"Farm-Tuning" Yields Best Results

Penn State researchers were surprised to learn in a recent study that they could take the exact same number of seeds from the same plants, put them in agricultural fields across the Mid-Atlantic region, and get profoundly different stands of cover crops a few months later.

"The study came to be known as 'farm-tuning' cover crop mixtures," noted researcher Jason Kaye, professor of soil biogeochemistry, who added that the findings are significant because they show the need to customize cover crop mixes to achieve desired ecosystem services, depending on soil and climatic conditions.

Cover crop mixtures composed of multiple species planted in rotation between cash crops provide a suite of benefits such as erosion reduction, weed control, and adding carbon and nitrogen to the soil. But it turns out, the expression of species in a mixture can differ greatly across locations.

The researchers tracked a five-species cover crop mix planted over two growing seasons on eight organic dairy farms in Pennsylvania and New York and on research plots at Penn State's Russell E. Larson Agricultural Research Center. In the University's experimental plots, the team manipulated cover crop expression with nitrogen inputs and planting dates to learn the responses of the various species to soil conditions and growing days.

"There have been very few studies like this--especially looking at cover crop mixtures that comprise more than two species--that analyze how species interact with each other, so I think it's important research," Kaye said. "There has been a misguided assumption that you plant a cover crop mixture and you get the same result wherever you put it."

Commercial seed companies sell many preformulated seed mixtures, but they can also make customized mixes, Kaye said. "Our results show that with fixed preformulated mixtures, what you grow is not always what you expect."

In the study, all eight of the participating farmers seeded the standard mixture and a "farm-tuned" mixture of the same five species--canola, Austrian winter pea, triticale, red clover, and crimson clover--with seeding rates adjusted to achieve farmer-desired services. At each location, the researchers parsed out the effects of soil inorganic nitrogen and growing days on cover crop mixture expression.

When soil inorganic nitrogen and growing days were high, they found that canola dominated the mixture, especially in the fall.

From the same seed mixture, cover crop mixture expression varied greatly across farms, and researchers hypothesized that this variation was correlated with soil inorganic nitrogen concentrations and growing days, explained lead researcher Barbara Baraibar, who was a postdoctoral scholar in the Department of Plant Science when the study was conducted.

Kaye's laboratory has been conducting a continuous experiment evaluating the effectiveness of various cover crop mixtures since 2011.

In findings published in PLOS ONE, the researchers reported that low soil inorganic nitrogen favored legume species while a shorter growing season favored triticale. Changes in seeding rates influenced mixture composition in the fall and spring but interacted with growing days to determine the final expression of the mixture.

--Jeff Mulhollem