Planting a cover crop in late summer into a standing crop of soybeans, or planting a cover crop in a field in the fall immediately after harvesting soybeans or corn, is an idea more farmers have started putting into practice the past few years in the Midwest. "Seeding cover crops to protect your land from erosion over winter is not a new practice, but we've not done this a lot in Iowa," observes Tracy Blackmer, director of research for the On-Farm Network, a program offered by the Iowa Soybean Association.
Recently though, there's been more interest in using cover crops here in Iowa. There are several potential benefits from establishing cover crops, if they're managed in the right way and are planted in the right place. No one will argue that the establishment of a cover crop will help control soil erosion. But there are many other issues – both good and bad that may have effects in some places and not others.
"In general, most Iowa farmers have not made use of cover crops, so most of our farmers have a very limited understanding of how to capture the benefits and avoid the negatives," Blackmer observes.
After the drought of this past summer and a less-than-stellar corn yield, many farmers in Iowa have asked whether they should plant a cover crop this fall to "soak up" some of the nitrogen left in the soil. The idea is to capture that leftover N this fall, as the cover crops will take it up, instead of letting it escape. Then when the cover crop is killed next spring, the nitrogen will be available for the corn planted in that field in 2013.
However, at the same time, farmers are also wondering if the cover crop will suck up too much moisture from the soil and aggravate the already excessively dry subsoil moisture conditions. "These two questions are good questions, and they are just a few of the questions we're hearing from farmers," says Blackmer.
In order to collect Iowa data that will better address growers' questions, the On-Farm Network is coordinating a number of cover crop trials on the fields of cooperating farmers this fall.
More on-farm trials will be conducted this fall to find better answers to these questions
"We have conducted cover crop studies in the past and they have shown that a cover crop can produce a significant amount of cover to protect soil and a lot of nitrogen can be taken up with less chance of the N being lost to leaching," says Mick Lane, communications director for the On-Farm Network. Lane and Blackmer encourage you to go online to 2008 Replicated Strip Trial Summary pages 12-13 and read the article and look at the results of those previous trials in the tables accompanying that article.
"One thing to keep in mind is that since the nitrogen taken up by the cover crop is then tied up in the organic matter, just when it will again become available for the corn crop or soybean crop to use is unclear," notes Lane. "What we do know is nitrogen release from organic matter (such as crop residue and manure) is dependent on a number of factors including soil moisture, soil temperatures and activity of soil microbes. Even in states like Indiana where there's much broader use of winter cover crops and they've been using cover crops for a number of years, there are no nitrogen credits for cover crops listed in their fertilizer recommendations at this time."
What most growers seem to be concerned about is how cover crops might impact yield of the corn or soybean crop that's planted in the spring after the cover crop is killed. "To answer this question for Iowa soils and Iowa conditions, we need a lot more data for many different scenarios in Iowa," says Lane.
So, if you're seeding cover crops this fall (or just considering the idea) and would like to be part of a project to collect the data needed for a more complete assessment, "please contact us," says Lane. "We have seed available for a few trials, or if you have your own seed, we can help you design a replicated strip trial that will generate the type of data needed to advance our knowledge of cover crops for Iowa."
Whether you have cover crops or are just interested, if you have questions about them, email them to Mick Lane, the On-Farm Network communications manager and he will attempt to collect the information to answer your questions.