Graduate student David Robb (left) and Geoff Zehnder, director of the Sustainable Agriculture program, stand in a field of cover crops at Clemson's Student Organic Farm.

Graduate student David Robb (left) and Geoff Zehnder, director of the Sustainable Agriculture Program, stand in a field at Clemson’s Student Organic Farm.
Image Credit: Jim Melvin / Clemson University

CLEMSON — Clemson University’s Sustainable Agriculture Program has received a $175,000 collaborative grant to study and refine no-till cover-crop management for weed control in vegetable production.

The three-year grant (No. 2015-7006-24163) was awarded by the National Institute of Food and Agriculture’s crop protection and pest management program. NIFA is a division of the U.S. Department of Agriculture.

Field trials will be held in three separate locations: the Clemson Student Organic Farm; Clemson’s Coastal Research and Education Center in Charleston; and City Roots Farm, a Columbia-based farm operated by Robbie and Eric McClam.

“The growing conditions are different at each area, so we can’t do this at just one location and say that this will apply statewide,” said project leader Geoff Zehnder, the coordinator for Clemson’s Sustainable Agriculture Program, which is part of Cooperative Extension. “The three areas we have chosen are more representative of South Carolina as a whole. This will help legitimize our eventual recommendations to farmers throughout the state.”

No-till vegetable production offers a more sustainable approach to weed management than the frequent use of herbicides and tillage. This is especially true for organic farmers, who are not permitted to use synthetic herbicides and therefore must rely on frequent cultivation and tillage for weed control. Though this method does help control weeds, it often has negative impacts on soil health. Preventing weeds from competing with crops without degrading soil quality remains a major challenge in organic crop production.

Many studies have demonstrated that cover crops will suppress weed seed germination by shielding daylight from the soil surface, reducing soil temperature fluctuations and physically hindering seedling emergence.

But most growers have been reluctant to transition from conventional tillage techniques without first seeing the no-till system in action and forming a better understanding of its costs and benefits. Zehnder and his collaborators will address these concerns through on-farm research and farmer training in the use of cover crops and no-till vegetable systems. They also will establish field trials to demonstrate and refine cover crop mixtures for weed management in spring/summer and late-season vegetables. Finally, they will document the benefits of cover crops on soil fertility and health.

Many studies have demonstrated that cover crops will suppress weed seed germination by shielding daylight from the soil surface, reducing soil temperature fluctuations and physically hindering seedling emergence.

Many studies have demonstrated that cover crops will suppress weed seed germination by shielding daylight from the soil surface, reducing soil temperature fluctuations and physically hindering seedling emergence.
Image Credit: Jim Melvin / Clemson University

“The idea is to use the cover-crop mulch as a way to prevent weed growth early in the season,” said David Robb, a graduate student at Clemson who will be conducting research at the on-campus organic farm. “While in their growth stage, cover crops will outcompete weeds. Once they are terminated, the mulch left behind will continue to prevent weed growth. And as the residue breaks down, it will enrich the soil with carbon, nitrogen and other nutrients.”

Robb will use a bulky tool called a roller-crimper to flatten and crimp the stalks of cover crops, which kills the plants while simultaneously creating a thick, weed-suppressing mat. “I’ll plant the vegetable crop right into that residue, so it’s almost like having a plastic mulch used by a lot of vegetable growers, only in this case it’s made of organic rather than synthetic material.”

Many factors contribute to the success or failure of cover-crop-based, no-till vegetable production. Issues addressed by the project will include:

  • Degree and duration of weed suppression by cover crop residue
  • Timing of cover-crop planting, termination and vegetable planting operations
  • Effectiveness of using a roller-crimper in killing the cover crop
  • Adaptation of cover crops to local climate, soil type, soil texture and soil quality
  • Adaptation of vegetable species and varieties to the no-till system
  • Benefits of cover-crop residue for soil health

“The reason vegetable growers don’t do this more often is there are management challenges, including when is the best time to plant cover crops in order to get the most efficient amounts of biomass,” Zehnder said. “If you don’t plant at the correct times, you might not have enough biomass and, therefore, when you roll it down it won’t effectively suppress the weeds. The timing is critical. So we’ll be looking at the timing of planting cover crops and also terminating them— for both fall-planted and summer-planted cover crops.”

During the three-year project, soil nutrition and health measurements will be conducted from samples taken at all three sites. Nishanth Tharayil, an associate professor and plant ecophysiologist at Clemson, will document soil health benefits in hopes of creating yet another incentive for growers to adopt the no-till process.

“Soil micro- and macro-organisms are integral to sustaining the overall health and long-term productivity of soils,” Tharayil said. “There is now a heightened interest in monitoring different biological processes, including the microbial communities and enzymes that facilitate the recycling of nutrients. Cover crops significantly contribute to the overall health of soils by enhancing these processes.”

“We are really expecting great things to come from this research,” said Brian Ward, organic research specialist at Clemson’s Coastal REC Organic Research Farm.

“We are really expecting great things to come from this research,” according to Brian Ward, organic research specialist at Clemson’s Coastal REC Organic Research Farm.
Image Credit: Scott Miller / Clemson University

Over the coming months, all three locations will conduct workshops based on the project findings. Farmers from the Upstate, Midlands and Lowcountry will be offered specialized training and recommendations based on their particular climates, rainfall and soil conditions.

“We are really expecting great things to come from this research,” said Brian Ward, organic research specialist at Clemson’s Coastal REC Organic Research Farm. “We expect a better understanding in the variability of soil ecology and its effects on cover-crop and no-till vegetable production. This will ultimately translate to more conventional, sustainable and organic growers adopting the cultural practices proven through this research, which in turn will give growers from across the state another tool for sustainability and profitability.”

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Clemson University Research and Education Centers
Clemson University’s five Research and Education Centers and six campus-area farms provide science-based solutions that directly support South Carolina’s $42 billion agribusiness industry through research in crop production, disease and pest control, sensor-based irrigation, forest management and cost-effective food production. PSA funds provide the facilities and basic operating structure necessary to enable teams of talented scientists and staff to successfully compete for external funds and to address the state’s most urgent agricultural and natural resources challenges.