Cover crops occupy the soil during fallow periods. In the busy harvest season, it may be easy to postpone cover-crop planting until a later date, losing valuable growing time for the cover crop, says Sjoerd Duiker, Penn State University soil management specialist.

That can be a mistake, Duiker says.

"Cover-crop biomass accumulation and root growth depend on when the cover crop is established," he says. "This determines how much cover the cover crop provides and this is important for erosion control, especially when establishing a cover crop in a tilled seedbed, or with no-till in low-residue situations, such as after corn silage, after soybeans or when corn fodder is removed."

Duiker says early establishment is also important so that the cover crop can absorb soil nitrate before it leaches to groundwater. In a study in the Mid-Atlantic region, cover-crop nitrogen accumulation was about 120 pounds per acre in December when rye was established early, but was negligible in December if the cover crop was established late.

"The nitrogen that is absorbed by the cover crop is protected against leaching and is released next year when the cover crop biomass decomposes," Duiker says.

A committee of cover-crop scientists determined that early planting is 2 weeks or more prior to first killing frost, normal planting is from 2 weeks prior to first killing frost and late is from killing frost to 3 weeks after killing frost.

The first killing frost (28 F) normally occurs mid-October in the very southeastern tip of Pennsylvania, mid-September in central Pennsylvania and end of August in northern Pennsylvania. This information shows the importance of having the drill with cover-crop seed in the field when you harvest your crop, Duiker adds.