Organic oat response to variety, seeding rate, and nutrient source and rate

Oat (Avena sativa L.) is an important crop for organic production systems in the upper Midwest, but limited information on optimal nutrient management and seeding rates is available. Oat varieties representing three maturity groups were evaluated during 2015 and 2016 in Lamberton, Minnesota on organically certified ground previously planted to alfalfa (Medicago sativa L.). Two oat seeding rates (110 and 145 kg ha⁻¹ ), two nutrient sources (raw and composted beef manure), and four N application rates (0, 50, 100, and 150 kg ha⁻¹ ) were studied. Plant population; number of tillers; grain yield; grain nutrient removal (primary and secondary macronutrients); and post-harvest soil nitrate, Bray P-1, and K in the top 0 to 15 cm layer were measured. Grain yield was 4.8, 4.0, and 3.8 kg ha⁻¹ for late maturing Deon, early maturing Tack/Saber, and medium maturing Shelby, respectively. Yield was optimized at a nutrient application rate of 82.3 kg N ha⁻¹ and decreased at higher rates. Grain N content was not related to yield, suggesting that the other nutrients in manure and compost may have been responsible for optimizing yield. High application rates resulted in increased residual soil test P and K levels, which could become problematic if not managed appropriately.