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Research Highlights

Research Highlights
What Crop Management Practices Alleviate Iron Deficiency Chlorosis?

Soybean plant showing symptoms of IDC. Photo: Mary Love Tagert

By Laura Temple

Soybeans need iron to make chlorophyll for photosynthesis. In soils high in calcium carbonate and pH, many soybean varieties struggle to take up iron. This problem, known as iron deficiency chlorosis (IDC), shows up as interveinal yellowing of young leaves. 

“Variety selection has typically been the primary way to manage IDC,” says Mary Love Tagert, associate professor for the Mississippi State University Extension Service. “Research and observation has noted other management factors that have helped alleviate IDC symptoms, but they haven’t been evaluated together.”

The Mississippi Soybean Promotion Board checkoff has been funding a research study led by Tagert to do just that. Since 2019, she has been comparing seven cropping systems using different combinations of management practices to learn what helps reduce the impact of IDC. 

“Our plot study looks at these systems with both tolerant and susceptible varieties,” she explains. “We plant six different varieties within each management system, three with tolerance and three that are susceptible to IDC.”

Crop System Comparisons

The seven cropping systems in Tagert’s trials incorporate various combinations of crop rotations, oat cover crops, higher seeding rates, and compaction with a roller packer. 

“Some research has found that growing oats as a companion crop with soybeans can reduce IDC symptoms,” she says. “The thought is that their use of nitrogen in the soil helps soybeans better access iron. However, a companion crop isn’t practical to manage in our cropping systems.”

Instead, some systems in these trials use oats as a cover crop planted between mid-October and early November. The cover crop is terminated two to three weeks before planting soybeans. 

Compaction is usually considered a problem for soils, but Tagert says IDC may be an exception. “In some fields with IDC symptoms, locations of tire tracks are clearly visible due to greener soybeans,” she explains. “That may be because compaction causes soil nitrates to break down faster, making iron more available to the crop.”

Crop rotations compare soybeans following corn to continuous soybean systems. The higher seeding rate is about 33 percent higher than average recommended planting rates in Mississippi.

During the growing season, the research team took visual ratings of IDC symptoms in each plot on a scale of 0 to 10, with 0 indicating no symptoms and 10 identifying extremely chlorotic plants. They also took chlorophyll ratings to better quantify the visual ratings. Though crop ratings for each system showed no statistically significant differences across the years, the different cropping systems produced significant differences in yield. This work is helping to develop some recommendations for IDC beyond variety selection.

“After three years of trials, overall the best system for managing IDC appears to be crop rotation with soybeans following corn with a high seed population,” Tagert says. “This system has yielded the best, followed by the system of soybeans at the high seeding rate following corn with oat cover crop.”

She notes that her team is analyzing bulk density soil samples, especially from the systems using compaction. These samples will verify if the roller packer actually created compaction similar to tractors.

Soil Moisture

“We are also looking closely at the impact of soil moisture,” Tagert continues. “In the upper Midwest, moisture appears to make IDC symptoms worse, and as soils dry out, soybeans improve. But, in the Southeast, our producers have noted that dry soils seem to make IDC symptoms worse.”

Letters represent statistical significance – groups that do not share letters are statistically different from each other.

Farmers have observed that irrigating soybeans with IDC can improve symptoms. Her team has collected soil moisture data for two years. Preliminary data shows that when comparing season average soil moisture and visual ratings across cropping systems, higher soil moisture resulted in higher visual IDC ratings.

Tagert notes that the systems rotating with corn and those with an oat cover crop have stayed drier throughout the growing season. Those systems also had higher yields. Another year of the plot-scale study will be conducted in 2022 to see if those trends hold true for a third year.

Management Decision Support

The main goal of this research is to help farmers make more informed decisions to manage IDC. Many fields just have spots that are prone to IDC and need a tolerant variety. But the IDC-tolerant soybean varieties may not be the best yielding variety for the remainder of the field.

“In these cases, management practices may allow farmers to better manage those problem spots, while using the best variety for the field as a whole,” Tagert says. “We are gathering additional data to allow farmers to use precision management for IDC.”

Drone imagery of trial plots provided vegetative indices for soybean growth. Tagert’s team is trying to correlate this data with soil electrical conductivity maps, to see if they can identify and predict zones likely to experience IDC. This would allow farmers to develop management zones for IDC that are likely to stay the same every year.

“In 2022, we plan to expand this research to work with a farmer and apply our plot-level observations and precision work at the field level,” she adds. “Precision planting and management of IDC-affected areas of the field could improve overall yield and profitability.”

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.