As northern growers gear up for colder weather, it’s a good time to consider whether cover crops can have any impact on winter temperatures and global warming. While cover crops have many benefits, such as controlling runoff and erosion, improving weed control, reducing fertilizer needs and increasing soil productivity, recent research suggests they can also increase “winter warming” of the atmosphere.

Heat Absorbers

Researchers at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., found the darker surface of a cover crop field absorbs more heat from the sun than a snow-covered field. The study, which also involved scientists from the University of New Hampshire and Cornell University, showed that tall, leafy cover crops could influence surface temperatures by as much as 37 F. This occurs when cover crops extend above the top of the snow pack, as snow reflects the sunlight back into space so heat from the sun that’s absorbed by plant stems and leaves actually warms the ground surface.

Danica Lombardozzi, plant ecologist with NCAR, says researchers tested cover crop characteristics that included 4- and 20-inch-tall plants with two different amounts of leafiness. 

Cover crops that were both tall and leafy resulted in the most significant warming during December, January and February. With cover crops that protruded above the snow, plants absorbed more of the sun’s energy than the reflective snow while shorter ones did not.

While tall cover crops with fewer leaves also increased winter temperatures, the increase was much less. Shorter cover crops, even when leafy, did not significantly change winter temperatures since they were often buried by the snow. 

Reducing Winter Warming

Lombardozzi says this study illustrates the fact that cover crops sticking above the snow pack can significantly increase winter temperatures. However, the impact of winter warming can be reduced by selecting and planting shorter cover crops and/or mowing or grazing taller cover crops.

Farmers can still gain all the benefits of planting cover crops, such as soil health, weed suppression and increased cash crop productivity. Some researchers say to seed cover crops, and no-till to improve soil health, sequester carbon and mitigate climate change.

Growers might say you can’t have it both ways, but this study indicates poorly managed cover crops could potentially contribute to climate change instead of helping solve the situation.