Balancing Objectives in an Organic Oat Rotation Year: Implications of Planting Date and Crop Density

Abstract

Core Ideas Yield, test weight, and returns over seed cost were greatest at early planting dates. Early planting optimized forage establishment and weed suppression in one site‐year. Increasing oat density increased yield in one site‐year, and test weight overall. Target oat density had no effect on returns over seed cost. Oat (Avena sativa L.) is an important component of organic row crop rotations in the Upper Midwest. Our goal was to determine the effects of planting date and crop density on oat grain yield and yield components, test weight, straw yield, underseeded alfalfa and ambient weed biomass, and returns over seed cost. We conducted an experiment on certified organic farmland on an agricultural experiment station near Boone, IA, USA, over 2 yr. A randomized complete block split‐plot design was used to test effects of planting date (6, 17, and 28 Apr. 2015, 22 Mar. 2016, 4 and 15 Apr. 2016) as whole plot and target crop density (161, 236, 312, and 386 plants m–2) as subplot. Planting date had the greatest effect on response variables. Yields decreased by 33 and 9%, respectively, over 2015 and 2016 planting periods. Delayed planting decreased test weight in both site‐years. Alfalfa biomass decreased and weed biomass increased (as a function of delayed planting) in 2016, but had no effect in 2015. Increasing oat density had a positive linear effect on grain yield and test weight, and no effect on alfalfa biomass in both site‐years. Increasing oat density had a negative effect on weed biomass in 2016 and no effect in 2015. Returns over seed cost did not differ among our density treatments in both site‐years. Our results highlight potential no‐cost improvements that can be made to organic oat management to improve grain yield and quality, without negatively impacting forage establishment or weed suppression.