Cover crops incorporated into a continuous no-till field crop rotation can produce enough nitrogen to complement, or in some cases, replace corn nitrogen fertilizer applications, according to long-term Ohio State University Extension research.
Seven years of research at Ohio State University’s South Centers at Piketon have found that cover crops, such as cow peas or winter peas worked into a corn/soybean/wheat rotation can produce enough nitrogen to support at least 150 bushels of corn per acre.
The findings indicate farmers can save money on spring nitrogen fertilizer applications while reaping the environmental benefits of cover crops.
“Cover crops produce enough nitrogen to where farmers may not need to add nitrogen fertilizer to their corn crop. But if they want to be sure of maximizing their yields, farmers can supplement the cover crops with 25 to 30 pounds of nitrogen fertilizer,” says Rafiq Islam, an Ohio State University soil scientist. “That’s more than enough nitrogen that a farmer needs to support the corn crop.”
Islam claims that practicing continuous no-till is a challenge for many Ohio farmers because of the hits they take in yields, soil compaction, weeds and other environmental difficulties.
“No-till farmers face yield reductions right off the bat — 20% to 25% — and those yield reductions last a good 4 or 5 years until the soil adjusts to the new production system,” Islam says. “Also, they face compaction issues, weed control problems, wet fields and the immobilization of nitrogen because of the increased carbon being stored in the surface soil.”
Throw cover crops into the production mix and the time it takes to recover from yield losses is cut in half, Islam says.
In addition, cover crops help alleviate environmental problems. For example, including a few pounds of oilseed radish with legumes can substantially improve the benefits of cover crops.
“The roots of oilseed radish can reach deep into the soil — as much as 30 inches —breaking up compacted soils (natural strip tillage), supporting microbial diversity, facilitating drainage and improving soil structure,” Islam says. “If you grow a legume cover crop along with oilseed radish, you don’t need to subsoil or deep plow. The crops work together as a natural biological plow.”
In addition, oilseed radish stores massive amounts of reactive nitrogen and phosphorus, preventing any of it from leaching out of the soil or surface runoff and making it available to corn when it needs it.
“We also found that because oilseed radish does such a good job of improving the soil quality, it forces associated cover crops (legumes) to fix more nitrogen of their own, making even more of the natural fertilizer available,” Islam says. “It’s a mutually beneficial relationship.”
Not only do cover crops serve an environmental purpose, but they serve an economic purpose as well.
“In the 1980s, the U.S. imported 24% of nitrogen fertilizer. Today, we import more than 60%,” Islam says. “Cover crops are an ideal alternative to that market situation. We have to think in terms of fossil fuel dependency and food security issues.”
Islam offers one cover crop rotation scenario that research has shown works: In a corn/soybean/wheat rotation, harvest corn in the fall, plant cereal rye over the winter and roll over in May in preparation for soybean planting. Cereal rye helps control weeds.
After soybean harvest, grow wheat, then plant another cover crop following wheat, such as winter peas or cow peas. Combine that cover crop with oilseed radish to increase nitrogen production needed for next year’s corn crop. Winter kill the cover crops and plant corn the following spring.
Islam says that despite the benefits of cover crops, there are still some challenges growers face in incorporating them into their no-till system. A few include finding available seed, crucial timing of planting cover crops following wheat, planning ahead for planting cover crops and knowing the right cover-crop combination.
