The Impact of Fertilizer Source, Application Rate, Application Timing, and Application Method on Losses of Nitrogen through Nitrous Oxide in Sugar Beets.

Half of all sugar beets grown in the U.S. are grown in Minnesota and North Dakota, approximately 700,000 acres. Careful nitrogen (N) management is critical in the production of sugar beets to produce optimum root yield and quality.  Many fine textured, poorly drained soils in the Red River Valley can require substantially greater N rates than other soils to achieve production goals.  Farmers are asking if there are alternative strategies which can lead to greater N use efficiency. The current study examined N loss as measured by N₂O flux as affected by the N source , timing of application and/or the method of application, with a secondary goal of determining if other greenhouse gas (CO₂, CH₄) losses are affected by the source, timing or method of application.  Optimal and suboptimal N rates were applied as Urea, ESN or a 50/50 mixture.  Application method was fall or spring applied broadcast or broadcast with in-season UAN sidedress application. This study was initiated in 2012 and will be completed in the summer of 2014.  Preliminary findings collected during the 2012 and 2013 growing seasons show high N₂O fluxes associated with high temperature or high moisture content of the soils (p<0.0001).  The highest fluxes were observed in the spring or immediately after sidedress incorporation.  At times of high N₂O flux, the spring applied treatments had significantly (p<0.05) higher fluxes than the fall applied treatments, with the exception of the sidedress treatments which showed the opposite trend.  In addition, the urea treatments had significantly (p<0.05) higher fluxes than the ESN treatments when significant differences existed.  Generally, N₂O flux peaks are small in mid-season and remain close to zero for most of season.  Soil gas flux trends from a fine textured, poorly drained soil during three sugar beet growing seasons will be discussed.