Earl Lamb of Cedar Springs Farm, Rochelle, VA, speaks during an American Forage & Grassland Council tour of his farm.
Planting forage radishes as a cover crop to combat compaction is one of the best decisions the Lamb family has made in years at Cedar Springs Farm.
The Lambs — brothers John and Earl and their three sons — began experimenting with the crop four years ago. They hadn’t tilled in years and wanted to see if radishes could loosen up fields at their 5,000-acre, 550-head dairy in the rolling hills of Rochelle, VA.
They liked the results, and two years ago went all out, planting more than 200 acres with radishes.
“We don’t need to till this field, even when I seed alfalfa,” Earl Lamb said during a farm tour in May. “The radishes have just eliminated any compaction. There were holes when we planted the corn; you could see that land melding back together.”
The Lambs were early adopters of radishes as a cover crop in their central Virginia region, but across the country they weren’t alone. The use of forage radishes has taken off in recent years, stretching from Vermont to North Dakota.
Radishes, and to a lesser extent other brassica species, have root systems unique among cover crops, says Charlie White, sustainable agriculture Extension specialist with Penn State University.
Radish taproots drill about a foot into the ground, opening large pores that let water filter in. Smaller, fine roots also create channels through the soil to as deep as 5’, White says. When the radishes rot away, the openings remain.
“You’re left with a network of pores deep into the subsoil, and the roots of the next crop can follow those same paths.” The channels also improve surface drainage and soil warming, he adds.
Radishes should be planted at least six weeks before a regular frost, White says. That can pose problems for crop rotations that include corn and soybeans, but works well for small grains or corn silage.
Any crop can follow forage radishes, he points out. But radishes, as they decompose, release a lot of nitrogen into the soil. That can especially benefit nitrogen-demanding, early planted crops, such as corn or spring grains.
The Lambs plant it following silage corn and rye used as ryelage. They have radishes in the ground by Sept. 15, so the crop develops before cold weather sets in.
The rotation has made their fields more productive. “It’s gotten to the point where we are looking at 3-4 tons more per acre (of corn silage) because of that,” Earl Lamb said.
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Radishes can have some downsides. They respond powerfully to nitrogen (N), so an N deficiency can limit the brassica’s ability to outcompete weeds and bust through compacted soil. Radishes don’t handle cold well; they can survive light frosts but show injury when temperatures are in the mid-20s or colder. The cover crop usually won’t live much past January and usually completely decomposes by March or April.
Last year at the Lambs’ farm, however, radishes survived the winter and had to be sprayed down in the spring.
White recommends planting the brassica with another crop, such as annual ryegrass or crimson clover, so there is still spring cover. The Lambs plant radishes with winter peas and leftover rye or barley.
Producers who are considering grazing radishes, which contain up to 85% water, should feed a high-fiber supplement, White says.
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