How cover crops affect corn, beans
In fall 2008, six farmers began a study to test the effect of a cereal rye cover crop on grain yields of corn and soybeans. Five additional farmers joined in fall 2009, and 10 sites were maintained from 2009 to 2012. Eight sites now remain in this long-term project, done as part of a partnership between Iowa Learning Farms and Practical Farmers of Iowa. Its main objective is to find how a cover crop affects corn and soybean yields.
The study uses “paired strips,” with alternating strips in a field either receiving a cover crop in the fall or not receiving a cover crop. Each farm is in a corn-soybean rotation. The same strips of corn or soybeans have received the cover crop or no cover crop each year since the onset of the study. At least two replications of the treatments were implemented at each of the farms.
Depending on the farm, the cereal rye cover was either aerially seeded into standing crops in late summer or drilled after corn or soybean harvest in the fall. The following spring, the cereal rye cover crop was terminated either by tillage or herbicide before planting corn or soybeans.
Since 2009, the first growing season that yield data was collected, the study has amassed bean yields from 18 “site-years” and corn yields from 28 site-years. The major benefit of conducting a long-term study at multiple farms is generating large amounts of data from which to make inferences and “tell the story” about cover crops and grain yields.
Effect on corn, bean yields
The story of how a cereal rye cover crop affects corn yields can be divided into two parts: beginning years and later years.
Farmers from three of the 10 site-years from the beginning years (2009-10) reported corn yield reductions due to the cover crop. The primary culprits, according to farmers, appeared to be insufficient termination of the cover crop before planting corn and incorrect planter settings when planting the corn into the cover crop residue.
In the later years (2011-14), farmers from 18 site-years reported no difference in corn yields from the strips with the cover crop compared to those without. In 2014, five of the six farms reporting saw yields above 200 bushels per acre (with or without the cover crop).
In the soybean phase of the farm rotations, the farmers observed no difference in yield between the strips that had a cover crop and those that did not in 13 of the 18 site-years (2009–13).
In four of those site-years, the farms reported an increase in bean yield by about 6.2 bushels per acre due to the cover. In only one instance did the cover result in a soybean yield reduction. It’s becoming clear that when properly managed, cover crops will not harm corn or soybean yields.
As with most things, it takes time, patience and experience to hone one’s skills when adopting a new practice. After a few years of using cover crops as part of this study, the farmers say they are figuring out how to properly manage them in their systems.
“Like any new change, there is a learning curve, and some management changes need to be made to make adding cover crops a paying proposition,” says Rob Stout, who farms near West Chester in Washington County and is participating in this study.
Rick Juchems, near Plainfield in Bremer County, concurs, saying participating in the study for a few years “actually showed how easy it is to grow cover crops and make them work.”
George Schaefer, farming with his brother Steve near Kalona in Washington County, is another participant. He points out there’s been a big increase in knowledge about cover crops since this project began. The two brothers have learned soybean yields following a rye cover crop are better than when not following a rye cover. Corn yields are about equal following a rye cover compared to no cover crop.
“I like the idea of on-farm research that local farmers can buy into,” says Jerry Sindt, on why he chose to participate in this study. Sindt, who farms near Holstein in Ida County, says, “I’ve learned that having cover crops planted in a field ahead of corn requires increased spring management, and that rye ahead of soybeans seems to be the most beneficial simply because the cover crop has a longer growing season.”
It’s about soil and water
Ultimately, it’s about soil and water conservation. Because cover crops do not affect corn and soybean yields, farmers should embrace this soil conservation technique with less hesitation. Farmers in this study all agree: It’s all about getting more farmers to add cover crops to their conservation programs.
“Looking at just one practice to minimize our soil loss problems will have a small impact, whereas a suite of practices that could include no-till, cover crops, prairie strips, waterways, buffer strip, terraces and others could have a huge positive impact on our environment,” says Juchems. “I would hope the information we are gathering in this long-term study will influence others to grow cover crops to help replenish the loss we’ve seen in the last few years of intense row crop farming.“
Stout agrees that just employing one conservation method isn’t enough. “Even with long-term no-till, I was experiencing some soil erosion from heavy spring rains. I knew I needed to do more to hold soil in place.”
Cover crops are often championed for their ability to prevent erosion and the loss of nutrients from the soil. But another common question about incorporating cover crops into a cropping system pertains to potential soil quality and soil health benefits.
This summer, PFI and Iowa Learning Farms are collecting soil samples for the Haney soil test, as well as conducting earthworm counts on the remaining seven sites. Taken together, this will provide an indication as to whether multiple years of using a cover crop in a corn-soybean rotation has an effect on soil health.
“Hopefully, we can learn a little about improving soil health at the same time we’re learning about the effects on yields,” says Stout. “I’m hoping to see some soil health benefits and increasing soil organic matter, so in the long-term I can potentially reduce my added nitrogen fertilization because of the extra nitrogen released from the soil organic material.”
Juchems shares Stout’s sentiment when thinking about this long-term effort, and adds, “We’ve only scratched the surface of what can happen if the right practices are used to promote soil health and protect our soils and water supplies. With the results of this project, I hope we can improve the way people look at cover crops as an investment in their farming operation.”
Gailans is a researcher and cooperators’ program manager with Practical Farmers of Iowa.
Cover crop resulted in:
yield improvement no change yield decline
This article published in the July, 2015 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2015.