of sunn hemp hay measured in indigenous cattle reached 90% after 72h. At a low passage rate (2%), protein degradability was 78%, equal to that of prickly sesban (Sesbania aculeata) foliage, and higher than that of all other forage grasses, including oat forage (Avena sativa), elephant grass (Pennisetum purpureum), dhal grass (Hymenachne pseudointerrupta), and also than that of legume hays, including grasspea (Lathyrus sativus) hay, or black gram (Vigna mungo) hay (Khandaker et al., 1996).
In a trial with rams in India, DM intake was 2.57 kg/100 kg BW. Digestibility coefficients on consumption basis showed that the portion consumed was highly digestible (OM digestibility 65%). However, on feed basis the digestibility coefficients were very poor (OM digestibility 33%) due to the fact that the rams chose the leafier parts of the plant and rejected the stems (Balaraman et al., 1974 cited by Sarwatt et al., 1988).
Sunn hemp has been used as an alternative to winter legume cover crops. It can improve soil properties, reduce soil erosion, conserve soil water, and recycle plant nutrients (USDA, 1999).
Sunn Hemp’s vigorous growth rate and nitrogen fixing capabilities make it an attractive cover crop to build residue, sequester nitrogen, suppress weeds and improve soil health. When planted as a summer annual it regularly produces 2.5 tons of biomass and 120 lbs N/acre. Sunn hemp is a tropical plant and requires a warm soil temperatures germination and when planted it needs at least 45 days to accumulate growth before the first frost. Sunn hemp grows extremely fast in the heat and can reach heights of 6-7 feet in 60 days. Sunn hemp has also been found to greatly reduce soybean cyst nematode populations.