AMES, Iowa – Iowa State University researchers have been awarded a $649,000 grant from the 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. Detritus input and removal treatments investigate the effects of plant litter and root inputs on the stability, accumulation, and chemical composition of soil organic matter.

Marshall McDaniel, Iowa State associate professor of agronomy, who will lead the DIRT component of the grant, said their purpose is to track how plant litter inputs over decades control the stability, accumulation, and chemical nature of soil organic matter.

“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,” he said.

Thought to be the first detritus input and removal treatment investigation of an agricultural system, the project is modeled on an international network of detritus input and removal treatments that started with forests, and now include grasslands, he said.

Joining McDaniel during the three-year study will be Alison Robertson, Iowa State professor of plant pathology; Mark Licht, Iowa State associate professor of agronomy; and Peter O’Brien, USDA Agricultural Research Service research agronomist.

Robertson said the first three years of a long-term study will focus on explaining how agricultural practices effect carbon cycling (the process in which carbon atoms continually travel from the atmosphere to the Earth, and then back into the atmosphere).

“We do not expect to measure any difference in soil carbon in this study,” she said. “The data will be used to inform future research, develop management recommendations for cover crops ahead of corn, and the data may inform policy.”

Robertson said the idea for the project came from several years of research on cover crops before corn.

“We have a hunch that cereal rye biomass plays a role in negative effects on corn, and this grant was the result of conversations,” she said. “The funding will be used to fund a graduate student, staff time, supplies and tests.”

Licht said, “As we had discussion, we realized that what we needed to understand better was whether cereal rye roots or shoots were responsible for the negative effect to corn,” he said. “Plus, we wanted to better understand if applying nitrogen could alleviate some of the challenges around nitrogen availability and disease incidence. It was really a progression of our previous work.”

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; 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. Robertson will lead these aspects of the study.

Licht said, “It’s our hope to understand whether it is the cereal rye roots or shoots causing the problems.

“We presume the cereal rye roots are ‘hosting’ the Pythium inoculum (from soil and infected plants) and likely, through the decomposing process, which immobilizes nitrogen,” he said. “But we don’t know what role the above-ground biomass plays in either process.”

In addition, he said, “We really want to hone in if there is a higher corn nitrogen demand following a cereal rye cover crop. Interestingly, in time, we’ll be able to look at how nitrogen dynamics change as the cereal rye cover crop becomes fully established within the system (no soil equilibrium is reached).”

Robertson said, “Rye is susceptible to the same Pythium pathogens as corn. So, when we plant rye, it can get infected by Pythium, so the populations increase above the background level.

“When the rye is terminated, the Pythium are released into the soil,” she added. “If corn is planted within 10 days, it is basically being planted into a petri dish of Pythium. After 7-10 days, the Pythium populations decrease to background levels if there is no host (corn). So, rye acts as a ‘green bridge’ by allowing Pythium populations to increase and pass over to corn.”

She said she, Licht and O’Brien will study this by killing the rye a few days before planting corn, and using molecular methods to monitor the Pythium populations in the soil, and rye and corn roots, as well as allelopathic chemicals (where one organism produces biochemicals that influence the growth, survival, development, and reproduction of other organisms).

“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,” she said.

“Some farmers have been very successful with cover crops,” she added. “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.”