Cereal rye can capture extra nitrogen in soil and reduce its loss through tile drainage. But some farmers, especially those new to cover crops, wonder how much cover crop biomass is needed without hurting yields.

As part of the University of Illinois’ virtual Agronomy Day, Lowell Gentry, agricultural research specialist in the College of Agricultural, Consumer and Environmental Sciences, shared results from a multiyear nitrogen and cover crop study on tiled fields.

“Can we grab the nitrogen that could be lost during the growing season and hold it in the cover crop?” Gentry asked.

Click here to view Gentry’s presentation and other Agronomy Day videos.

Gentry discussed cereal rye cover influence on corn and soybean crops on tiled fields. His study included different pre-planting termination dates and nitrogen applications. The biggest risk of a cereal rye cover crop is potential delay in planting, corn especially, Gentry said.

In one field study with 36 tiles, Gentry reported tile nitrate concentrations were reduced by more than 40% on soybean plots with a cereal rye cover crop compared to those with no cover crop. Yields across the field were 80 bushels per acre.

Gentry pointed out a 40% nitrogen loss reduction “is pretty close” to the 45% reduction goal of the statewide Nutrient Loss Reduction Strategy.

From other cornfield studies, Gentry determined the optimum biomass is a half of a ton per acre of cereal rye biomass. He explained cereal rye stems measuring 6 to 8 inches tall will produce that much biomass in a “decent stand.”

”This production (rate) doesn’t interfere with the subsequent corn crop,” Gentry added.

On another farm in the study, cereal rye biomass of 1.4 tons per acre preceded corn and “caused problems,” Gentry said.

A termination date study involved terminating cereal rye plots at four weeks, two weeks and the day before planting corn. The cornfield with the latest termination date suffered a 6% yield reduction, according to the researcher.

Gentry’s study included three nitrogen management practices: split applications in fall and spring, all spring preplant, and half at planting with the other half as an early side dress.

“We found it was best to frontload the nitrogen and have it all on in the spring,” Gentry said. “The fall nitrogen didn’t do as well, I think, because the cereal rye took up too much of it (nitrogen) and didn’t give it back.”

Cereal rye preceding a soybean crop gives farmers more flexibility with termination, Gentry reported.

One year, a cold spring prevented preplanting termination so the soybeans were planted into the growing cover crop, which was sprayed with Roundup after planting. At 2.7 tons of biomass per acre, the cereal rye “greatly reduced tile (nitrogen) concentrations to 1 part per million,” he said.

“Looks like there’s a magic number for corn production,” Gentry said summarizing results.

He recommended cereal rye of 0.5 ton per acre biomass with stems between 6 to 8 inches and a canopy of about 10 inches in height as optimum growth to terminate ahead of corn planting. Termination at least two weeks before planting corn is also recommended.

“There is a balance between cover biomass production and the potential for the cover crop to decrease plant available nitrogen, which can lead to delays in early corn growth,” Gentry said. “We believe with cereal rye ahead of soybeans, let it grow longer than ahead of corn, and greatly reduce tile nitrate concentrations.”