Grazing and cover crop effects on cover crop biomass and crop productivity during transition to organic production

Abstract We conducted a 4‐year organic transition field study to evaluate the effects of objective‐based cover crop mixtures and grazing on cover crop and forage biomass, residue, and carryover effects on the yield of the first organic certified crop. The experiment, conducted at the USDA‐ARS Northern Great Plains Research Laboratory near Mandan, ND, was a split‐plot design with grazing (grazed or ungrazed) as whole plots and cover crop mixture (soil‐building cover crop mix, pollinator cover crop mix, weed suppression cover crop mix, multipurpose cover crop mix, annual crop rotation, or perennial forage biculture) as subplots. Weed biomass decreased over the years, and cover crop biomass was three‐ to fourfold greater in the perennial cover crop treatment compared to annual mixtures. Grazing did not affect aboveground biomass but affected the botanical composition of aboveground biomass. Weed biomass was 65% greater in the grazed treatments in 2017 and 20% greater in the grazed treatments in 2018 compared to the ungrazed treatments. Annual crop mixtures had the greatest residue cover, and perennial biculture had the least. Cover crop mixtures or livestock integration did not affect grain yield in the first year of certified organic production. We found that in a drought year, grazing reduced the benefits of cover crops on weed suppression and the carryover of cover crop biomass from the previous year. These results highlight complex interactions among cover crop mixtures, grazing, and environmental conditions on biomass, residue, and carry‐over effects of cover crops.