As summer turns to fall and the temperatures cool, many farmers in our region will begin to prepare their fields for the end of the season by planting cover crops that play an important role in replenishing the soil.
“Cover crops have been used for many years to rebuild soil, manage pests, and reduce pollution, and their use is growing among farmers nationally,” says Denise Finney, an assistant professor of biology at Ursinus College.
Typically, cover crops are planted in monocultures (one species in a field) or bicultures (two species in field), but there are a few pockets in the country — and Pennsylvania is one of them — where farmers have started using multi-species mixes of cover crops in their fields. It’s a practice that has grabbed Finney’s attention. In research she is leading that was recently published in the Journal of Applied Ecology, the Ursinus scholar is analyzing cover crop diversity and its impact on crop production.
“A lot of my motivation in doing this is that it is my job as a researcher to make sure the farmers are getting the benefits they think they are getting from cover crops and to help them plan and plant the best mixture,” Finney says. “Any seed you plant is time and money. As researchers, we need to do the background work that helps farmers apply this idea in a cost effective way.”
Finney, who joined the Ursinus faculty this fall, started the research as a doctoral student at Penn State University. It’s the first time cover crop diversity has been analyzed in this way, and she plans to continue the research at Ursinus with the help of student researchers though greenhouse studies and field work.
“The goal of my research is to help address the grand challenge in agriculture: how do we produce enough food for a growing global population, while at the same time reducing environmental pollution,” she says.
Cover crops aren’t typically harvested, but they are used to provide specific benefits or ecosystem services. “Cereal rye, for example, is something a farmer would plant if he or she thinks there is a lot of nitrogen sitting in their field,” Finney says, citing one example of a beneficial cover crop.
Nitrogen is critical to plant growth. Farmers are focused on providing enough nitrogen to their crops, but a lot of times farmers must make their best guess as to how much their crops will use.
“So, they can end the growing season with a lot of nitrogen sitting in their fields,” Finney says. “Certain types of nitrogen are very mobile, so if we have a rainy fall, it can leach into our waterways.”
Cereal rye — a “nitrogen scavenger” — helps prevent that. On the flip side, some cover crops help provide nitrogen. Legumes like clovers and hairy vetch can use nitrogen from the atmosphere and leave it in the field for the next crop.
“As we look at all of the different cover crops, they are known for having certain strengths, and that can mean they don’t do other things very well,” Finney says. “That’s the idea behind planting these multi-species cover crop mixtures. If we’re using more than one species, we have an opportunity to select species that do different things well and really get more bang from our buck.”
“It’s an idea that’s rooted in ecology, and this is a strategy farmers can use to bring ecology into our agricultural system. In grasslands and forests, we’ve seen that as the diversity of plants increases, those systems produce more plant biomass. The rationale behind cover crop mixtures is that if we can increase the diversity of plants in our cropping system, we have the opportunity to increase the benefits we gain from our cover crops,” she says. –by Ed Moorhouse