Conservation is a priority for John Traub, who farms in the Indian Creek Watershed in east central Illinois. He's not afraid to try new strategies, including planting cover crops. But so far, they have not provided the benefits he knows other farmers have seen from the practice.

"We struggled with tillage radishes and turnips as cover crops. It was difficult to get them established early enough. Even flying seed in did not work," says the Fairbury, Ill., corn and soybean farmer. "You need early growth. Our season is just too short."

Traub, who has been honing his conservation farming practices since the late 1970s, says less tillage in corn and soybeans has led to better soil tilth and health. He likes to tinker with ways to fine-tune crop production practices in order to manage soil and water quality. Today, nearly all of his soybean acreage is in no-till, and more than 75% of his corn is planted as strip till.

"Our tillage plans go hand in hand with our participation in the Conservation Stewardship Program (CSP)," he says. "That is also why we are evaluating cover crops."

Traub is now testing cereal rye to see if it works better in his rotation. Other area farmers have had success planting by Labor Day following winter wheat or seeding after silage chopping. He is also monitoring one farmer's operation in neighboring Milford, Ill., to learn if planting cover crop seed between rows of late-standing corn is successful using a "Rowbot," a self-driving, GPS-linked robot currently under development.

"You almost have to be in with the existing crop to make the timing work," he says. "Otherwise, farmers who can get an extra two- to three-week jump on us will have better luck. Farmers in southern Illinois, Missouri, Tennessee and Kentucky all have a longer growing seasons, and it seems you need good fall growth if you are going to have a cover crop that will winter kill."

Timing and agronomic impact

Andy Heggenstaller, DuPont Pioneer agronomy research manager, says timing is the most important factor in keeping cover crops from interfering with the next corn or soybean crop. And while more southern climates may offer better timing, cover crop strategies can work anywhere, says Ryan Stockwell, a corn, soybean and wheat farmer who uses no-till and cover crops in his operation near Medford, Wis. Stockwell is also is a senior agriculture program manager with the National Wildlife Federation (NWF).

"I know farmers from all over the country who are using cover crops successfully. You just have to be aware of limitations and figure out how and what will work best in your rotation," he says.

First, Stockwell says farmers must define their needs. Why plant cover crops? Is it to get ahead of weeds, build soil tilth, control soybean cyst nematode or something else?

"These all require different crops and timing," he says. "For example, tillage radishes will address compaction and weed issues. Cereal rye or ryegrass before soybeans may increase your soybean yield and soil health. They are easy to use and can solve common problems."

Cover crops can have positive or negative effects on crop yields, though, depending on environment, cover crop species and management. In a 2012 survey, the Conservation Technology Information Center (CTIC) found corn following cover crops had a 9.6% yield increase and soybean yields improved 11.6%. Legumes and grass-legume mixtures were better suited than grasses prior to corn. Grasses were better than broadleaves before soybeans.

When it comes to weed control, Eileen Kladivko, Purdue University agronomist, says farmers should consider the potential effects of residual herbicides on cover crop establishment.

"While cover crops can pull up nutrients that might otherwise be lost, dry weather can cause herbicide carryover," adds Wayne Crook, University of Missouri Extension regional agronomist. "That could prevent cover crop germination and lead farmers to run afoul of label restrictions, should the cover crop be harvested for forage or grazed."

In addition, some cover crops can suppress weeds, but others can become weeds in subsequent crops if not carefully managed, Kladivko says.

While cover crops won't solve every challenge in every type of practice, Stockwell says they can help farmers who are willing to manage reasonable expectations.

"Transitioning from a heavily tilled, corn-on-corn system to planting a cover crop will not yield immediate agronomic benefits," he says. "Understand and identify the specific issues you want to address, select cover crops you want to use, learn how they work and determine where they fit into your rotation. Talk to neighbors who are using them and find out what they are doing."

Cover crop or not?

Missouri's Crook advises considering the pros and cons when deciding whether to use cover crops: