UNH crops

Researchers conduct experiments at the Kellogg Biological Station at Michigan State University.

DURHAM — Rotating crops over time increases the yield of corn, even during unfavorable weather conditions such as droughts, according to new research from the NH Agricultural Experiment Station at the University of New Hampshire.

The findings in collaboration with and the University of California, Berkeley, demonstrate that diversifying crops may be an effective, long-term strategy for strengthening food production globally.

Stuart Grandy, associate professor of natural resources at the University of New Hampshire and director of the UNH Soil Biogeochemistry and Fertility Lab, said in a UNH news release that the research required “massive collaboration and data-sharing among university and government scientists.”

“The trend toward fewer crops in our agro-ecosystems is alarming, with massive amounts of U.S. land dedicated to producing corn year after year, or rotating corn one year with soybean the next,” Grandy, an experiment station researcher, said. “We show that increasing yield resilience is a robust outcome over many years and across geographically distinct sites of diversifying rotations by growing a greater variety of crops over time.”

Grandy said the research findings should extend to agricultural sites in New England and other regions, “whether in large or small fields, wherever there is concern about sustaining crop yields under variable climates.”

The research is presented in the recent issue of the journal “One Earth.” The research was led by Timothy Bowles, assistant professor of agroecology at the University of California, Berkeley, who started while he was a postdoctoral researcher in Grandy’s lab. He now directs the Berkeley Agroecology Lab.

According to the news release, over the last two decades, farmers in the central United States have moved toward monocultures — growing just one crop at a time, sometimes for years in a row. This is especially true for corn. While this may increase profits in the short term when markets are favorable for corn, such as during the biofuel boom, the long-term impact can be profound, researchers said.

“Here, we show that loss of crop rotational diversity can undermine resilience to stressful conditions, possibly contributing to the observed increases in weather sensitivity of central U.S. corn production,” Bowles said in the news release.

Researchers analyzed long-term crop yield data at 11 locations across the United States and Canada to assess how crop diversification affects corn yields in intensively managed grain systems.

Crop rotations that are more diverse increased corn yields over time and across all growing conditions an average of 28 percent, including 23 percent in favorable weather conditions. Notably, crop rotations that are more diverse also showed strong, positive effects of 14 percent to 90 percent on yield from a wide range of sites, even under unfavorable weather conditions.

Drought and excess moisture were the most common sources of climate stress.

Specifically, the researchers found that crop rotations including crops like alfalfa, spring barley, corn, oats, red clover, rye, sorghum, timothy, hairy vetch, and winter wheat resulted in substantially higher corn yields over time than planting only corn or corn and one other crop.

Scientists theorize improved soil health, reduced plant diseases, pests, and weeds may explain the “rotation effect” on corn yield. More diverse crop rotations also have been found to improve nitrogen retention in soil and boost the supply of nitrogen available to plants during critical periods.

“Increasing crop rotation diversity could help mitigate the impacts of more frequent and intense droughts and heat waves that will likely affect corn production, farmers’ livelihoods, and the food system,” Grandy said. “Systematic approaches to environmental sustainability and yield resilience like diversifying crops are a central component to reduce risk and should inform agricultural policies.”

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