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Title: Allelopathic effects of sunnhemp (Crotalaria juncea L.) on germination of vegetables and weeds

Author
item SKINNER, EMILLIE - University Of Georgia
item DIAZ-PEREZ, JUAN CARLOS - University Of Georgia
item PHATAK, SHARAD - University Of Georgia
item Schomberg, Harry
item VENCILL, WILLIAM - University Of Georgia

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2011
Publication Date: 1/2/2012
Citation: Skinner, E.M., Diaz-Perez, J., Phatak, S., Schomberg, H.H., Vencill, W. 2012. Allelopathic effects of sunnhemp (Crotalaria juncea L.) on germination of vegetables and weeds. HortScience. 47(1):138-142.

Interpretive Summary: Cover crops are important in sustainable agricultural systems because they help improve soil organic matter and reduce soil erosion, among other benefits. Sunnhemp (Crotalaria juncea L.) is a tropical legume that could be an important summer cover crop in the Southeastern U.S. Although it could be a good cover crop because it has the potential for suppressing weeds, it might also have a negative impact on crop germination and establishment. In addition to its ability to suppress weeds, because it is a legume, sunnhemp fixes a large amount of N in a short time and could thus be a useful source of N for following crops. Plant suppressive (allelopathic) effects of sunnhemp on weeds, vegetable crops, and cover crops were evaluated in growth chamber and greenhouse experiments at the University of Georgia. Sunnhemp residues reduced germination of lettuce and smooth pigweed. The plant suppresive effect was greater for leaves than for roots or stems. Reduction in germination caused by water extracts of sunnhemp leaves was: bell pepper (100%), tomato (100%), onion (95%), turnip (69%), okra (49%), cowpea (39%), collard (34%), cereal rye (22%), sweet corn (14%), Austrian winter pea (10%), crimson clover (8%), cucumber (2%), and winter wheat (2%). In lettuce, carrot, smooth pigweed and annual ryegrass, the leaf extract reduced seedling length similar to that observed for rye leaf extract. Sicklepod germination was not inhibited by sunnhemp or rye extracts. The suppressive activity in sunnhemp was primarily in the leaves; it reduced the germination percentage and seedling growth of various crop species; and it remained active at least 16 days after harvest under dry conditions. Sunnhemp’s allelochemical effect may be a useful attribute for weed management in sustainable crop production systems. However, plant growth in crops such as bell pepper, tomato, onion, and turnip may be impacted due to germination and growth suppressive activity of sunnhemp residues. This information will be useful for vegetable producers and crop consultants.

Technical Abstract: Sunnhemp (Crotalaria juncea L.) is a tropical legume that could be an important summer cover crop in the Southeastern U.S., but it has the potential for suppressing both crops and weeds. Allelopathic effects of sunnhemp on weeds, vegetable crops, and cover crops were evaluated in growth chamber and greenhouse experiments. In the greenhouse, sunnhemp residues reduced percent germination of lettuce (Lactuca sativa L.) and smooth pigweed (Amaranthus hybridus L.) to a similar degree as that caused by cereal rye (Secale cereale L. subsp. cereale) residues. The allelopathic activity of sunnhemp was greater in the leaves than in the roots or stems. In growth chamber studies, the mean reduction in germination (relative to the control) caused by sunnhemp leaf aqueous extracts was: bell pepper (100%), tomato (100%), onion (95%), turnip (69%), okra (49%), cowpea (39%), collard (34%), cereal rye (22%), sweet corn (14%), Austrian winter pea (10%), crimson clover (8%), cucumber (2%), and winter wheat (2%). In lettuce, carrot, smooth pigweed and annual ryegrass, sunnhemp leaf extract reduced seedling length to a degree similar to that produced by rye leaf extract. Sicklepod germination was not inhibited by any of the sunnhemp or rye extracts. In conclusion, the allelochemical activity in sunnhemp was primarily in the leaves; it reduced the germination percentage and seedling growth of various crop species; and it remained active at least 16 days after harvest under dry conditions. Sunnhemp’s allelochemical effect may be a useful attribute for weed management in sustainable production systems. However, plant growth in crops such as bell pepper, tomato, onion, and turnip may be impacted due to allelopatic activity of sunnhemp residues