A few years back, before farmers intensified their interest in cover crops, picking species and varieties offered few challenges.
Options were limited.
"As cover crops became more prevalent, so did more species and varieties," said Virginia Sykes, assistant professor, plant sciences, University of Tennessee Institute of Agriculture, during a virtual Milan No-Till Field Day presentation July 23.
Species and varieties make a difference in biomass and cover, Sykes said. She's conducting field trials in three locations across Tennessee to determine the best options among cereals, legumes and brassicas. Each, she said, has a place in a cover crop mix, but selection depends on overall production goal and adaptability to a specific region or soil type.
She noted varietal differences within species for both biomass production and percent of cover.
Trials showed as much as a ton per acre differences in biomass within the top varieties. No brassica variety made the top 25 list for biomass per acre or percent cover established, she said.
She measured percent cover in November and February in her trials.
Cereals dominate early
"All top 25 cover performers were either cereal or legumes," Sykes said. Cereals established more quickly in November, but legumes came on strong in February evaluations. April and May biomass evaluations showed winter pea and hairy vetch as top legumes and cereal rye as the best cereal species.
She reported some location differences among varieties, including radishes and crimson clover.
The full report, available at https://search.utcrops.com/cover-crops, shows that one month after planting, all top-performers for percent cover were cereal species, which averaged 22% cover, compared with only 9% for brassicas and 4% for legumes. In February, legumes were dominating the top, especially varieties of common, hairy, and woolypod vetch, and winter pea.
"In February, legumes averaged 31% cover, compared to 21% in brassicas, and 24% in cereals," Sykes reported.
She said two hairy vetch varieties topped the legume list for coverage in February measurements. Significant differences showed between the lowest performing legume at 40% coverage and the top performing legume at 80% coverage.
"Biomass tripled or doubled among top performers between April and May," she said. "Production among the top 25 performers varied by 1.1 ton per acre."
In the online report Skyes noted that within the top-performing species, cereal rye exhibited the greatest difference in biomass between top and bottom performing varieties, with a difference of 0.9 dry matter ton per acre in April and 1 dry matter ton per acre in May. "This was also true for hairy vetch varieties, with a difference in top and bottom performing varieties of 0.5 dry matter ton per acre in April and 0.7 dry matter ton per acre in May. For winter pea, variety differences were less pronounced in April (0.2 dry matter ton per acre) but increased by May (0.6 dry matter ton per acre).
"Varieties that had high biomass in April, generally also had high biomass in May," she said.
Sykes noted in the online report that cover crop height may play a role for producers interested in grazing cover crops. Cereal varieties were among the tallest in all four evaluation months. "In April, some brassica species were included in the top 25% for height, due primarily to the rapid elongation of flowering stalks. By May, several legumes were also in the top 25% for height," Sykes said.
Brassicas did not make the top 25 performers in either coverage or biomass, Sykes said, "but producers should consider including brassicas in a mix based on variety trials to determine which variety is best."
Cover crop benefits
Sykes said cover crops offer significant benefits to row crop producers. "Cover crops increase water infiltration, organic matter, habitat for beneficial insects, nutrient content, and weed suppression. They decrease nutrient runoff and soil erosion. In some cases, cover crops may provide income — winter wheat or grazing, for instance," she said.
To achieve those benefits, producers need to look at best varieties, she said. Top performers in her percent coverage trials include Bates RS4, Yankee, and Elbon cereal ryes, and 140797 barley. Biomass top performers include AU Merit hairy vetch, Bates RS4, NF 95319b and NF97325 cereal rye and Patagonia Inta hairy vetch.
She encourages producers to look at the full list of varieties and compare locations at the website cited above.