Spring nitrogen and cultivar effects on winter canola (Brassica napus L.) production in western Oregon

Graduation date: 2015Limited information is available on the effects of applied spring nitrogen (N) and cultivar on winter canola (Brassica napus L.) production in high-rainfall environments. The objectives of this investigation were: (i) to determine the effects of spring N and winter canola cultivars on seed and oil production characteristics, and (ii) to ascertain the influence of spring N and winter canola cultivars on dry matter partitioning and expression of seed yield components. Field trials for both objectives were conducted over a three-year period at Corvallis, Oregon with four spring N application rates: 0, 56, 112, and 156 kg N ha⁻¹.\ud Four winter canola cultivars were used (Athena, Baldur, Virginia and Kronos) to study spring N effects on seed and oil production characteristics. Lodging severity determined seed yield responses to spring-applied N. Under low or moderate lodging severity, yield was increased in proportion to spring N rate. When lodging was severe, yields were reduced by application of 168 kg N ha⁻¹. Yield increases attributable to spring N ranged up to 75% while losses under lodged conditions ranged up to 11%. Seed number m⁻² was the main contributor to increased or decreased yields observed in\ud response to spring N. Seed oil content was largely reduced by increased N rate, but seed protein was unaffected. Oil yield was increased by spring applied N with low or moderate lodging but not when lodging was severe. Seed yield and seed weight varied among cultivars in each of the three years. Athena, Baldur, and Virginia averaged 2800 kg ha⁻¹ with a different cultivar producing the highest average yield each year while Kronos consistently yielded the lowest at 2550 kg ha⁻¹. Expression of seed 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 seed yield while minimizing the loss in yield associated with lodging.\ud Two winter canola cultivars (Athena, Baldur) were used to study effects of spring N on dry matter partitioning and expression of seed yield components. Dry matter partitioning and expression of seed yield components were differentially affected by lodging. Biomass tended to increase with spring N rate and with advancement in developmental stage except with severe lodging. Tissue N content was incrementally increased in proportion to spring N rate. Spring N had no effect on tissue C content except when lodged where C content declined with increasing N rate. Mixed results were observed with harvest index (HI); spring N rates > 56 kg N ha⁻¹ caused reductions in HI in two years but no trend was evident in the third year. Racemes plant⁻¹ were not affected by N except when lodged. Nitrogen rates ≥ 112 kg N ha⁻¹ increased mainstem siliques raceme⁻¹ by 36% in 2008 and by 39% in 2010, but not when lodged in 2009. Seed yield components varied in their contributions to yield, but mainstem siliques raceme⁻¹ produced the most consistent effects on seed yield by increasing seed number m⁻². The\ud results of this study improve our understanding of winter canola production in a wet environment