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College of Food, Agricultural, and Environmental Sciences


Worried About Fuel Prices? Grow Cover Crops for Fertilizer Needs

May 14, 2007

PIKETON, Ohio -- Cover crops, if planted at the right time and used with the proper crop rotation, can be biomass workhorses.

Based on the results of five years of Ohio State University research, cover crops supply ample nitrogen and recycle phosphorus for fertilizers while maintaining soil quality and suppressing weeds, insects and diseases.

Rafiq Islam, a soil scientist with the South Centers at Piketon in Piketon, Ohio, studied 32 different cover crops on field crops and a variety of vegetables to evaluate their biomass production and nutrient management capabilities. He found nine varieties that generated the minimum nitrogen requirements and recycling for crop production: cow peas, hairy vetch, crimson clover, red clover, green bean, annual ryegrass, radish, cereal rye, buckwheat and winter peas.

"Our main goal was to provide enough nitrogen through cover crop residues so that commercial application was not needed, while using cover crops to recycle nutrients like phosphorus and to enhance soil carbon sequestration," said Islam. "Basically, what we found is that these cover crops, especially cow peas and winter peas, produced enough nitrogen to support crop production without the need to add commercial fertilizer, or very little of it. The minimum these cover crops were producing is equal to 100 to 150 pounds per acre of commercial nitrogen fertilizer, which is what is generally needed to maintain a good crop. That's saving farmers money."

Islam said that cover crops offer a myriad of benefits for field crops, especially in no-till production systems. They are excellent sources of nitrogen, have almost a 15:1 carbon-to-nitrogen ratio essential for maintaining soil quality, and produce chemicals (allelochemicals) that are antagonistic to soil-borne diseases and pests. Cover crops also fit in well with field crops because of their short rotation and winter cover, and many cover crops are killed off by winter weather, eliminating the need to use chemicals for burn-down.

But few farmers make use of cover crops and their benefits because of the overall lack of knowledge of what cover crops can offer, their moderate-to-high seed prices, availability, and the challenges of getting them established in the field, said Islam.

"If seed costs more than fertilizer prices, no one will use the crop. But with fuel prices continuing to rise, many can now make a case for trying cover crops for their nitrogen needs," said Islam. "A cover crop is not an immediate magic bullet, but over time it will produce magic results. Cover crops won't replace nitrogen fertilizer completely, and they are difficult to establish. In some cases, farmers may face initial lower crop yields. But if a farmer is willing to tackle the challenges, a cover crop can be a good alternative to commercial nitrogen fertilizer over time."

Out of the nine cover crops that performed well in the studies, the two varieties that produced the most consistent and best results were winter peas and cow peas. Winter peas produced over 135 pounds per acre of total nitrogen fertilizer, while cow peas produced nearly 150 pound per acre of nitrogen fertilizer.

Islam said that the performances of the cover crops are impressive, but for farmers to get the most out of their benefits, it's important to know when to plant and what cover crops to use with what agronomic crops is important.

"Being knowledgeable about each cover crop and its capabilities, and what to plant when is essential," said Islam. "Know what cover crops are grasses and what are legumes, and whether they are a winter crop or a summer crop. Like cover crops impact the performance of like agronomic crops, and some cover crops immobilize nitrogen so crops can't use it."

The following are just some examples of the most effective cover crop/agronomic crop combinations:

• Use winter peas in corn/soybean rotations immediately after harvesting soybeans.

• Use winter peas in continuous corn rotations.

• Use cow peas in corn/soybean/wheat rotations after harvesting wheat.

• Cereal rye, which is effective in suppressing diseases, can be added to a cow pea/corn/soybean/wheat rotation after harvesting corn, or a winter pea/corn/soybean/wheat rotation after harvesting corn. The rye is grown between corn and soybeans.

• Annual ryegrass is very effective in uptaking and accumulating nitrogen into biomass from dairy or swine manure application in the early fall.

• Hairy vetch is effective in a corn/rye/soybean/wheat rotation. Hairy vetch is integrated between the wheat and corn crops.

For more information on Ohio State's research on cover crops, contact Rafiq Islam at (740) 289-2071, or e-mail

Candace Pollock
Rafiq Islam