There are many benefits cover crops offer when they are properly established. These benefits range from protecting soil, to reducing run-off of soil particles in an effort to retain nutrients, to increasing soil productivity and overall farm profitability. In some crop rotations, establishment is a challenge. Often, depending on the maturity of the cash crop, the establishment window is too late in the season to be successful for many of the species.
“Especially in a corn-soybean system, after the cash crop has been harvested for grain, it is often difficult to drill the cover crops and get sufficient growth,” said Sjoerd Duiker, Professor of Soil Management and Applied Soil Physics with Penn State University. “Many have tried to establish a cover crop while the main crop is still growing in the field. Many times, the seeding applications are very inconsistent. One year it may be a good catch, but sometimes it is unsuccessful.”
A living mulch is another approach to establishing a cover crop in fields that may have a crop rotation limitation.
“A lot of work has been done at Penn State with living mulches,” Duiker said. “Some of the more common ones used are crown vetch, field peas, and birds foot trefoil. These crops are in the field and growing there all the time. For management, they are suppressed and then the corn is planted into them. Sometimes it is a challenge because they can be too competitive with corn and cause a yield reduction. That has led guys to more seriously explore inter-seeding into a standing crop. For field corn, it is before or at the V6 growth stage when there is still some open ground showing and we can still get into the field.”
The concern for cover crops to act as a weed when it is inter-seeded into a growing cash crop is a common question.
“Studies have shown that when the over crop is inter-seeded at the V6 growth stage, that is does not compete with the corn crop,” Duiker said.
There are many different types of equipment that can be used for inter-seeding of cover crops.
“An inter-seeder has been developed that is a 3-in-1 pass operation. It can side-dress apply liquid nitrogen for the corn, apply post emerge herbicides (under the corn canopy), and then it has drill units to seed the cover crop between the rows,” Duiker said. “We have also done work with it in 60-inch row corn and add another row unit for seeding the cover in wider rows. This is actually a no-till drill, so it can successfully inter-seed the cover crop with relatively little soil disturbance in the process.”
Penn State has done several studies with inter-seeded multi-species mixes.
“One thing that needs to be considered is what species of cover crops are shade tolerant. They need to be able to sit below the canopy for a while and still survive,” Duiker said. “Things like cow peas and hairy vetch and radish are not very shade tolerant. They have not been that successful in the trials. Things like annual rye grass and red clover have worked well. The other nice thing about annual rye and red clover is that they have a small seed, so we can keep our seeding rate low (per pound) and still cover a lot of acres, and keep the cost down.”
Research has also been done with inter-seeding cover crops into soybeans.
“The biggest challenge when inter-seeding cover crops into soybeans has been at the time of soybean harvest,” Duiker said. “Because soybeans need cut so low to the ground when harvested, in order to get all the pods, a lot of the cover crop plant matter was also cut and run through the combine. A more successful approach has been to broadcast the cover crop seed just prior to leaf drop. Then it is not emerged enough to cause harvest issues.”