In 2023, Maryland’s Department of Agriculture Cover Crop Program began reimbursing growers for cover crops applied by drone technology. Field trials and research completed by University of Maryland Extension during 2020 and 2021 paved the way for the inclusion of this practice.

For Erika Crowl, agricultural Extension agent for Baltimore Co., MD, using drones to seed cover crops seemed interesting and practical given the geography of northern Maryland.

“We have a lot of small and irregular shaped fields up here. They have power lines running through them. They are hilly. They have overlapping tree lines on them. They can be a pain when we’re trying to get bigger equipment into them,” said Crowl.

Crowl and her colleague Andrew Kness started in 2020 by drone seeding daikon radishes into a 26-acre field of standing corn. Since neither Crowl or Kness are drone pilots, they hired a licensed operator who came with his DJI drone outfitted with a 16-pound seed hopper. Each flight carried 12.5 pounds of seed, which covered 1.2 acres. The drone was able to complete two flights per battery.

They seeded the field on Aug. 27, 2020. The drone operator stood on a ladder or the top of his pickup in order to maintain visuals on the drone at all times. From the controller, he also had a bird’s-eye view of the field since the drone has an attached camera.

“He can watch it pretty much like he is riding on top because it has a little video camera,” Crowl said.

The corn was harvested on Sept. 15, 2020, and Crowl and Kness went back on Oct. 21 to evaluate the daikon stand. Across the 26 acres, they randomly threw down a one square foot form and counted the plant population. Using this counting method, the average cover crop plant population was 3.1 plants per square foot.

Drone cover crop seeding: No longer fringe

In the tests, a drone seeded daikon radishes into a 26-acre field of standing corn. Photo courtesy of Andrew Kness and Erika Crowl

They also calculated the canopy density using a smartphone app called Canopeo. This app is used to determine the quantity of canopy cover for live vegetation of any crop, and finding this information is accomplished by taking a photograph that is downward-facing of the vegetation. Crowl took photos of the daikon radish stand from 2.5 feet off the ground. The average canopy coverage for the 2021 cover crop stand was 39.1%.

Once Crowl and Kness collected the necessary data, the farmer grazed the daikon radish with his cattle. Then, the plants were allowed to regrow again and act as a cover crop during winter. “They serve multiple purposes – not just a cover crop,” Crowl said.

The trial was replicated during the 2021 growing season with a planting date of Aug. 30. The corn was harvested slightly later, on Oct. 15. In 2021, the average cover crop plant population was 1.95 plants/square foot. Canopea calculated that the average canopy coverage was 30%.

“Why were the two years different if we basically did the same thing?” Crowl queried. She believes the answer lies in differences in precipitation levels in 2020 and 2021.

“If you look at the precipitation in 2020, it was 27 inches between August and November, where in 2021 it was only 17 inches,” she said.

According to Kness, aerial-seeded cover crops are heavily dependent on precipitation, but they also found that the corn variety played a role – shorter hybrids allowed for better cover crop establishment than taller hybrids. This is presumably due to the amount of light that can penetrate the canopy of shorter hybrids versus taller corn hybrids.

Despite the impact of precipitation on establishment of the daikon radish in the 2021 trial, Crowl believes that cover crop establishment via the use of drones is effective. Precipitation amounts, and harvest timing, however, are critical to good stand establishment.

Crowl said, “We are definitely facing a new thought. Maybe when these drones get a little bit bigger and they have larger seed capacity, this won’t take as long. This was an all-day event, whereas if I’m going out with my tractor, I can do this within an hour versus all day. So we hope the technology catches up with what we’re doing, and I think it will. In the next five years, we’ll see a big difference, and this will be the way of the future.”

by Sonja Heyck-Merlin