Cover crops are a valuable tool for farmers to reduce nutrient loss and help ensure clean water in Iowa waterways. But some farmers have reported that planting winter rye as a cover crop may reduce corn yield. A team of researchers at Iowa State University is investigating why there may be an occasional decrease in corn yield after planting winter rye.
“We want farmers to understand any risks involved before they plant cover crops,” says Alison Robertson, associate professor in plant pathology and microbiology. “If there appears to be a downside to this practice, we want to understand it more fully and hopefully develop management practices to reduce the risks.”
Robertson leads a group of ISU faculty and USDA scientists, including Tom Kaspar, Matt Bakker and Andy Lenssen, on a project funded by the Iowa Nutrient Research Center at ISU. It’s one of 31 projects funded by the center since 2013.
1. Cover crops can help reduce nitrate loss from fields
Cover crop research shows the potential for their use in nutrient management. Studies in Iowa have found that planting a cover crop of winter rye can reduce nitrate loss by 15% to 55% depending on location, year and amount of cover crop growth. Cover crops are encouraged as a good conservation practice on Iowa farms.
Winter rye is the most common cover crop in Iowa due to its low cost, fast growth, winter hardiness and ability to reduce nitrate concentration in drainage water.
2. Long-term cover crop users don’t seem to have yield problem
Cover crops have many benefits when grown on the field between harvest and planting the next crop. “Not only do they manage nitrogen, they also improve soil health by reducing erosion, enhancing soil structure and increasing soil organic matter,” says Robertson. However, she adds, the potential for occasional corn yield loss following a winter rye cover crop could make farmers hesitant to adopt the practice.
Tom Kaspar, a USDA scientist and collaborating professor in agronomy, notes that long-term cover crop users do not appear to have problems with reduced yield. He says poor planter performance and reduced early season nitrogen availability are possibilities for the yield reduction. “If we understand that this potential problem exists, we can manage or avoid it and release the true potential of cover crops,” Kaspar says.
3. Another possible cause for corn yield loss is root rot disease
Robertson says another possible cause of corn yield reductions may be stand loss due to soilborne pathogens that can cause seedling diseases. If the soil is cool and wet, these seedling diseases can result in root rot that may lead to seedling death or corn plants with reduced growth. Research shows rye is a host for root-rot pathogens that could also infect young corn plants. ISU scientists hypothesize that when the winter rye cover crop is terminated, these root rot pathogens may then infect young corn plants, if conditions are favorable for disease.
In a combination of greenhouse and field trials, Robertson and research associate Jyotsna Acharya found that corn emergence and early growth was significantly reduced when planted after winter rye particularly when rye was terminated within 14 days of planting corn. They found that the shorter the time period between terminating the cover crop and planting the corn crop, the higher the likelihood of seedling disease. Additionally, the roots of the young corn plants showed evidence of root rot.
4. Use alternative practices to reduce seedling disease factors
“Our next steps will be to determine the effect of other production practices such as starter fertilizer applications, banded herbicide application to terminate cover crops and modified planting procedures on the risk of seedling disease after rye cover crops. This year, in our 2016 field experiments, we also will be examining the use of a different cover crop, camelina, in corn and soybean rotations,” Acharya says.
The research also indicated that in some cases, alternative management practices to limit seedling disease may be required by farmers to reap the full benefits of cover crops. These can include selecting corn hybrids with better disease resistance or tolerance, alternative cover crop species and precise planting to maintain separation between rye plants and corn rows to manage the potential risk of disease.
Robertson says a better understanding of using winter rye before corn production in a field will lead to improved management practices to ensure the optimum use of cover crops for environmental and crop production benefits.
A better understanding of the problem, thanks to ISU research
The Iowa Nutrient Research Center has funded 31 research projects conducted by scientists at ISU, University of Iowa and University of Northern Iowa since its establishment in 2013 by the Iowa Board of Regents in response to legislation passed by the Iowa Legislature and signed by Gov. Terry Branstad. The center, administered by ISU, is meeting the need for continued research and innovation to address Iowa’s water quality concerns.
The center supports research to evaluate the performance of current and emerging nutrient management practices, providing recommendations on implementing the practices and developing new practices. The center’s director is John Lawrence, associate dean for Extension in ISU’s College of Agriculture & Life Sciences and director of ISU Ag and Natural Resources Extension.