At the same time, the machine strategically applies a fertilizer and herbicide. The research team created a prototype using a number of existing technologies from agricultural equipment manufacturers.

According to Roth, the best time to use the device is six weeks after the corn is planted. If the cover crop is planted too early, it can compete with the corn plants; if it is planted too late, the corn crop may be too competitive for the cover crop to grow.

A single pass through a field costs the farmer approximately $10 an acre, Roth said. By saving one to two trips through the fields, farmers could save $10 to $20 per acre.

Other methods of planting cover crops during the growing season -- such as using an airplane to drop seeds on the field -- are expensive and only moderately successful. Roth said the alternative methods are only effective in establishing a cover crop about half the time.

The researchers tested the seeder last summer in three studies at Penn State's Russell E. Larson Agricultural Research Center, said William Curran, professor of weed sciences. In each of the studies, the crop seeder was successful in establishing cover crops without any impact on corn yields.

The researchers tested three cover crops -- annual ryegrass, red clover and white clover. They also tested a mixture of ryegrass and clover. Because ryegrass and clover can prevent soil erosion and serve as a natural source of nitrogen, farmers also may not need to purchase as much fertilizer.

"We picked cover crops that we thought would work and chose the ones that we thought had the best chance to be successful," Curran said.

The researchers said they are pleased with the results of the first tests, but have more work to do to perfect the seeder.

"We really had just one season for research and we basically tested things that we were pretty sure would be successful," said Curran. "Now we have to do more research before we feel the results are of value and we feel confident in what we're doing."

If the seeder is marketed, the researchers believe that the device will be inexpensive enough for use on smaller farms.

The researchers have filed a provisional patent on this device.