Sudangrass as companion crop to establish alfalfa

Abstract When establishing alfalfa ( Medicago sativa L.), the use of companion crops often suppresses weed growth and increases harvestable forage biomass. In Quebec, small‐grain cereals are traditionally used as companion crops, but the use of other recently introduced species such as sudangrass [ Sorghum × drummondii (Nees ex. Steud.) Millsp. & Chase] has not yet been evaluated. This project was conducted to evaluate the impact of sudangrass, annual ryegrass ( Lolium multiflorum Lamarck), and oat ( Avena sativa L.) used as companion crops on alfalfa establishment, forage yield, forage quality, and persistence. When sown in June, sudangrass used as a companion crop may result in higher forage yields in the sowing year than other species. Moreover, sudangrass was less competitive overall with alfalfa than annual ryegrass, resulting in higher alfalfa yields and limited impact on alfalfa stand density. However, when weed pressure was high, sudangrass appeared to have lower weed suppression potential than other species. Alfalfa established with sudangrass produced forage with a similar nutritive value to alfalfa established with oat or annual ryegrass when sudangrass was planted in May but lower nutritive value than with annual ryegrass or solo‐sown alfalfa when sudangrass was planted in June. The effects of companion crops on alfalfa yields in the post‐sowing year were minimal overall. The results apply to the specific sowing rates used here and further studies should evaluate the performance of each companion crop at a wider range of sowing rates.