Oat companion seeding rate, herbicide, and irrigation effects on alfalfa stand establishment

Abstract

AbstractAlfalfa (Medicago sativa L.) is often grown in water‐limited climates where available soil moisture is a key factor in determining the success or failure of new stand establishment. This study was conducted to determine optimal oat (Avena sativa L.) companion seeding rates for alfalfa establishment across a range of soil moisture levels. The effects of five oat seeding rates (0 [with and without herbicide], 11, 22, 45, and 89 kg ha−1) under five water levels on alfalfa stand establishment, forage yield, and nutritive value were evaluated at North Logan, UT, on a Millville silt loam soil (coarse‐silty, carbonatic, mesic Typic Haploxeroll) in 2019 and 2020. When soil moisture was adequate, first cut alfalfa stem density increased twofold as oat seeding rates decreased from 89 to 11 kg ha−1, but at low soil moisture levels stem density increased fivefold to sevenfold. At second cut, the only stem density differences that remained were at low irrigation. First cut forage yields were lowest in 0 kg ha−1 treatments and increased with increasing oat seeding rates. The opposite was true at second cutting, where yields were greatest where no oat had been planted. Yield differences were more extreme as soil moisture was reduced. The highest oat seeding rate had comparable weed control effects to the herbicide. Generally, the presence of either oat or weeds reduced forage nutritive value when compared to alfalfa alone. Reducing oat seeding rates or eliminating the companion crop altogether appears to improve alfalfa stand establishment when soil moisture is limited.