Growing more from every acre

Iowa farmers explore relay cropping to improve soil health, diversify production.

Maximizing financial and environmental re­­turns in a cereal rye and soybean relay-cropping system comes down to fine-tuning management details, such as planting longer-maturity soybeans, seeding rye early in October and harvesting the grain before summer heat sets in, according to farmers and agronomists who are testing the system.

Relay intercropping - the planting of soybeans into a growing cereal grain in the spring - allows farmers to harvest two cash crops from a single field in one growing season.

While fall-seeded cereal rye maintains living roots during the winter to anchor soil and scavenge leftover nutrients, spring-planted soybeans grow underneath the rye canopy. After the rye is harvested in July, soybeans flourish with additional sunlight until reaching maturity in the fall.

Multiyear field trials conducted separately by Iowa State University (ISU) and the Iowa Soybean Association (ISA) demonstrate that while relay-cropping systems require precise management, the financial and environmental benefits can be significant for Midwest operations.

Managing two crops separately

Lucas DeBruin, a Mahaska County Farm Bureau member, says executing a relay system requires treating each crop as an independent enterprise despite sharing the same footprint.

"You've got two crops in one field, but you're still managing them separately," said DeBruin, who is part of a three-year ISA study. "So as individual crops, you're still following all the recommendations for fertility or fungicide timing wise."

DeBruin plants 70 pounds of rye per acre in his relay system. Soybeans are planted as early as possible in the spring at a rate of 140,000 plants per acre, and he applies about 40 pounds of nitrogen per acre at the same time. "Most of the time, you will see a ding (on soybean yields). The rye yield makes up the difference (financially) plus some," DeBruin said.

To cut overhead, DeBruin cleans his harvested rye seed to reuse across his farm's cover crop acres. Rather than purchasing commercial equipment, he retrofitted an old combine into a stationary seed cleaner. "We kind of made a homemade seed cleaner," DeBruin said. "It's not perfect, but it's good enough for what we need and cheaper."

PICTURED ABOVE: An aerial view of DeBruin's cereal rye and soybean relay-cropping field near Oskaloosa. PHOTO / CONRAD SCHMIDT

Maturity group and seeding rates

Data from ISU research trials led by Mark Licht, ISU associate professor and Extension cropping systems specialist, highlight specific management tweaks that can mitigate soybean yield drag in relay cropping systems.

According to the study, planting a longer soybean relative maturity group resulted in significantly higher soybean yields across three of four site-years. For every full maturity point increase, soybean yield losses were reduced by 0.8 bushel per acre.

Field data also indicate that higher soybean seeding rates pay off in a relay environment.

ISU's targeted soybean population of 120,000 seeds per acre consistently outyielded the lower rate of 90,000 seeds per acre. Additionally, maintaining soybean row spacing at 30 inches or wider provides critical clearance for combine tires during summer rye harvest, preventing crop trampling.

For the cereal rye phase, early planting in October produced higher grain yields than late October or early November seedings. Lower rye seeding rates of 25 to 50 pounds per acre proved sufficient when established early, allowing farmers to keep initial input costs low.

Navigating moisture, harvest

Relay cropping isn't without risk. Be­cause the two crops draw from the same soil profile simultaneously early in the season, water availability remains the primary limiting factor, according to researchers.

In dry years, soybean yields can drop noticeably. Timely rye removal is crucial.

"Our first year it did not rain in August," which drove down soybean yields, DeBruin said.

ISA trial metrics show that every day after July 1 that rye harvest is delayed, developing soybeans suffer an additional yield loss.

Draper combine heads are recommended to neatly clip rye heads above the soybean canopy.

Despite seasonal moisture risks, farmers report long-term soil benefits, including faster water infiltration after heavy rainfall events and improved field trafficability in the spring.