Influence of Nitrogen Fertilization Sources and Rates On Grain Protein and Yield in Hard Red Spring Wheat.

Price discounts at the market associated with low grain protein in hard red spring wheat (HRSW, Triticum aestivum L.) in recent years has increased interests in using controlled-release nitrogen (N) fertilizers to enhance protein concentration while maintaining grain yields. Field experiments conducted over six site-years in Minnesota from 2007 to 2009 examined the effects of a polymer-coated urea [PCU, ESN (Environmentally Smart Nitrogen), Agrium Inc., Alberta, Canada] and urea on two HRSW cultivars, Knudson and Alsen, that vary in grain yield and protein potential. PCU and urea were spring applied at six rates that supplied 0 - 110 kg N ha^-1 in 2007 and 0-168 kg N ha^-1 in 2008 and 2009. Knudson produced greater grain yield and had greater apparent nitrogen use efficiency (ANUE) than Alsen in all site-years and could be attributed to genetic differences among cultivars. PCU increased protein concentration and whole tissue N concentration and decreased grain yield compared with urea in site-years that were cold and dry early in the growing season that may have caused a delayed N released from PCU. From this study, we cannot determine if increased protein concentration with PCU is due to increased N availability late in the growing season or because of decreased grain yield caused by reduced N availability early in the growing season.