NORTHFIELD, Minn. — Soil-saving cover crops can be interseeded in corn without decreasing corn yields, according to the results from a number of farmer-led on-farm trials in recent years. In some cases, farmers even saw slight yield increases, according the study results which were published in the Minnesota Department of Agriculture’s 2018 Green Book.
Eight farmers in Rice, Goodhue and Waseca counties teamed up with the Northfield-based Cannon River Watershed Partnership during the 2016 and 2017 growing seasons on a $24,000 project called “Interseeding Cover Crop into Standing Corn in June.” The farmers interseeded a variety of cover crop seed mixes into corn at the V-5 to V-7 stage.
“The results showed that while weather, herbicide carry over, and equipment availability are challenges to interseeding cover crops at this stage of corn growth, this method is viable and can be a successful and cost-effective method for farmers to establish cover crops,” the report stated.
The question as to whether or not cover crops create a yield drag on corn was secondary to whether cover crops can be successfully interseeded early in the growing season, Alan Kraus of the Watershed Partnership said.
“We had two of the eight farms that did well on measuring yield,” Kraus, who joined the Watershed Partnership after the project was designed, said. “The project could have been designed better, but on the farms that we checked we just didn’t see a yield reduction. One way to look at it is they didn’t lose yield; but another way to look at it is that they had an additional cost that they didn’t cover.”
Kraus estimates it costs between $40 to $50 an acre to get a successful cover crop going.
“At $3.50 a bushel for corn that’s more than ten bushels of corn that you should get to make up for that added expense,” Kraus said.
Like the farmers in the Cannon River Watershed, Keith Hartman was interested in seeing if he could establish interseeded cover crops early in the growing season. Hartman, who farms near Gibbon, Minn., had an on-farm research project funded by the Minnesota Department of Agriculture during the same time period as the Watershed Partnership farmers. He called his project, “Interseeding Cover Crops and In-Season Nitrogen in One Pass.”
Hartman’s primary goal was to reduce fall tillage and maintain a living root system in the soil so as to keep soil in place during the winter. He kept his costs down by adjusting his seed mix and adapting equipment that allowed him to plant the cover crop at the same time as he side-dressed nitrogen onto V-6 stage corn in early July. In the second year of the project, Hartman seeded annual rye grass and radishes using a Yetter Magnum 10,000 fertilizer to apply the seed and fertilizer at the same time.
“With the Yetter Magnum units I positioned the seed tube to distribute the seed at the base of the firming wheel to ensure that the seed was only covered by a quarter to half-inch of soil,” Hartman wrote in his project report.
Using that equipment and seeding mix, Hartman experienced no difference in corn yield between side-by-side corn with and without a growing cover crop. Additionally, he was able to establish a post-harvest cover crop to protect his soil for $15 in seed costs per acre.
Hartman met his goal of economically protecting his soil over winter; but, as Kraus would point out, he still had an added cost he didn’t cover. And, as Kraus points out, reduced soil erosion and increased organic matter are not items which show up on today’s balance sheet. Increased soil organic matter will increase yields and reduce costs in the long run; but, on a year-to-year basis, they are difficult to account for.
Kraus points out, however, there can be some short-term cost reductions from using cover crops.
“If you get a good cover crop establishment you will get good biomass carryover into the spring; and there can be definite opportunities for weed control. You may need to apply less herbicide,” he said.
The Watershed Partnership, along with its farmer partners, has also learned cover crops can reduce fertilizer requirements.
“In another project, we’ve seen that the fields with cover crops that had increased organic matter had a better conversion of nitrogen into corn,” Kraus said. “That means it takes less pounds of nitrogen to grow a bushel of corn. That’s something you can measure and it’s better for the water too.”
The farmers in the Cannon River watershed are continuing to experiment with, and learn how to use, cover crops to improve water quality in a way that works economically for each farm. The use of early-planted cover crops for a source of late-season forage is of particular interest to livestock farmers in the watershed.
“We’ve got a study where we’re looking specifically at cover crops for forage with four farmers,” Kraus said. “We’re interseeding in June and varying the row width. We’ve got corn planted in 30-inch rows, 60-inch rows, and then we have a series where we plant four rows at 30 inches and then skip two rows, so we’ve got this really wide space. We're looking at which of those treatments yields the highest cover crop quantity and quality along with the total amount of corn grain that’s harvested.”
“We don’t have any data yet, but in general, if you get that cover crop planted in June so it’s immediately available in the fall when the beans or corn are harvested, that cover crop will be immediately available as forage for livestock.”
Kraus warns when planting early interseeded cover crops, farmers need to be very thoughtful about their herbicide use. Herbicide carryover can kill a cover crop, or it may not be labeled for livestock.
With that in mind, the experiences of Keith Hartman and the farmers in the Cannon River Watershed Partnership establish that cover crops can have both short-term financial benefits as well as long-term environmental benefits.