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Farmers have several seeding, timing options with cover crops
 
By DOUG SCHMITZ
Iowa Correspondent

AMES, Iowa – With both cover crop planting and harvest seasons fast approaching, farmers may be wondering what the latest is on cover crop seeding methods and timing.
“We know that drill seeding after crop harvest gives the most uniformity, but that can limit establishment and biomass accumulation because of later seeding time,” said Mark Licht, Iowa State University associate professor of agronomy and extension cropping systems specialist.
“However, broadcast seeding (a method of seeding that involves scattering seed, by hand or mechanically, over a relatively large area) into nearing mature crops (late August or early September) improves establishment and biomass accumulation when rainfall/soil moisture are not an issue,” he added. “The downside of broadcasting seeding is that it is not as uniform – especially if by airplane – as compared to drill seeding.”
Virgil Schmitt, Iowa State University extension field agronomist, said, “People are trying new things, such as seeding attachments on combines, mixing seed in manure and then spreading manure and seed, interseeding cover crops early in the season, perennial cover crops, etc.
“However, the big ones are still seeding aerially or with a highboy (a rig that can go through fully-grown corn to apply cover crops into tall corn) just as crops start to senesce (a developmental process which in annual crop plants overlaps with the reproductive phase), or with a drill immediately after harvest,” he said.
Meaghan Anderson, Iowa State University extension field agronomist, said, “The brilliant thing about cover crops is there has been so much development in new seeding methods and information about timing to meet a farmer’s needs.
“As far as timing goes, earlier seeding allows for more fall growth,” she said. “This is ideal for species that are going to winter-kill, or in the case of cattle producers wanting fall grazing. It also helps with fall weed suppression of winter annuals.”
Regarding yield reduction concerns, Licht said soybeans typically don’t have a negative yield following cover crops.
“When they do, it’s typically because of dry soil conditions or letting the cover crop hang on too long before termination after the soybean has been planted,” he said. “Corn is another thing. The best practice is to terminate winter cereal grains 10-14 days before planting corn, or limiting spring biomass to less than 1,000 pounds. This is typically enough to minimize yield penalties.”
Schmitt agreed, saying for farmers concerned about yield reduction, soybeans are quite forgiving.
“If the planter will go through it, you can plant soybeans into standing cover crops and then spray to kill the cover crop immediately after planting and not reduce yield,” he said. “Corn is more sensitive. The best practice is to spray to kill the cover crop 10 – 14 days before planting.”
He said another strategy for corn is to plant a cover crop that winterkills, making the need to spray and then wait to plant a non-issue. 
“We recommend this for people who are just starting with cover crops planted before a corn crop, but it also works well for people who have been into cover crops for some time and do not want to worry about potential corn planting delays caused by having cover crops there,” he said.
“This strategy does not provide all of the environmental and soil benefits of having cover crops that survive the winter, but it is much better than doing nothing and eliminates the delayed corn planting concern,” he added.
When dealing with yield reduction concerns, Rebecca Vittetoe, Iowa State University extension field agronomist, said, “It’s important to think about how cover crops fit into your system and what adjustments may need to be made to fit cover crops in, so this would include things like fertilizer applications, termination, planting, harvest, etc. They aren’t just an add-on.”
For rye ahead of corn, she said farmers should consider putting nitrogen on at planting, or close to planting.
“You don’t need to add more nitrogen necessarily than what you’re planning on, but it seems to help having nitrogen applied with planting or close to planting,” she said.
“Taking the time to make proper planter adjustments is key, especially on the corn side, and making sure getting seed placed at the right depth and the furrow is closing,” she said. “Soybeans tend to be more forgiving and tend to see less of a yield impact on the soybean side than on the corn side.”
According to a 10-year, on-farm study by Iowa Learning Farms and Practical Farmers of Iowa, 90 percent of the time, properly-managed cover crops had little to no negative yield effect on corn or soybeans, said Rebecca Clay, Practical Farmers of Iowa field crops viability coordinator.
“In fact, 32 percent of soybean site-years and 8 percent of corn site-years experienced a yield increase with cover crops,” she said. “The site-years that experienced lower yield were typically on farms where farmers were new to cover crops.”
She said the biggest piece of advice she has for farmers is to “talk to an experienced cover cropper in your area who has already been through the learning curve.”
“In the few cases when farmers saw yield declines while cover cropping ahead of soybeans, they were able to mitigate the decline the following year by making planter adjustments to increase down pressure and handle more residue,” she said.
“To put it simply, we need to get out of the tractor and check soybean seed placement.”


9/13/2022