Yield and protein response of wheat cultivars to polymer-coated urea and urea

Discount payments associated with low grain protein concentration in hard red spring wheat (HRSW, Triticum aestivum L.) in recent years has increased interest for using controlled-release N fertilizers to increase protein concentration while maintaining optimal grain yields. Field experiments were conducted during 6 site-years in Minnesota from 2007 to 2009 to examine effects of a polymer-coated urea (PCU, Environmentally Smart Nitrogen [ESN], Agrium Inc., Calgary, AB, Canada) and non-coated urea on grain yields and protein concentrations of two HRSW cultivars, Alsen and Knudson, that vary in grain yield and protein concentration potentials. Polymer-coated urea and urea were applied in spring at six rates that supplied 0 to 110 kg N ha^-1 in 2007 and 0 to 168 kg N ha^-1 in 2008 and 2009. Because of genetic differences, Knudson produced greater grain yield than Alsen in environments (site-years), which were cooler and drier early in the growing season and the yield differences between the two cultivars increased with increasing N rates. In the same environment, PCU decreased grain yield compared with urea, which could be related to a reduced N release early in the growing season. Compared with urea, higher N (at Zadoks scale 85) and protein concentrations (at Zadoks scale 92) with PCU were observed due to increased N availability later during the growing season. To increase wheat protein concentrations from using PCU, future studies should evaluate different mixtures of PCU and urea.