Split Application of Nitrogen on Irrigated Sugarbeet

Fertilizer nitrogen (N) on sugarbeet (Beta vulgaris L.) must be managed carefully to optimize sucrose yield. Excess N reduces sucrose content and increases impurities, while N deficiency reduces root yield and consequently, sucrose yield. The objective of this study was to compare response ofsugarbeet produced using the recommended rate of N with sugarbeet produced using a reduced rate of N with three ap­ plication schedules. The study was conducted for three years under furrow flood irrigation at Sidney, Montana. Soil was tested to 120 cm to determine residual soil N, and applied N rates were calculated. The recommended rate of N or 80070 of the recommended rate was applied under three strategies: 1) a single preplant application, 2) a single postemergence ap­ plication, and 3) a split application with a small portion ap­ plied preplant and the remainder applied post emergence. Petiole nitrate contents were measured several times during the season in two of the three years. Root yield, sucrose COlt­ tent and yield, and root impurities were measured. June petiole nitrate contents were greatest when all N was applied preplant and continued to be greatest in July. By August, no difference in petiole nitrate was detected among treatments, indicating rapid uptake of available N early in the season. Root yield was not affected by N rate or time of application. Sucrose content was reduced when N was applied in a single postemergence application at both N rates. Reduced N resulted in significantly lower amino-N content, but timing of N application had no effect on impurities. Harvest date in all years was relatively early. Greater differences in response to N rate may have been seen at a later harvest date. Additional key words: nitrogen management, Beta vulgaris, root yield, sucrose