Study shows cover crops are effective in reducing nitrate loss in drainage tile

To better protect water quality throughout Minnesota, the state’s corn growers are investing in research preventing nitrogen loss on the farm. Cover crops have recently emerged as an effective tool to help keep the vital nutrient for corn productions where it belongs—in the soil.

The Minnesota Corn Growers Association (MCGA) and Minnesota Corn Research & Promotion Council (MCR&PC) supported a study that examines the role cover crops play in reducing nitrogen loss to surface waters through tile drainage. Led by Jeff Vetsch, a researcher at the University of Minnesota’s Southern Research and Outreach Center, the study is finding cover crops are indeed effective management strategies to reduce nitrate losses in tile drainage water.

Over the last two years, Vetsch and his team tested the impact of no cover crops, cereal rye cover crops, and annual blend cover crops on a corn-soybean rotation using appropriate rates of N fertilizer. The cover crops were overseeded in standing crops at around R5 for corn and just before leaf drop for soybeans.

Using a nitrogen rate prescribed by the MRTN method (about 120 pounds), preliminary analysis found cereal rye, terminated in the spring, produced a 60-percent reduction in nitrate concentration and load in drainage water, compared to no cover crops. The annual blend variety produced only a marginal reduction in nitrate concentration.

Vetsch hypothesized cereal rye was proven more effective due to its hardiness in Minnesota’s climate. While cereal rye has the ability to overwinter, the annual blend dies off with the first frost. In the study, the rye was terminated in the spring, having survived off the nitrogen it was able to scavenge in the soil.

While two more years are left in the study, Vetsch said he is confident cover crops will prove to be an effective strategy in reducing nitrogen loss, but it is only part of the equation.

“Cover crops are one of the tools in the toolbox to help reduce nitrates leaving our fields,” he said. “They certainly have an application, but other tools include making sure the nitrogen rate is correct, making sure the timing and sources of fertilizer N are optimized and we are following best management practices.”

Vetsch emphasizes the other tools because some of the most important come at no cost—specifically the right rate and source. Both his research and studies performed by colleagues in neighboring states have shown great promise for cover crops. Still, Vetsch looks forward to more research on best management practices for cover crops that allows them to thrive in northern climates while making sense economically for the farmer.

“We have struggled getting good cover crop establishment, especially last growing season. Those are some of the challenges that growers in northern climates will have to deal with,” Vetsch said. “Those management situations and scenarios still need to be evaluated to determine how we can make the greatest impact on water quality and soil health.”

Cover crop analysis will continue at their Waseca research center, Vetsch said his team will be planting corn during the 2019 growing season, followed by soybeans in 2020.

Learn more about other research supported by MCGA and MCR&PC at mncorn.org/research.

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