Winter-annual Groundcovers

Winter-annual groundcovers - Choosing a cover crop

Winter rye and hairy vetch are the two most common winter-annual groundcovers in Pennsylvania. They have been used with various degrees of success for the last 50 years or more.

Winter rye is planted more commonly today in southeastern Pennsylvania where the longer autumn allows a little more time for establishment. Winter rye should be seeded between early September and early October to allow for the production of enough biomass to provide a good groundcover and to absorb excess nitrate from the soil. Seedings have been broadcast by helicopter and other methods into standing corn, but if the soil is dry, as it often is, stands tend to be poor and competition from corn is too great unless the corn is harvested for silage.

The best stands are achieved when rye is broadcast on tilled ground and lightly worked in or drilled in with a grain drill after the main crop is harvested. Winter rye normally cannot be established after corn or soybeans harvested for grain since harvest of these crops is too late in Pennsylvania. Winter rye must be harvested for silage in the spring if the full nitrate removal benefit is to be realized. Unfortunately, whether winter rye is removed for silage or killed and left as a dead mulch, it will have tied up available nitrogen and extra nitrogen must be applied to corn planted into it to prevent a yield loss. This may not be a problem if there is excessive nitrogen-rich manure to dispose of anyway.

Hairy vetch should be seeded a month earlier than winter rye, making hairy vetch virtually impossible to seed into or after corn. The best hairy vetch stands are achieved by no-till or min-till seeding after small grains in August. A good hairy vetch stand fixes enough nitrogen so that no additional N is required for a succeeding corn crop. Hairy vetch normally is not harvested for forage, although it could be. If it were, however, much of the nitrogen that would be available to the corn crop would be removed with the forage.

Both winter rye and hairy vetch, if seeded early enough, produce enough growth to smother out winter-annual weeds and suppress some summer annuals the following spring. Also, winter rye and hairy vetch will regrow if harvested just before corn planting; thus an effective herbicide program is required for complete kill and for weed control since weed control by the cover crop does not last long enough. Anything less than complete cover crop kill usually results in corn yield losses from competition. Use normal herbicide treatments for this purpose.