Shalamar Armstrong has spoken at a number of meetings about cover crops this past year. The Purdue University agronomist says he’s always excited to talk about the potential benefits of cover crops. But he can count on getting one question at almost every meeting.

“Someone always wants to know when they will get the nitrogen back that cover crops scavenge and save from loss through tile lines,” he says.

NITROGEN PAYBACK: Purdue agronomist Shalamar Armstrong says farmers always want to know when cover crop residue will break down and release nitrogen back to the crop.

Eileen Kladivko, also a Purdue agronomist, has conducted cover crop research for the past several seasons. She has noted previously that you likely don’t get all of the nitrogen back early in the season. Nitrogen is tied up in the cover crop residue and is released as the residue breaks down over time. However, there isn’t solid research data on when N is released and available for use by growing crops, she notes.

“It appears to be an education and information gap,” Armstrong says. “So we’ve set up a study to try to focus in on answering that question.”

The study, underway at the Purdue Agronomic Center for Research and Education, consists of different cover crops, crop rotations and tillage systems, he says. The work is partially funded by the Indiana Corn Marketing Council, with help from USDA.

“We’re looking at hairy vetch, cereal rye and combinations of these two species, with a control with no cover crops,” Armstrong says. “One reason we chose them is because they are very different species.”

Hairy vetch is a legume that can fix nitrogen from the air and release it to the next crop for use. The education gap is in knowing exactly when and how this release happens, Armstrong notes.

Cereal rye is very aggressive. “It can produce lots of growth above- and belowground, and it is very good at scavenging N in the fall and spring,” he adds.

The overall goal of the study is to examine when N is released from various cover crop residues, and compare that timing to when modern corn hybrids need N the most during the season, he concludes.