When it comes to cover crops, earlier seeding is better to achieve maximum soil health benefits, according to research by Practical Farmers of Iowa (PFI). The same could be said for yield benefits, with multi-year data from the Sustainable Agriculture Research and Education (SARE) program showing improved yields in fields where cover crops are planted year after year.

Cereal rye seeded into standing corn with a highboy sprayer attachment produced four to 10 times more biomass than rye drilled after harvest last fall in trials at three northern Iowa locations, reports PFI research director Stefan Gailans.

A rye, rapeseed and radish cover crop mix found similar results — with the highboy seedings significantly outperforming the drilled plots, he said. The only location where radish seeds established in the drilled mix was at Eagle Grove, which was the farthest south of the three.

While there is a lot of interest in the soil health benefits provided by cover crop mixes, cereal rye remains the best option for getting a cover crop established in Iowa, especially in the northern part of the state, regardless of seeding method.

"We know (cereal rye) works really well, whether you broadcast it or drill it," Gailans said. "The earlier you seed, the more growth you get."

Aerial seedings are another method for establishing cover crops before corn or soybean harvest. But the broadcast seedings are highly dependent on rainfall to work the seed into the soil and establish a good stand. They also generally require higher seeding rates, increasing the cost.

Steve Berger, a long-time cover crop user in Washington County, has found drilling cereal rye works best on his farm. In order to maximize growth, Berger follows the combine with a grain drill to plant cover crops within hours after corn or soybeans are harvested.

Yield benefits showing

Information about yield benefits of cover crops continues to show improving results, although it can vary depending on management systems.

More than 2,000 growers surveyed by SARE say they are seeing improved corn and soybean yield when they use cover crops. Corn yields rose an average 3.4 bushels per acre, or 1.9 percent, after cover crops, and soybean yields increased 1.5 bushels per acre, or 2.8 percent, according to the SARE report.

The survey showed yield increases rose to 8.3 bushels per acre of corn after cover crops had been used for more than four years on a field. In soybeans, the average yield gain increased from 0.1 bushel per acre after a single year in cover crops to 2.4 bushels after four years of cover crops.

"Cover crops really shine in challenging years, when the improvements they influence on soil moisture holding capacity and water infiltration can minimize cash crop yield losses to stress," notes Rob Myers, regional director of the Extension Programs for SARE at the University of Missouri. "In a favorable growing season, we expect to see less of a yield impact. However, the link between the length of time in cover crops and yield improvements points to the long-term benefits of building soil health."

Slowing erosion

Berger and other early adopters of cover crops say they are primarily motivated by the desire to slow soil erosion during the months when their farmland was otherwise bare between harvest and planting.

Mark Mueller, who farms near Waverly, simply hopes to avoid a yield penalty. Mueller said after a couple years of experience with cover crops, he’s confident that they don’t negatively impact soybean yield. He’s less certain about corn yields, but research has shown that negative impacts can be abated with proper management.

That’s consistent with the SARE report, which said most farmers reported no change in profit, or not enough data to evaluate profit impact. Some 33 percent of farmers reported profit benefits from using cover crops, while only 5.7 percent said it decreased.

"The vast majority of cover crop users report the most important benefits of cover crops to be improved overall soil health, reduced erosion and increased soil organic matter," says Chad Watts, executive director of the Conservation Technology Information Center.

"Though the yield benefits, profitability and resilience provided by cover crops are widely recognized by the farmers in the survey, the benefits they highlight most are long-term soil health impacts," Watts said.

Mueller says he has also noticed other benefits from his rye cover crop, including superior weed control.

"The rye chokes out all of the broadleafs," he said. "I won’t have a weed problem in the (cover crop) strips. The bare earth has had more weeds than the rye, by far."