Nitrogen Fertilizer Optimization for Sugarbeet in the Red River Valley of North Dakota and Minnesota

Fertilizer N application is critical to optimize sugarbeet (Beta vulgaris L.) yield and sugar concentration. Regardless of observed yields, current fertilizer recommendations in North Dakota and Minnesota suggest a single application rate of 146 kg N ha(-1) (considering both fertilizer N residual soil N of 120 cm depth) for the Red River Valley (RRV) irrespective of soil type and organic matter content. Field experiments were conducted at three sites to determine sugarbeet response to N application rates, 0, 112, 146, 179, and 213 kg N ha(-1) and optimal N rate during 2015 and 2016 growing seasons. Year and site had a significant effect on yield and sugar concentration. In 2015, fertilizer-N significantly increased yield for all three sites, but in 2016, only one site responded to N. The highest N rate (213 kg N ha(-1)) reduced sugar concentration in 2016. In-season soil available N (of 0-120 cm) significantly correlated with yield (R-2 = 0.35) and economic return (R-2 = 0.28). In season, red edge normalized difference vegetative index (RENDVI) based on the handheld optical sensor was significantly (P < 0.05) related to fertilizer-N application rate. Economic optimum N rate for three sites varied from 0 to 405 kg N ha(-1) depending on year and site characteristics. Our results suggest a revision of current sugarbeet fertilizer N recommendation to replace the single rate with N rates based on site characteristics and profitability to N applications.