On a hot, dry, and extremely windy day in early June, Neal Hentzen surveys the dryland field on the edge of Seward where his corn is ankle high. The leaves on the plants whip in the wind like green streamers running in long, straight rows from the road to a faraway fencepost. Hentzen is semi-retired, but he still farms this field and one other, 160 acres in all. In the distance, a tractor slowly rolls down the rows pulling a blue piece of equipment. The device is gently breaking the soil between the rows of corn and depositing a multi-variety cover crop mixture.
“I’ve been farming around here for 50 years,” Hentzen says. “When I heard about this research project with cover crops, I thought, why not give it a try?’”
Hentzen is one of 11 producers in the Upper Big Blue Natural Resources District participating in an on-farm research study that looks at the many effects of interseeding cover crops into standing corn at an early stage of development. The study is a collaboration between the NRD, Nebraska Extension, and The Nature Conservancy.
Hentzen has used cover crops for many years in his seed corn, planting once the male rows were destroyed. He experimented with using different planting methods and seed varieties to find the best outcomes for winter grazing cattle and reducing soil compaction in his fields. This year he is growing commercial corn and is eager to see how interseeding the cover crops (a method he has not used before) will change the operation. “It will be an experiment. Since they were providing the equipment and were going to plant it for me, I thought I would see if it would work. If it does, I will probably do it again,” he said.
Cover cropping has numerous benefits, from preserving soil moisture and decreasing flooding, to adding carbon and other nutrients to the soil ecosystem, to preventing nitrogen leaching to the groundwater supply. Many previous studies have established the value of cover crops. This new study will look specifically at timing. How does planting the cover crop into an immature growing crop, as opposed to a newly harvested field, impact the system?
It’s an important question, as farmers who are interested in introducing cover cropping may struggle to do so in the fall. There is a small window of time between harvest and when the soil is too cold for plants to get established. Interseeding the cover crop in late spring or early summer extends the window of opportunity.
Even in spring, the timing is tricky. Plant the cover crop too early and it will crowd out the cash crop. Too late and it will not have sufficient time to get established before the canopy of the corn leaves block out the sunlight. The best time to do it is between corn growth stages V4 and V6, when the plant is about four inches high, the study organizers predict.
NRD Water Conservationist Dan Leininger is behind the wheel of the tractor in Hentzen’s field. A farmer himself, Leininger is at home in the cab as he slowly steers the machine between the rows of green, planting the cover crop in eight row strips. Leininger is the resident cover crop evangelist at the NRD; for the past four years he has maintained the Project GROW demonstration fields in York, where cover crops are an essential component of restoring soil health.
“What I wish more farmers understood about cover crops is that they’re not going to rob your cash crop of water and nutrients. The cover crops lock up leftover nitrogen [during its fall and spring growth] in the above ground biomass, which is going to be available for next year’s crop,” Leininger explains over the rumble of the tractor’s engine. “This system keeps any residual nitrogen from leaching into the underground aquifer,”—an important consideration, as many rural Nebraskans are exposed to the health risks associated with increased nitrate in their drinking water as a result of incomplete plant uptake of nitrogen fertilizer.
The cover crops Leininger is planting today will emerge in the next two weeks then will lie dormant for a time when the canopy of the corn closes over them. When the corn reaches senescence in the fall and the leaves dry out, the cover crop will spring back to life and continue to grow, protecting the soil when the cash crop has been harvested.
For this research project, cooperating producers were given the choice between two cover crop mixes: a legume mix to add nitrogen to the soil and a diversity mix better for grazing, increasing biodiversity, and building organic matter and activity.
Hentzen’s is the second field Leininger has planted so far for the research project. “That field we planted near Beaver Crossing yesterday had had some cover crops on it over the winter, so that planting was really different. The ground was a lot softer,” he says, noting how the roots of the cover crops keep the soil loose and porous. At the end of the row, Leininger swings wide, skipping eight rows before starting down another stretch of the field. This is intentional, as the alternating sections of cover crops provide a control group in the experiment, giving side-by-side verification of the practice’s effectiveness. The process will be repeated in this field for the next three years.
According to Steve Melvin, UNL extension educator based in Hamilton and Merrick Counties, the three-year period will even out weather variations from one growing season to the next and will provide more reliable data than a one-year snapshot approach. Data on soil health and yield will be analyzed and reported annually through UNL’s On-Farm Research Network publications and events as well as through the NRD, but the overall effectiveness of the project won’t be known until after harvest in 2022. In future years of the project, they may expand to interseed cover crops into soybeans as well.
Nelson Winkel, soil health specialist with The Nature Conservancy, describes how the project came to be. “When we start a new project, we’re always looking for ways to amplify the good work of others already underway. When we learned from the Upper Big Blue NRD and UNL that farmers in the area were starting to experiment with interseeding, we knew there was a great project waiting to be funded.” In collaboration with Kellogg’s Company and a pending grant from The Nebraska Environmental Trust, The Nature Conservancy purchased the project’s interseeder drill and will cover the costs of soil and plant tissue analysis.
“We are a science-based organization, and to make the science do its best work we put farmers at the center of our projects. When a farmer tells us that they’re experimenting with soil health, we ask them ‘what are you doing, what’s working, how can we get you the information you need to further assess the practice?’” Winkel adds. “Working with the NRD and UNL to deliver that science to farmers has been a great experience so far.”
Melvin is also pleased with the research collaboration between the three agencies. “I’ve heard from a lot of farmers in the last few years that they are interested in trying cover crops but find it difficult to get them planted in a timely manner in the fall after harvest. This project is a good coming together of these three different groups, working together to test this idea,” he said. More than yield data or soil health breakdowns, Melvin says the first year of this project is about one question: will this work in Nebraska?
“There are a lot of questions about the practicality of interseeding and a lot of things we will measure, but we are looking at the big picture, a systems approach. How can we make cover crops work in the Nebraska corn/soybean cropping system? Is this the right time and method for cover crops?”
Time will tell.