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red clover frost-seeding rig built by north-central Iowa farmer
SPECIAL SEEDER: This is the red clover frost-seeding rig built by north-central Iowa farmer Doug Alert. He uses it to get the clover seeded quickly in the small window of time available.

Frost-seeding red clover into winter small grains

Clover can provide a major source of nitrogen for the following corn crop.

The research is clear: If you can find a market for small grains, adding a third crop to your rotation yields economic, agronomic and environmental benefits.

Iowa State University professor Matt Liebman’s research near Boone shows corn and, especially, soybeans yield better when grown in rotation. Soybeans have less incidence of disease, soil health metrics improve, erosion decreases, and water quality improves — all this with equal returns to land and management.

In Iowa, most of this research and most farmers’ experiences have been with adding oats or hay to their rotation. Now, with more farmers planting cover crops — and most of them planting cereal rye — more are raising it for seed. Saving a few dollars on cover crop seed is great, but the real opportunity comes after rye harvest when another crop is grown.

Many people in that boat are planting multi-species cover crop mixes, and for farmers with cattle, that’s tough to beat. A balanced grazing ration that likely includes a few protein sources and plenty of sorghum-sudan grass can save on hay costs later in the year and possibly rest some permanent pastures in the fall so they’ll produce better the next year.

Opportunity to grow some nitrogen
But for row crop farmers, harvesting small grains during the summer presents an opportunity to grow some nitrogen. It’s something organic farmers have been doing for years to augment manure as a nitrogen source. However, most organic farmers either have hay in their rotation or grow oats, a spring small grain, and seed red clover with the legume or forage hopper of their drill at oat planting time.

But what about seeding clover into an already established winter small grain, like rye or winter wheat? Can you do it?

“It’s always worked for us,” says Doug Alert and Margaret Smith, of Ash Grove Farm near Hampton in north-central Iowa.

They’ve been frost-seeding red clover into winter small grains for the past 10 years and have always managed to get a stand of clover established.

And because they’re organic, clover establishment is crucial. “We can’t afford to have a failure because that’s a major source of nitrogen for the corn crop,” Alert says. ISU research has shown farmers can expect a nitrogen credit anywhere from 75 to 100 pounds per acre.

Benefits of red clover
Professor Bill Deen studies cropping systems and nitrogen management at Guelph University in Ontario, where winter wheat is a more predominant part of cover crop rotations. Many of his findings stem from a long-term crop rotation study started in 1980 that, among other things, includes a rotation with red clover frost seeded into winter wheat ahead of corn.

“What’s remarkable about red clover is you get the N credit while simultaneously increasing corn yields,” he says. In other words, the clover provides added benefits that increase yields above and beyond its contribution to nitrogen, a phenomenon known as the rotation effect. “We’re not quite sure what the mechanisms are. Certainly, it does add N to the system,” says Deen, “but it also seems to improve the use of N by the corn crop.” He suspects it may have something to do with how clover affects the soil.

The other advantage of red clover over other cover crops is the nitrogen-release pattern works well ahead of corn. “It seems to have an effect on soil nitrate that is very favorable when you look at the pattern of demand by corn,” Deen says. Radishes, for example, may release the N too early, and rye might hold onto it for too long. “Red clover is the most consistent supplier of nitrogen,” he says.

Red clover in practice in Iowa
Two challenges to working red clover into a winter small-grain system are planting and terminating. For planting, Deen agrees with Alert and Smith: As soon as the snow is off, but the ground is still frozen, it’s time to frost seed. “Going from impassable snow to mud is often a very short time frame,” Alert says. “You have to be ready to go when you hit that window.”

Doing the seeding isn’t that tough. ISU recommends broadcasting 10 to 15 pounds per acre onto frozen ground, and the seeding method is likely to be dictated by what equipment you have available. “I like that you don’t have to have a top-of-the-line system for it to work,” Smith says. When they first started seeding red clover into rye, Alert used a three-point mounted fertilizer spinner. He could cover a 20- to 25-foot swath. Later, he switched to a grain drill and used it as a drop seeder, but that was only 15 feet of width, and trying to cover a lot of acres quickly is tough on a drill.

So last year, he built a toolbar specifically for seeding red clover. It adds seeding capacity and links into his autosteer, which is important because he’s doing a lot of this seeding at night, when the ground is hard.

His setup is a Gandy Orbit-Air seed hopper mounted on a used sprayer boom with a hydraulic metering system. With this setup, he can seed 40 acres between fills, and because he can drive 7 to 8 mph, he can cover about 20 acres per hour. “This is all very important because of the small time window,” he says.

No seeding failure, so far
Some years the window is too short; they don’t get a chance to frost-seed. But they still seed it, even if it’s a little late and haven’t had a failure so far.

“Clover’s low-light tolerance is phenomenal,” Smith says. “To me, it looks like it should never survive,” when looking at a thick blanket of rye that soon covers the clover. She adds that they’ve never had a problem getting a stand of clover established.

Once it’s seeded, there’s little management of clover between seeding time and termination before corn planting. For organic farmers Alert and Smith, herbicide termination isn’t an option. Instead, they have traditionally plowed the clover as soon as they could in spring, often after oat planting. They’ve been debating whether the plow is the right option for termination — or whether a lighter tillage pass would be sufficient — and whether spring or the previous fall is the appropriate time to terminate.

For conventional farmers, light tillage and plowing are still options, but termination with herbicide can also do the job. Penn State University Extension, where red clover in the state is more commonly used as a cover crop, has good guidelines. It recommends: “An excellent herbicide program to terminate a red clover stand prior to planting corn is one pint of 2,4-D LVE and one pint of dicamba (Banvel or Clarity). Apply 2,4 D or dicamba seven to 14 days prior to or three to five days after corn planting if corn seeds are planted at least 1.5 inches deep.

“Do not plant soybeans after a dicamba application. Applying 1 to 2 pounds per acre of atrazine will help provide additional control of red clover. Glyphosate or paraquat alone isn’t recommended to kill a legume such as red clover.”

For more information, see Management of Red Clover as a Cover Crop online.

Practical Farmers of Iowa continues to conduct on-farm trials on use of red clover as a cover crop. To find results, visit and search for “red clover.”

ISU also has a good production guide on using clover with winter small grains; see Intercropping Winter Cereal Grains and Red Clover, PM 2025.

Ohde writes for Practical Farmers of Iowa.

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