OAT COMPANION CROP SEEDING RATE EFFECT ON ALFALFA ESTABLISHMENT, YIELD, AND WEED-CONTROL

Companion crops have been used in alfalfa (Medicago sativa L.) establishment to increase forage yield and decrease weeds. When oat (Avena sativa L.) is used as a companion crop, the typical seeding rate is 50 to 75 kg ha-1. In irrigated situations this seeding rate has depressed alfalfa yield and stand density. This study was conducted under irrigated conditions to evaluate alfalfa yields, forage composition at first harvest, and alfalfa and weed densities at four oat seeding rates; 0 to 36 kg ha-1. Two field experiments were established at Madera and one at Courtland, CA. The interplanting of oat with alfalfa increased first-harvest forage yields 2.45 to 8.62 Mg ha-1, relative to alfalfa planted alone. Alfalfa yields at subsequent cuttings during the first season were reduced by the oat companion crop. By the last cutting in the first season and all cuttings in the second season, yields were equal for all treatments. First-season forage yields were increased 1.54 to 5.05 Mg ha-1 by an oat companion crop. The oat component of the first cutting ranged from 71 to 98%. Alfalfa and weed biomass were both reduced by the oat companion crop. The oat companion crop reduced alfalfa stand density during establishment, but density was higher at the beginning of the second season at two of the three sites when the oat seeding rate was 18 kg ha-1. Alfalfa established with an oat companion crop had an average of 30% fewer weeds in the second year when 9 kg ha-1 were used and almost 50% fewer weeds at 18 kg-1. Thus, the seeding rate of an oat companion crop considered best for optimizing yields and reducing weeds under irrigation in California is approximately 18 kg ha-1.