Ten southern states cooperate to test top performing cover crops through the Southern Cover Crop Variety Trial. A unique cover crop variety trial started at University of Tennessee in 2019 joined with the Southern Cover Crops Council in 2022 expanded cover crop data over a broader region, combining university research with industry input to put cover crop varieties to the test in unique growing environments. 

“We trial whatever industry wants to plant,” said coordinator Virginia Sykes, University of Tennessee. “Every year we send out a call for entries, the same as we do for our corn and our soybean variety trials. And whatever industry is interested in trialing, that's what we trial. The good thing about it is we can always provide information that is highly relevant to our producers.” 

Cereals, brassicas and legumes were tested on the basis of establishment, weed cover, biomass and nitrogen release to help guide farmers into finding the best cover crop fit. Varieties enrolled in the trial typically follow trends in industry, with noticeable changes from 2023 to 2024. 

“The varieties we evaluate change from year to year. Overall, 10 of the 20 cover crop varieties evaluated were the same across the last two years,” Sykes said. 

In 2024, the rise of oat varieties followed a drop in brassicas, with just one radish put to the test this year. Despite changes in region and growing conditions, varietal performance in the trial remained consistent for some stand-out entries.  

Related:Consider spring-planted cover crops

Best for biomass  

For testing purposes, cover crops in the multi-state trial are treated exactly the way farmers would be utilizing the seed in the field, with an eye toward performance ahead of cash crops. 

“Typically for cover crops, we're not going to fertilize them in the fall, because our goal is for this to be a cover crop, not a secondary crop,” Sykes said. “The last two years we've also provided information on forage quality for some locations. And so, we do have additional information on crude protein, total dry matter digestibility. But our primary goal for this is just to see how much biomass we would get, pre-soybean and pre-corn.” 

Checking biomass results is relatively simple, but the benefits of regional knowledge of biomass performance, especially in relation to growing conditions, can help farmers make educated selection decisions. 

“We do two biomass ratings where we measure how much cover crop is out there in the field at those two time points, pre-soybean and pre-corn,” Sykes said. “Because typically, the more biomass you have, the more benefits you're going to get from cover crops.” 

While two varieties of cereal rye – FL405 and FL406 – topped the biomass scale at over 9,000 pounds per acre, Sykes said the trial produced a wide variation in biomass from location to location.  

“I think that's important, because our producers in Tennessee might be looking at data out of North Carolina and thinking, ‘Oh, I can get 10,000 pounds per acre of biomass,’ and that might not be something that's as feasible in our region,” Sykes said. “The regional information is good for seeing how much this biomass actually varies from location to location.” 

Next level nitrogen  

In addition to biomass, the Southern Cover Crops Variety Trial also focuses on released nitrogen. AU Easy Cover Vetch topped the nitrogen category with an estimated 75 pounds per acre of nitrogen released. FIXatioN Balansa Clover was a close second with 60 pounds per acre. 

Marking an area for biomass sampling on site at the University of Tennessee cover crop trial plots. (Photo by Virginia Sykes)

“The past two years, we also evaluated some of the varieties for forage value and nitrogen release, with funding from the Tennessee Corn Promotion Board” Sykes said. “We will take that biomass, dry it down, run it through the near infrared spectroscopy and that's what gives us the forage nutrient values, including nitrogen content.” 

In addition to the basic forage nutrient evaluation, techniques used by the Southern Cover Crop Variety Trial can help pinpoint just how much nitrogen a cover crop will leave behind. 

 “We can input those nutrient values, along with location and termination date, in the precision sustainable agriculture nitrogen calculator,” Sykes said. “That's going to give us a more precise estimate of how much nitrogen you would expect from the cover crop to go to the subsequent cash crop.” 

New for 2025  

Planting dates for the Southern Cover Crop Variety Trial begin in mid-October. The 2025 varieties have already been planted for next year’s results. Sykes said the distribution of the trial shifted to include more brassicas again this year, as well as including two completely new entrants – ervil and carinata.  

Sykes said ervil, also known as bitter vetch, is a completely new species to the trial and carinata is typically studied for seed production rather than biomass, so it will be interesting to see how each performs.  

Overwhelmingly, Sykes said the trial studies find that selecting both a quality species and variety makes a difference for cover crop quality. The finite details explored in the test can help farmers navigate the selection process. To read the full report visit https://search.utcrops.com/cover-crops. 

“The surprising thing was that in a lot of regions, many of the top performing species and varieties were the same, where I expected there would be more variation in what did best regionally,” Sykes said. “The exception to this was in the clovers, which did show a lot of variation from state to state and between termination timings. This also changes from year to year, with less consistency across locations in 2024 compared to 2023.”  

Variety continuity over time, as well as continued participation in the project can help researchers get a clearer picture of cover crops and their capacity to change crop productivity over time.  

“Continuing this trial will give us a much clearer picture of what does best regionally,” Sykes said. “This has really been a highly collaborative effort that wouldn’t be possible without support from scientists across the South, putting in the work of planting and evaluating these trials each year, and from our industry partners who enter their varieties into the trial.”