Broadcast interseeding hairy vetch in early September resulted in more groundcover and biomass than later interseeding or post-harvest seeding, but drone seeding resulted in issues with stand evenness. Credit: Heidi Reed, Penn State Extension

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Investigator(s)

Principal Investigator: Paul Esker, Ph.D., Professor of Epidemiology and Field Crop Pathology
Co-Investigator: Heidi Reed, Ph.D., Agronomy Educator

Background

Farmers struggle to establish cover crops other than winter cereals after soybean harvest. One way around this problem is to drone interseed cover crops into standing soybeans. Previous years of this trial revealed that hairy vetch is the most viable legume species for broadcast interseeding, but best practices have not been established for our region.

Objective

The objective of this trial was to evaluate the establishment success of drone-seeding hairy vetch into standing soybeans at three different dates compared with drill-seeding after soybean harvest.

Methods

Five farmer cooperators were selected across a range of climates, geographies, soil types, and management strategies in Berks, Lancaster, Lebanon, and York Counties. An additional site was included at the Southeast Ag Research and Extension Center (SEAREC) in Lancaster County.

Hairy vetch was interseeded at 25 pounds per acre at all sites within a few days of September 1, September 15, and October 1, 2024. Post-harvest seeding was done as soon as possible after soybean harvest, which ranged between October 12 and November 15, 2024. There was one replication at each cooperator site, and sites were used as replicates. Drone service was provided by Snyders Crop Service, LLC; Sky Apply, LLC; Willard Agri-Service; and The Mill.

At SEAREC, broadcast interseeding was done with a chest-mounted spinner spreader on September 6, 20, and 30. Post-harvest drill-seeding was done on October 30, 2024. The field was arranged in a randomized complete block design with four replications. Data for SEAREC replicates were averaged before doing a combined analysis on all sites.

We took similar measurements to prior years of this trial: soil nitrate (0 to 6 inches), cover crop density (plants per square foot), and groundcover (percent) in the fall and spring using the Canopeo app; and cover crop biomass (pounds per acre) in the spring.

Results

At one York County Cooperator site, no fall or spring measurements were done because no hairy vetch emerged; this site is considered a complete failure and data are not included. The Lebanon County Cooperator site was terminated before spring measurements could be taken, so data are not included for spring measurements.

For the remaining sites, neither fall nor spring hairy vetch density was significantly impacted by seeding date or method. Treatment also had no impact on soil nitrate. There was a simple effect of season on groundcover (p=0.0032) with significantly more in the spring (45%) than in the fall (16%) (Figure 1). Although not significant, percent groundcover trended higher the earlier the hairy was seeded, when measured in the spring.

: Percent green cover as measured with the Canopeo app is shown on the vertical axis; hairy vetch seeding timing and method are shown on the horizontal axis, with blue bars representing fall groundcover, and orange bars representing spring groundcover. Groundcover does not differ between treatments in the fall, but in the spring, drone seedings have numerically higher groundcover than post-harvest drilled hairy vetch. There is significantly more groundcover in the spring compared to the fall. — Figure 1. Hairy vetch fall (blue) and spring (orange) green groundcover as measured with the Canopeo app across all sites. At each site, drone 1 was seeded within 5 days of September 1; drone 2 was seeded within 5 days of September 15; and drone 3 was seeded within 5 days of October 1. Post-soybean-harvest drill-seeding took place between October 12 and November 15.

Hairy vetch accumulated twice as much biomass when seeded at the earliest seeding date (drone 1, 1,033 pounds per acre) than the latest drone seeding date (drone 3, 332 pounds per acre) and waiting to drill or broadcast/incorporate hairy vetch until after soybean harvest reduced spring biomass by 85 percent (150 pounds per acre) (p=0.0996, Figure 2).

Pounds of dry matter per acre is shown on the vertical axis, with hairy vetch seeding timing and method shown on the horizontal axis. We see a trend of lower biomass as seeding date gets later, from the first drone interseeding to post-harvest drill-seeding, and the first drone seeding accumulated significantly more dry matter than the drill seeded hairy vetch. — Figure 2. Hairy vetch biomass measured within three days of spring cover crop termination. At each site, drone 1 was seeded within 5 days of September 1; drone 2 was seeded within 5 days of September 15; and drone 3 was seeded within 5 days of October 1. Post-soybean harvest drill seeding took place between October 12 and November 15.

Conclusion

Drone seeding in early September can help farmers include hairy vetch as part of their crop rotation. Broadcast interseeding hairy vetch into standing soybeans results in more successful establishment than when hairy vetch is seeded after soybean harvest. However, the large seed size and high seeding rate of hairy vetch, as well as issues with seed distribution and weed competition, are remaining challenges with drone interseeding.

Acknowledgements

This project was funded by the Pennsylvania Soybean Board. Farmer cooperators J. Marlin Miller, Jeremy Meck, Mike Schrum, Dan Innerst, and Jesse Maulfair.