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Corn+Soybean Digest

Nitrogen Concerns No Reason To Run For Cover Crops

Incorporating cover crops into a production rotation may have conservational benefits, but their short- and long-term agronomic value is still being evaluated. With new research, Ohio State University soil fertility specialists are hoping to provide more concrete answers.

Robert Mullen, an Ohio State soil scientist with the Ohio Agricultural Research and Development Center, and his colleagues plan to seed red clover into this season's wheat crop to determine whether the cover crop provides a sufficient nitrogen (N) benefit for the incoming corn crop.

"It's true that cover crops capture some of the nitrogen in the soil, but questions remain as to how much of that nitrogen is available for a corn crop's use and whether cover crops can take credit for improving nitrogen availability," Mullen says.

"The current body of literature shows that the agronomic value of legume cover crops is well established, but the amount of nitrogen provided to the subsequent corn crop may not offset the cost of establishing the cover crop. Non-legumes established prior to corn do not seem to show much of a nitrogen contribution at all, though they may provide a rotational benefit."

The message to farmers is that they should approach using cover crops with a sharp eye on whether the economics outweigh the production benefits, Mullen says.

Cover crops – legumes and grasses – are touted for their conservation benefits that may provide some economic benefit to producers. When planted between crop rotations, cover crops decrease the amount of N being transported off the field during non-peak production times.

The debate has centered on how much N a cover crop actually captures and how much of that is released to a subsequent corn crop. Another issue is whether those unknowns provide economic justification to use cover crops, when doing without may be just as beneficial when it comes to N availability.

"Farmers don't establish cover crops for free," Mullen says. "Obviously, there's an investment involved when buying seed, not to mention the extra time and production management to plant and to burn down or till the cover crop when it comes time to plant the corn crop.

"There has to be a significant amount of nitrogen being generated and made available to the corn crop, or a substantial rotational benefit that would justify using cover crops solely from an agronomic and economic standpoint. And, so far, no research has been published to substantiate that."

Several factors, most notably environmental conditions, may play a key role in how cover crops interact with the soil when it comes to N availability, Mullen says.

"Additionally, how successful a cover crop is established also determines how much nitrogen is captured," he says.

One thing that is known is that legumes tend to provide more of an N benefit than non-legumes, Mullen says.

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