Preliminary results from a from a two-year suggest high-residue cover cropping is “a promising tool,” according to a news release from the Rodale Institute’s California Organic Center. The study compared high-residue cover crops and termination methods on weed suppression, soil moisture retention and yield in organic vegetable production.
The center said the practice could help organic growers seeking to transition away from plastic mulch.
“I think this system has a future,” COC Research Director Arianna Bozzolo told The Packer.
Study overview and findings
The study compared two high-residue cover cropping mixes: oats and vetch, as well as oats and field peas. It also examined tillage or roller crimper termination methods.
Researchers compared these experimental efforts and a fallow control in 2023 and 2024. The cover crops were seeded in March, then terminated in June. Organic pumpkins were planted in late-June and early-July, then harvested in November. The test crop was under drip irrigation to simulate local growing conditions.
COC called the preliminary results promising. It reported the oat and field peas mix terminated via crimping had the most cover-crop biomass at 2,741 pounds per acre. Weed biomass was “significantly lower” in crimped cover crop plots compared to either the tilled plots or the control plot, the center noted.
On soil health metrics, the center said soil moisture was consistently higher in the crimped plots versus the others. This trend continued into the hotter parts of the summer as well. On yields, COC reported the oat and vetch cover crop — especially the crimped termination version — produced more pumpkins per acre.
“These findings suggest that even in the first year of transition, cover crop-based no-till systems — particularly those using oat/vetch mixtures — can support competitive yields while delivering additional soil health and weed suppression benefits,” COC concluded.
The study ran in Camarillo, Calif. Funding came from the California Department of Food and Agriculture’s Healthy Soils Program.
Study designed with growers in mind
Bozzolo said researchers try to keep the needs of organic growers in mind when designing studies. They chose oats as part of the cover cropping mix for their ability to produce a lot of biomass and selected legumes for the nitrogen fixation abilities, though there were other factors involved in the legume selection.
“I particularly like the peas because the peas can give an additional income to the growers,” she said, adding that many small farmers in the area have found success selling pea tendrils for salad and fresh markets.
“Especially here where we are so close to LA, it’s easy to reach out to local restaurants that are interested in these types of crops,” Bozzolo said. “It’s a little niche, something you don’t find in the store.”
Organic growers in California don’t often use cover cropping, she said. High-value specialty crops plus a year-round growing climate makes giving up two to three months for a cover crop unattractive, so Bozzolo said she tries to test cover crops that might hold an economic opportunity for growers.
Some commercial organic farms are trying cover cropping systems for the soil health benefits — but they approach it differently, Bozzolo said.
“Maybe they don’t allocate a whole three months for cover cropping, but they’re doing intercropping,” she said.
Bozzolo described it as looking like “a mohawk of cover crop” between rows of salad greens or broccoli, for example.
“People are trying to include [cover crops],” she said. “They are doing as much as they can to improve soil health, but it’s challenging here.”
Potential for all organic vegetables
While the study was targeted, and Bozzolo stressed the need for more research, she said the concept has the potential for wider application.
“The high-residue cover-cropping system is a system that can be applied to several different kinds of crops,” she said.
The COC research farm had another high-residue cover-cropping trial running on peppers, eggplants and zucchini, for example. However, Bozzolo said finding an efficient way to terminate the cover crops is a challenge.
“If we can find a way to terminate the cover cropping efficiently, that will a good step toward having this system that can be scaled up basically in every state where you can grow vegetables.”
