New USDA grant supports research to initiate Ag DIRT experiment, refine cover crop recommendations

June 6, 2023

Cereal rye biomass after termination between rows of growing corn crop. Photo by Barb McBreen. 

AMES, Iowa — A team of scientists led by Iowa State University has won a $649,000 grant from USDA’s National Institute for Food and Agriculture to study the intricacies of cereal rye cover crops.

One of the grant’s top objectives is to launch an innovative Ag DIRT (Detritus Input and Removal Treatments) study to quantify how biomass from cover crops impacts long-term soil carbon levels. Thought to be the first DIRT investigation of an agricultural system, the project is modeled on an international network of DIRT projects that started with forests and now include grasslands. Their purpose is to track how plant litter inputs over decades control the stability, accumulation and chemical nature of soil organic matter.

“This is an exciting project, but it represents just the beginning of work we hope to learn from over decades,” said Marshall McDaniel, associate professor of agronomy at Iowa State, who will lead the DIRT component of the grant. “It can take a long time to see significant changes in soil carbon, but we’ll also be looking for some potential changes in indicators of soil health that can show up more quickly.”

At field plots on Iowa State’s research farm property near Boone, Iowa, the project team will establish 24 test plots with three biomass treatments of cereal rye: roots only (below-ground); shoots only (above-ground stems and leaves); and roots and shoots, and compare them to a control plot without cover crops. The treatments will also compare the effects of varying nitrogen fertilizer rates.

These test plots will also be the setting to study the research grant’s other main objective – intensively exploring the interplay between the rye and corn to better understand why Iowa’s most popular cover crop poses an increased risk for yield drag in the next season’s corn crop.  

These aspects of the grant will be led by Alison Robertson, professor of plant pathology, entomology and microbiology and extension plant pathologist, working with Mark Licht, associate professor of agronomy and extension cropping systems specialist, and Peter O’Brien, research agronomist with the USDA Agricultural Research Service.

In several earlier projects funded by the Iowa Nutrient Research Center at Iowa State, Robertson, Licht and others found that roots of rye, a species related to corn, can provide a “green bridge” for pathogens like Pythium to cross and more easily infect corn. They also found rye roots exude allelopathic chemicals that discourage competition and can make corn seedlings more susceptible to disease.

Other possible reasons for yield drag they have been studying include:

  • Nitrogen immobilization, when soil microbes decomposing the rye compete with corn seedlings for available nitrogen.
  • Inadequate moisture, if the rye soaks up water the growing corn crop needs.
  • Shade-avoidance, where young corn plants are shaded by cover crop biomass still standing in the field.

The researchers have documented this mix of challenges and explored ways to reduce the related impact on yields, for example, by distancing the rye and corn in time (killing the rye at least 10 days of planting corn) or in space (physically distancing the rye and corn roots).

“This grant will support foundational research to help build a more complete understanding of cover crops’ influence on factors like disease, nutrient cycling and crop response for corn, in addition to cover crops’ potential contributions to long-term soil quality,” Robertson said.

“Some farmers have been very successful with cover crops,” she said. “They tend to be the ones who keep tweaking their practices. They know which tweak helped even if they don’t completely understand why. We want to understand the ‘why’ so we can make recommendations farmers can rely on.”

News Type: