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What’s Up With Cover Crops

Cover crops have been around for a long time. Until recent
years, they prompted little interest. That’s changed.

“There is a lot of momentum for cover crops in the Midwest,”
says Jeremy Singer, research agronomist for the National Laboratory
for Agriculture and the Environment (NLAE) in Ames, Iowa.

Perks are plenty. Cover crops curb soil erosion
while adding soil organic matter. Cover crops also can protect nutrients
and capture 20 to 40 pounds per acre of nitrogen (N), 2 to 5 pounds per acre of
phosphorus (P), and 30 pounds per acre of potassium (K). Wildlife
also thrives.

Singer spoke earlier this month at the Iowa
State University Southeast Iowa Research Farm near Crawfordsville. 

 Cover crops work well in areas like wheat growing regions of
Michigan. There, radishes can follow wheat during a fallow period in late July
or August.

Cover crop choices are more limited in states
like Iowa, where corn and soybeans are in fields the bulk of the growing

“We are looking at winter wheat or rye,” says
Singer. “They germinate in cool weather in the fall, and are winter hardy,”
says Singer. They are relatively inexpensive.” Seeding costs for overwintering
cover crops tally around $30 per acre.

It’s cheaper to establish a non-wintering cover
crop like oats. Costs tally around $20 per acre. These costs can be deferred by
cost sharing through the federal program EQIP. Seeing cut-off dates exist,
though. For non-wintering crops, the cutoff date in Iowa is September 15. For
winter-hardy cover crops like rye or winter wheat, the seeding cutoff date in
Iowa is October 15.


Planting a winter cereal in September and October
is challenging in row corps. Aerial seeding that deposits these grains in
between corn or soybean rows is one solution. Seeding choice will impact
seeding rates. Small grain seeding rates normally tally 1 bushel per acre by
ground, 1.5 bushels per acre by air. Oat seeding rates are higher. Its ground
seeding rate is 2 bushels on the ground, 3 bushels per acre by air.

Aerial seeding costs around $12 to $18 per acre. Corn
plants can capture some seed, preventing them from reaching the soil and

“Losses will vary, depending on the hybrid and timing, says
Singer. “Overall, though, it is not a major concern.”

Reduced yields of next year’s crop are a concern. There’s
good news for soybeans. In Iowa, all data shows cover crops won’t reduce
soybean yields.

Not so with corn. “There is potential to lose up to 3% of
grain yield if corn follows an overwintering cover crop,” says Singer.

There’s another hitch to planting cover crops prior to corn.
After killing cover crops with a non-selective herbicide prior to a 6-inch
height, it’s recommended to wait 10 to 14 days prior to planting corn.

The data that supports the 10- to 14-day waiting period are
limited. “We just feels like it allows the herbicide to translocate and start
to kill the plant,” he says. “It also allows a flush of chemicals from the
cover crop to be removed from the root zone.

Still, waiting 10 to 14 days before planting is not easy to
do, adds Singer. 

There are ways to deal with this delay, though. Singer notes
some enterprising farmers have entered fields in April and sprayed a
non-selective herbicide from an all-terrain vehicle. This kills the cover crop
while allowing sufficient time to plant later in the spring.

Killing a cover crop requires a non-selective herbicide like
glyphosate. Singer notes there was a case where an Iowa farmer was advised that
spraying liquid nitrogen would kill the cover crop. “He had to spray another
two times with glyphosate to kill it,” he adds.

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