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| ## sunn hemp {#sunn-hemp .Title-Header}                               |
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| *Crotalaria juncea* L.                                                |
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| Plant Symbol = CRJU                                                   |
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Contributed by: USDA NRCS Soil Quality Institute and the National Plant
Data Center

![](media/image2.jpeg){width="2.5729166666666665in"
height="1.676388888888889in"}

##### Uses {#uses .Header-3}

*Cover Crop & Green Manure*: Used as a cover crop, sunn hemp can improve
soil properties, reduce soil erosion, conserve soil water, and recycle
plant nutrients.

When grown as a summer annual, sunn hemp can produce over 5,000 pounds
of biomass and 100 pounds of nitrogen per acre. It can produce this
amount within 60 to 90 days, so it has the potential to build organic
matter levels and sequester carbon in the soil. It is known to suppress
nematodes.

Sunn hemp originated in India where it has been grown since the dawn of
agriculture. It has been utilized as a green manure, livestock feed, and
as a non-wood fiber crop.

##### Status {#status .Header-3}

As of 2005, Arkansas considered the genus *Crotalaria* as a noxious
weed. Please consult the PLANTS Web site and your State Department of
Natural Resources for this plant's current status (e.g. threatened or
endangered species, state noxious status, and wetland indicator values).

#####  {#section .Header-3}

##### Weediness {#weediness .Header-3}

This plant may become weedy or invasive in some regions or habitats and
may displace desirable vegetation if not properly managed. Please
consult with your local NRCS Field Office, Cooperative Extension Service
office, state natural resource, or state agriculture department
regarding its status and use. Weed information is also available from
the PLANTS Web site at plants.usda.gov. Please consult the Related Web
Sites on the Plant Profile for this species for further information.

##### Description {#description .Header-3}

Legume family (Fabaceae). Branched, erect, herbaceous shrubby annual
growing 3 to 9 feet high with bright green simple, elliptical leaves. It
has deep yellow terminal flowers (open raceme to 10 inches long) and the
light brown pods are small (1 inch long and 1/2 inch wide) and inflated.
It has a well-developed root system, with a strong taproot. The number
of seeds per pound is 15,000.

*Distribution*: For current distribution, please consult the Plant
Profile page for this species on the PLANTS Web site.

##### Adaptation {#adaptation .Header-3}

Sunn hemp is a tropical or sub-tropical plant that when grown in the
continental United States performs like a summer annual. It can be
planted year round in Hawaii below an elevation of 1,000 feet. However,
it does not perpetuate itself well and is not found in the wild. Sunn
hemp is adapted to a wide range of soils and performs better on poor
sandy soils than most crops. It is for such situations that it has
attracted attention. It grows best on well-drained soils with a pH from
5.0 to 7.5.

##### Establishment {#establishment .Header-3}

To establish a successful stand, seed should be broadcast or drilled and
covered ½ to 1 inch deep into a well prepared, weed-free seedbed. If
broadcasted, seed at a rate of 40 to 60 pounds of live seed per acre. If
drilled, the rate should be 30 to 50 pounds per acre in 6-inch rows. The
higher rates should be used if the crop will be terminated in less than
60 days or if severe weed competition is expected. Where weed
competition is mild, drilled rates as low as 20 pounds of live seed per
acre have been satisfactory. Inoculate with the cowpea-type rhizobia
bacteria.

Using a winter cover crop/green manure is a conservation practice that
provides soil-improving characteristics. A common problem, however, is
that the relatively short period between cash crop harvest in the fall
and planting the following spring can result in less than optimum
biomass production of the cover crop. Sunn hemp, because of its rapid
growth and relatively short growing season requirement, can be an
excellent alternative. Where conditions are favorable, it can provide
the benefits of a winter legume prior to a killing frost in the fall and
also in the summer after the winter crop has been harvested.

##### Management {#management .Header-3}

Warm weather (frost-free) is needed for 8 to 12 weeks to provide biomass
and nitrogen. Small grains following sunn hemp can utilize the
symbiotically produced nitrogen, thus reducing or eliminating the loss
of nitrogen. It must be plowed under before reaching the full bloom
stage or it becomes too fibrous when using it as a green manure.

##### Pests and Potential Problems {#pests-and-potential-problems .Header-3}

Some species of *Crotalaria*, including *Crotalaria juncea*, contain
toxic alkaloids, particularly the seeds and pods. 'Tropic Sun' is
non-toxic and is resistant to root-knot and reniform nematodes. The
genus *Crotalaria* has been known for its suppression of plant-parasitic
nematodes.

**Seed Production**

-Drill 3 to 4 live seeds per foot about 1/2 inch deep in 36 to 42 inch
rows. This will give a live seeding rate of about 4 lb/acre. Isolate the
seed field from other *Crotalaria* plants.

-Test soil and apply fertilizer and amendments per recommendations
(broadcast before planting or banded next to seed at planting).

-Irrigate if needed until about 75% of plants are flowering (usually
occurs at end of the third month). Stop irrigating after the 75% bloom
stage. 'Tropic Sun' is easily threshed when dry. To enable the plants to
dry naturally, time the planting so that flowering, seed set, and
harvest occur during the dry season.

-Cultivate as needed to control weeds. Fields should be weed free at
harvest to prevent contamination of crop. Remove any wild *Crotalaria*
before harvest.

-Combine when seeds rattle in the pods, about 5 months from planting.
Raise the combine header as high as possible without leaving seed pods
on the plants (which prevents excess straw from slowing combine).
Initially set the concave clearance at 1/8 to 3/16 inch and the cylinder
speed at 1150 to 1200 RPM. Adjust as needed according to crop
conditions.

-When seed crop is ready for harvest, the plants should be dry and
self-defoliated. If crop is still green, desiccate by spraying with an
approved desiccant 1-2 weeks before harvest.

-Clean seed with standard commercial seed-cleaning equipment. Dry the
combined material before cleaning.

-If commercial seed-drying and storage facilities are available, dry
seed to below 10% moisture and store at low temperature and humidity.

-Seed yields have ranged from 500 of over 2200 lb/ac, varying with
environmental conditions and cultural practices.

##### Cultivars, Improved, and Selected Materials (and area of origin) {#cultivars-improved-and-selected-materials-and-area-of-origin .Header-3}

'Tropic Sun': This has promise as an alternative to winter legume cover
crops as an organic matter builder and as a symbiotic nitrogen producing
legume. The USDA NRCS and the University of Hawaii Institute of Tropical
Agriculture and Human Resources cooperatively released the cultivar
'Tropic Sun' sunn hemp in 1983. This cultivar is non-toxic to poultry
and livestock as shown by laboratory tests and feeding trials. Since
sunn hemp is a short-day plant and will not set seed consistently north
of 28° N latitude (slightly north of Corpus Christi, TX), it has little
potential for becoming a weed in most of the U.S. 'Tropic Sun' sunn hemp
should receive a minimum of 1 inch of moisture per week for maximum
growth, however it is quite drought tolerant.

The supply of sunn hemp seed is limited due to few growers and the need
for the plant to be grown in tropical regions to produce seed.
Currently, limited supplies of seed can be obtained from the University
of Hawaii and www.groworganic.com. If sufficient demand develops, it may
be possible to produce seed in areas like south Texas or south Florida.
The NRCS does not endorse any certain company over another.

Contact your local Natural Resources Conservation Service (formerly Soil
Conservation Service) office for more information. Look in the phone
book under "United States Government." The Natural Resources
Conservation Service will be listed under the subheading "Department of
Agriculture."

##### Control  {#control .Header-3}

Please contact your local agricultural extension specialist or county
weed specialist to learn what works best in your area and how to use it
safely. Always read label and safety instructions for each control
method. Trade names and control measures appear in this document only to
provide specific information. USDA NRCS does not guarantee or warranty
the products and control methods named, and other products may be
equally effective.

##### References {#references .Header-3}

##### University of Hawaii. 2005. Sustainable agriculture in Hawai'I -- green manures -- 'Tropic Sun' sunn hemp. Accessed: 050927. \<http://www2.ctahr.hawaii.edu/sustainag/GreenManures/tropicsunnhemp.asp\> {#university-of-hawaii.-2005.-sustainable-agriculture-in-hawaii-green-manures-tropic-sun-sunn-hemp.-accessed-050927.-httpwww2.ctahr.hawaii.edusustainaggreenmanurestropicsunnhemp.asp .Header-3}

#####  {#section-1 .Header-3}

##### USDA NRCS. 2003. Sunn hemp: A cover crop for southern and tropical farming systems. Soil Quality -- Agronomy Technical Note No. 10. Washington, DC. {#usda-nrcs.-2003.-sunn-hemp-a-cover-crop-for-southern-and-tropical-farming-systems.-soil-quality-agronomy-technical-note-no.-10.-washington-dc. .Header-3}

#####  {#section-2 .Header-3}

##### Prepared By:  {#prepared-by .Header-3}

*Robert Joy*, Plant Materials Center, Hoolehua, Hawai'i and *J.S.
Peterson*, USDA NRCS National Plant Data Center, Baton Rouge, Louisiana.

##### Species Coordinator:  {#species-coordinator .Header-3}

*Robert Joy*, USDA NRCS Plant Materials Center, Hoolehua, Hawai'i.

##### Edited: 23sep05 jsp; 05jun06 jsp {#edited-23sep05-jsp-05jun06-jsp .Header-4}

For more information about this and other plants, please contact your
local NRCS field office or Conservation District, and visit the PLANTS
Web site\<[http://plants.usda.gov](http://plants.usda.gov/)\> or the
Plant Materials Program Web site
\<[http://Plant-Materials.nrcs.usda.gov](http://Plant-Materials.nrcs.usda.gov/)\>

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orientation, and marital or family status. (Not all prohibited bases
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large print, audiotape, etc.) should contact USDA\'s [TARGET
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*To file a complaint of discrimination write USDA, Director, Office of
Civil Rights, Room 326-W, Whitten Building, 14th and Independence
Avenue, SW, Washington, DC 20250-9410 or call 202-720-5964 (voice or
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*Read about [Civil Rights at the Natural Resources Convervation
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