Purdue tests effects of perennial cover crops on soil health and corn production

“This added ecological complexity, combined with biological nitrogen fixation, presents a unique opportunity to enhance soil carbon accumulation by fostering stronger plant-microbe interactions,” Rui said.

Rui’s collaborators on the project are Sylvie Brouder, the Wickersham Chair of Excellence in Agricultural Research and professor of agronomy; Jeffrey Volenec, professor of agronomy; and Pratishtha Poudel, assistant professor of agronomy. The researchers conduct their experiments at the Water Quality Field Station (WQFS) located at Purdue’s Agronomy Center for Research and Education.   

The new NIFA study adds a soil health dimension to a variety of ongoing tests at the field station. These include greenhouse gas and water quality studies involving corn, both with and without Kura clover for comparison. Also underway: trials related to grasses used in bioenergy production and restored prairie systems.

Purdue launched the field station in 1992 with USDA funding. Since then, it has been used to track the movement of pesticides, nutrients, and hormones and antibiotics from manure into lakes, streams and rivers. The field station’s subsurface drainage system and special instrumentation facilitates these critical research activities.

“The environmental performance of the Kura clover system has yet to be fully understood,” Volenec said. Preliminary data suggests that planting corn into this sod of clover improves the system’s water quality. Greenhouse gas emissions, which the WQFS also monitors, are another focal point since they contribute to climate change.

The dynamics and outcomes of soil carbon are a novel focus for researchers studying Kura clover. Soils globally store about 1,550 gigatons of soil carbon to a depth of 1 meter. “That’s more carbon in the soil than carbon in global vegetation and the atmosphere put together,” Rui said. Carbon in the soil means more soil organic matter, better soil health and more nutrients to support crop production.

Somewhere between one-third and one-half of Midwestern soil carbon has been lost to the atmosphere since intensive farming began in the 1850s, Rui said. Before then, prairie plants covered the ground year-round, performing photosynthesis, fixing carbon from the air and forming dense root systems firmly linked to soil microbes.

Modern corn crop root systems are shallow and less robust because they have access to abundant water and synthetic nitrogen at the surface. This also loosens the link between corn roots and soil microbes, reducing the latter’s ability to pump carbon into the soil where it becomes a stable source of organic matter. Kura clover may reverse the process while also reducing erosion and retaining moisture.

Like alfalfa and wheat, Kura clover originated in the Caucasus Mountains that run between Europe and Asia. “This is a spreading clover,” Brouder said. It dies back in the summer heat, then regrows in the fall to serve as a winter cover crop. “You don’t have to plant the cover crop. It’s just there, and then in the spring, you whack it back and plant your corn.”

Kura clover produces aggressively growing underground runners that aid the plant’s ability to adapt and thrive, even as it withers above ground. “But the leaf tissue that you’ve killed will fall on the soil and decompose, and that nitrogen will be available to the corn crop,” Brouder said.

It sounds simple in theory. But putting the system into practice comes with some complex logistical and management issues. Kura clover seed is difficult to obtain. “Like a weed, it competes with the corn for water, nutrients and light if not managed properly,” Volenec said. Farmers would need to learn new procedures. And even the clover’s response to varying herbicide regimes comprises a study in itself at the field station.

“That’s all going to have to be figured out before anybody tries this at scale,” Brouder said.