The neighbor stopped by on his side-by-side to see what Dave and Mike Unruh were up to. The ground was just starting to thaw. There was a solid month yet before corn planting, and it was too early to start working the fields. Yet here Dave and his son were — with the tractor and a seeder out in early March.
“Normally, seeding in the first week of March is pretty crazy,” Mike said. But Mike was trying something new. He was frost seeding: scattering cover-crop seeds just as the soil is beginning to thaw. There was still snow on the ground as Mike drove around with an air seeder, blowing frosty burseem clover and winter cereal rye seeds on top of the snow. When the snow melts, the freeze-thaw cycle will heave the ground and bury the seeds shallowly, ready to start growing as soon as the soil warms.
“The mechanics of it, I think, are like maple syrup,” Dave explained. “You want it thawing during the day and freezing at night.”
Mike and Dave started using cover crops because they did not have much choice. After a wet spring in 2013, many farmers could not get corn or beans planted in time, so they planted cover crops just to hold on to their soil.
“Whatever acres we put that on,” Mike said, “the next year our yields were —” “Just phenomenal,” Dave finished his son’s sentence. “Fields we normally don’t expect much from were some of the best,” Mike added.
The cover crops boosted soil fertility so much that the Unruhs said they were able to cut back their nitrogen applications from the University of Minnesota Extension-recommended one unit per bushel to 0.7 units, which saves them money on fertilizer and is good for the environment.
On plowed, bare fields during heavy spring rains, Dave said, “We’d just see sheet erosion — all gone.” With cover crops and minimum tillage, he stated, “Not that we didn’t have erosion, but if I’d have worked it, I would have lost it all down to rock.”
So the Unruhs saw these all benefits from cover crops and started planting them on all 800 acres they farm. However, farming with covers is not all sunshine and clovers. One of the biggest challenges is the clock. It can be hard to make time for cover crops, especially in Minnesota, where there are often just enough days in the growing season for a decent cash crop.
Take last fall. Some farmers might plant cover crops in the late fall after harvesting their cash crop, and certain plants will survive through the winter and provide a nice green cover in the spring. However, last fall’s corn harvest stretched right up until heavy snow fell. For many farmers, there was hardly enough time to harvest corn, let alone time to plant cover corps and give those cover crops enough warm days to germinate and grow.
“Corn doesn’t come off until the 15th of September, and radishes — if you want a good crop of radishes, you want that in by the 15th of August, probably,” Dave said. Radishes are a cover crop.
The same goes for spring, when farmers often race to plant corn as soon as the ground is dry enough or risk not giving the corn enough days in the growing season to properly mature. Farmers’ time and the number of warm, dry days in the year are at a premium.
That’s the advantage of frost seeding. “It’s kind of buying us that extra window to try to get [the covers] established,” Mike said. Frost seeding can be done at a time of year when other fieldwork is impossible, and it allows farmers to get live roots growing in their fields weeks before they otherwise could. Those live roots are key for soil health and erosion prevention, and the Unruhs said the cover crops also help soak up spring rains and dry out their fields more quickly, so they can start the work of planting cash crops sooner, too.
The Unruhs are experimenting with frost seeding. They tried it out for the first time on 60 acres this spring. They attached an air seeder to an implement they had on hand — a beefy vertical-disc plow that is a bit overkill for hauling an air seeder around. Next year, Mike said he will use something lighter. It is a good idea to try out new techniques before buying too much equipment, Winona County Soil and Water Conservation District (SWCD) Resource Specialist Lance Klessig said. “You make do with what you’ve got and then, if you like it, you can go get something else,” he advised.
Later in the spring, the Unruhs will plant no-till or minimum-till corn straight into the growing clover and rye they frost seeded. Then, as the corn seedlings starts to emerge, they’ll terminate the cover crops with herbicide to make way for the corn.
“I’m honestly hoping it just helps yield even more,” Mike said. “The rye is such a fibrous root mass down there and coupled with all the earthworms, I think it makes it that much easier for the corn to send roots down because there are those channels,” he stated.
People used to say that cover crops were a waste of money on seed or that it was too much extra expense to terminate the covers, Dave said. However, he stated. “Those same people who were naysayers are doing it on a lot more acres than I am. So it’s coming around.”