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Home HortScience Cover Crops Show Potential for Controlling Weeds in Organic Vegetable Production
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ST. PAUL, MN—Specialists in organic agriculture are increasingly interested in the advantages of using winter annual cover crops with no-tillage systems. These no-tillage organic systems rely on cover crops to replace herbicides, which are widely used in conventional reduced tillage. The cover crop systems can reduce weed populations, preserve soil structure, soil quality, and soil moisture, and have the potential to produce yields equivalent to traditional production methods.

Annual cover crops such as winter rye and hairy vetch are being studied for their abilities to reduce weed density and build soil quality in organic systems. Researchers at the University of Minnesota conducted a study to determine the efficacy of the cover crops in environments with short growing seasons and cool soils. Craig C. Sheaffer and colleagues evaluated no-tillage production of three vegetable crops planted into winter rye, hairy vetch, and a winter rye/hairy vetch mixture that were mechanically suppressed with a roller–crimper at two locations in Minnesota. "We also evaluated the impact of rolled–crimped winter annual cover crops on soil properties, weed populations, and mulch characteristics," said Sheaffer, professor in the Department of Agronomy and Plant Genetics at the University of Minnesota and lead author of the study published in HortScience.

To test the treatments in different soil types, the team conducted experiments on tomato, zucchini, and bell pepper at two locations: at the University of Minnesota, St. Paul, and at the Southwest Research and Outreach Center in Lamberton, Minnesota.

Cover crop treatments consistently reduced marketable yield of all vegetable crops compared with the no-cover control. When tomato, zucchini, and bell pepper were grown in rolled winter cover crop residue, average marketable yields were reduced by 89%, 77%, and 92% in the first year of the study and 65%, 41%, and 79% in the second year, compared with those of the no-cover control. Yields of all vegetables were consistently higher in the second year than the first, which the scientists attributed to increased rates of fertilizer and more uniform application of water from the irrigation system.

Winter rye and the winter rye/hairy vetch mixture reduced average annual weed density at St. Paul by 96% for 8 to 10 weeks after rolling and hairy vetch mulch reduced weeds 80% for 2 to 8 weeks after rolling, whereas at Lamberton, there was no consistent effect of cover treatments on weed populations.

According to the report, the use of a tractor-mounted roller–crimper was effective during the anthesis growth stage to end a winter rye cover crop. The roller was not an effective tool for ending hairy vetch at the vegetative growth stage that corresponded with winter rye anthesis.

"Our data showed that winter rye and hairy vetch demonstrated excellent potential for non-herbicidal management of annual weeds in organic vegetable production in the upper Midwest," Sheaffer said. "However, organic no-tillage vegetable production using winter cover crops presents unique implementation challenges in cool, northern states where growing seasons are short and low soil temperatures can reduce crop growth. Additional research is needed on methods to increase vegetable crop yields in rolled cover crops."


The complete study and abstract are available on the ASHS HortScience electronic journal web site:

Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at


Original Article:

Rolled Winter Rye and Hairy Vetch Cover Crops Lower Weed Density but Reduce Vegetable Yields in No-tillage Organic Production
Matthew J. Leavitt, Craig C. Sheaffer, Donald L. Wyse, and Deborah L. Allan
HortScience 46:387–395. [Abstract] [Full Text] [PDF]

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