Yield, nutritive value, and profi tability of direct-seeded annual forages following spring-terminated alfalfa

Winter-kill of alfalfa (Medicago sativa L.) causes substantial yield losses in northern environments, requiring alternative forages to meet livestock needs. This study explores the forage yield, nutritive value, and N response of seven annual forage species and one grass–legume biculture, no-till planted into spring-terminated alfalfa. Forages were planted in late May at Rosemount, MN, in 2014 and 2015 and at Waseca, MN, in 2015 with split-plot factors of three N fertilizer rates (0, 56, and 112 kg N ha^–1) and were harvested on approximately 30-d intervals. When successfully established, teff [Eragrotis tef (Zuccagni) ‘Summer Lovegrass’] and sudangrass [Sorghum bicolor (L.) subsp. drummondii (Nees ex Steud.) ‘PCS 3010’] were among the highest-yielding species, with yields ranging from 4.2 to 9.9 Mg DM ha–1 and 6.8 to 8.9 Mg DM ha^–1, respectively. Fertilizer N increased yields of all species at Rosemount in 2014; however, N needs were met by terminated alfalfa at both locations in 2015. Weed biomass increased with added fertilizer N in site-years when weeds were present. Nitrogen fertilization improved forage nutritive value through decreased neutral detergent fiber concentration and increased crude protein concentration and neutral detergent fiber digestibility (48-h in-vitro) in all site-years. However, N fertilization had no effect on economic net return in 2 of 3 site-years. Annual ryegrass [Lolium multifl orum (Lam.) ‘Jumbo’] most consistently resulted in the greatest net return. No-till planting annual forages into terminated alfalfa can provide forage to off set losses and utilize alfalfa N in situations of alfalfa winter-kill.