Cover crops don’t compete with corn

IOWA STATE (US) — Using a perennial cover crop on corn fields benefits soil and water quality,  and may even increase farm profits, according to a new study that finds farms that do so can yield 200 bushels of corn per acre.

For the three-year study, researchers looked at 36 potential ground cover species, different corn hybrids, and various tillage practices to best keep soil, nutrients, and carbon in the fields, and found that strip till planting using Kentucky bluegrass as the cover crop offers the best environmental benefits while maintaining yield.

“We evaluated all these ground covers and decided to work with Kentucky bluegrass, because it’s as good as anything else,” says Ken Moore, professor of agronomy at Iowa State University.

“Kentucky bluegrass is out in every lawn in Iowa. Every farmer grows it already. Every farmer knows how to kill it. We think farmers will be more likely to accept it as a ground cover.”

Using ground cover to sustain and improve soil has become a focus of research because the need for biomass is increasing for use in producing biofuels.

Corn residue, or stover, usually remains on the ground after corn is harvested and helps reduce soil erosion and replenishes nutrients and organic matter, so the prospect of removing it to make biofuels causes worry that soil erosion will increase, while the remaining soil will suffer nutrient loss, Moore says.

Researchers wanted to identify ground covers that are compatible with corn, find corn that is competitive with the ground cover, and develop management systems that minimize competition between the two.

“Yes, we can do it,” Moore says of using perennial cover crops. “We don’t know all the potential pitfalls of doing it. Under the circumstances that we tested, it does work.”

Jeremy Singer, collaborator and assistant professor at the National Laboratory for Agriculture and the Environment, says the system has potential.

“The bottom line is that with our best treatment, all three years we found yields in the control and yields in the Kentucky bluegrass with herbicide suppression and fall strip till were not different, which is very exciting,” he says.

One focus of the research was to measure if cover crops help replace carbon in the soil that would be lost as stover is removed.

Singer estimates that the Kentucky bluegrass treatment likely replaces as much carbon in the soil as stover would have, although says it’s difficult to measure precisely. Cover crops provide weed and insect suppression and also at least 85 percent ground cover, meaning only 15 percent of the soil is exposed and susceptible to erosion.

To reduce competition between corn and Kentucky bluegrass, bluegrass needs to be chemically treated in the spring to force it into dormancy while the corn gets started.

Generally the two species co-exist well. “Growing two (or more) plants in one field is not a new idea. Ecosystems have been doing it for millennia,” Moore says.

Land in the Midwest used to naturally support different species of plant—each performing different functions for the soil and water quality. There are now just a few plant species dominating the landscape, each performing just one function, says Moore.

“We are trying to put those functions into a simple, easy-to-manage system that can have positive environmental impacts.”

The research was supported by the Sun Grant Initiative is a national network of land-grant universities and federally funded laboratories.

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