After years of struggling to consistently establish cover crops in the fall on cropland in Iowa’s northern counties, more than a dozen Allamakee County farmers are participating in a new USDA-sponsored soil health demonstration project that, after one growing season, is showing promising results.

USDA’s Natural Resources Conservation Service awarded the Allamakee Soil and Water Conservation District $236,000 through a three-year grant to lead, manage and analyze a series of data from interseeding cover crops at the V4 to V7 corn growth stages.

Interseeding allows cover crops to establish prior to corn canopy. After canopy, the cover crop can go dormant from being shaded out and then restart growth once the corn is harvested.

LuAnn Rolling, district conservationist for NRCS in Allamakee County, says it’s been disappointing to see the lack of cover crop success in her county. “Our window to establish cover crops in the fall is smaller than much of the state,” she says. “Aerial seeding hasn’t worked well for us. Our SWCD commissioners pushed for this grant to encourage producers to try something different.”

Why grow cover crops?

Iowa farmers have used cover crops for many years, but they’ve grown in popularity during the past decade. Cover crops help:

• reduce soil erosion
• use excess soil nutrients
• suppress weeds
• minimize soil compaction
• increase soil organic matter
• improve soil moisture efficiency
•  lift overall soil health

Cover crops also provide soil cover at the most vulnerable times, anchor corn and soybean residues, increase water infiltration, and reduce compaction. In addition to the environmental and soil health benefits, some cover crops may be used for grazing forage for livestock and wildlife.

Demonstration details

Fifteen Allamakee County producers participated in the Conservation Innovation Grant (CIG) On-Farm Soil Health Demonstration Trials in 2020, the first year of the grant. Most participants planted four interseeded 30-inch corn row plots and four 30-inch corn row plots with no interseeding. Each plot was at least the width of a combine and at least 300 feet long.

Producers planted a cover crop mix between corn rows at the V4-V7 corn growth stage, choosing from four different seed mixes, including species such as ryegrass, buckwheat, brassica and cow peas. Participants used various cover crop seeding methods: a no-till drill, broadcast spreader, Monosem planter and various custom air seeders.

Aarik Deering, farming near Postville, has been growing cover crops for five years. Besides soil health benefits, he uses cover crops to supplement feed for the cow-calf operation he manages with his wife, Haley.

“I’m trying the CIG trial to see if it will help extend the grazing period in fall and spring,” he says. “We typically can’t get enough cover crop growth in fall for grazing, and that often leads to being too short to graze in the spring.”

Brady Kruger farming with his dad near Waukon, sees the soil health benefits of cover crops and wants to get it right. “This trial provides a way to try to get early cover crop establishment and have it there when the corn is harvested,” he says. “We’ve only had sporadic success with fall cover crop growth until this year.”

Analyzing first year’s results

Farmers completed a minimum of four replicated strip trials on each demonstration site. Eric Novey, project coordinator for Allamakee SWCD, is working with farmers to collect data. He’s evaluating yields, cover crop biomass, nutrient uptake, soil microbiology, soil loss and several soil health measures using the Haney Test. Novey also installed temperature loggers in interseeded and non-interseeded rows with each participant to assess season-long differences in soil temperature.

A sampling of the first year's results:

Corn yields. Plots interseeded with cover crops yielded slightly better than plots with no cover crops (188 bushels per acre, compared to 187). Ten of the 15 participants produced better corn yields in fields with cover crops.

Cover crop biomass. Novey measured biomass monthly beginning in July and continued through September. Data collected indicates a sharp increase in biomass from July to August (400 pounds per acre to 525 pounds per acre) and then a slower rate of increase from August to September (550 pounds per acre).

Soil temperatures. Novey says cover crops kept soil temps more consistent during the growing season. “The seeded strips were slightly cooler in the summer, but what was more noticeable was the seeded strips had fewer extremes in temperature.”

One component that’s harder to measure is time. “Fall is such a busy time already,” says Kruger. “Interseeding cover crops early in the growing season takes weight off us when we’re trying to get crops out. It’s hard to find time to do other things in the fall.”

Trying 60-inch corn rows

NRCS allowed CIG participants to interseed up to 50 additional acres through the trial, so Kruger and Deering tried 60-inch-width corn rows with interseeding. Kruger planted 60-inch twin rows with the same population as his 30-inch rows. The growth difference was substantial.

“I enjoyed walking the 60-inch plot throughout the summer and seeing the difference and how cover crop species performed much better when given more sunlight,” Kruger says. “The corn yield came out to be the same as the rest of the farm, so I was pleased with that considering how dry August was.”

Deering was worried the interseeded cover crops would rob moisture from corn during grain fill but that didn't appear to be an issue. “I’m planning more 60-inch twin row corn for 2021 and will put a lot more effort into it. I feel there’s great potential,” he says.

Cover crop biomass samples taken between Kruger’s 60-inch corn rows totaled about 3,100 pounds compared to an average of 395 pounds of biomass in his 30-inch rows. Kruger feels the increased biomass on the 60-inch rows will provide better weed control, more nitrogen fixation and a bigger “bump” in soil health. He says he plans to no-till corn into the interseeded cover next spring and hopes to eliminate a herbicide pass based on the amount of ground cover and its ability to suppress early-season weeds.

Biomass from Deering’s 60-inch rows averaged 5,000 pounds compared to 854 pounds from his 30-inch rows. “I’m excited about the 60-inch-row biomass production and forage value it will offer our cattle this winter,” he says. “I’m really happy with corn yields on my 60-inch rows and found it comparable to my 30-inch rows.”

Sharing successes

Kruger enjoyed sharing ideas with other trial participants. He hosted a small field day to exchange ideas. “It’s been good to get together with other like-minded farmers. I’ve learned a lot already.”

Kruger says many producers commented on cover crop growth rates. “Early on, some of the species we thought failed came on later. Throughout the season, we saw different species rise and fall,” he says. For example, buckwheat was dominant very early on, and late in the year it seeded out and laid down. Later in the year, turnips and ryegrass really started to “pop.”

2021 on-farm trials

Producers were excited about first-year trial results, but the group also learned some lessons. “Farmers who opted to broadcast the cover crop seemed less satisfied,” Novey says. “They had issues with growth consistency and overall delayed growth, leading to less biomass.” He says for 2021, “We are considering looking harder at the 60-inch corn row option. That generated a lot of interest during our field days.”

Novey hopes the on-farm trial receives a similar strong response in years two and three. Participants signed up for just one year, but they can sign up for multiple years. “We are looking for participants for 2021,” he says. For more information about the CIG project, contact the Waukon NRCS office at 563-568-2246.

Authorized in the 2018 Farm Bill, On-Farm Conservation Innovation Trials support more widespread adoption of innovative approaches, practices and systems on working lands. On-Farm Trial projects feature collaboration between NRCS and partners to implement on-the-ground conservation activities and then evaluate their impact. Incentive payments are provided to producers to offset the risk of implementing innovative approaches.

Johnson is the state public affairs specialist for NRCS in Des Moines, Iowa.