> We are using sunn hemp here in south Florida as a summer cover crop for
> winter vegetables. The sunn hemp performed well and we were hoping to get
> seed. It has been blooming profusely since September - but no seed! Any
> ideas- are we lacking the proper pollinator? too hot? too humid? I would
> appreciate any ideas anyone might have.
Your question was (almost?) answered in the recent Sustainable
Agriculture Network book: Managing Cover Crops Profitably, 2nd Edition.
I say *almost* because the paragraph from the Sunn Hemp section says:
**Seed can be produced only in tropical areas, such as Hawaii, and
currently is imported only by specialty seed companies.**
I don't know whether sunny, southern Florida is tropical enough. See the
contact information below for Seth Dabney, our *expert* on Sunn Hemp.
I have appended the section on Sunn Hemp from the book. NOTE that
coverage of this cover crop in the appendix was extremely abbreviated,
due to limited resources ($$, time, and page counts) for the book. Other
cover crops are addressed in great detail in 8- to 16-page chapters.
for more information about this and other SAN publications, including
EXCERPT FROM Managing Cover Crops Profitably, 2nd Edition. 1998.
Published by the Sustainable Agriculture Network (SAN). SAN is the
outreach arm of the USDA-CSREES Sustainable Agriculture Research and
Education (SARE) program.
Up-and-Coming Cover Crops
We chose the major cover crops in this book for their range of benefits,
reliability, availability and wide adaptability. They're not the only
cover crops to choose from, of course. Here are a few others you might
want to consider, either for their regional appeal or because they show
strong potential once seed becomes readily available.
A tropical legume that grows rapidly, sunn hemp (Crotalaria juncea) can
produce more than 5,000 lb./A of dry matter and 120 lb. N/A in just nine
to 12 weeks. It can fill a narrow niche between harvest of a summer crop
and planting of a fall cash or cover crop. Sunn hemp sown by September 1
following a corn crop in Alabama, for example, can produce an average of
115 lb. N/A by December 1.
Sunn hemp is not winter hardy and a hard freeze easily kills it. Sow
sunn hemp a minimum of nine weeks before the average date of the first
fall freeze. Seed at 40 to 50 lb./A, with a cowpea-type inoculant.
Sunn hemp seed is expensive, about $2.25/lb., so the cost may be
prohibitive for large-scale plantings. Seed can be produced only in
tropical areas, such as Hawaii, and currently is imported only by
specialty seed companies.
A management caution: Many Crotalaria species contain alkaloids that are
poisonous to livestock. However, the sunn hemp variety 'Tropic Sun,'
developed jointly by the University of Hawaii and USDA-NRCS, has a very
low level of alkaloid and is suitable for use as a forage.
Research suggests that sunn hemp is resistant and/or suppressive to
root-knot (Meloidogyne spp.) and reniform (Rotylenchulus reniformis)
For further information, contact: Seth Dabney, USDA-ARS National
Sedimentation Lab, P.O. Box 1157, Oxford MS 38655-2900, (601) 232-2975,
END of EXCERPT FROM Managing Cover Crops Profitably, 2nd Edition. 1998.
Andy Clark, Ph.D.
c/o AFSIC, Room 304
National Agricultural Library
10301 Baltimore Ave.
Beltsville, MD 20705-2351
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