Spreading liquid manure laden with forage seeds onto fractured, loosened soil is an efficient way to establish a cover crop, says Tim Harrigan.

Called slurry seeding, it saves time, labor and fuel compared with no-till drilling, and is at least as effective, this Michigan State University ag engineer adds.

“We find that cover crops and manure are really great companions,” says Harrigan.

Seed is added manually to a loaded slurry tank, then the mixture passes through a rotating chopper-distributor and through drop tubes behind a rolling-tine aerator.

Harrigan uses and recommends an Aer-Way aerator, a ground-driven machine with sets of four adjustable 8” tines spaced 7½” apart. Any slurry tank will work, but he says the pto pump on most models creates an application flow rate that’s too high for this use.

“So we close the valve part way to get the correct flow rate … and then the remaining slurry is recirculated through the tank, similar to a sprayer. That’s what keeps the seed in suspension,” he explains.

When the slurry-seed mixture is dropped into soil openings directly behind the aerator tines, the manure quickly carries the seed below the surface to an environment ideal for germination, with manure nutrients readily available to the seedlings. Harrigan uses the same cover-crop seeding rates as when drilling.

“Typically, because we don’t have the nicely engineered seedbed that we have with a drill or planter, we end up with less plants but with really vigorous plants. So we see fewer plants but equal or greater biomass compared to drilled crops.”

Liquid swine, dairy and beef manure work equally well if the slurry is dilute enough to quickly fill the soil openings, he says.

He has successfully slurry-seeded a number of cover crops, including cereal rye, annual ryegrass, oats, oilseed radish and forage turnips. Usually seeded into silage-corn or wheat stubble, some have supplied late-season grazing. He’s also gotten a “pretty good stand” of red clover by slurry-seeding it into winter wheat in spring. The aerator didn’t harm the young wheat plants, and when grain was harvested, the clover was already established and ready to begin fixing nitrogen for the following corn crop.

Cover crops are gaining popularity because they increase soil’s productivity by improving its quality and structure.

“Also, we’re seeing increased awareness of the environmental impacts of some farming practices and the importance of keeping vegetative cover on the surface throughout the year,” says Harrigan. “There’s a long list of reasons why cover crops are a really good idea.”

In 10 years of research, he’s always had good luck with slurry seeding, but it requires a specific set of equipment that most crop-and-livestock farmers don’t have. So he and his colleagues are researching additional methods of combining cover crops and manure.

“We see other options that are going to get the job done quickly and are going to work well for folks,” he says. “We probably will be writing about that in the pretty near future.”