Until recently Sunhemp was one of the most popular green crops. Then stem break fungus became prevalent. The hay is nutritious but fibrous and the stems make an excellent thatch which outlasts many of the so‐called thatching grasses. The fibre is suitable for grain bags but yields are too low to make this profitable. Other species are used as green manures and fodder but care must be taken as the majority is toxic to stock.
Sunhemp needs a period of 150 days of warm conditions in which to produce seed which is mostly produced in areas under irrigation. The crop endures mild frost but is sensitive to colder conditions. For seed production a short day‐length is required. Under long day length conditions much vegetative growth and very little seed is produced. Sunhemp is drought‐resistant and will thrive on rainfall of 600 mm or more. It tolerates wet but not water‐logged conditions.
Somerset is the most common variety of sunhemp (C. juncea). Most sunhemp species are toxic to livestock. Crotalaria Anagyroides is a variety used as a nurse plant in tea plantations.
The crop is sown from October ‐ December for seed production and from mid‐January for hay or green crop. Seed is sown 2 – 5 cm deep, depending on the soil‐moisture and texture. Spacing between rows should be between 220 to 300 mm for green manure and 370 to 600 mm for seed. Seed rates per hectare vary as follows:
Drilled Broadcast 20 – 25 kg/ha For Seed 25 – 30kg/ha
For green manure 40 – 50 kg/ha
Heavy seeding promotes stem‐break. 22 – 33 Kg/ha of sunhemp plus 11 – 22 kg/ha of munga can be broadcast for green manure. Dry planting is very satisfactory.
If broadcast, roll the land with a roller before planting and lightly disc in the seed afterwards. Use a seed drill or maize planter with suitable plates for drilling arranging the runs to overlap so as to halve the distance between the planting shoes.
Depending on the fertility of the soil, the following fertilizer dressings should be applied to the seedbed and disced into the soil:
Good Soil Moderate SoilPoor Soil
|Nitrogen (N)||20 kg/ha|
|Phosphate (P)||30, 60 or 90 kg/ha|
|Potassium (K)||40 to 60kg/ha|
Sunhemp is Nematode (Eelworm) resistant. Due to stem‐break disease, which is carried over, it should not be planted in the same field more than once in 4 years. Sunhemp fits in well into rotations with potatoes, maize, winter cereals and rice. It can also be grown between rows in orchards.
5. PESTS AND DISEASES
This disease is caused by a fungus which can cause defoliation and brown lesions appear on the stem. The stems of young less fibrous plants may break. The disease is seed‐borne and can survive at least 2 rainy seasons in the soil. Storm and irrigation water spread it through a field. Alternate the green‐manure crop in the rotation with other crops which are resistant.
Cause much damage by eating the cotyledons of the newly emerged seedlings. Planting after mid‐ December and rotations assist in reducing the damage.
If difficulty is found in turning the crop in, it can be rolled and disced first. It should be ploughed when in flower after about 80 – 100 days growth, i.e. March, April or May, but preferably before the soil dries out. It will then be well rotted by the next season. It normally takes 5 – 6 weeks to rot down in a warm moist soil.
This should be cut when the crop begins to flower after 65 – 70 days of growth. One part of sunhemp can be mixed with three parts of maize or alternatively 2 – 4% of Molasses, i.e. green matter should be added. Sunhemp cut at too late a stage will not chaff readily.
This should be cut at the same stage as silage, windrow it to wilt, cure in cocks for 5 – 7 days and then thresh. Yield should be up to 3 tons per hectare.
Combine the seed or reap when the pods turn yellow and stack for 15 – 30 days and then thresh.
This should be cut by hand when the stems turn yellow and the seed is well set. Labour requirement:
12 labour‐days per hectare. No efficient decorticators are at present available for this crop.