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Sunnhemp

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Summary

Common Name
According to Duke (1981), the common names of Crotalaria juncea are sunnhemp, Indian hemp, Madras hemp, brown hemp, and sannhemp. Other names applied include sunn hemp (McLeod, 1982), and sunn (Burton and Martinez, 1980).

Scientific Name
The scientific name is Crotalaria juncea L. (Duke, 1981).

Cultivar
According to Duke (1981), there are several types, including 'Madaripur,''Serajganaj,' 'Bhadai san,' 'Rabi san,' 'Somerset,' kharif, rabi, 'T6,' 'Cawnpore 12,' 'Kharif sunn,' ' Beldanga Early,' and 'Ullapora.'

Seed Description
According to McKee et al. (1946), seeds of Crotalaria spp. remain viable for a number of years. Deterioration is slow and gradual, unless during or subsequent to harvest the seed has been scarified, that is scratched to aid germination. Once the seed is, scarified, deterioration is much more rapid, but even then it remains viable for several years under good storage conditions. The percentage of hard seed is high. Since threshing with an ordinary thresher may scarify only 40% of the seed, about 60 % or more hard seed will ordinarily remain in untreated seed and this will produce volunteer growth in cultivated fields for a number of years without reseeding. The weight of crotalaria seed is about 60 lbs. per bushel.

For C. juncea, there are approximately 15,000 seeds/lb, according to McKee et al. (1946), and 33,000 seeds/kg according to Duke (1981).

Seedling Description
Crotalaria juncea seedlings are tender and susceptible to mechanical damage. This may restrict its use as a relay intercrop where field operations would occur at this stage (Yost and Evans, 1988).

Mature Plant Description
This is a tall herbaceous shrubby annual, 1-3 m tall, with vegetative parts covered with short, downy hairs, taproot long and strong with many well-developed lateral shoots and numerous branched, lobed nodules up to 2.5 cm in diameter. Stems are up to 2 cm in diameter. Flowers are bright yellow and showy (Duke, 1981). Plants branch at about 75 cm above the ground when not crowded, but branching is higher and sparser when grown in the high populations favored for green manure or fiber production (Yost and Evans, 1988).

Temperature
Duke wrote that the plant tolerates mean annual temperatures from 8.4 to 27.5 degrees C with the mean of 29 cases being 22.5. Warm temperatures with moderate humidity are best (McKee et al., 1946). Growth may be slowed by cool seasons (Yost and Evan, 1988), and the plant is susceptible to frosts (Miller et al., 1989), with 28 F the minimum tolerated without injury (McKee et al., 1946).

Geographic Range
Duke (1981) listed the species as being native to India and Pakistan, and it is now cultivated throughout India, as well as in Uganda, Zimbabwe, and Brazil. It is native to the Cool Temperate Steppe to Tropical Very Dry through Tropical Wet Forest Life Zones. Most species of crotalaria are tropical or subtropical in their requirements, as recounted by McKee et al. (1946). McKee et al. (1946) also wrote that C. juncea has failed to mature in experiments in Maryland. Under irrigation in the Southwestern States, several species have been tried. C. spectabilis, C. mucronata, and C. juncea have made fair growth but establishment is difficult. Seedings must be made after the threat of frost, and the quick drying and baking of soil interferes with seedling emergence . Crotalaria juncea is best adapted to the tropics and subtropics, and has given good results in U.S. experimental plantings (McLeod, 1982). It grows best at elevations below 300 m (Yost and Evans, 1988).

Water
This species is listed as drought tolerant yet reported as receiving irrigation every 10-15 days when cultured for fiber (Duke, 1981). Reports from Davis, Yolo County, California suggest that pre-irrigation (planting to moisture) and one subsequent irrigation are all that is required for a 60-day green manure (Van Horn, pers. comm.).

Nutrients
Sunnhemp is said to be tolerant of laterite and poor soil and is grown in India without any special fertilization (Duke, 1981). The species is mentioned as less demanding of soil fertility than is cowpea (Miller et al., 1989). In general, Crotalaria spp. tolerate infertile soils and have been much used on sandy soils. Continued production on sandy, infertile soils requires the addition of superphosphate and potash for other crops in the rotation (McKee et al., 1946).

Soil pH
Duke (1981) mentioned that sunnhemp tolerates soil pH from 5.0-8.4, with the mean of 24 cases being 6.2. The species tolerates moderate alkalinity, but soil acidity below pH 5 appears to reduce growth on manganiferous Oxisols (Yost and Evans, 1988).

Soil Type
Crotalaria juncea or cultivars thereof are said to tolerate laterite and poor soil (Duke, 1981). In general, according to McKee (1946), the genus tolerates poor, sandy soils. On more fertile soils it grows better, but other crops can be grown there. Crotalaria spp. need good drainage and do not do well on heavy clay; most soils of the Coastal Plain region of the southeastern states are suitable (McKee et al., 1946).

Crotalaria juncea does best on well-drained acid soils (McLeod, 1982; Miller et al., 1989) and does not grow as well as sesbania on low, wet lands (McLeod, 1982). Yost and Evans (1988) agreed that the species is adapted to lighter, well drained soils, although good growth is obtained on heavy soils during dry periods; poorly drained soils are the major limitation, although constant wet weather is detrimental to growth on any soil type.

Shade Tolerance
In discussing tolerances of sunn hemp, Duke (1981) did not mention shade.

Salinity Tolerance
The species is not tolerant of salinity, according to Duke (1981), although Yost and Evans (1988) claimed that moderate soil salinity is tolerated.

Herbicide Sensitivity
No information is available on C. juncea, but Crotalaria spectabilis is sensitive to herbicides, particularly 2,4-D (Duke, 1981).

Life Cycle
Sunnhemp is a summer annual (Yost and Evans, 1988). It is the fastest growing of its genus, and is good at smothering weeds. Vegetative growth is favored by long days, with flowering induced by short days for most varieties. In India, the variety 'T6' is day neutral. In Zimbabwe, the species flowers during July and August (Duke, 1981). Seed set may be poor (Duke, 1981). In the continental U.S., Crotalaria spp. are treated as summer annuals (McKee et al., 1946). In California, the species is fast growing as a cover crop; like sesbania, and cowpea, it can make rapid growth during short 60 to 90 day summer growing periods (Miller et al., 1989).

Seeding Rate
McKee et al. (1946) recommended broadcasting at 20-40 lbs/acre, or seeding in wide (3.5 ft) rows at 5-7 lbs/acre. McLeod (1982) recommended 35 to 40 lbs/acre. According to Yost and Evans (1988), sowing rates vary from 25 to 90 kg/ha; within this range, broadcast rates are higher than for drilling. Higher densities lead to prolonged stem succulence. High sowing rates are recommended if the crop is to be grown only for four to five weeks. When incorporation is to be after six to 8 weeks, seed 35-40 kg/ha broadcast or 30-35 kg/ha drilled are adequate. For seed production, lower rates are used.

Seeding Depth
No specifications were available for sunnhemp, but Crotalaria spectabilis is sown at 3/4 inch depth (McLeod, 1982).

Seeding Method
Because the percentage of hard seed is high for Crotalaria spp., seed should be scarified or scratched to aid germination. Commercial seed scarifying machines are available in the trade. The abrasives used in their construction usually are sandpaper, emery cloth, or sandstone. A small concrete mixer can be used as a scarifier by first adding to the seed coarse stones the size of marbles or larger. If the concrete mixer is rotated for about 1 hour with stones and seed in equal bulk, reasonably good scarification should be effected. This method of scarification is described in Dept. of Agriculture, Leaflet 107, The Barrel Seed Scarifier. The scarified seed can be easily separated from the stones by screens (McKee et al., 1946.).

McKee et al. (1946) stated that seed of Crotalaria spp. is comparatively small, so thorough seedbed preparation is necessary for the first seeding to ensure a prompt and good stand. Subsequent volunteer stands require only disking to reduce weeds and. Crotalaria does well in cultivated fields either as a first crop or volunteer.

Seedings can be made broadcast or drilled. In drilling, the rows can be close, as with small grains, or wide, as with corn and sorghum. Rows can be wide when seed is limited or it is desired to control weeds by cultivation. They also may make seed harvesting by hand easier (McKee et al., 1946).

Scarification of seeds is unnecessary for some varieties (Yost and Evans, 1988).

Seeding Dates
According to McKee et al. (1946), for maximum growth on prepared seedbeds, seeding should be done after all danger of frost is past, about the same time as corn planting or a little later. Earlier seeding is advisable in oat or other small grains. When planted early under such conditions, the seed becomes covered and is ready to grow by the time the weather is warm.

Use of a combine in harvesting the grain will be facilitated if time of seeding is delayed so as to reduce the height of the plants (McKee et al., 1946).

Inoculation
Inoculant type "EL" (Nitragin Co.) is appropriate to this and other species of Crotalaria (Burton and Martinez, 1980; Duke, 1981). Wherever planted in the U.S., Crotalaria has made good growth and developed many nodules so that artificial inoculation seemed unnecessary to McKee et al. (1946); other researchers have stated that inoculation is probably a good idea because it generally improves N-fixation potential (Yost and Evans, 1988).

Seed Cost
Cost is $3.50 to $4.00 per pound. (Fred Thomas, pers. comm.)

Seed Availability
Seed has been difficult to obtain due to negligible production in the continental U.S.; the principal source during the early 1990's has been Hawaii (Mark Van Horn, pers. comm.).

Days to Flowering
Sunnhemp is a short-day plant, although the cultivar 'T6' is day neutral (Duke, 1981). Flowering occurs in from 100-108 days, but in India, intervarietal difference in maturation date can be as great as 10 weeks (Duke, 1981). In Davis, Yolo County, California, flowering has occurred during August and September (Bugg, pers. comm.). Plants remain succulent until six to eight weeks after sowing, at which time flowering begins and stems begin to lignify (Yost and Evans, 1988).

Days to Maturity
This is the fastest-growing species in its genus (Duke, 1981). In tropical areas, maturity may be reached in four months or more (Yost and Evans, 1988). Intervarietal difference in maturation date can be as great as 10 weeks (Duke, 1981). In Davis, Yolo County, California, flowering has occurred during August and September (Bugg, pers. comm.). Plants remain succulent until six to eight weeks after sowing, at which time flowering begins and stems begin to lignify (Yost and Evans, 1988).

Seed Production
Seed yields have exceeded 2.25 Mg/ha for HA-6 selected at the USDA Plant Materials Center on Molodai, Hawaii (Yost and Evans, 1988). World-wide seed yields range from 500-1,000 kg/ha of seed (Duke, 1981). McKee et al. (1946) cited seed production as 200 to 500 lbs/acre, but the species, although blooming freely, usually sets very little seed. Seeds are seldom produced in California, because of long days during summer (Miller et al., 1989). Seed production is difficult in the subtropics, where days short enough for flowering occur during unfavorable winter months (Yost and Evans, 1988). In the United States, seed is obtained in commercial quantity only from southern Texas (McKee et al., 1946; Yost and Evans, 1988).

In the tropics, flowering can begin at six weeks, with maturity reached at four months or more. Seed pods do not dehisce in the field, so seed may be combine-harvested when mature and dry. Hand harvesting and threshing are easy. Seed yields of over 2.25 Mg/ha have been recorded with the accession HA-6 selected at the USDA Plant Materials Center on Molodai, Hawaii (Yost and Evans, 1988.)

Shortage of seed has prevented C. juncea from being commonly used (McKee et al., 1946).

Seed Storage
No information is available on sunnhemp, but for the congeneric C. spectabilis, seeds remain viable for a relatively long time (McLeod, 1982).

Growth Habit
Sunnhemp is a tall, herbaceous, shrubby annual, with erect fibrous stems reaching a height of from 1-3 m (Duke, 1981), or six feet, according to Miller et al. (1989).

Maximum Height
Crotalaria juncea reaches a maximum hieght of between 1-3 m (Duke, 1981; Yost and Evans. 1988).

Root System
The taproot of Crotalaria juncea is long and strong (Duke, 1981).

Establishment
Seedlings emerge after three days and form a thick cover (Duke, 1981). Only under optimum conditions, planted thickly (i.e. with a grain drill.) (Mark Van Horn, pers. comm.)

Maintenance
When crotalaria is seeded along with a small grain and continues to grow following the harvesting of the grain, allow the crotalaria to mature some seed each year to ensure subsequent volunteer stands. Alternatively, one could occasionally allow a crop to mature fully. Crotalaria grown with corn should be seeded several weeks before the corn is laid by, or it may be volunteered from a previous crop. In most seasons, this allows enough time for some seed to mature and ensure subsequent volunteer stands (McKee et al., 1946).

After a good seed crop is obtained, reseeding is assured. The quantity of seed that matures before frost varies from 200 to 500 lbs/acre. Light frosts do not kill crotalaria. After the first year, even the complete loss of 1 year's seed crop does not greatly affect volunteering because sufficient hard seed remain for 2 years (McKee et al., 1946).

Mowing
Plants grazed at 6 to 12 inches height produced many lateral branches but never fully recovered compared to ungrazed plants. (Mark Van Horn, pers. comm.)

Incorporation
For maximum immediate N yield for subsequent vegetable crops, crotalaria should be plowed under in its early stages of growth, when the nitrogen concentration is high and decomposition rapid. If gradual availability of N will suffice, as in an orchard, incorporate mature crotalaia as tree growth begins in spring (McKee et al., 1946).

The bud or early flowering stage is preferred for ploughdown. Early incorporation is prefered to risking overmaturation where wet soils are likely to preclude field operations. In dry regions, irrigation may be advisable prior to incorporation. One incorporation method is mowing, then disking and plowing before the material dries. Alternatively, the standing crop may be plowed after laying down the crop by "planking" or light disking in the direction to be plowed (Yost and Evans, 1988).

Harvesting
Harvesting is by combining, mowing, or hand-picking. Some species ripen seed fairly uniformly, and these are best suited for handling with machinery. In Texas, July-sown C. juncea made about half as much growth as when planted early, and it matured seed which could be easily harvested with a combine. Crotalaria can be threshed when dry but is difficult before fully mature. Threshed seed must be dried artificially or spread thinly on shed floors to dry. Heating seed reduces germination. Hand-harvested seed pods can be gathered and spread to dry before being hulled or threshed. Special crotalaria threshers have been built, but ordinary threshers can be adjusted satisfactorily. Screens and ordinary fanning mills can be used to clean seed (McKee et al., 1946).

Equipment
No information is available in this database on this topic.

Uses
Sunnhemp is grown for its fiber, which makes durable twine, rope, rug yarn, paper, etc. It is also used as a green manure and and as forage (Duke, 1981).

Various species of Crotalaria can grow on infertile soils, do not harbor pest nematodes, and are good at adding N; thus, they are good soil improvers (McKee et al., 1946).

Like sesbania or cowpea, in northern California, sunnhemp can follow crops such as early sweet corn and early processing tomatoes, or precede fall-planted crops such as vegetable brassicas and cereal grains (Miller et al., 1989). The genus is especially good on nematode-susceptible soils in rotation with truck crops and for reducing damage to peach trees (McKee et al., 1946).

Crotalaria juncea is the species most widely used as in situ green manure for upland crops in the tropics (Yost and Evans, 1988).

As a green manure (McLeod, 1982), it grows rapidly in height and can be used as an intercrop amid maize or sugarcane (Yost and Evans, 1988).

Crotalaria spp. are often used as green manure in tung groves (an Asian tree whose seeds yield a drying oil). Crotalaria spp. can be intercropped or rotated with peanuts, truck crops, and corn. One of the best soil-improving practices is to plant crotalaria in spring in small grain and allowing it to continue after the grain has been harvested (McKee et al., 1946).

No species of crotalaria is used extensively as forage (McKee et al., 1946), but hay of Crotalaria juncea is fed to livestock (Duke, 1981). Seeds are fed to pigs and horses, although said to be poisonous (Duke, 1981).

Lack of seed has limited use of sunnhemp in the U.S.A. (McKee et al., 1946).

Mixtures
When intercropping with a small grain, crotalaria seed is broadcast during February or early in March amid the young grain at the rate of about 25 lbs/acre. A drag (spring-tooth?) harrow or weeder can then be used to incorporate the seed. The grain will mature late in spring or early in summer and can be harvested with binder and combine when the crotalaria plants are a few inches high. Crotalaria plants then grow rapidly in the stubble and by October are 4-6 feet high. If crotalaria is allowed to mature seed for reseeding, subsequent grain crops must be seeded late. An early strain of C. spectabilis is often desirable, permitting earlier sowing of the grain (McKee et al. 1946).

In rotation with corn, seed several weeks before corn is laid by or use a volunteer stand from seed derived from a previous crop. This usually allows some seed maturation to ensure subsequent volunteer stands. When corn follows crotalaria that was allowed to mature seed or crotalaria was seeded early in the season, 8 to 10 tons of cover crop may ultimately be obtained. Crotalaria overseeded at the time of laying by the corn sometimes failed because of the late start. Carry-over seed germinates as soon as cultivation is stopped and makes satisfactory growth (McKee et al., 1946).

Biomass
Sunnhemp can produce between 12.5 and 14 Mg/ha of dry above-ground biomass (Duke, 1981).

N Contribution
In an experiment conducted in India, sunnhemp yielded more nitrogen than five other legumes, including cowpea, which was the second highest. At eight weeks of growth, these two legumes yielded the same quantity of green cuttings. Nevertheless, cowpea may be preferable as a green manure because it is more leafy and less fibrous (McLeod, 1982).

Non-N Nutrient Contribution
No information is available in this database on this topic.

Effects on Water
No information is available in this database on this topic.

Effects on Microclimate
No information is available in this database on this topic.

Effects on Soil
No information is available in this database on this topic.

Effects on Livestock
The suitability of sunnhemp as forage is an area of controversy. According to McKee et al. (1946), species of crotalaria reported as poisonous to livestock include C. spectabilis, C. juncea, C. burkeana, C. dura, and C. sagittalis. On the other hand, Yost and Evans (1988) asserted that Crotalaria juncea has been found non-toxic to livestock, unlike most congeners. Palatability may be a limitation, and multiple use of the crop as a fodder source requires further investigation. Duke (1981) noted that hay is fed to livestock, and seeds to pigs (in Zimbabwe) and horses (in Russia) although seed are said to be poisonous (Duke, 1981).

USDA grain standards limit the amount of sunnhemp seed allowed in grain crops. (D. Cohen pers. comm. to Mark Van Horn.)

Effects on Workers
No information is available in this database on this topic.

Pest Effects, Insects
Sunn hemp when in flower harbors high densities of Lygus hesperus (Mark Van Horn, pers. comm.).

Pest Effects, Nematodes
Duke (1981) reported that sunnhemp hosts 20 types of plant-parasitic nematode. McKee et al. (1946), however, noted that the genus does not harbor nematodes and is, therefore, good in rotation with nematode-susceptible crops and at reducing nematode damage to peach trees.

Pest Effects, Diseases
Duke (1981) reported that sunnhemp is attacked by 38 species of fungi, 6 bacteria, 8 viruses, and 3 parasitic plants. No widespread disease epidemics have been reported in farmers' plantings (McKee et al., 1946). Damping-off caused by Rhizoctonia solani may be damaging during cool, wet weather in spring (McKee et al., 1946).

Pest Effects, Weeds
Sunnhemp is reported as tolerant of weeds and is very effective at shading them out (Duke, 1981). This probably relates to the six-foot high canopy providing dense shade late in the growth cycle of the plant (Miller et al., 1989). Nonetheless, sunnhemp will not choke out Bermuda grass because the latter grows all summer, whereas the former produces dense shade only during the late summer after Bermuda grass has already had half a season's growth (McKee et al., 1946).

Pest Effects, Vertebrates
No information is available in this database on this topic.

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