EDITOR'S NOTE: This article discusses overseeding. This is the first in a four part series highlighting different cover crop seeding techniques. Next month: Broadcast seeding.

As cover crops continue to grow in popularity, there are many questions to consider when first getting started. One of the most common questions we hear at Iowa Learning Farms field days and workshops is: "How do you plant the cover crop?"

HIGH CLEARANCE: The high clearance interseeder is prepped and ready to plant cover crops at the ISU Northern Research and Demonstration Farm near Kanawha on August 27, 2015.

There are a variety of cover crop seeding techniques out there including overseeding, broadcast seeding, aerial seeding and drilling. The Iowa Learning Farms (ILF) and Iowa Cover Crop Working Group (ICCWG) have cover crop research projects all across the state using various seeding methods and will be highlighting four of these methods in a new cover crop seeding techniques series.

First up: this article discusses cover crop "overseeding"
In Iowa, one of the biggest challenges cover crop users mention is timing. Our window of time for fall cover crop growth is limited, particularly if the cover crop is seeded post-harvest. The overseeding technique (seeding the winter cover crop into a standing grain crop) extends that window, allowing for earlier seeding, germination and growth (provided there is adequate precipitation and soil moisture to get started).

TALL CORN: Overseeding of cover crops into standing corn just outside Clarion on August 27. Cover crop seed travels down through the drop tubes shown here, and is dropped below the canopy of the standing corn.

During the last week of August 2015, we established three of our cover crop demonstration sites in north-central Iowa with a high clearance seeder. The project's goal is to evaluate cover crop mixtures and single species establishment using different seeding techniques, including overseeding. The work was done in partnership with Hagie Manufacturing of Clarion using their Cover Crop Interseeder, which was developed in 2013, allowing their high clearance sprayer to be converted to a seeder.

High clearance crop sprayer can be converted to a seeder
With the seeder kit equipped, there are individual drop tubes that can be attached to drop the seeds directly in the inter-rows while driving through the field even through standing corn. The cover crop seed is loaded in a Gandy dry box to hold and move the cover crop seed through the boom system.

The boom on the high clearance seeder can be adjusted to different heights to accommodate the height of the cash crop. Our demonstration plots were seeded at two different heights for comparison. One set of plots was overseeded below the canopy with drop tubes, while other plots were seeded above the canopy (drop tubes were removed). Later in the fall, a third seeding technique, post-harvest drilling, was completed.

VIEW FROM THE TOP: Looking out across the field with the cab of the interseeder and the seed hopper (loaded with cereal rye) in the immediate foreground.

Stay tuned, more to come on cover crop seeding methods
These demonstrations are part of a USDA-NRCS Conservation Innovation Grant titled "Evaluating Planting Techniques for the Successful Establishment of Cover Crop Mixtures and Single Species in Iowa."

This was the second year of seeding at these demonstration sites; the mixture seeding into standing corn included cereal rye, rapeseed and radish while the single species was rye. The first year, seeding into standing soybeans, included a mixture of oats, hairy vetch and radish and a single species of oats. Fall and spring cover crop biomass are being collected, as well as crop yields to evaluate the different seeding techniques in a corn and soybean rotation.

Visit ILF's Cover Crop Resources page at extension.iastate.edu/ilf/content/cover-crop-resources to learn more about the ICCWG, our ongoing cover crop demonstration projects, and the many cover crop information resources we have available. And stay tuned for additional cover crop seeding techniques to come!

Staudt is assistant program manager and Juchems is events coordinator for the Iowa Learning Farms program, based at Iowa State University.