Nitrogen Economy and Partitioning in Sunflower from Split-Applied or Slow-Release UAN.

In general, sunflower (helianthus annuus L.) will respond to modest amounts of applied nitrogen (N) fertilizer. To ensure crop N needs are met, it is important to have N in place as it is needed throughout the growing season. During years where high rainfall promotes excess N leaching or denitrification, a split-application of N may improve seed yield and oil content.  This presentation will discuss a two-year study with four site-years in central and western South Dakota examining the effects of at-planting and/or split-applying N to sunflower using 15N-labelled UAN. Results include yield and oil content along with a discussion on the partitioning of N to seed and biomass as related to the timing of N application.