Spring Nitrogen and Cultivar Affect Seed Production in Winter Canola

Limited information is available on the effects of spring‐applied N on winter canola ( Brassica napus L.) seed yield in seasonally high‐rainfall environments. The objective of this study was to investigate spring‐applied N effects on four winter canola cultivars: Athena, Baldur, Virginia and Kronos. Trials were conducted over a 3‐yr period at Corvallis, OR, with four spring N rates: 0, 56, 112, and 168 kg N ha −1 . Lodging severity affected seed yield responses to spring‐applied N. Under low or moderate lodging, yield was increased incrementally with spring N rate. When lodging was severe, yields were reduced by 168 kg N ha −1 . Spring N increased yield up to 75%, but losses in yield due to N when lodged ranged up to 11%. Seeds m −2 was the main contributor to increased or decreased yields in response to spring N. Seed oil content was reduced by increased N rate, but seed protein was unaffected by spring N. Oil yield was increased by spring N when lodging was low or moderate but not when severe. Seed yield varied among cultivars with a different cultivar producing the highest yield each year. Athena, Baldur, and Virginia averaged 2800 kg ha −1 , while Kronos yielded the lowest at 2550 kg ha −1 . Expression of yield by cultivars was governed by a combination of seed number and seed weight. The best spring N rate for winter canola was 112 kg N ha −1 because it provided high potential yield while minimizing yield losses associated with lodging. Core Ideas Spring N increased seed and oil yield in winter canola except with crop lodging. Seeds m −2 was the most influential factor in determining seed yield in winter canola. Seed oil content was high but was inversely related to the rate of spring N applied. Seed and oil yield was maximized at 112 kg N ha −1 while minimizing lodging losses. First study on winter canola in the seasonally wet environment of western Oregon.