Cover crops are really being tested. Not only are farmers interested in how to incorporate cover crops into their cropping rotations, but University of Nebraska researchers also are looking at cover crops and trying to help producers find out where they fit.

Planting more than 70 different cover crops at different sites across Nebraska, with different planting times, in corn and soybean cropping systems is an extensive undertaking. Katja Koehler-Cole, Nebraska Extension statewide soil health educator, told attendees at a recent online Forage Field Day sponsored by the University of Nebraska-Lincoln and the South Dakota State University Extension that the selection of cover crop varieties can be a difficult task for many farmers.

“It depends on your goals and planting window,” she said. “We always want the crop to germinate fast and emerge fast, so in these studies we looked at stand count, percentage of cover three weeks after planting, forage quantity, forage quality and nitrogen fixation.”

When it comes to cover crops, summer annuals are not the ones producers hear about most often, but there are distinct advantages to planting summer annuals as cover crops, Koehler-Cole said. Two specific research sites at an irrigated location at Green Cover near Bladen, Neb., and a dryland location at UNL Rogers Memorial Farm near Lincoln studied summer annuals last season.

Related:My first attempt at cover crops

Why summer annuals?

“Planted as a full-season cover crop or after wheat, for instance, summer annuals need the heat of summer,” Koehler-Cole said. “They provide a lot of benefits and are really productive. They can provide soil health, [and] they work in situations where producers can’t get into the field because of excess moisture or for pivot corners. These are great places for summer annuals as a cover crop.”

Summer annual cover crops were planted May 24 at the Bladen site and July 9 at the Lincoln site and lasted through October, terminated by a hard freeze. Species included sorghum-sudan, millets, teff, buckwheat, sudangrass, grazing popcorn, sunnhemp, cowpea, sunflower, African cabbage and mixtures of several species.

CROP PLOTS: These cover crop demonstration plots at Husker Harvest Days were planted in cooperation with Green Cover, based in Bladen, Neb. The popular plots at the show are just another signal that cover crops are growing and expanding in the state, also highlighted by recent research on summer annuals conducted at Green Cover and at UNL Rogers Memorial Farm near Lincoln.

At the irrigated Bladen site, 80 pounds of nitrogen were applied preplant. After three weeks, some species of cover crops canopied over 25% of the ground. Others that didn’t provide ground cover had greater weed biomass when they took samples eight and 20 weeks after planting. On this site, the sorghum-sudan yielded 20 tons of biomass per acre by fall. This same cover offered quality crude protein ratings. Pearl millet was another outstanding species, with crude protein at 10% to 11%. Legumes in this location also were of good quality but obviously produced less biomass.

Related:Cover crop tips from farmers, researchers

“We know that many of these species, especially sorghums and sudangrass, can have high nitrate levels,” Koehler-Cole said. “We tested nitrates on July 18, and the nitrate levels were all safe in all treatments. We did not test for prussic acid.”

Dryland site

At the Rogers Memorial Farm, the cover crops were rainfed with no applied nitrogen to the plots. “The cover crops were planted into wheat stubble with a drill, and we measured them eight weeks after planting and at the end of the season,” Koehler-Cole said. “It was a dry summer in 2023, and the covers were not as dense or lush. The whole season, we only had 2 inches of rainfall.”

Looking at the dry matter and biomass, the cover crops still produced more than 1 ton per acre on most of the treatments.

From studies like this, researchers can offer guidance on the planting of summer annuals as cover crops. “Many cover crops can be successfully established,” Koehler-Cole said, “but species differences do exist.” That’s why on-farm, peer-to-peer efforts comprised of small groups of producers work well in helping to establish management strategies that work in specific areas.

“The goal is to have living plants in the ground year-round,” she said. “Having farmers involved in these studies makes the results more relatable.”