Cover crop research from the United States suggests that planting a mixture of different cover crop species in between cash crops is better for the agro-ecosystem than planting a monoculture of one single species.

Researchers at Penn State’s College of Agricultural Sciences studied 18 different cover cropping patterns, using from one to eight cover crops preceding a maize crop. The researchers used cover crops including oats, canola (OSR), sunn hemp, soybean, barley, perennial ryegrass, forage radish, cereal rye, millet, sudangrass, red clover and hairy vetch either in monocultures or in combinations.

They looked at five different benefits provided by the cover crops, including weed suppression and nitrogen retention during the cover-crop season, cover-crop aboveground biomass, inorganic nitrogen supply during the subsequent cash-crop season and subsequent maize yield.

The Penn State researchers, who published their findings in the Journal of Applied Ecology, said theirs is the first study to look at the relationship between cover crop species and multifunctionality - the crops’ power to provide multiple benefits. They hope that with more research, farmers will be able not only to mi species for slight improvements, but tailor the different proportions of cover crop species to deliver specific benefits, like maximising weed suppression, delivering more nitrogen, enhancing soil quality or reducing nutrient run-off.

Professor Jason Kaye, a member of the research team, explained, "This kind of ecological study identifying a positive relationship between biodiversity and ecosystem services suggests that higher plant diversity will increase services from agroecosystems, and that has immediate implications for management practices and policies for sustainable agriculture. In a corn production system, simply increasing cover-crop species richness will have a small impact on agroecosystem services, but designing mixtures that maximize functional diversity may lead to agroecosystems with greater multifunctionality."

Detailing the finer points of the findings, Lead researcher and biology Professor Denise Finney said, "For example, nitrogen cycling is an area where trade-offs can occur among services. In our research, we have found that cover-crop mixtures that excel at nitrogen retention can decrease soil nitrogen supply to cash crops and limit their yield. However, bi-cultures - correctly formulated to combine legume and nonlegume species - can both supply inorganic nitrogen and retain nitrogen."

The researchers said follow-up studies are underway in Pennsylvania and New York to look further into multifunctionality, and that their ultimate aim is to help farmers design cover crop mixtures that combine species to focus on different ‘ecosystem services’ whilst increasing the biodiversity of the farm environment.