AMES, Iowa — A poster by Iowa State University graduate student Ally Larson recently won top honors from the Midwest Cover Crop Council at its annual meeting in Mankato, Minnesota.
The poster presents findings from the first year of the Agricultural DIRT (Detritus Input and Removal Treatments) study, looking at how above- and below-ground plant inputs from cover crops affect soils and nearby cash crops.
Larson, from northern Iowa, is working on a master’s in crop physiology and soil science. At Iowa State’s research farm near Boone, she helped establish 288 30x40-inch test plots, half planted to corn and half to soybeans, where biomass levels were compared after three cereal rye treatments (and a control plot without cover crop):
- roots only (below-ground);
- shoots only (above-ground stems and leaves);
- and roots and shoots.
The rye was harvested and spread on top of the plots. In addition, the roots-only and shoots-only treatments had small mesh bags in their respective plots filled with greenhouse-grown rye raised with different levels of fertilization. These were retrieved weekly over the growing season to test for decomposition.
“At the end of the summer, our initial findings were that the biomass levels and decomposition rates were the same for both treatments, even with clear differences in soil moisture and temperature between the plots,” Larson said. “That was interesting and not what we expected.”
The DIRT team’s next steps are to better understand their findings. They plan to conduct similar treatments this summer and next year to learn more.
This part of the project, assessing cover crops’ potential contributions to long-term soil quality, is led by Marshall McDaniel, associate professor of agronomy at Iowa State, one of Larson's advisors. He credits Larson's important contributions to the project.
"She's very hard-working,” he said. “She started in our lab as an undergraduate and, over time, has really been taking on a leadership role."
A unique aspect of the project they are developing is a soil “dendrogram.” This involves taking deep soil cores and using them to map and visualize the soils in new ways. Larson plans to incorporate this component into her master’s thesis.
“I hope I will have a chance to be involved in revisiting the cores over time to build on what we can learn from them,” she said.
Their work connects to a network of international DIRT studies in forests and grasslands tracking how plant litter inputs over decades affect the stability and chemical nature of soil organic matter and carbon levels. Iowa State’s investigation is thought to be the first DIRT study focused on cropping systems.
“The opportunity to be involved in a project that combines lab work, field work, writing -- and problem-solving -- is the reason I decided to stay at Iowa State for graduate school. It’s been a good decision,” said Larson, who studied agronomy as an undergraduate student.
Other researchers on the DIRT project are Mark Licht, associate professor of agronomy and extension cropping systems specialist; Alison Robertson, professor of plant pathology, entomology and microbiology and an extension plant pathologist; and Peter O’Brien, research agronomist with the USDA Agricultural Research Service. Funding has come from USDA’s National Institute for Food and Agriculture and the Iowa Nutrient Research Center.
Contacts:
Ally Larson, aclarson@iastate.edu
Marshall McDaniel, Agronomy, 515-294-7947, marsh@iastate.edu