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Cover crops

06/02/2011 @ 9:21am

Cover cropping has gotten contagious. At field days, on farm tours, and in computer forums, commodity-minded corn, wheat, and soybean farmers are clamoring to learn how to grow new and novel crops they likely last saw in their salad (radishes), soup (peas), or breakfast cereal (oats). There's a long list of benefits to such diversity, and it's proving to be enough to knock traditional crop rotations out of their rut. “Farmers are rapidly learning to appreciate the benefits that cover crops offer,” says Dwayne Beck, no-till guru and director of the Dakota Lakes Research Farm in Pierre, South Dakota.

“Cover cropping can solve many of the problems that long-term no-tillers have encountered. It helps dry the soil when it's too wet, keeps it moist when it's too dry, warms it when it's too cold, and keeps it cool when it's too hot. Cover crops look like they're the next step in no-till.”

Western Eyes On Moisture

By Larry Reichenberger

No-till farmers in South Dakota were among the first to give cover cropping its newfound popularity. Heavy wheat residue hampered their ability to plant corn in wheat/corn/soybean rotations.

Brassica crops (radishes, turnips, and canola) planted after wheat harvest provided a way to speed the decay of this residue — the low carbon-to-nitrogen ratio (C:N) of these crops increases microbial activity, which degrades the excess residue. Also, mixing in a winter small-grain crop (such as winter wheat, rye, or triticale) utilizes moisture in the late fall and early spring while also providing a living root system to improve trafficability.

Cover cropping has grown rapidly from that initial start, and it's now doing far more than drying out springtime soils. Innovative farmers are using cover crops to improve soil quality, reduce erosion, increase organic matter, fix atmospheric nitrogen, cycle nutrients, reduce compaction, suppress weeds, increase water infiltration, and even more.

Developing cover crop mixtures, or cocktails, has become a popular way to pursue several of these objectives at the same time and to fine-tune their impact. For example, Beck says South Dakota no-tillers quickly learned they could misuse brassicas as a cover crop because those plants destroyed too much wheat residue.

“It's critical for later in the season that we keep the soil covered, so we've learned to use grass crops, which have a high C:N ratio, in a mixture to balance the residue decomposition,” he says.

“There are different approaches depending on what you want to accomplish,” continues Beck. “Deep-rooting cover crops like radishes and sunflowers will cycle nutrients back to the surface and break compaction layers. Legumes will produce nitrogen, and grass crops with fibrous root systems will build soil structure. You've got to know what you want to do. Cover cropping isn't just a matter of planting 7 pounds of radishes.”

Wheat growers have a leg up on cover cropping, according to Bladen, Nebraska, farmers Keith and Brian Berns. “Going into wheat stubble after harvest provides a window of opportunity not only to get cover crops planted, but also for cover crops to develop enough growth to accomplish their objectives,” says Brian.

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