Summer interseeding may be a good cover-crop strategy for shorter growing seasons. That’s the finding from a soil-health demonstration project in northern Iowa. Interseeding enables cover crops to grow and take root prior to corn canopy. After canopy the cover crop goes dormant due to being shaded. It then regrows after corn harvest.
Fifteen producers who struggled for years to consistently establish fall-seeded cover crops are working with the U.S. Department of Agriculture’s Natural Resources Conservation Service. They’re interseeding cover crops at the V4 to V7 corn-growth stage, which typically occurs in June in northern Iowa.
Most participants planted four interseeded 30-inch cornrow plots and four control 30-inch cornrow plots. Each plot was at least the width of a combine and at least 300 feet long.
Producers interseeded cover crops when corn was at the V4 toV7 growth stage. They chose from four different seed mixes composed of ryegrass, buckwheat, brassicas and cowpeas. The producers used various cover-crop seeding methods such as no-till, broadcast spreader, Monosem planter and custom air seeders.
Two participants also interseeded 60-inch cornrows through the trial. Brady Kruger of Waukon, Iowa, planted 60-inch twin rows at the same population as his 30-inch rows. The difference in growth was substantial, he said.
“I really enjoyed walking the 60-inch plot throughout the summer and seeing how cover-crop species performed much better when given more sunlight,” he said. “The corn yielded about the same as the rest of the farm so I was pleased considering how dry August was.”
Aarik Deering of Postville, Iowa, discovered that the interseeded cover crops didn’t rob moisture from corn during grain fill.
“I’m planning more 60-inch twin-row corn for 2021,” he said. “I feel there’s great potential there.”
Cover-crop biomass samples taken between the 60-inch cornrows outperformed the 30-inch rows by an average 3,400 pounds. The increased biomass will provide better weed control, more nitrogen fixation, and additional winter forage for cattle.
Farmers completed at least four replicated strip trials at each demonstration site. Eric Novey, project coordinator at the Allamakee Soil and Water Conservation District, is working with participants to collect data. He evaluates yields, crop biomass, nutrient uptake, soil microbiology, soil loss, soil temperature and several soil-health measures using the Haney Test, which allows producers to evaluate overall soil health. A sampling of Year 1 results are shared.
- Corn Yields – Plots interseeded with cover crops yielded slightly better than plots with no cover crops – 188 bushels per acre compared to 187 bushels. Ten of the 15 participants produced better corn yields in fields with cover crops.
- Cover Crop Biomass – Novey measured biomass in July, August and September. Data showed a sharp increase in biomass from July to August – 400 pounds per acre to 525 pounds per acre and a slower rate of increase from August to September – 550 pounds per acre.
- Soil Temperatures – Cover crops kept soil temperatures more consistent during the growing season. The seeded strips were slightly cooler in the summer, but what was more noticeable was they had fewer temperature extremes, according to Novey.
The trials revealed not all seeding methods provided equal results.
“Farmers who broadcast the cover crop seemed less satisfied,” he said. “They had issues with growth consistency and overall delayed growth, leading to less biomass.”
The USDA awarded the Allamakee Soil and Water Conservation District a three-year, $236,000 Conservation Innovation Grant to lead, manage and analyze a series of field-based trials.
Jason Johnson is a public-affairs specialist with the U.S. Department of Agriculture's Natural Resources Conservation Service in Des Moines, Iowa. Contact Jason.firstname.lastname@example.org for more information.