Cover Crops a Sustainable Method of Soil Management in Strawberries

RALEIGH, North Carolina – A combination of summer cover crops and native beneficial fungi to increase available nutrients, combat weeds and improve overall soil health may be a sustainable alternative to methyl bromide applications in strawberry production, according to North Carolina State University research.

The two-year study, funded by a $200,000 Southern Sustainable Agriculture Research & Education (SARE) grant, found that a pearl millet/soybean combination significantly reduced weed pressure, increased soil organic matter, broke weed and pest cycles, and reduced the amount of commercial nitrogen needed as fertilizer. In addition, native arbuscular mycorrhizal fungi performed equally to commercial mycorrhizal fungi as inoculants on strawberry plugs. In some cases, they may even outcompete and persist longer than commercial products.

The results, said NCSU agroecology scientist Michelle Schroeder-Moreno, can help both organic and commercial producers develop an integrated soil management approach to strawberry production.

“Growers in North Carolina use cover crops in a variety of organic vegetable crop production systems. We are transplanting that idea for strawberries. Using cover crops in strawberry production is not a common practice,” said Schroeder-Moreno. “We wanted to develop a sustainable system that is successful for organic strawberry producers, as well as commercial producers looking to phase out methyl bromide and other synthetic fumigates.”

Sam Bellamy, owner of Indigo Farm and project participant

Two separate studies were conducted that included a two-year field experiment and a one-year on-farm trial.

In the field experiment, NCSU researchers studied the effects of eight cover crop treatments combined with two arbuscular mycorrhizal inoculants on strawberries. The cover crop treatments included two grasses (Sudangrass and pearl millet), two legumes (soybean and velvet bean) and two grass/legume combinations (Sudangrass/velvet bean and pearl millet/soybean). A native mycorrhizal fungi species mix was compared to a commercially available mycorrhizal inoculant.

“After strawberries are harvested in June, the field is normally left fallow until September planting, so you have this short window to squeeze in a summer cover crop,” said Schroeder-Moreno. “We found that the legume/grass combination, specifically the soybean/pearl millet combo, performed the best when it came to reducing weed pressure, breaking pest cycles, and producing the most biomass. The additional nitrogen produced by the legume helped to replace some fertilizer inputs, saving money and reducing potential environmental impact.”

In the on-farm trials, researchers worked with three strawberry producers to identify the challenges of integrating summer cover crops in strawberry production.

“Overall the farmers were satisfied with the cover crops, although they wanted to see a yield increase in strawberries, which we found didn’t happen in both the field experiments and the on-farm trials,” said Schroeder-Moreno. “However, we are thinking that using cover crops is a long-term management plan that, over time, will produce higher yields, increase organic matter and help sustain important below-ground organisms, like mycorrhizal fungi.”

The researchers did identify some challenges with a cover crop system that they want growers to be aware of:

• There is not a one-size-fits-all cover crop system. The challenge is finding the right cover crop(s) to meet the specific needs of a field.
• If you use a cover crop system as part of an integrated soil management approach for organic production, know the market for fresh-picked organic strawberries.
• For organic producers, it’s important to find a good source of strawberry plugs that are disease-free. “Diversity is important across the board and it may be a good strategy not to buy all of your plants from one source,” said Schroeder-Moreno.
• Be mindful of cover crop management. “Sudangrass, for example, keeps weeds down like nobody’s business, but it produces so much biomass that many small producers may not have the equipment to properly control it and its thick stems can persist and poke through the plastic during strawberry production,” said Schroeder-Moreno.

NCSU agroecologist Michelle Schroeder-Moreno

“Our goal is to make these sustainable approaches a natural part of a set of integrated soil management practices,” said Schroeder-Moreno. “We really need to find sustainable solutions for fundamental soil management practices rather than just another synthetic chemical approach.”

To read more about the study (LS07-200), “Selecting Cover Crops for Diverse Functions: An integrated soil management approach for organic strawberry production in North Carolina,” visit the national SARE project database.

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Photo credits: Michelle Schroeder-Moreno

Published by the Southern Region of the Sustainable Agriculture Research and Education (SARE) program. Funded by the USDA National Institute of Food and Agriculture (NIFA), Southern SARE operates under cooperative agreements with the University of Georgia, Fort Valley State University, and the Kerr Center for Sustainable Agriculture to offer competitive grants to advance sustainable agriculture in America's Southern region.